Modern Day Satellite Photos

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http//weather.msfc.nasa.gov/GOES/goeseastconuswv.
html
Weather Service began as part of the War
Department September 1, 1872
Modern Day Satellite Photos Geostationary
Operational Environmental Satellite (GOES)
Program Operated by National Weather Service
(NWS)
http//www.cdc.noaa.gov/cgi-bin/db_search/SearchMe
nus.pl
Cloud charts, Thermometers, Wet Bulb shoelaces,
Humidity charts. pinwheels
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Density falls off with altitude pressure is
caused by impacts, dense air has more impacts
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Buoyancy Lifting
Start Local Heat Air
Expands Dense Air
Jiggles Underneath
(heated atoms speed up paddle board analogy)
forces warm air up
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Air Masses

• An air mass develops when the atmosphere is
  located above a relatively uniform land or water
  surface for several days.
• The lower atmosphere assimilates some of the
  properties of the underlying surface.

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Air Masses

• Large regions (1,000s km2) of the lower
  troposphere with uniform characteristics
  (temperature, moisture content) originally
  defined by a source area.
• Labels refer to temperature (arctic vs. polar vs.
  tropical) and source area (continental vs.
  maritime). The source area determines the
  moisture content.
• Labels around here cT cP mT mP

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http//www.met.tamu.edu/class/Metr304/Dir-surface/
surface.html
Polar air moves further south during winter and
retreats northward during summer.
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Typical Air Mass Changes
Heating (cP air moving south) will lead to
instability as air near the ground surface rises,
mixing the air column.
Cooling (mT air moving north) has the opposite
effect, because cold air cannot rise but remains
in a stable configuration near the land surface.
Orographic Lifting forces maritime mP and mT air
upward over mountain ranges in the western U.S.,
leading to condensation and precipitation that
converts the formerly humid air to a much dryer
air mass.
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Air Mass Interactions
cP
mT

• Weather in any region is influenced by the
  interactions between air masses. Recall that the
  boundaries between contrasting air masses are
  called FRONTS

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Mid-latitude Cyclones
ExtraTropical Cyclones
are up to 2,000 km
across control
the weather for
three days
to a week. Winds circulate
counter-clockwise (CCW) around the Low
surface Northern Hemis.
L
Def Synoptic Scale space and timescales of
mid-latitude depressions i.e. several thousand
kilometers and timescales of several days
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8.
Cold air sinks
HIGH
Polar Cell
LOW
7. Mid-Latitude Cyclones are dominant where
Ferrel meets Polar
4. Ferrel Cell Mid-Latitude Cyclones north Dry
south
5.
HIGH
6. Gyre
2.
3. to E
0. Maximum heat from Sun
LOW
1. ITCZ
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Dishpan Experiment
Why are the boundaries between cold and hot not
straight?
Camera rotates with dish Cold Center hot
edge Large scale waves and eddies form They flow
CW CCW
Rossby Waves
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cP
mT
Heavy rains can result from the interaction
between the continental polar cP air mass and the
maritime tropical mT air mass
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Mid-Latitude Cyclones

• This clash between cP and mT air masses is the
  most common source of frontal systems in the U.S.
  
• Weather conditions, and cloud types, change in a
  predictable sequence as warm and cold fronts pass
  over an area.

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Frontal Systems

• Recall a front is a transition from one air mass
  to another
• Advancing frontal systems bring a predictable
  sequence of clouds and precipitation and are
  accompanied by regular changes in moisture,
  temperature, pressure, and wind direction.

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http//www.met.tamu.edu/class/Metr304/Dir-surface/
surface.html
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DBZ is Decibels received back
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Map Symbols These show surface
positions
cP
mT
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Regular progression of clouds
A useful slide for forecasting.
Symbols at surface
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Warm Front

• Ahead of a warm front, warm, humid air is
  transported upward over a distance of
  approximately 1,000 km (625 miles).
• Rain may last longer than for a cold front
  because the warm front moves slowly and extends
  over a larger area.

Dangerous storms if cold air is very cold
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Warm Front Clouds and Winds

• First sign of warm front is sequence of clouds
  (cirrus, cirrostratus, altostratus).
• If winds are right, up to 12 hours after the
  cirrus, the higher clouds will be replaced by
  lower nimbostratus with associated light to
  moderate precipitation.
• Temperatures and humidity rise and winds
  typically shift direction (first from the south
  or southeast, then from the southwest) with the
  passage of the warm front.

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Warm Front Width
Expect increasing Temperature and Humidity as the
warm front passes
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Cold Fronts

• Cold, dense continental polar air cP replaces
  moist, warm maritime tropical air mT across a
  cold front
• Expect decreasing temperature and humidity and
  increasing atmospheric pressure with the passage
  of the cold front.

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Warm Air Rises

• Warm wet air has lowest density, so it will
  always rise over cooler air.
• Both the cold and warm fronts are inclined toward
  the warm air mass.

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Approaching Cold Front is behind Thunderstorms
Warm air is pushed up and over the advancing cold
front, causing relatively rapid cooling and
condensation that results in the development of
tall cumulonimbus clouds. They host heavy
but relatively short-lived precipitation
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Cold Front Animation
Most of the cloud formation associated with a
cold front is actually in the warm moist air mass
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Cold Front cloud bands are narrow because cold
front wedges are steep
Most of the cloud formation associated with a
cold front is actually in the warm moist air mass
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A Cold Front Squall Line
Rapidly advancing cold fronts may be marked by
the growth of a squall line of thunderclouds
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Cold Fronts are narrow because the edge of the
cold air mass is steep
http//www.emc.ncep.noaa.gov/mmb/gmanikin/nas125/t
storm/squall1.gif
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Cyclogenesis 1 Stationary Front A small scale
wave forms
cP
mT
These persist if the air masses have equal
pressure Then many small waves form, and storms
are very frequent
Mid-Latitude Cyclones start as Stationary Fronts.
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Cyclogenesis 2 Warm and Cold Fronts
cP
mT
In the Ferrell cell, winds have a strong westerly
component, and storms move East. As they mature
and move, Warm Fronts pass over, followed by Cold
Fronts.
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Cyclogenesis 3 Occluded Front forms
Where the cold front catches up, they are called
Occluded Fronts. Note symbol.
cP
mT
Cold front catches warm, forcing warm air aloft.
Broad precipitation area results.
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Occluded Fronts

• The cold front is faster than a warm front and
  will eventually close the gap between the fronts,
  forcing the intervening warm air upward
  generating additional rain

mT
Nimbostratus
cP
Rain then covers a wide area
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Storm evolution
1. Surface map, so winds cross Isobars and
spiral into the LOW
Along the occluded front warm moist air is force
aloft, resulting in a broad band of rain
2. Wide precipitation band
mT
mT
cP
cP
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Thunderstorms

• Thunderstorms form where warm, humid air is
  forced upward to altitudes of up to 15 km (20 for
  supercells).
• Condensation occurs as the air cools, releasing
  latent heat and ensuring that the rising air
  remains unstable (warmer than surrounding air).

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Rising Warm air overshoots into stratosphere
Prevailing Wind Aloft
Freezing Line
Condensation Line
Surface
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Type 1 Isolated Thunderstorms from unstable air
Rain, plus gusty winds caused by downdrafts
Droplets coalesce 15 minutes Only updrafts. No
rain.
All downdrafts
Rain and Ice too heavy for updrafts Lasts
15 to 30 minutes
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2. Aloft
1.
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Lightning
http//www.nssl.noaa.gov

• Most dangerous and frequently encountered weather
  hazard that people commonly experience each year.
  
• Second most frequent weather killer in the United
  States with nearly 100 deaths and 500 injuries
  each year,
• after floods and flash floods

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Lightning equalizes large charge differences
between storm levels and the ground
Ice often positive
marks concentrations of rising and falling ice
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Supercells

• Severe thunderstorms, or supercells, are
  associated with frontal lifting along the cold
  front between the continental polar and maritime
  tropical air masses in mid-latitude cyclones. The
  lower portion of these storms, the mesocyclone,
  rotates. They often contain severe hail and
  sometimes tornadoes.
• Most common during spring and early summer, when
  the contrast in temperatures and moisture between
  air masses is greatest.

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Tropopause
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3. The strong updrafts lift falling ice and it
gets covered with another layer of ice. If this
happens enough times, large hailstones are the
result.
Tropopause
Hail Formation
2. Strong updrafts pull in more air from below.
1. Condensation heats the moist air, which
accelerates upwards
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Supercell Hail
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Tornadoes

• Funnel clouds that rotate at speeds of up to 500
  km/hr beneath supercells.
• Ranked from F0 (weakest) to F5 (strongest) using
  the Fujita Intensity scale.
• Most move to the east or northeast at an average
  speed of approximately 50 km/hr.
• Develop in association with mesocyclones

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Wind Shear (different wind directions at
different altitudes) causes rolling
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Updrafts can pick up the roll
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Jet Stream winds result from large pressure
gradients at the boundary between Tropical and
Polar air, where a large difference in Tropopause
height exists.
The Jet Stream
N
The jet stream and tornadoes Divergence aloft
in the extreme
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Tornados are narrow areas of extremely fast
updrafts
A strong tornado often is associated with rapid
removal of updraft air by the Jet Stream aloft
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Jet Stream Aloft
cP
mT
Potential for wind shear with hot dry unstable
cT Similar temp but different density than mT
which is moist and therefore light
cT
The Dry Line
Tornado Conditions
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Mostly Spring Early Summer
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Multiple vortices in an F5
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May 3, 1999
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Supercell tops overshoot into stratosphere
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Stecker
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http//www.nssl.noaa.gov/teams/swat/Cases/990503/A
_images/stecker.gif
A Stecker, Oklahoma Home
Only F3
May 4th, 1999
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A Perfect Hook
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Hurricanes Typhoons (Tropical Cyclones)
When extremely hot ocean surface temperatures
(gt26oC) cause hot, moist surface air, huge
clusters of thunderstorms develop at sea. If
uplift gets extreme, these can organize into a
gigantic Low with spiral storm lines, and winds
exceeding 74 mph, a



Tropical Cyclone, aka
Hurricane
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Hurricanes are fueled by Latent Heat of
Condensation release. One day equals the energy
production of US for a year
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Jeanne
Hurricanes need hot moist air as fuel. This is
why they weaken over land
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Trapped in House, swept away
Storm Surge
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Storm Surge
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Freshwater (rain) floods cause most fatalities
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