Weather and Climate

Weather and Climate

First attempt at analysis . . .

Weather and Climate(Lecture 26)Instructor: Prof. Michael C. MorganTeaching Assistant: Dianna N. Nelson

Questions from last lecture

Which of the following conditions isbest for air mass development?A. flat terrain, light winds, high pressure regionB. mountainous terrain, light winds, low pressureregionC. flat terrain, strong winds, low pressure regionD. mountainous terrain, strong winds, lowpressure regionE. flat terrain, strong winds, high pressure regioncontrasts, pressure change, changes in windspeed

What kind of air mass originates over Alaska?A. maritime polarB. maritime tropicalC. continental polarD. continental tropical

Fronts are best identified on a weather map byA. temperature contrasts, pressure change,changes in wind speedB. pressure changes, changes in moisturecontent, changes in cloud heightC. changes in wind speed, pressurechange, regions of precipitationD. temperature contrasts, pressure change,changes in wind direction

A front is identified on asurface weather map by:1. Sharp temperature change overa short distance2. Shifts in wind direction3. Pressure (trough) and pressurechanges4. Changes in air’s moisture content5. Clouds and precipitation patterns


A front is identified on asurface weather map by:Temperature ChangeWind ShiftMoisture Change

A stationary frontA. acts as a boundary between polar andtropical air massesB. brings cold air into regions of warm airC. brings warm air into regions of cold airD. is an area of deep convection andintense

Madison, WI is located inA. the tropicsB. the sub-tropicsC. the mid-latitudesD. the subpolar regionE. the polar region

Map discussionhttp://weatherbonk.com


Types of fronts• There are three basic types of fronts:1. Stationary front2. Cold front3. Warm front

Stationary front• This type of front has essentially no movement• The weather along the front may be quitevariable with respect to clouds and precipitation• If the air on either side starts to move, thestationary front will become a cold or warmfront.• Generally is a boundary between polar andtropical air

Cold front

Slow moving (15kt) vs. fastmoving (25kt) cold fronts• Fast moving cold fronts are steeper• Slow moving have a broad area ofprecipitation and cloud cover behind thefront.• In front of a fast moving cold front, squalllines may develop.– Squall lines are a lone of active showers andthunderstorms with heavy rain and gustywinds.

Warm front

Warm front

Warm front

Thunderstorms• A thunderstorm is a storm containinglightning and thunder.• Thunderstorms occur all over the world

Formation - Ingredients• Moisture (water vapor) in the lowest levelsof the atmosphere• Cold, dry air aloft (2-3 miles above thesurface)• Lifting mechanism

Air Mass (Single-Cell)Thunderstorms• Formed by uneven heating of the earth’ssurface• Brief, but well-defined lifespan with threestages– Cumulus Stage– Mature Stage– Dissipating Stage

Three stages

Mature Thunderstorms• The updraft can become so strong that itpenetrates into a region of stable air,resulting in a overshooting top.

Which is mature and which isdissipating?

Lifespan of a Thunderstorm• A single cell, consisting of an updraft anddowndraft, lasts 20 minutes.• But we have all observed thunderstormsthat appear to last longer than 20minutes….WHY?

Multicell storms• Sometimes when the cold downdraft reachesthe surface, it may force the warm, moistsurface air upward• This rising air can condense and build a newthunderstormMulticell clusterMulticell line (Squall Line)


Gust fronts

Gust front


Straight-line winds• Associated with a cluster of severethunderstorms• May exceed 90 knots• If wind damage extends 250 milesalong storm path, it is called aderecho.

Tree damageWhat does it look like from adownburst vs. a derecho?

What makes a thunderstorm asevere thunderstorm?

Severe thunderstorm• Hail ¾” or greater• Winds in excess of 50 knots (57.5 mph)•Tornado

Severe thunderstorms

Supercell thunderstorms

Capping inversion• An important component of creating asevere thunderstorm is the strength ofthe boundary layer cap.– Too strong nothing develops– Too weak numerous cumulus clouds– Just righthelps to funnel the air into astrong updraft

Supercell thunderstormsRadarWeather and Climate

Squall line

Squall line




Tornado alley

Photos courtesy of Ross Lazear

Photos courtesy of Ross Lazear

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