-regions where are masses originate are known as source regions

-ideally high surface pressure

-humid regions are generally where air masses crash from different source regions

-done acording to temperature and humidity

 -done according to their source regions as well

cA (continental/arctic) - extremely cold, dry, stable... ice and snow covered surface

cP (continental/polar) - cold, dry stable

cT (continental Tropical) - hot, dry, stable air aloft; unstable surface air

mP (maritime/polar) - cool, moist, unstable

mT (maritime/tropical) - warm, moist, usually unstable

*****Winds aloft determine trajectories for air masses***

Airmass Weather - persistent weather caused by a certain airmass

*****real weather generally does not occur within air masses, but rather at their margins, where air masses with sharply contrasting properties meet- in the zone marked by weather fronts

-responsible for very cold weather in winter

-these air masses originate over the ice and snow covered regions of the north

-eventually moves south in an enormous shallow high pressure area

-known for producing LAKE-EFFECT SNOWS as the cold, dry air masses move over relatively warm bodies of water (ie. great lakes)

-associated with very stable air

-generally blow in a south-easterly or easterly direction (westerlies)

cP air in summer is generally warmer

-generally brings relief from the oppressive heat in the central and eastern states

-can quickly assume the properties of a maratime air mass

-by the time is reaches the pacific coast, from over Asia and frozen polar regions, and then over hundreds or thousands of kilometers, it is cool, moist, and conditionally unstable.

-when the mP air moves inland, it loses much of its moisture as it crosses a series of mountain ranges

-it is slow changed back to cP (referred to as Pacific Air east of the rockies)

-these airs often form chinooks

-due to westerlies, atlantic mP winds are uncommon

-the only real source region for these hot, dry air masses in North America is found durig the summer in northern Mexico and the adjacent arid southerwestern United States

-hot dry and unconditionally stable

-clear skies, hot weather, and practically non-existant rainfall

-the transition zone between two air masses of different densities

**the upward extention of a  front is referred to as a frontal surface, or a frontal zone

-fronts are generally associated with lower pressure and they separate different air masses

-has essentially no movement

-on a colored weather map, it is drawn as an alternating red and blue line

-semicircles face toward colder air on the red line and triangles point toward warmer air on the blue line

-represents a zone where cold, dry, stable polar air is replacing warm, moist, conditionally unstable subtropical air

-triangles show direction of movement (where warmer air is)

-isobars kink as they cross, forming troughs (accounts for wind shift)

-a cold front is a trough of low pressure

- the lowest pressure usually occurs as the front first crosses a station

-the slope of a cold front is generally 1/50 (50 km in, 1 km up)

*usually cirrostratus and cirrus clouds come in advance of a cold front, and the front itself brings cumulonimbus rain clouds as the is wedging itself beneath warm air, which lifts and condences

- very dry weather, a marked change in dew point, accompanied by a slight wind shift may be the only clue to a passing front

***know table 8.2

1)sharp temperature changes over a relatively short distance

2)changes in the air's moisture content (marked changes in dewpoint)

3)shifts in wind direction

4)pressure and pressure changes

5)clouds and precipitation patterns

-cold fronts that move in from the east, or northeast, are called this

-typically, as the front passes, westerly surface winds shift to easterly or northeasterly, and temperatures drop

-is drawn along the solid red line

-the leadind edge of advancing warm, moist subtropical (mT) air from the Gulf of Mexico replaces the retreating cold maritime polar air from the North Atlantic

-half circles indicate direction of movement

-warm fronts have an average slope of 1:300.... much more gentle than cold fronts

Figure 8.18 check out!!!

Table 8.3!!

rising of warm air over cold

-produces clouds and precipitation well in advance of the front's surface boundary

if a cold front catches up to an overtakes a warm front, the frontal boundary created between the two aire masses is called an occluded front.... on simply an occlusion

-represented by a purple line with alternating shapes

COLD OCCLUSION - the air behind the occluded front is colder than the air ahead of it

WARM OCCLUSION - the cold front rides 'piggyback' along the sloping warm front

-the upperlevel cold front precedes the surface occluded front, whereas in a cold occlusion, the upper warm front follows the surface occluded front

Check out Table 8.4!!!

-when hazardous weather is likely, the NWS (National Weather Service) issues advisories in the form of watches and warnings

WATCH- indicates that atmospheric conditions favor hazardous weather occurring over a particular region during a specified time period, but the actual location and time is uncertain

WARNING- indicates that hazardous weather is either imminent or actually occuring within the specified forcast area

ADVISORIES- issued to inform the public of less hazardous conditions caused by wind, dust, fog, snow, slett, or freezing rain

-Asdaves Weather Interactive Processing System

-coomunication system used by the National Weather Service

-has data communications, storage, processing, and display capabilities

-ASOS is designed to provide continuous information about wind, temperature, pressure, cloud-base, height, etc at ariports

-much of this information is process with algoritms (pre-determined formulas) before it reaches the forcaster

METEOGRAM

-a chart that shows how one or more weather variables has changed at a station over a given period of time

SOUNDINGS

-another aid in weather forecasting is the use of soundings, a two-dimensional vertical profile of temperature, dew points, and winds.

-can be especially helpful when making a short-range forecast that covers a relatively small area

Types of Satellite

GEOSTATIONARY SATELLITES - orbit the equator at the same rate that the earth spins, and hence, remain at nearly 36000km above a fixed spot on the earth's surface.... allows continuous monitoring of a specific region

-uses a 'real time' data system

POLAR-ORBITING SATELLITES

-closely parallel the earth's meridian lines-

-these satellites pass over the north and south polar regions on each revolution.

-each pass monitors an area west of the previous pass

 -have the advantage of photographing clouds directly beneath them

-much lower and much more detailed

Geostationare Operational Environmental Satellite

-has the capacity to obtain cloud images and, at the same time, provide vertical profiles of the atmospheric temperatures and moisture by detecting emitted radiation from atmospheric gases such as water vapor

-uses 'imagers' and 'sounders'

infrered cloud images/computer enhancement

-used by satellites to make the distinction between high, medium, and low clouds

-high clouds appear white, low clouds appear gray

-computer enhancement is used to distinguish clouds from background

-typically, bringht colors such as blue, red, or purple are assigned to the coldest/highest tops

-this is where the stormiest weather is probably occuring

-devised to explain the many weather variables that are constantly changing

-mathematical models consisting of mathematical equations that describe how atmospheric temperature, pressure, winds, and moisture will change with time

-the models are programmed into the computer, and surface and upper-air observations of temperature, moisture, winds, and air density are fed into the equations

-mathematical formula is used to predict weather in, say, 5 minutes... and these data are refed into the formula over and over again until desired time of prediction is reached

-the final forecast chart representing the atmosphere at a specified time is called a prognostic chart

prognostic chart

-The computer analyzes the data for it's prediction and draws the projected positions of pressure systems with their isobars or contour lines

-the final forecast representing the atmosphere at a specified future time is called a prognostic chart

*currently, forecast models predict the weather reasonably well 4 to 6 days into the future. These models tend to do a better job of predicting temperature and jetstream patterns than predicting precipitation

1)the model makes assumptions about the atmosphere

 2)most models are not global in their coverage, and errors creep in along a model's boundaries

3)models with large grids may miss something

4)many models cannot accurately interpret many factors that influence surface weather, such as the interactions of water, ice, surface friction, and the local terrain on weather systems

-the countless small, unpredictable atmospheric fluctuations

-ie. small eddies are much smaller than the grid spacing on the computer model, and, therefore go unmeasured

-CUMULATIVE IMPACTS!

-becasue of the atmosphere's chaotic nature, meteorologists are turning to a technique called ensemble forecasting to improve short and medium range forecasts

-the ensemble approach is based on running several forecast models, or different versions or a simgle model, each beginning with slightly different weather information to reflect the errors inherent in the measurements

-basically, run the modle a bunch of times with different initial conditions, and see how much results fluctuate

-often referred to as SPAGHETTI PLOT

-if ensemble model runs match each other fairly well

-allows for a prediction with a high degree of confidence

-probably the easiest weather forecast to make

-is simpy a prediction that the future weather will be the same as present weather

-principle involved here is that surface weather systems tend to move in the same direction and at approximately the same speed as they have been moving, providing no evidence exists to indicate otherwise

-ie. a cold front is going at a certain speed... when will it pass city X?

-yet another form of weather forecasting

-basically, this method relies on the fact that existing features on a weather chart may strongly resemble features that produced certain weather conditions sometime in the past

-forecaster uses pattern recognition

-this method is used to predict maximum temperature, among other things

STATISTICAL

-are made routinely of weather elements based on the past performance of computer models

known as MOS (model output statistics)

-they are statistically weighted analogue forecast corrections incorporated into the computer model output

PROBABILITY FORECAST

-a forecast of the probability of the occurance of one or more weather features

-ie. 50% chance of rain

***********this means that on any given area for the forecast, there is a 50% chance that it will rain

-predicting the weather with these employs the analogue method

-in general, weather patterns are categorized into similar groups, or "types" using such criteria as the position of the subtropical highs, the upper-level flow, and the prevailing storm track

-a forecast based on the climatology of a particular region

-grouped according to how far into the future the forecast extends

VERY SHORT RANGE FORECAST

-for up to a few hours, usually not more than 6

-also called a nowcast

-the techniques used in making such a forecast normally involve subjective interpretations of surface observations, satellite imagery and Doppler information

SHORT-RANGE FORECASTS

-forecsats that range from about 6 hours to a few days (2 and a half)

-uses satellite imagery, Doppler, surface weather maps, upper air winds, and pattern recognition

MEDIUM RANGE

-one that extends from about 3 to 8.5 days into the future

-almost entirely based on computer derived products, such as forecasts progs and statistical forecasts (MOS).

*any forecast that extends beyond 3 days is an extended forecast

LONG-RANGE FORECAST

-extends around 8.5 days.

-computer progs are available for up tot 16 days, though they are not accurate in predicting temperature and precipitation

-at best, only show broad scale weather features

outlooks are monthly 'forecasts' based how 'how things should be'- very general

-outlooks use that statistical analysis of teleconnections (ie. El Nino)

-forecasts b/w 12-24 hours quite accurate

-2-5 days = fairly good

-beyond 7, accuracy falls sharply

-what determines a "right" or "wrong" forecast?

-How does forecast accuracy compare with forecast skill? To show skill, it should be better than one based solely on the current weather (persistence) or the "normal" weather (climatology)

-meteorological forecasts show skill when they are more accurate than a forecast utilizing only persistence or climatology

-though, long range forecasts ususally mean extremely little difference between skill and climatology predictions

1)For short time intervals, mid-latitude cyclonic storms and fronts tend to move inthe same direction and at approximately the same speed as they did during the previous six hours (providing there is no evidence to indicate otherwise)

2)Low-pressure areas tend to move in a direction that parallels the isobars in the warm air ahead of the cold front

3)Lows tend to move toward the region of greatest surface pressure drop, whereas highs tend to move towards the region of greatest surface pressure rise

4)Surface pressure systems tend tot move in the same direction as the wind at 5500m, the 500mb level. The speed at which surface systems move is about half the speed of the winds at this level.

-a theory developped by a group of Scandinavian meteorologists that explains the formation, development, and overall life history of cyclonic storms that form along the polar front

-because the mid-latitude cyclone forms and moves along the polar front in a wave-like manner, the developing storm is referred to as a WAVE CYCLONE

**the polar front itself tends to develop into a series of loops, and the apex of each is a cyclone

-any development or strengthening of a mid-latitude cyclone

-areas such as eastern side of rockies (LEE-SIDE LOW) SHOW HIGH PROPENSITY FOR CYCLOGENESIS

-ALSO, GREAT bASIN, Gulf of Mexico, and Atlantic Ocean east of Carolinas

-Hatteras Low (North Carolina)

-Alberta Clipper

-Colorado Low

-Gulf Low

-For the surface low to develop into a major storm system, upper level divergence of air must be greater than surface convergence of air (ie. more air removed than brought in)

-When this even happens, surface air pressure decreases, and we say that the storm  system is intensifying, or deepening

-if the reverse happen, it is called FILLING (low, becoming weaker)

-*in orer for the surface high to strengthen, upper level convergence of air must exced low level divergence of air

called BUILDING

**for a surface mid-latitude cyclone to intensify, the upper level trough of low pressure must be located behind (or to the west of) the surface low

-this means more divergence at top of low pressure system (see Figure 5 pp 228)

-a region of high wind speed that moves through the axis of a jet stream

-also called a jet maximum

-occurs when deep troughs and ridges exist in wavy jetstreams aloft

-produces regions of strong convergence and divergence

**creates an area where air from the low pressure system is being removed faster than can be replaced.... greatly increases strength....

**additionally, supplies air to surface anticyclone

-this is why mid lat cyclonic storms are better developed adnd move more quickly during the coldest months (polar jet stream is strongest and moves farthest south)

WMO - World Meteorological Organization - is the big guy, standardizes world's weather

NCEP - National Centers for Environmental Prediction

Environment Canada

USA NWS - National Weather Service

NCDC - National Climate Data Centre

filling - weakening of a low pressure system (weak divergence aloft

building- increased high pressure system strength (strong convergence aloft)

-Automated Surace Observing Systems

-operational at many airports... designed to provide nearly continuous information about weather

-model output statistics

-computer model analogue method statistics