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Chapter 30
WEATHER
FORECASTING &
SEVERE WEATHER
Severe Wx BFRB Pages 125-129
Wx Forecasting Pages 130-132
FORECASTING
Station Models
• Used on weather maps to show
the current weather conditions for
a particular location
• They are easy to read and
understand
• ESRT’S Page 13 Bottom
• The circle at the center shows the
amount of cloud cover
• The “flag pole” coming out of the
circle shows the direction that the wind
is coming from
• Each “flag” shows approximate wind
speed. A half flag shows an approx. 5
knot wind, and a whole flag shows an
approx. 10 knot wind
• *Add up the amount for all of the flags
to get the total wind speed
• Air pressure is shown by using the last 3
digits of the pressure in millibars
(coded)
– Ex. 1018.6mb = 186 on the station model
• To determine the air pressure from the
numbers on the station model, use the
following rule: (aka to decode)
– If the first number is 5 or less, put a 10 in
front of it
– If the first number is 6 or higher, put a 9 in
front of it
– Put the decimal point between the last
two numbers
• Ex. 892 for air pressure on the station
model
• The first number (8) is greater than 5, so I
will put a 9 in front of it (becomes 9892)
• Then I put the decimal between the last
two numbers (becomes 989.2mb)
• The correct air pressure is 989.2mb from
the number 892 on the station model
• **Remember, surface air pressure is
usually between 960mb – 1050mb
• If your answer is not in this range, then it is
wrong. Check your work!
Encode this weather data:
Cross River – Cloudy, 61°F, 58° DP, 8.0 mile
visibility, 30.35 inches falling, wind speed 9
mph, from SW.
61
280
8
\
58
0
Decode this Station Model!!!
88
¼
862
-11\
86
.35
SEVERE WEATHER
Thunderstorms
• small area storms formed by the strong
upward movement of warm, moist air
• usually occurs ahead of a cold front as
the colder, denser air shoves the
warmer air upward
• This forms the cumulonimbus clouds
that produce thunderstorms
• These storms are accompanied by
heavy rain, thunder, lightning,
sometimes hail, and can also produce
tornadoes
• All thunderstorms produce lightning
• Lightning is the discharge of huge
amounts of static electricity (think of
walking across a carpet in your socks
and then touching something-ZAP)
• Lightning can travel from the cloud to
the ground, cloud to cloud, or even
from the ground to a cloud!
• Thunder is the result of the air quickly
expanding from the heat of the
lightning bolt (causes a sound wave)
• You cannot have lightning without
thunder and vise versa!!
Supercell
Thunderstorm
formations – will form
SEVERE storms and
tornadoes! THIS IS ONE
BIG STORM SYSTEM!
Tornadoes
• Form from very powerful thunderstorms
(cumulonimbus clouds)
• These are funnel shaped columns of
spiraling winds that extend down to the
ground from the base of a cloud
• The winds move into a tornado (low
pressure), and can reach a maximum
of 318 mph!
• The actual funnel is made by water
droplets (clouds) and dust
• Tornadoes are especially dangerous
because it is so difficult to predict
where they will form
• Damage is usually along a narrow
path where the tornado traveled
• They usually last less than one hour
• Most fatalities are caused by flying
debris
• Tornadoes are rated on the Fujita scale
(F0 – F6)
• An F6 is very rare, and can have wind
speeds up to 318 mph
NEW YORK TORNADOES!
Tornadoes will pick
up dust and debris
from the ground
when they “touch
down” – this
creates a wider
swirl at the bottom
of the tornado
Hurricanes
• Huge tropical low pressure systems
that get their energy from the
tremendous amount of warm ocean
water that is evaporated and
condenses inside the storm
• Hurricanes MUST form over open warm
ocean water (WARM WATER = FUEL)
• VIF - Since this is where it gets its
energy from, hurricanes weaken as
they pass over land or colder water
• Since hurricanes are extreme low pressure
storms, the winds blow into the storm, and it
spins counter-clockwise (to the left)
• The lowest air pressures on Earth have been
recorded inside the eye of hurricanes
• Hurricanes are associated with very high
winds and heavy rains
• Storm surge is the term used for the water
that a hurricane blows onto the shore,
causing severe flooding
– Spring Tides = more severe flooding
– Neap Tides = less severe flooding
• Most fatalities are caused by drowning in the
storm surge (many foolish people do not
evacuate areas when told to do so)!!
• A “tropical storm” is designated a
“hurricane” when its winds reach 74 mph
and vice versa.
• Hurricanes are classified as Category 1 –
Category 5 (strongest)
• All hurricanes are named in each ocean in
alphabetical order, alternating male and
female names
• Pacific, Atlantic and Indian Oceans all have their
own names for their Hurricane Seasons!!!
The Eyewall of a Hurricane
Airforce Meteo planes fly through Eyewalls of
Hurricanes to collect data to help meteorologists
determine where a Hurricane will travel to
Hurricane damage can range
from broken windows to
complete demolition of
buildings. Until Katrina, Andrew
was the costliest hurricane to
date for the USA with a price tag
of over $20 BILLION! Katrina is
now estimated to have a $200
BILLION price tag!!!