Weather & Climate Unit 4

Front 1

What is a cold front?

Back 1

A cold front is when cold air actively advances into a region formerly occupied by warmer air; has a steep slope (1:50).

Front 2

What kind of fronts often result in severe weather and less severe weather in Texas?

Back 2

cold fronts ---> severe

warm fronts ---> not severe

Front 3

What is a warm front?

Back 3

A warm front is when the surface position of a front moves such that warmer air occupies territory formerly occupied by colder air; has a more gentle slope (

Front 4

What is a stationary front?

Back 4

A stationary front is what occurs when there is little forward movement of either air mass. Usually upper level winds are parallel to the surface frontal boundary.

Front 5

What is an occluded front?

Back 5

An occluded front is when a cold front overtakes a warm front in the vicinity of a surface low.

Front 6

Where are occluded fronts more common and to what do they give a clue?

Back 6

Occluded fronts are more common in the northern US and they give a clue that the LOW is about to end.

Front 7

What do fronts separate?

Back 7

Fronts always separate air masses.

Front 8

Is a Dry Line a front?

Back 8

NO, a dry line is not a front

Front 9

What is a Dry Line?

Back 9

A dry line is a boundary between cT (continental tropical...hot, dry air) and mT (warm, moist air) air masses.

Front 10

How is it that dry lines cause severe weather?

Back 10

Because the molecular weight of cT air is heavier than that of the mT air, the dry line scale lift occurs, which acts just like a cold front in moving up the warm front, hence a major reason t-storms & tornados occur.

Front 11

How is Numerical Weather Prediction done?

Back 11

Numerical weather prediction uses current weather conditions as input into mathematical models of the atmosphere to predict the weather.

Front 12

What is Analog Forecasting?

Back 12

It involves examining today's forecast scenario and remembering a day in the past when the weather scenario looked very similar (an analog). The forecaster would predict that the weather in this forecast will behave the same as it did in the past.

Front 13

What is Persistence Forecasting?

Back 13

The persistence method assumes that the conditions at the time of the forecast will not change. For example, if it is sunny and 87 degrees today, the persistence method predicts that it will be sunny and 87 degrees tomorrow.

Front 14

What is Climatological Forecasting?

Back 14

Very similiar to Persis. Method; This method involves averaging weather statistics accumulated over many years (aka, the climate) to make the forecast.

Front 15

What is Steady State / Trend Forecasting?

Back 15

when a system is maintaining a steady speed, a forecast is made based on its probable trajectory.

Front 16

AMS (American Meteorological Society), National Weather Association (NWA), American Meteorological Society (AMS)

Back 16

All are volunteer profeesional organizations (not lincensed), related to scientific quality of forecasts

Front 17

National Weather Service (NWS): Watches

Back 17

keep an eye out because "conditions are favorable" for a given system

Front 18

National Weather Service (NWS): Advisory

Back 18

sign that the situation is materializing; mainly used to increase awareness - usually not a life/death situation

Front 19

National Weather Service (NWS): Warning

Back 19

conditions are occurring or are imanent; usually a life/death situation

Front 20

What are the 3 essential ingredients for a thunderstorm?

Back 20

1) moisture
2) unstable atmosphere
3) lift

Front 21

What are the 3 stages of a thuderstorm?

Back 21

1) cumulus: updraft dominates, no precip/lightening; 2) mature: up/down draft coexist, severe weather (lightening/rain/gusty) occurring; 3) dissipation: down draft oriented

Front 22

How many t-storms are in progress at any given moment worldwide?
Where are they more common?

Back 22

2,000
common in warmer, equatorial climates

Front 23

Of the 2,000 t-storms in a given day, how many are nonsevere? severe? will produce a tornado?

Back 23

nonsevere: 95%
severe: 5%
tornado producing: 1%

Front 24

What is the average lifespan of a t-storm?

Back 24

~ 1 hour

Front 25

What are normal thunderstorms also referred to as?

Back 25

mT Air Mass

Front 26

What dangerous element is not incorporated into the severity of thunderstorms? Are most thunderstorms severe?

Back 26

Lightening

No

Front 27

Stronger winds aloft in the upper atmosphere will help do what to a thunderstorm?

Back 27

Stronger winds aloft in the upper atmosphere will help reposition the down draft of a thunderstorm, which will help increase its lifespan by keepign it from "killing" itself. This could also leading to twisting the t-storm, which can lead to tornado development.

Front 28

What defines a t-storm as being "severe"?

Back 28

A severe t-storm is one that produces one or more of the following: hail 3/4"+ in diameter; "t-storm wind gusts" of 50+ knots/58+ mph; the occurance of a tornado

Front 29

What happens on Jan. 4th, 2010?

Back 29

NWS will change standard in severe weather for hail size to be 1"

Front 30

What are the 4 types of t-storms?

Back 30

single cell
multicell clusters
multicell lines
supercell

Front 31

What is a single-cell t-storm?

Back 31

Applies to a single thunderstorm with one main updraft and downdraft. These are the typical summer thunderstorms in many temperate locales. They also occur in the cool unstable air which often follows the passage of a cold front from the sea during winter.

Front 32

What is a multicell cluster thunderstorm?

Back 32

Most common t-storm. Has more than 1 up/downdraft.

Front 33

What is a multicell line thunderstorm?

Back 33

Also known as a squall line, it is an elongated line of severe thunderstorms that can form along and/or ahead of a cold front.

Front 34

What is a supercell thunderstorm?

Back 34

It is the strongest t-storm, ALWAYS bringing severe weather. It has separate up/downdrafts and often has an anvil.

Front 35

What is a derecho?

Back 35

a widespread and long-lived, violent convectively induced straight-line windstorm that is associated with a fast-moving band of severe thunderstorms in the form of a squall line

Front 36

What is a mesocyclone?

Back 36

a vortex of air, about 3-7 miles in diameter, within a convective storm. It is air that rises and rotates around a vertical axis. Gives clue to upper winds. < 20% produce tornados (thanks to Dopplar)

Front 37

The intensity of squall line storms is based on what?

Back 37

storm density

Front 38

Describe the properties of lightening?

Back 38

1/4-1/2" in diameter, 50-55,000 F (says Troy), 30,000 F (says online), can stike up to 15 miles away, even out in the sun

Front 39

Terminal velocity of baseball-size hail? softball-size?

Back 39

85-95 mph
~ 125 mph

Front 40

straighline winds vs tornado

Back 40

straightline winds: winds are divergent
tornado: damage is folded in, convergent wind pattern

Front 41

Why is central Texas the "flash flood capital"?

Back 41

1) subsoil composed of limestone = low infiltration
2) topography of land (many hills)
3) urbanization = increased runoff and less infiltration