Download Basic Weather for Mariners

WELCOME TO
BASIC WEATHER FOR MARINERS
PRESENTED BY:
HANK POMERANZ, KIM CURRY
Carolina Yacht Care, LLC (cYc)
ORIENTAL, NC
7 FEBRUARY 2015
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• Hank and Kim each
bring more than 30
years in Navy forecasting
experience.
- Includes operational
forecasting and briefing
for ships, aircraft and
ground forces
• Hank is a long time cruising
sailor and Kim brings both
USCG Aux crew and VE
experience
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Kim
2
Today’s Goal
• Our goal:
– Help improve your safety, confidence and selfreliance on the water by • Providing a basic understanding of:
•
the atmosphere,
•
the causes of weather impacting your experience
on the water and
•
the foundation for anticipating significant weather
(forecasting).
• We call this last goal: developing a Seaman’s Eye.
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3
Seminar Outline
•
Some Basic Meteorology and Definitions
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•
•
Weather Maps
Local Forecasting
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•
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A little about the structure and gasses making up our atmosphere
Water Vapor and Clouds
Scale of Weather Systems - from global to local
Atmospheric pressure and frontal systems
Weather reporting and reports
Winds
Atmospheric Stability
Precipitation
Thunderstorms
Winds (shifts, direction and speed)
Fog
Seas
Government and Commercial Sources of information
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Exercises
4
Basic Meteorology
DEFINITIONS OF WEATHER
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Weather is:
• …the short-term variation of the atmosphere.
It includes changes in:
– air pressure,
– air temperature,
– humidity,
– wind,
– clouds,
– precipitation, and
– visibility.
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6
Weather happens in
• The Troposphere –
– The lowest layer of the
atmosphere
– Has 75% of our atmospheric
molecules
– Varies in height from ~5 miles
at the poles to ~10 miles at
the equator
– Where our weather forms
• In only rare instances does a
thunderstorm “pierce” the
Tropopause and they are
extremely severe Copywrite 2015, Carolina Yacht Care, LLC,
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Troposphere Structure
Temperature generally
decreases with altitude in
the troposphere
But not always. When temperatures
are steady or warm with height we
call it a temperature inversion.
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Tropopause
Troposphere
International Space Station astronauts captured this photo of Earth's atmospheric layers on July 31, 2011,
revealing the troposphere (orange-red), stratosphere and above.
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The Atmospheric Makeup
Although a very small percentage of the atmospheric gases, Water Vapor plays
a key role in our weather.
Miscellaneous Gasses
Neon, Ne 0.0018
Helium, He 0.00052
Methane, CH4 0.0002
Krypton, Kr 0.00011
Nitrogen(I) oxide, N2O 0.00005
Hydrogen, H2 0.00005
Xenon, Xe 0.0000087
Ozone, O3 0.000001
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Basic Meteorology
RADIATION – THE EARTH’S WEATHER
DRIVER
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Incoming Solar Radiation
The Inter-Tropical Convergence
Zone (ITCZ)
March /September
Unequal heating of the earth’s atmosphere is the engine that
12
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drives the weather Copywrite 2015,
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Global General Airflow Pattern
Oriental Latitude
35.0deg N
~5 miles
thick
Jacksonville, FL Latitude
30.3deg N
Ferrel Cell
~10 miles
thick
Ferrel Cell
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The 5 Air Masses
AIR MASS DEFINITION
•
•
•
•
•
•
If a body of air moves slowly or
stays over an extensive area that
has fairly uniform temperature and
moisture characteristics, the air
takes on those characteristics and is
called an air mass. Five main types
of air masses ultimately influence
U.S. weather:
Continental Polar (cP): cold, dry
Continental Arctic (cA): extremely
cold, very dry
Maritime Polar (mP): cool, moist
Maritime Tropical (mT): hot, moist
Continental Tropical (cT): hot, dry
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Basic Meteorology
ATMOSPHERIC MOISTURE
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Water Vapor
The atmosphere contains water vapor. Although small by
percentage of the atmospheric gases (up to 4%*), it:
• Is an important constituent contributing to water and
ice clouds that produce various types of precipitation
• Stores and releases great quantities of heat energy,
that powers Thunderstorms and
Hurricanes.
*Water Vapor in the atmosphere varies from
a trace (<1%) to 4%. Greatest over the
tropics and least over the poles and deserts.
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Water Vapor Distribution
Almost half of all water vapor is found
within the lowest
three miles of the atmosphere, where amounts
vary with region, elevation
and season.
Changes of water from
liquid to gas or gas to
liquid greatly affect the heating and
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cooling of the atmosphere.
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Critical Term - Condensation
• Condensation is the phase change
of water from a gas to a liquid.
Condensation adds heat energy to
the environment and is thus a
WARMING process in the
atmosphere.
• As this heat is released, it helps
storms, including thunderstorms
and hurricanes, to form and
grow.
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Critical Term - Evaporation
• Evaporation is the phase change
of water from a liquid to a gas.
Evaporating water removes heat
from the environment and is
therefore a COOLING process in
the atmosphere.
• Evaporation adds moisture to the
atmosphere. If enough moisture
is added to the atmosphere by
evaporation, dew, fog, clouds,
and precipitationCopywrite
can2015,
form.
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The Hydrologic Cycle – What
Goes Around, Comes Around
These physical
processes
continually release
and take in heat
energy to/from the
environment –
helping to maintain
the earth’s heat
balance.
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Soil Moisture Active Passive
(SMAP) Satellite
Helping scientists better understand the
Hydrologic cycle and the effect on the
earth’s well being
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Launch
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January 31, 201521
Basic Meteorology
CLOUDS
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What is a Cloud?
• A cloud is composed of tiny water droplets or ice
crystals that coalesce around tiny “hygroscopic
nuclei”** and are suspended in the air.
– A series of processes have to happen in order for these water
droplets or ice crystals to form into clouds in the atmosphere,
and
– Different types of clouds form from different processes.
**Particles in the atmosphere – including dust, sand, salt, pollutants, etc. that
tend to attract and condense ambient water vapor
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The Basics - “Changes of State”
are Constantly in Progress
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How Clouds Form (1)
In addition to the hygroscopic
nuclei, almost all cloud
formation requires the cooling
of air.
Why?
It’s all about condensation –
atmospheric moisture as water
vapor (a gas) condensing and
becoming liquid or ice (a solid).
So, how do we get condensation?
Cool the water vapor!
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How Clouds Form (2)
We know now that air needs to cool. What are the
general processes whereby air will be cooled?
Catalysts causing air to rise and cool
•
•
•
•
Surface heating
Mountains and Terrain
Fronts (cold and warm)
Low pressure
Catalyst causing air to cool without rising
• Earth Surface cooling and cooling the air above
it
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Air Rising and Cooling
Catalyst #1 - Surface Heating
• The Sun heats the ground,
which then heats the air.
• Lighter and less dense than the
surrounding air, it rises, expands
and cools.
• Cooler air means slower
molecular movement and the
water vapor particles start to
coalesce into water droplets.
• The higher the air parcel gets,
the cooler it gets, and more
moisture condenses out of it –
eventually forming a cloud.
• The types of clouds that form
from the process of surface
heating are cumulus type.
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Air Rising and Cooling Catalyst
# 2 - Mountains and Terrain
• When air encounters a
mountain range or other types
of terrain the air rises and
cools, and this slows molecularAir rises, cools and condenses
motion and causes coalescing
(condensation).
Air warms and holds moisture
• The types of clouds that form
Precipitation (wet) side
from encounters with
mountains are cumulus clouds
and lenticular clouds.
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Dry Side
28
Air Rising and Cooling
Catalyst # 3 - Low Pressure
In a low pressure system, wind moves in
towards the center from all directions
because air moves from high to
low pressure. When this air converges
(meets) in the center, there is nowhere for
the air to go but up.
As air rises it cools, resulting in
condensation.
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Air Rising and Cooling Catalyst
#4 - Cold and Warm Fronts
Weather fronts can cause clouds to form. Fronts occur when two large air masses
collide at the Earth's surface.
•
Cold fronts occur when heavy cold air
displaces lighter warm air, pushing it
upward. Cumulus clouds are the most
common cloud types that are produced
by cold fronts. They often grow into
cumulonimbus clouds, which produce
thunderstorms.
•
Warm fronts produce clouds when
warm air replaces cold air by sliding
above it. Many different cloud types
can be created in this way: altocumulus,
altostratus, cirrocumulus, cirrostratus,
cirrus, cumulonimbus (and associated
mammatus clouds), nimbostratus,
stratus, and stratocumulus.
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Earth Surface Cooling the Air
Above it
• In contrast to surface heating, the
cooling of the Earth's surface may
lead to the development of fog
and stratus clouds.
• Stratus clouds belong to the Low
Cloud (surface-6,000’ up) group.
They are uniform gray in color
and can cover most or all of the
sky. Stratus clouds can look like a
fog that doesn't reach the
ground.
• Light mist or drizzle is sometimes
associated with stratus clouds.
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To summarize
• 4 Mechanisms for lifting air and resultant
cooling
– Surface Heating
– Mountains and Terrain
– Low pressure centers
– Frontal Systems
• 1 mechanism for cooling from below
– Earth’s surface cooling and cooling the air just
above.
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Main Groups of Clouds
•
FOUR main groups of clouds, based on their
height, form and appearance:
•
(I) High Clouds (20,000’ to 40,000 ‘above sea
level)
•
•
•
•
(II) Medium Clouds (6000’ – 20,000’)
•
•
•
Altocumulus
Altostratus
(III) Low Clouds (below 6000’)
•
•
•
•
Cirrus
Cirrocumulus
Cirrostratus
Stratus
Stratocumulus
Nimbostratus
(IV) Clouds With Great Vertical Extent
(stretching from Surface – >30,000’)
•
•
Cumulus
Cumulonimbus
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High Clouds (20,000’-40,000’)
Cirrus clouds are
ice-crystals.
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Mid Clouds (6,000’ – 20,000’)
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Low Clouds (Surface to 6,000’)
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Clouds with Vertical Growth
(Surface to >30,000’)
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Other Clouds
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Cloud Wonders in the
Antarctic Sky
Photo credit: NASA
Project scientist
Michael Studinger
On Nov. 24, 2013,
he took this
photograph of a
multi-layered
lenticular cloud
hovering near
Mount Discovery,
a volcano about
70 kilometers (44 miles)
southwest of McMurdo Station on Antarctica’s Ross Island.
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Basic Meteorology
SCALES OF WEATHER SYSTEMS
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From the Big Picture to Your
Backyard
• The largest weather features occur on the global scale. At this scale,
forecasters are thinking about large patterns of winds, temperature, and
pressure.
• Weather patterns that affect one or several states are called synoptic
scale events. Examples are circulations around high and low pressure
areas, large snowstorms, large-scale droughts, and hurricanes.
• Smaller and shorter-term weather events such as tornadoes, flash floods,
and similar “local” events are called mesoscale phenomena. These events
are often the most hazardous—and the most difficult to forecast.
• All these scales are interrelated.
– A mesoscale event will have its roots in global and synoptic patterns.
– Likewise, a synoptic scale event will have a variety of consequences on the mesoscale.
These complex connections explain why forecasting is so difficult.
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The Global Scale
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The Synoptic Scale
• Traditionally, forecasters
have been trained in
synoptic scale meteorology.
This type of meteorology
deals with analyzing and
forecasting meteorological
features of scales in excess
of 1200 miles. Features such
as troughs, ridges, highs,
lows and frontal boundaries
are well understood.
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The Synoptic Scale
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The Mesoscale
Small Scale events – Thunderstorms, fog, precipitation, etc.45
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The Mesoscale
• As meteorologists and savvy
boaters, our challenge is to
predict what will happen at
this scale based on our
knowledge of the Synoptic
Scale and local effects.
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Basic Meteorology
ATMOSPHERIC PRESSURE
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Atmospheric Pressure
Pressure is the force per unit area exerted on a
surface by the weight of the air above it
Units are “inches of mercury,” “pascals,” or most
commonly: “millibars”
When we talk about atmospheric pressure, we are
really talking about the weight of all those air molecules
above us at a given location
At sea level, the average force exerted by all the
molecules in a column of air resting on your head and
extending up to the top of the atmosphere (at about 30
miles) is approximately 14.7 pounds per square inch (psi),
29.9 inches of mercury (in. Hg), or 1013.25 millibars (mb),
the most common measure of pressure used by
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meteorologists.
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Pressure Tidbits
On average, a column of air, one square inch in cross section
measured from sea level to the top of the atmosphere would
weigh about 14.7 lbs.
Mercurial barometer (84 cm in length) immersed in a bowl of
mercury – weight of mercury causes a vacuum in the top of the
tube. Atmospheric pressure on bowl causes mercury to rise Toricelli’s simple
Mecurial Barometer
in the graduated tube – measured as “in. Hg”
The aneroid barometer consists of a closed sealed
capsule with flexible sides. Any change in pressure
alters the thickness of the capsule. Levers magnify these
changes, causing a pointer to move on a dial, or
numbers to change in a digital read-out device
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Aneroid Barometer
Pressure Tendency
Perhaps more important than
actual pressure reading is your
awareness of the Pressure
Tendency.
Set the manually set needle
to current pressure then a
few hours later compare to
current pressure reading to
determine rise or fall
Seaman’s Eye Note:
Pressure falling rapidly
(6 Mb per 3 hours) – look for
deteriorating weather
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50
HIGH VS LOW PRESSURE CENTERS
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LOW PRESSURE GENERATION
Extra-tropical Cyclone Development “Cyclogenesis”
- normally associated with a weak frontal zone
near the surface with an upper level trough.
Extra-tropical – poleward of tropics, i.e. poleward
of 23.5 Deg North (and South)
Life cycle of traditional low pressure
system. Many frontal wave low pressure
centers never continue to develop to
maturity Copywrite 2015, Carolina Yacht Care, LLC,52
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Hatteras Low
Approx. 12 hours earlier
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Surface Reports
Total Cloud Cover
Temperature = 98 Deg F
Pressure = 1012.4 Mb
Winds = Southeast at 15 Kts
Dew Point = 78 Deg F
Pressure Trend = -3 Mb last
three hours
Clouds = Cumulus Bases at 2000’
Cirrus above
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Basic Meteorology
FRONTAL BOUNDARIES
COLD / WARM / OCCLUDED
SQUALL LINES / DRY LINES
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FRONT
An “air mass” is a large body of air that has similar
moisture and temperature characteristics. A front
is the transition zone between two air masses.
As depicted on a surface
weather chart
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COLD FRONT
As the cold front moves, warm, moist
unstable air is usually replaced by cold,
dry stable air.
Blue triangles indicate
direction of frontal movement
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WARM FRONT
A warm front typically replaces cool dry air
with warm moist air.
*
Red half-circles indicate
direction of frontal movement
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OCCLUDED FRONT
As central low pressure matures (lowering pressure),
Cold front moves faster and overtakes the Warm front.
Warm air is pushed aloft and the Occluded front is
formed.
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Squall Lines
Squall Line Development
Cold
Front
Warm Unstable Air
Downdrafts
Cold
Front
Cold
Front
Warm
Unstable
Air
Downdrafts
Large quantities of cold air from
aloft descend in downdrafts
along the front and form a wedge
of cold air ahead of the front.
The wedge of cold air then serves
as a lifting mechanism for the
warm, moist, unstable air; and a
line of thunderstorms develops
several miles in advance of the
front
Warm
Unstable
Air
Downdrafts
30 to 100 miles
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60
SQUALL LINES
A narrow band or line of active thunderstorms
that is well ahead of a cold front, and may
contain heavy precipitation, hail, frequent
lightning, dangerous straight line winds, and
possibly funnel clouds, tornadoes and
waterspouts.[
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Squall Line - Near Frontal
Passage 4/25/14
• This squall line resulted
in significant damage
from tornado activity
AND “straight-line”
winds across NE NC.
Courtesy: Intellicast.com
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62
Dry Line
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Basic Meteorology
WIND
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Basic Meteorology
Wind is the movement of air across the
Earth’s surface and is produced by
differences in air pressure between one
place to another.
Within the atmosphere, there are several
forces that impact the speed and direction
of winds. The most important though is the
Earth’s gravitational force. As gravity
compresses the Earth’s atmosphere, it
creates air pressure- the driving force of
wind. Without gravity, there would be no
atmosphere or air pressure and thus, no
wind.
Wind is a balance between three
Forces – two real, one not so real
Pressure Gradient
Friction
Coriolis
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Pressure Gradient
Think of Highs as mountains
and Lows as valleys. The
larger the difference
between central pressures,
the steeper the contours
(packed isobars) – meaning
stronger “pressure gradient”
----Resulting in stronger winds
H
H
1028 mb
1028 mb
1016 mb
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L
1000 mb
66
Pressure Gradient
Weak PGF
Strong PGF
On most surface weather charts produced by NOAA
agencies, isobars (lines of equal pressure) are plotted
at 4 mb intervals. It is difficult to accurately determine
wind speeds by looking at a surface weather chart, but
it is possible to identify areas where the wind is
relatively stronger or weaker by examining the spacing
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of the isobars.
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67
Coriolis Force
Coriolis force is an “apparent”
force resulting from the fact
that the earth is constantly
rotating. Coriolis always acts
at a 90 Deg angle to the right
of the motion of a parcel of air
(Northern Hemisphere).
A northbound parcel of air
(winds from the south) would
have a Coriolis force acting
toward the east.
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Friction
Friction will always act
In the opposite direction
of flow
Factor of surface
roughness, height
above the surface and
wind speed
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Streamline Analysis
L
H
L
H
it is difficult to find a straight line among the many twisting and turning arrows
covering the United States. And it is very evident that there isn't a wind arrow
originating near the high in Virginia and ending in the low in eastern Nebraska.
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70
Basic Meteorology
Any resemblance to Kim is
completely coincidental
STABILITY
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Stability
• In a stable environment, air
that is forced upward is cooler
(shown in yellow) than its
surroundings (shown in white)
and will tend to sink or spread
out.
• Because the air resists being
moved upward, clouds
formation is limited, and those
that do form will be more
horizontal than those in in
unstable atmosphere.
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72
Stability
•
An unstable environment is one in
which air parcels can maintain their
upward motion. The rising air cools at
a rate that is slower (shown in yellow)
than the rate of the atmosphere
(shown in white).
•
As long as the rising air remains
warmer than its environment, it will
continue to rise. The vertical motion
will cease when it is cooler than the
surrounding environment.
•
Instability is important because rising
air is conducive to vertical cloud
development that can result in severe
storms.
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73
Stability
•
A temperature inversion occurs when a
layer of warmer air lies above colder air. In
this graphic, the inversion layer lies where
the environmental temperature (white
line) warms from 48°F to 52°F.
•
Inversions are key factors in air pollution
incidents and fog events because they act
like lids, trapping the pollutants or fog.
They are common early in the day, but if
the atmosphere heats up enough, the
inversion can be destroyed. If this
happens, usually the fog will dissipate
and/or air pollutants will disperse
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74
Weather Maps
KEY SYMBOLOGY/LABELS/COLORS
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Weather Maps
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Weather Maps
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Local Forecasting
Whether power or sail, as
mariners we care about:
• Precipitation
• Thunderstorms
• Winds (shifts, direction and
speed)
• Fog
• Seas
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78
Forecasting Precipitation
• Since we need clouds for precipitation AND
different types of clouds bring different types
of precipitation (for example showers versus
steady rain), our ability to predict
precipitation is a matter of anticipating the
arrival of clouds AND the type of cloud.
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There’s More to it Than This
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Forms of Precipitation
• Precipitation exists in two forms:
– Frozen (snow, sleet, hail, and ice
pellets)
– Liquid (drizzle and rain)
• The type of precipitation that falls
to the ground depends on the
temperature of the air above.
• If the atmosphere is entirely
below freezing, all of the
precipitation will fall as snow.
• If it's above freezing, the
precipitation will be rain. But if
there are layers of warmer and
colder air, forecasting the
precipitation type can be tricky.
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81
Seaman’s Eye for Precip from Clouds
Associated with Fronts
• A quick glance at forecast frontal positions
provides our first hint of what to expect.
• With or without looking at Weather Charts, we
can frequently observe the changing nature of
the clouds over time and anticipate an
approaching front and potential precipitation.
• Check radar for current precipitation locations
and movement.
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82
Cold Fronts – As Cloud and
Precipitation Makers
Analysis Valid Time 1800Z Tue
48 hr Valid Time 1200Z Thurs
24 Hr Valid Time 1200Z Wed
72 hr Valid Time 1200Z Fri
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SEAMAN’S EYE – ADVANCING
COLD FRONTAL CLOUDS
30 miles
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Warm Fronts – As Cloud
and Precipitation Makers
Analysis Valid Time 1800Z Tue
48 hr Valid Time 1200Z Thurs
24 Hr Valid Time 1200Z Wed
72 hr Valid Time 1200Z Fri
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85
Seaman’s Eye – Advancing
Warm Frontal Clouds
370 miles
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Local Forecasting
THUNDERSTORMS
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Critical Elements for
Thunderstorm Formation
1. Lift – due to thermal, frontal,
orographic or upper level
effects In this picture we see
lower layers heated by warm
surface
2. Instability – allows for sufficient
rise of air to form the
cumulonimbus cloud.
Unstable layer
Moisture
None of this is sufficient without
the third ingredient –
Warm Surface
3. Available moisture
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Initial CUMULUS Stage
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MATURE stage
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Classic “Anvil” of Mature stage
Anvil is formed as rising cumulonimbus cloud reaches a very stable upper
level known as the “Tropopause” and upper level wind carries cloud top
downwind - storm is at peak intensity
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Dissipating stage
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Limitations of Models to
“Predict” Local Thunderstorms
• The resolution of
numerical models is
defined by the space
between grid points.
• Local events such as
Thunderstorms typically
form between the grid
points and are thus
missed by the models
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The Seaman’s Eye for
Precip Not Associated With Fronts
• The primary precipitation in this category
comes from “air mass” thunderstorms.
• We previously said that thunderstorms require
– Moist, unstable air and
– A lifting mechanism
– Conditions in the upper atmosphere
conducive to enhancing the “lift”
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The Seaman’s Eye for
Precip Not Associated With Fronts
• In the Pamlico region,
particularly in spring and
summer, we frequently get
plenty of moist, unstable,
tropical air up from the Gulf
of Mexico AND lifting from
normal daytime heating.
• In our area, heating is more
pronounced further inland,
west of here, or out over
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The Seaman’s Eye for
Precip Not Associated With Fronts
• While it is beyond this
seminar to present upper
atmospheric conditions
conducive to thunderstorm
development, a practiced
Seaman’s Eye can keep you
out of trouble.
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The Seaman’s Eye for
Precip Not Associated With Fronts
• Be aware of wind direction
and speed.
– A long blowing (days)
southerly breeze is pumping
moisture laden air into the
region.
– Light winds are conducive to
allowing lift from daytime
heating.
– If a sea breeze (onshore
wind) kicks in during the
afternoon you know there’s
plenty of heating over land.
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The Seaman’s Eye for
Precip Not Associated With Fronts
– Cumulus clouds indicate some
level of moisture and instability.
– The “taller” they get, the more
instability is evident.
– Fair weather cumulus, towering
cumulus and Cumulonimbus
(thunderstorms) are varying
intensities of the same general
cloud type – Cumulus
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Increasing Instability
• Watch the trend of cumulus
cloud development over days
98
The Seaman’s Eye for
Avoiding Thunderstorms
• How do you know if you are
on a collision course with a
thunderstorm?
– Constant Bearing
– Site over your compass. If the
bearing does not change with
time, the storm is not crossing
your path and is moving
towards or directly away
– Remember that First Gusts,
downbursts can extend many
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center.
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The Seaman’s Eye for
Estimating Distance to Thunderstorms
• If lightning is visible and
thunder is audible…
– Lightning arrives ~immediately
– Thunder (sound) travels at 1/5
miles per second.
– Divide the time between
lightning and thunder by 5 =
distance to thunderstorm in
miles.
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The Seaman’s Eye
Critical Considerations - Lightning
• Note in this image that the
thunderstorm is about 10 miles
across and that ground flashes
originate anywhere inside the storm
at a height of about 5 miles.
• Further, lightning channels usually
slant away from vertical and can even
emerge from the side of the storm.
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The Seaman’s Eye - Critical
Considerations – Bolt out of the Blue
• Boaters frequently
underestimate the danger
of being struck by lightning
well outside the immediate
area of the thunderstorm.
The “bolt out of the blue”
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Strike Probabilities
Courtesy BoatUS – Seaworthy Magazine
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Courtesy BoatUS – Seaworthy Magazine
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And a few thoughts on “Grounding”
Systems
Ungrounded Boat
Electrical charge exits through
through hulls and will melt hull.
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Grounded Boat
Electrical charge is directed
to hull mounted grounding
plate and discharged into
Water.
105
Lightning Protection Systems –
Not Just for Sailboats
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Local Forecasting
WINDS
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Winds – Synoptic Scale
• Remember – Synoptic Scale is looking at the
broader picture – in our case over the U.S.
• Knowing current and forecast locations of
highs, lows and fronts that dominate our
region is key to knowing the near term general
wind pattern.
• Knowing the forecast movement of these
systems is key to knowing long term changes
to the general wind pattern.
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Synoptic Scale Winds Analysis
Current Analysis
Our interpretation of Pamlico
region winds from the current
pattern
• Flow is Clockwise around
the high pressure to our
east = Wind direction S to
SW winds for Oriental
region.
• Isobars (lines of equal
pressure) are loosely spaced
indicating light winds = 5 to
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10 knots.
Synoptic Scale Winds – 72
Hour Forecast
72 hour prognosis
Our forecast for Pamlico
region winds in 72 hours
• Flow is still clockwise
around the High to the East
and ahead of the advancing
cold front = Winds direction
S to SE.
• Isobars are closer spaced in
72 hours indicating
increased wind speed. This
pattern might indicate 10Copywrite 2015, Carolina Yacht Care, LLC,
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15 knots.
Synoptic Scale Winds – 5
Day Forecast
5 Day prognosis
Our forecast for Pamlico
region winds in 5 days
• Flow is clockwise around the
High to the west, behind the
cold front that is forecast to
move offshore = Wind
direction N to NW.
• Isobars are slightly more
closely spaced behind the
front and winds can be gusty
around the front = 10 to 15
knots with gusts to 20.
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Synoptic Scale Winds – 7
Day Forecast
7 Day prognosis
Our forecast for Pamlico
region winds in 7 days
• Flow is still clockwise around
the High to the west, but the
center is closer to the
Pamlico/Neuse region =
Wind direction is NE.
• Isobars are loosely spaced
indicating light winds =
Winds speed 5 to 10 knots.
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LOCAL SCALE WINDS THAT UPSET THE
SYNOPTIC FLOW –
LAND AND SEA BREEZES
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Land and Sea Breezes
Land and Sea breezes result from temperature differences between the land and local
water bodies.
During daytime the land heats up At night, the land looses heat more rapidly
significantly more than the water
and the relatively warm air over the water
and the air over the land rises to
rises to be replaced by air from over the
be replaced by air from over the
cooler land.
114
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cooler water.
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Ideal Conditions
• Sea Breeze
– Spring and Summer (seasons with greatest
temperature difference between land and sea)
– Sunny day that allows for maximum heating.
– Light prevailing (synoptic scale) winds.
• Land Breeze
– Clear night to allow for radiation cooling of the
land thereby increasing the temperature
difference between land and sea.
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Ocean to Oriental
Prevailing
Summer
Wind direction
Nighttime cooling
over land
~18 nm
Land Breeze
Daytime heating
over land
Sea Breeze
July SST ~78-85 Deg F
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November
SST ~ 74o
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January 2015
SST ~66o
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July Southerly Wind
SST ~82-84o
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July 1st – Classic Light
Southerly Winds
SST ~82o
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July 4th Gale
SST ~82o
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Race Courses
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Sea Breeze and
Thunderstorms
• At the bend at MCAS Cherry Point, afternoon
sea breezes and summer thunderstorms often
converge.
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LOCAL SCALE WINDS THAT UPSET THE
SYNOPTIC FLOW –
THUNDERSTORMS
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Thunderstorm First Gust
This sailboat
Is heeling
under bare
poles In a
first gust
• One of the most significant weather
hazards to boaters!
• A rapid change in wind direction
and speed many miles from the
storm.
• Results from the horizontal
spreading of downdraft winds at
the earth’s surface.
• Normally the highest recorded
speed for the storm and as much as
a 180 degree change in direction.
• Occur in ALL shower producing
convective clouds and are
predictable and expected
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Thunderstorm Downbursts
• In addition to the First Gust,
other strong, violent and
dangerous downdraft winds
are associated with
thunderstorms.
• Macro bursts –
– Large Scale, widespread
damage similar to tornadoes
– Can last 5-20 minutes with
speeds up to 130 knots
Note the lateral spreading as the
downburst reaches the ground. The
surface wind speed will greatly increase
and the direction may change up to 180o
• Micro bursts –
– Small Scale, can last 2 to 5
minutes with speeds up to 130
126
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knots
Local Forecasting
FOG
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Coastal Fog Formation
Coastal Fog can take on many forms:
Radiation
Dynamically Forced
Advection
West Coast (obviously not stressed)
Steam Fog (High Lat. – cold regions)
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A closer look at Condensation
• Fog is a cloud and is atmospheric moisture in a liquid
state.
• And we said: “Apply enough cooling to Water Vapor (Gas)
and the molecules slow down, may coalesce and change
state to Liquid (condensation) ”
– “enough cooling” is the Dewpoint Temperature – the
temperature at which some of the water vapor must
condense into liquid water.
• It is always equal to or lower than the air temp.
– So…if the air temp cools to the dewpoint (OR CLOSE) or the
dewpoint rises to the air temp, - fog, clouds or dew begin to
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• When they are equal
have
100%
Relative Humidity
129
Fog
Radiation Fog
- Radiation fog is a ground-based cloud
caused by nocturnal cooling at and near
the ground surface
Advection Fog
- Advection fog is a ground-based cloud
caused by the cooling of an air mass as it
moves over a colder surface
- Typically occurs under clear skies and
moist low-level conditions.
- That surface may be cold ground, snow
cover, water, or ice.
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Radiation Fog
.
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Seaman’s Eye for Conditions
Favorable for Radiation Fog
• As learned, Radiation Fog results from a cool earth’s surface, cooling the
air above it to the point that the molecules slow down enough to coalesce
– forming water droplets.
• The point at which condensation occurs is called the “dew point” (the
point at which dew forms due to condensation) and it is expressed as
“Dew Point Temperature”.
– If Dew Point equals the air temperature = full saturation = 100%
Relative Humidity (RH)
– Simple approximation - For each 1.8 degrees F the Dew Point
temperature is less than the air temperature = 5% lower RH
• Examples: Air temperature = 75F and Dew Point = 73.2F then RH =
95%. Similarly, Air temperature = 75F and Dew Point – 71.4F then
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Seaman’s Eye for Conditions
Favorable for Radiation Fog
• So, we need
– Plenty of moisture in the air near the ground
– Moist ground also helps (such as after a rain) - adding to moisture
availability.
• Swamps also provide significant moisture to the lower atmosphere
– Clear skies AT NIGHT (to allow for the earth’s heat to escape into the
upper atmosphere (Radiation) and therefore cool the ground and the
air in contact with it
– Calm winds
• Then, if all is right, and the air cools to its Dew Point (usually
early morning when there’s been maximum cooling) we have
a strong probability for fog.
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Seaman’s Eye for Conditions
Favorable for Radiation Fog
• For the Pamlico region, moist air generally results
from a southerly flow (mT) bringing in moist tropical
air.
• Then, if the wind dies at night and the sky becomes clear all
night, allowing the air temperature to lower to the dew point
and become saturated, we have a strong fog potential.
• But it can be spotty here because:
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Seaman’s Eye for Conditions
Favorable for Radiation Fog
Our local topography, where raw land (which cools faster) is interwoven with
water bodies and can go from forest to farm, swamp to pavement quickly,
135
canLLC,make fog formation quite localized.
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Seaman’s Eye for Dissipation
of Radiation Fog
• When will it dissipate? Depends heavily on:
– Depth of the fog.
• Typically depth is 3’ to about 1000’
• If your visibility is near zero and you cannot see a lighter shade of gray as
you look up, chances are the layer is quite deep and will be slow to burn
off
– Strength of the sun - to provide warming at the top of the
layer
• Winter sun’s rays are more oblique and thus weaker = slower for “burnoff”
– Wind strength – Calm winds mean slower to dissipate. Stronger
winds = more atmospheric turbulence and mixing of warmer
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Advection Fog
So, when do we have warm moist air
moving over a colder surface?
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Current NWS Surface
Analysis
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December
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Advection FOG
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Seaman’s Eye for
Advection Fog
• We said that advection
fog is a ground-based
cloud caused by the
cooling of an air mass
as it moves over a
colder surface
• When do we have those
conditions in our
region?
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Seaman’s Eye for
Advection Fog
• When the land mass is
cold
– Typically Late Fall,
Winter, Early Spring
• When we have an
onshore flow of
relatively warm, moist
One Scenario
air from over the Gulf
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Local Forecasting
SEAS – WIND WAVES AND SWELL
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Some Definitions
• Fetch – the distance over
which the wind blows and
imparts energy to the sea.
• For a given wind speed a
minimum fetch and
duration is required to
generate a “fully arisen
sea”.
• Thus, we seek shelter in
the lee of a weather
shore.
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Ripples, Waves and Swell
Ripples - the instant effect of wind on water and they
die down as quickly as they form.
Wind Waves - If a wind blows steadily across a large
enough patch of water for a few hours then the ripples
become waves and these will not be dampened so easily.
Swell -
When strong winds blow for longer than a few
hours, it gives the water sufficient energy that it then
takes on a character of its own. It will march across open
areas of water independent of the wind and typically has
longer periods and an undulating/rolling type motion .
.
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Significant Wave Height
Commonly Referred to as Seas in the Marine
Forecast
The average of the highest
one-third (33%) of waves
(measured from trough to crest)
that occur in a given period
Statistically, if forecast Hs = 6 ft
• H (most probable) = 0.6 times Hs = 3.6
ft
• H1/10 (10% highest waves) = 1.27
times Hs = 7.6 ft
• H1/100 (1% highest waves) = 1.67
times Hs = 10 ft
• Hmax (highest wave you should be on
the alert for) = approximately 2
times Hs = 12 ft!
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Wind Wave versus Swell Wave
– Impacts to our Transit
Possible impacts:
Seas higher than forecast
Confused seas
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Seaman’s Eye for Wave
Height and Direction
• Look at the weather map and consider the direction and
speed of winds generating local waves.
• Look at the weather map for major storms up to 1000 to 1500
miles away!
• Anticipate wind waves coming from the direction of the wind
with a shorter period.
• Anticipate swell waves coming from the direction of the storm
with a longer period.
– If wind and swell waves are from same direction – the result will be
higher.
– If wind and swell waves are from opposite or perpendicular directions
– they will be “confused” and more choppy.
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Tides
As the moon rotates around the Earth, its gravitation
pulls the water on the nearest side of the Earth outward
into a bulge. The earth’s spin results in a second bulge
on the opposite side. These two bulges travel around
the globe, producing 2 high tides each lunar day.
During time of the new moon and full moon, when the
sun and moon are in a straight line, their gravitational
pulls combine and produce spring tides; high tides are
very high and low tides are very low.
When sun and moon are at right angles from the Earth,
during the quarter phases of the moon, the gravitational
pull on the oceans is less producing a smaller
difference between high and low tide known as a neap
tide.
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Seaman’s Eye for Depth /
Currents on the Neuse (1)
• First,
a bit about the Neuse
The Neuse River is a Coastal plain estuary, or
drowned river valley, and was formed when rising
sea levels flooded the area.
It is a shallow estuary with a mean depth of 12’,
mean width of 4 miles, and length of 43 miles.
• And
the Pamlico Sound
It is the largest Sound on the East Coast.
A Sound is a Saltwater Lagoon (Separated from
the sea by a sandy barrier).
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Seaman’s Eye for Depth /
Currents on the Neuse (2)
We are fond of saying that the Neuse River has
no astronomical tidal flow.
It is more correct to say that:
(1) Astronomical tides constitute less than 2% of the
variation in both water level and current velocity.
(2) Water exchange is dominated by winds for periods
of days.
(3) Fresh water discharge dominates water exchange
for periods of days to weeks.
(4) Less known is that significant cross river
circulation occurs and exhibits side to side sloshing.
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Ocean Currents
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Information Sources
NATIONAL WEATHER SERVICE
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NOAA/NWS ILM Office
http://www.weather.gov/ilm/
Choose overlays
Such as winds, seas,
sea water temperature
etc.
Offshore Buoy observations
Links to Near and Offshore
forecasts, Tides, Hurricane
info, etc.
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Your portal to local marine information
153
Local NOAA Broadcast
WX1 on your VHF Radio
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Other NWS Operational
Centers
• The Ocean Prediction
Center (OPC)
http://www.opc.ncep.noaa.gov/
– GRIB data
• surface (10-m) wind
speeds with direction (KT)
– surface (10-m) wind
gusts (KT)
– significant wave heights
(FT)
– marine hazards
– Marine Graphic and Text
Analyses and Forecasts
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Other NWS Operational
Centers
• National Hurricane
Center (NHC)
http://www.nhc.noaa.gov/?atlc
– All tracks, advisories,
forecasts
• Graphical and Text
– This is the horses mouth
on everything tropical!
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Other NWS Operational
Centers
• Storm Prediction Center
(SPC) – responsible for
prediction of severe
weather across the
country.
• http://www.spc.noaa.gov/
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Information Sources
COMMERCIAL
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Commercial Websites
WEB
• Oriental area Land and Marine Weather, Seas
and Tides
– www.towndock.net (Nice job Keith)
– www.intellicast.com/Marine/Boating.aspx
– www.passageweather.com
– Excellent source for
animated wind/wave/ pressure
charts
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EXERCISES
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Review Questions
1. Which of the following is not required for precipitation to occur?
a. condensation nuclei
b. source of lifting
c. moisture
d. southerly winds
2. Sleet and freezing rain are caused by a cold layer of air aloft (True or False)?
3. Which one of these clouds can produce heavy showers?
a. Stratocumulus
b. Cumulonimbus
c. Altostratus
d. Nimbostratus
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Review Questions
7. What is the surface temperature?
8. What is the surface visibility?
78
068
9. What is the surface wind
direction and speed?
07
05
10. What is the type of low
cloud?
72
15
11. What has been the pressure tendency over
the last three hours?
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Review Questions
12. Which type of cloud begins as a middle layer cloud, but as it develops
the base of the cloud lowers into the low-level clouds?
a. Altostratus
b. Stratus
c. Cumulonimbus
d. Nimbostratus
13. The best clue that this is mid-level Altostratus and not high-level
Cirrostratus is the lack of?
a. precipitation
b. other cloud types
c. halo
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Review Questions
14. Moist air weighs less than dry air.
(True or False)
15. At night, temperatures will normally be higher under cloudy skies
than under clear skies.
(True or False)
16. Your aneroid barometer indicates that pressure has been decreasing
rapidly over the past three hours. The type of weather that would
normally be expected to occur would be?
a. Fog
b. Thunderstorms
c. Drizzle
d. Clearing
17. A thunderstorm is approaching your anchorage, but rain has not
started – it is safe to assume that lightning will not affect your area
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(True or False)
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Review Questions
4. An easterly wind means that air is moving towards the east (True or False) ?
5. A high level cloud that forms in a layer would be called?
a. Cirrus
b. Cirrocumulus
c. Cirrostratus
d. Altostratus
6. The force that results from the rotation of the earth is known as the…
a. Pressure Gradient
b. Coriolis
c. Frictional
d. Convergence
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Weather Exercise
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Weather Exercise
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