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82 Cards in this Set

  • Front
  • Back

Weather/precipitation modification

seeding of clouds for enhancement of precipitation

Fog dispersal

Main reason to have is for aviation operations

Only success has been in colder weather when you have freezing temps

Hail suppression

Russian scientists have claimed success

Not looked at by scientists

Fronts blank air masses



Generalized name given to areas of low pressure



Mid latitude frontal cyclone

Extra tropical cyclone

Cold core low

Rare for frontal cyclones to become huricanes

going from extratropical to tropical is rare

tropicals will become extratropical

Occluded front

when a cold front overtakes a warm front


Boundary between 2 air masses


Dying out front


Front is beginning in an area


moisture that is overrunning the colder air

4 types of fronts

1. Cold front

2. Warm front

3. Stationary front

4. Occluded front

Cold front

colder air actively adv into a region formerly occupied by warmer air;

Always drawn in blue

Depicted only on a surface map

Triangle points into dir front is moving

Thunderstorms and hail; most severe weather

Perpendicular to air flow

Steep slope (1:50)

Warm Front

When the surface position of a front moves such that warmer air occupies territory formerly occupied by colder air

More gentle slope (1:150)

Red line with semi circle

Only on surface level map

perpendicular to air flow

Stationary front

Little forward movement of either air mass

Usually upper level wind are parallel to the surface front boundary

depicted by red semicircle and blue triangle

Depends on the upper level conditions

Occluded front

Cold front that overtakes a warm front in the vicinity of a surface low

very rare that we see this in TX, more common in N US

Purple and semi circle triangle

Dry line

not a front but is a barrier b/w fronts

Boundary b/w cT(hot dry air) and mT(warm moist air)

Found most commonly over the US plains states (Tx northwards)

cT air mass orig over deserts of SW US & N Mexico

Molecular weight of cT air is heavier than that of the mT air so when this feature moves eastward dry line scale lift occurs and thunderstorms can occur

What is weather forecasting

Predicting how the state of the atm will change w/ time

To be able to forecast the weather, current weather info over a large area must be known

The process of forecasting the weather is like putting a puzzle together

Geostationary satellites

As the earth rotates, satellites rotate w/ Earth and view the same spot


Dir over equator at 75 deg W lat


Dir over equator at 135 W long

New Zealand, Australia all the way to the Rocky's E Pars of Asia to US

Geostationary Satellite Imagery

Visible Imagery

Infrared Imagery

Water Vapor Imagery

Visible Imagery

Monochrome View; Depends on the light of the sun; only ava when sun is overhead on your part of globe

Infrared Imagery

Cloud top temp meas; the hotter the colors, the colder the temp; Red=cold

Water Vapor Imagery

Most imp in detecting mid to high atm water vapor; allows us to see where there is moist in the atm

Radar Data

Radars show the reflectivity from the rain drops

Larger the droplet, the more reflectivity and color there will be in the radar data

Velocity Data

Radars show the reflectivity from the rain drops

Larger the droplet, the more refl and color there will be in the radar data

Dopolar radar

Tells you the shape of the obj

Most recent type of radar

Radar Rules

Cone of silence d/n rotate directly up

W/ range from radar there is height

Modes Clear Air Vs Precipitation

Greens are inbound towards the radar

Reds are out bound away from the radar

Surface Weather Observation

Taken at thousands of locations around the world on an hrly bases(airports, military bases, ships)

Observations: automated, automated w/ manual augmentations; manual

NWS Cooperative Climate Data

Ppl give data on the highs and lows

Not very tech adv

Rain gauge therm

World Mete Org

Resp for the international exchange of weather and certifies that the observation process d/n very b/w nations since all weather obs must be comparable

Where do most ppl get their weather forecasts

Radio, tv, internat, newspapers


Radio/TV seal of approval programs

AMS certified Broadcast Meteorologists

These are voluntary professional orgs

No licensing of mete, so the use seals

Weather Watches

Atm cond are favorable for the type of weather specified (generally larger geog area, longer time span: 4-6 up to 24-48 hrs)

Only issued by National Weather Service

Weather Advisory

Type of weather specified is imminent or is occurring and is occurring and is a public inconvenience (smaller to larger geog area; generally in effect for 6-24 hrs)

Weather warning

Type of weather specified is imminent or occurring and an immediate threat to life and or prop (smaller geog area; smaller time period 1/2-1 hr)

Weather forecast tools: Computes

Numerical Weather Predictions (NWP)

Numerical Weather Predictions (NWP)

Computer atm "models" (programs)

Models are mathematical in nature, data in data out

Models are initialized and run generally one to four times a day

Problems with NWP

If bad in, bad out

Models make certain assumptions and therefore have certain biases

Data sparse areas of the World

C/N adequately interpret many of the factors that influence surface weather

Small disturbances/ small error tend to be amplified (chaos) esp w/ time

Methods of forecasting

Persistence Forecasting (in short term)

Steady state/trend forecasting

Ensemble forecasting

Climatological forecasting

Probability forecasting

Persistence Forecasting (in short term)

prob of most value in short term; loses value when weather is changing rapidly

Steady state/ trend forecasting

Look at what weather is doing in one place and calc dist to another city to know what will happen in that city, how fast sys moving

Analogue Method forecasting

Comparing sys thats happening to similar past sys

Ensemble forecasting

By product of NWP

Climatological forecasting

Most use in climates where the weather is stable

Probability forecasting

Very misunderstood fact of forecasting

Forecaster certainty x areal coverage expected

Ex 50%x20% = 1000 or 10.00%

Point prob expression

Accuracy inWeather Forecasting

Accuracy rates in short term = 55-90%
Short term forecasts (today-tonight) 85-90%
Medium term forecasts (2-3 days) 80-85%

Larger range forecasting (4-8 days) 70-80%

Ingredients for thunderstorm

1. Atmospheric instability

2. Moisture (mT airmasses)

3. Atmospheric lift

Most common in warmer equatorial climates

Types of thunderstorms

1. Single cell

2. Multicell clusters

3. Multicell lines

4. Supercenters

Single cell thunderstorms

Last 1-1.5 hrs



Multicell cluster thuderstorm

Can cover states

Multicell lines

Lines of storms


Extreme thunderstorm


Produce tornados

Stages of thunderstorm

1. Cumulus: updraft dominated, clouds build higher

2. Mature: updraft/downdrafts coexist; air gets cold and heavy, precipitation falls; lightning

3. Dissipating: downdraft dominated; Cold air dominates, air sinks and cuts off updrafts, fuzzy clouds b/c breaking down

Severe thunderstorm

Hail >= 1" in diameter

winds of 50 knots/58 mph or higher

presence of tornado

Difference in the structure of non-severe vs severe thunderstorms

non severe have weak upper air wind

severe have strong upper air wind

Both severe and non severe thunderstorms have

dangerous lighting

Mesoscale Convective Systems (MCSs)

Other thunderstorm phenomena

Complex sys that form near fronts

Mesoscale convective complexes (MCCs)

other thunderstorm phenomena

Special type og MCS

Long lived, nocturnal formation

Square line

Line of storms, better org than general multicell clusters

Bow echoes

produce strong winds


strongly rotating updraft

most d/n produce tornados


Widespread convection/ thunderstorm windstorm



Downbursts (Microbursts and macrobursts)

footprint of the downdraft

Microburst: 2.5 miles or less in diameter

Macroburst: > 2.5 miles in diameter

Straight line winds

Downdraft that diverges when it hits the ground

more common than tornadoes

most damages from thunderstorms are caused by this


Quarter sized hail


1 inch

50 mph

Baseball size

2.75 inches

85 mph

DVD/CD size

5 inches

125 mph

Can kill you


Forms as result of separation of charges b/c of presence of ice crystals and cloud droplets in the strong updrafts and downdrafts

begins at very end of cumulus stage into mature stage

Bolt of lighting is about the diameter of pencil

temp is 5 times the temp of outer surface of sun 54,000 F

Can strike up to 10-20 miles away from the thunderstorm; 5 sec = 1 mile away

Positive(more deadly) neg(less deadly) charges

Positive at ground and upper storm; neg at cloud base

Florida= lightning capital of US

Heat lightning

Heat d/n cause lightning

if you can't hear thunder then heat lightning

Not at risk

Sheet lightning

Result of rain concealing bolt but you see the whole base of the cloud

Ball lightning

lightning hits power lines; balls of fire travel down lines

Avg thunderstorm days in Austin

40-45 days


dependent on updraft and downdraft speed

Largest hail falls NE of tornado

In US hail occurs most freq central and S plains W/NW of Rockies

Resp for home and agricult damage

Largest hail in US history = 7 inch in diameter



Violently rotating column of air extending from base of cumulonimbus cloud

Reach earth surface

Flash floods

#2 killer

types of flooding

1. River flooding

2. Flash flooding: very quick

S central TX flash flood capital of US

1. Subsoil limestone layers

2. Urbanization

3. Hilly nature of Texas Hill Country

Summer heat

Number one killer in the US

Sign of heat stroke: we stop sweating

Evaporative cooling depends on the amount of envir moist present

Winter cold

Hypothermia and frostbite

Funnel cloud

like a tornado but d/n touch the ground

Ingredients for a tornado

1. mT air masses(warm, moist air)

2. Extremely unstable air mass

3. Strong lifting mechanism

4. Initial temp inversion: explosively releases thunderstorm

Climatology of tornado

1. < 1% of all thunderstorms produce tornado

2. Atm pressure in the strongest tornadoes is thought to be about 10% less than std pressure

3. 1300 tornados, 80% weak, 19% strong, 1% violent