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Introduction to G410
Daily telemetry observations
Go to www.nwac.us and click on Weather and Snowpack
Information.
Go to Alpental and make a table in your notebook that
records the following data. Next go to Snoquamlie Pass,
record 300’ data only.
Date
5400’ T
min/max
4300’ T
min/max
3120’ T
min/max
RH
5420’
RH
3120’
Wind
avg/max
Wind
Dir.
Hr prec
3120’
Tprec
3120’
24 hr
snow
Notes
Introduction to G410
Daily weather and avalanche forecasts
Go to www.nwac.us and click on Forecasts
Read weather and avalanche forecast on a daily basis.
Add notes that help explain your telemetry data
Introduction to G410
MOUNTAIN WEATHER FORECAST FOR THE OLYMPICS WASHINGTON
CASCADES
AND MT HOOD AREA
NORTHWEST WEATHER AND AVALANCHE CENTER SEATTLE
WASHINGTON
340 PM PST MON JAN 5 2009...corrected
WEATHER SYNOPSIS FOR MONDAY AND TUESDAY
Strong and moist post frontal flow continues Monday afternoon. However the
westerly flow is producing widely varying precipitation patterns with the
concentration of the heavy precipitation in the north central Cascades,
especially Stevens and Snoqualmie Passes where heavy precipitation has been
occurring since the warm front passes early Monday morning.
Introduction to G410
BACKCOUNTRY AVALANCHE FORECAST FOR THE OLYMPICS WASHINGTON
CASCADES AND MT HOOD AREA
NORTHWEST WEATHER AND AVALANCHE CENTER SEATTLE WASHINGTON
915 AM PST MON JAN 5 2009
ZONE AVALANCHE FORECASTS
CASCADE PASSES, STEVENS, SNOQUALMIE AND WHITE PASSESAVALANCHE WARNING FOR MONDAY THROUGH TUESDAY....
Monday morning: HIGH avalanche danger below 7000 feet. Monday afternoon:
HIGH avalanche danger above 4000 feet and CONSIDERABLE below.
Monday night: Slowly decreasing HIGH avalanche danger above 4-5000 feet and
CONSIDERABLE below.Tuesday and Tuesday night: Significantly increasing
danger Tuesday morning becoming EXTREME above 4000 feet and HIGH below.
Introduction to G410
Bring to class
1) Textbook – Avalanche handbook
2) Calculator
3) Pencil and eraser
4) Lecture 7:30 pm – 9:30 pm
Bring to field
1) Backpack
2) Transceiver
3) Shovel
4) Probe
5) Warm clothing -- see list on web site.
Mountain Weather and Energy Flux
Four factors that affect the formation and
release of avalanches
Variations in solar heating create our
dynamic atmosphere
Reasons Snow Important
•10% of the Earth's surface is covered by glacial ice, with
snow covering the glacial ice.
* Small changes in climate can have very large effects on
precipitation as snow, the amount of water stored as snow,
and the timing and magnitude of snowmelt runoff.
Hydrologic Cycle
 10% of the Earth's surface is covered by glacial ice, with snow covering the
glacial ice.
 Small changes in climate can have very large effects on precipitation as snow,
the amount of water stored as snow, and the timing and magnitude of snowmelt
runoff.
Phase diagram – H20
The phase diagram is
divided into three regions,
each of which represents
a pure phase.
The line separating any
two regions indicates
conditions under which
these two phases can
exist in equilibrium.
Phase diagram – H20
Lets change pressure, and
see how the boiling point
and freezing (melting),
point of water deviate
from normal magnitudes.
Here we change the
phase of a material
without a change in
temperature
General Circulation
Unequal heating between equator and
pole causes circulation cells
Location of cells correspond to
alternating belts of high and low
pressure regions.
Cells also correspond to wind.
Easterly winds from equator to 30°
latitude (trade winds) and 60° to
poles.
Westerly winds from 30° to 60°.
Jet Streams
Strong air currents produced by
pressure gradient between poles and
equator.
Location, strength and orientation
vary with season and day to day.
Summer and Winter positions
Jet Streams
Air Masses
Regional scale volume of air with
horizontal layers of uniform
temperature and humidity.
Form during episodes of high
pressure
Location name = origin
M = maritime
C = continental
T = tropical
P = polar
A = Arctic
Air Masses and Fronts
m = maritime
c = continental
T = tropical
A = arctic
P = polar
As these air masses move around the Earth, they acquire additional attributes.
Mountain Climates of Western North America
• Four mountain ranges
parallel west coast of
North America
 Coast Ranges
 Alaska Range
 Cascades Range
 Sierra Nevada
• Ranges - perpendicular
to the prevailing westerly
winds of the mid-latitudes
Mountain Climates of Western North America
Each mountain
range varies
w/respect to
elevation
Coast Range: Elevation varies from N to S.
Olympic Mtns are highest portion of Coast Range in the USA
Cascades: Highest peaks are volcanoes. The mean crest elevation is considerably
below the elevations of these isolated volcanoes.
North Cascades- somewhat higher elevations and heavy winter snowfalls produce
extensive glaciation
Mountain Climates of Western North America
• Significant barriers to maritime air
masses moving into the continent
from the Gulf of Alaska and northern
Pacific
• Moist air carried inland from the
Pacific Ocean is lifted:
• First over the Coast Range
• Then over the Cascades
Range
Mountain Climates of Western North America
• Low precipitation or rain
shadows on the lee side of
mountain ranges
West slope of Olympic Mts: 150” (381cm)
Sequim, WA = 16 “ (41 cm)
•Supports different ecosystem, semi-arid
shrub/steppe.
Coast Mountains: 2.3 SWE (1-7-2007; Hurricane Ridge, Olympic National Park, Washington)
Cascades Crest: 2.85 SWE (1-7-2007; Alpental Ski Area, Washington)
Eastern Washington: 0.12 SWE (1-7-2007; Mission Ridge Ski Area, Washington)
Mountain Climates of Western North America
• Precipitation is highly
seasonal
• Influenced by Aleutian Low
& Pacific High
•These two semi-permanent
pressure systems move in
tandem..
• Northward shift in
summer
• Southward shift in
winter
Mountain Climates of Western North America
Winter
• Storms develop in the area of the
Aleutian Low & bring near continuous
drizzle, rain and moderate coastal
winds along the west coast of N.
America
• Southwestery winds to the south of
low pressure storm systems bring the
heaviest precipitation
•Maritime influence moderates the
temperatures
Mountain Climates of Western North America
Spring
• Pacific High moves northward
and intensifies
• Milder, drier weather to the
Coast and Cascades Ranges
• Clockwise circulation exposes
the coast to winds out of the
NW
• High pressure suppresses
cloudiness and precipitation
Introduction to the Atmosphere
Synoptic (large-scale) weather systems
• Monsoons
• High & low pressure centers
• Fronts
Introduction to the Atmosphere
Composition
A. Three gases
Nitrogen (78%)
Oxygen (21%)
Argon (1%)
Introduction to the Atmosphere
B. Other gases
• Water vapor (0 - 4% vol)
• Carbon dioxide (0.034% vol)
Water vapor and CO2 absorb radiation
emitted by the Earth’s surface and reradiate
it back towards the Earth
C. Aerosols: natural or man-made
• Rain, snow, ice, dust, pollen,
• Carbon, Acids
Affect transmission of light - visibility
Serves as a nuclei for condensation of
water vapor
Introduction to the Atmosphere
D. Humidity
• Water content varies
over time and space
• Amount of water vapor
depends on air
temperature
• Warm air holds more water
vapor than cooler air
• High humidity areas are
found in warm
equatorial regions
Introduction to the Atmosphere
Relative humidity
Ratio of actual water content of
air to the water vapor content of
saturated air at the same
temperature
e
RH  100
es
e = actual water vapor pressure
es= water vapor pressure that
would
 have if it were saturated
at its current temperature
Introduction to the Atmosphere
Relative Humidity
• Percentage value
• Water vapor content at
saturation rises with T, but
actual vapor content does
not
• Diurnal variations are present
• Relative humidity reaches max
just before sunrise when temp is
lowest.
• Relative humidity reaches min in
mid-afternoon, when temp is
highest.
Introduction to the Atmosphere
Water phase changes in atmosphere
 Water vapor
 Liquid water
 Solid water
 Water changes between phases
• Phase changes release or store large
quantities of heat, called
• Heat must be supplied to change solid
to liquid or solid to vapor
• Heat is liberated with reverse phase 
• Amount of heat required to evaporate
water is equal to the amount of heat
liberated when water vapor condenses.
Latent Heat: the amount of heat
energy released or absorbed when
a substance changes phases (ice
to vapor, or rain to ice)
Introduction Atmospheric Structure
• Vertical Structure
•
• Stratosphere
• Mesosphere
• Thermosphere
• Defined by air temperature
w/r to height
Vertical structure, exponential decrease of
air density and pressure with height.
Introduction Atmospheric Structure
Air pressure: Mass per unit volume of atmosphere
• Millibars or pounds/sq inch
• Air pressure is the measure of weight of a column of air
above that level
• Temperature, density, and pressure are closely related.
Gas laws exponential decrease of air density and pressure
with height.
P  RT
P = pressure
 = air density
R = gas constant
T = absolute temperature
Introduction Atmospheric Structure
Atmospheric stability
resistance to vertical
motion.
• Stable atmosphere =
horizontal clouds
• Unstable atmosphere
= vertical clouds
In general, clouds form as a result of
warm air rising, cooling, and expanding
Introduction Atmospheric Structure
Unstable atmosphere =
vertical motions &
vertical clouds
These types of layered
clouds are called cumulus
clouds
Stable atmosphere =
horizontal clouds
These types of layered
clouds are called stratus
clouds
Air Parcel
• We used the term “parcel” when talking about
moving air up or down in the atmosphere
– Just a balloon-like volume of air that does not mix
with the surrounding air
• New term: Adiabatic - a process in which no heat is
exchanged between an air parcel and the surrounding
environment.
– If it rises, the air inside expands and cools
– If it sinks, the air inside compresses and warms
Adiabatic Process
• The rate at which a parcel cools as it rises or
warms as it sinks depends on whether or not
the air is saturated
• Average rate = 6.5º C per 1000 m
• If the air is unsaturated (RH<100%), this rate
is 10º C per 1000 m is is called the dry
adiabatic lapse rate
Introduction Atmospheric Structure
Adiabatic change in the atmosphere
as a parcel of air rises or sinks.
Moist Adiabatic Lapse Rate
• If an unsaturated parcel of air rises and
cools, it will eventually cool to its dew point
where it will be saturated (RH=100%)
• Further cooling results in condensation
– This is when a cloud begins to form
– Also, condensation represents a phase change
of water from a gas to a liquid. Latent heat is
released
So if the air still continues to rise, will it still cool
at the dry adiabatic rate?
Moist Adiabatic Lapse Rate
No, the rate will be less due to the release
of latent heat
 So, rising saturated air does not cool as
quickly as rising unsaturated air
 In fact, it cools at an average rate of 6ºC
per 1000 m which is called the moist
adiabatic lapse rate
Lapse Rates
3000 m
4º
RH = 100%
2000 m
10º
RH = 100%
1000 m
20º
RH < 100%
30º
RH < 100%
Surface
Determining Stability
• If a parcel rises and cools, and is then
colder than the surrounding air, it will
sink back to its original position – stable
• If the parcel is warmer than the
surrounding air, it will continue to rise unstable
Review:
Cloud Development and Stability
4 major ways air is forced to rise and
produce clouds
1) Heating at the surface (convection)
2) Topography (mountains, hills, etc.)
3) Convergence of surface air (air flows
come together)
4) Uplift along fronts
Cloud Development and Stability
Convection
 Hot surface heats air
 Warm air rises
 Cooler air from above
sinks to replace it
• If the condensation
level is low:
• One thermal may cause
a cumulus cloud
• If high:
• May take several
thermals
Sinking air at sides causes lots of blue
sky in between clouds
Introduction Atmospheric Structure
Surface Energy Budget
Amount of heat and
moisture transferred
between the lower
atmosphere & Earth’s
surface.
Net solar and terrestrial radiation (R) at the Earth’s surface must be
transformed into:
Latent heat flux (L) used to evaporate or condense water
Ground heat flux (G), used to warm or cool the ground
Sensible heat flux (H), used to warm or cool the atmosphere
Heat Definitions
Latent Heat: the amount of heat energy released or
absorbed when a substance changes phases (ice to
vapor, or rain to ice)
Sensible Heat: the heat that is transported to a body
that has a temperature different than it’s surroundings
(the heat difference you can “feel” or “sense”)
Introduction Atmospheric Structure
Net all-wave radiation term, R
All objects emit radiation.
The wavelength depends on the
temperature of the radiating body
The Sun (6,000°C) emits most
radiation in the wavelength range
of .015-3 micrometers.
Human vision responds to the
visible spectrum (0.36-0.75
micrometers).
Terrestrial objects have much lower
temperatures and radiate energy
at 3-100 micrometer wavelength.
Hot objects emit at short
wavelengths
Cold objects emit at long
wavelengths
Introduction Atmospheric Structure
Radiation from the Sun is
called shortwave radiation.
Radiation emitted from
objects or gases at normal
terrestrial temperatures are
called longwave radiation.

Longwave Radiation (LWR): heat
you can’t see

Shortwave radiation (SWR):
visible light
Introduction Atmospheric Structure
Net radiation, R
Both short wave and long wave radiation can be directed
upward from the ground or downward from the atmosphere
Four components of the net all-wave radiation term R
a) incoming short wave radiation
b) outgoing short wave radiation (fraction of the incoming shortwave
radiation)
c) incoming long wave radiation emitted by gases and clouds in the
atmosphere
d) outgoing long wave radiation emitted by the Earth’s surface and
objects on it.
Introduction Atmospheric Structure
Diurnal Variations in R
Introduction Atmospheric Structure
Diurnal Variations in R
Both solar terms begin at
sunrise and end at sunset.
Short wave R peaks at
midday
At night, short wave R is
zero
Why the lag between svr
and T?
Processes affected by energy exchanges
 Snow formation in the
atmosphere
 Snowpack metamorphism
 Surface hoar formation
 Near-surface facet formation
 Temp regimes and gradients