MET chapter 9-10

AWIPS

System that helps forecasters manage available charts/maps.

Meteogram

Chart that displays the change of a weather variable at a station over point of time.

Sounding(s)

Two dimensional vertical profile, dew point, winds, and can be used to make short range forecasters over small areas/mesoscale.

Numerical weather prediction

Daily forecasting of weather by computers using math equations.

Atmospheric models

Mathematical models containing equations that describe how atmospheric temperature, pressure, winds, and moisture change in time.

Data assimilation

Process of integrating into numerical models, more assimilation=higher quality forecast models.

Prognostic chart

Final forecast representing the atmosphere at a certain future time.

Chaos

Small unpredictable atmospheric fluctuations that limit model accuracy.

Ensemble forecasting

Production of multiple forecasts of a single model each with slightly different weather info to reflect measurement errors. The further you go out tje more compliacted it becomes.

Persistence forecast

A prediction that future weather will be identical to present weather. ex: If it’s raining today P.F’s will call for rain through tomorrow, and is most accurate for several of hours.

Trend forecasting

Determines the speed/direction of fronts, cyclones, clouds, and precipitation.

Analog method

Centered on the assumption that weather repeats itself, and is often referred as pattern recognition and can predict various weather elements like max temp.

Statistical forecasts

Based on MOS, ex: Tommorow’s max temp might use a numerical model’s equation forecast of relative humidity, cloud cover, wind direction, and air temperature.

Climatological forecast

Based on a certain region climate (avg weather statistics over many years).

Nowcast

Forecast shorter 6 hours and is a short range.

Watch

Atmospheric conditions favor hazardous weather occurring over a certain region during a certain time period.

Warning

Indicates that the hazard forming is a threat to life/property: Tornadoes, floods, thunderstorms,etc.

Short range forecasts

Ranges from 12 hours-few days.

Medium range forecasts

Ranges from 3-8 days and is based on progs and MOS.

Extended forecast

Extends beyond 3 days.

Long range forecast

Extends beyond 8 days (192 hours).

Seasonal outlooks

3 month periods that overlap and extend out to a year.

Forecast funnel

Outlines the forecasts steps to focus on smaller scales and longer time periods.

What is the function of the National Center for Environmental Prediction?

NCEP analyzes data, runs models, prepares weather maps/charts, and predicts weather on global scales. NCEP transmits observations/computer model output to U.S private forecasting firms/public agencies.

What are some tools that might be used when making short range forecasts?

A forecaster may use satellite imagery, Doppler radar, surface weather maps, upper-air wind data, and pattern recognition to create short range forecasts.

How does a prog differ from an analysis?

Analysis is the final chart that represents weather patterns after errors are corrected.

How have high-speed computers assisted the meteorologist in making weather forecasts?

Computers plot/analyze data, predict weather, can analyze large quantities of data very fast-carrying out trillions of calculations.

What are some of the problems associated with computer model forecasts?

Computer models make atmosphere assumptions, and inconsistent accurate progs about weather. Most models aren’t global in their coverage, and can’t interpret factors that influence surface weather: water, ice, surface friction, and local terrain on weather systems.

Whats an example of analog method?

Relating the max temp on a date where the avg max temp hasn’t changed over [x] amount of years to wind, cloud cover, humidity, and forecasters can predict the max temp’s for the day.

How does pattern recognition aid a forecaster in making a prediction?

Pattern recognition can allow previous weather events and can be utilized as a guide to the future.

Do monthly/ seasonal forecasts make specific predictions of rain or snow?

Seasonal outlooks overview the possible similarities between weather patterns, normal conditions, and don’t give specific times for precipitation and etc.

How are teleconnections used in making a long range seasonal outlook?

Teleconnections can show awareness of El Nino, La Nina and Southern Oscillation events. T.C’s= widely spaced interactions between ocean surface temp/weather.

Do all accurate forecasts show skill on the part of the forecaster?

For a forecast to show skill, it must be better than one based solely on current weather (predicting which days it will rain).

How does chaos present a problem in forecasting the weather 15 days into the future?

Chaos amplifies with time while the computer attempts to predict future weather.

What does 60% chance of rain mean?

There is a 60% chance in any area in the forecast that will receive rain.

Ordinary thunderstorms

Tend to form in a region where there is limited vertical wind shear, that is, where the wind speed/ direction don’t abruptly change with increasing height above the surface. Also often form along shallow zones where surface winds converge.

Cumulus stage

Also known as growth stage , dominated by updrafts, and as a parcel of warm/humid air rises, it cools/condenses into a single cumulus cloud or a cluster of clouds.

Mature stage

Precipitation starts as downdraft leaves the base cloud, the top of the cloud reaches a stable region as high as the stratosphere, begins to take on a anvil like shape as upper-level winds spread the cloud’s ice-crystals horizontally. =most active stage.

Dissipating stage

Occurs when the the updrafts weaken as the gust front moves away from the storm which no longer enhances the updraft, and 20% of the moisture precipitates while the rest evaporates.

Multicell thunderstorms

Contain multiple cells each in different stages of developmental and tend to form in moderate-to-strong vertical wind speed shear regions.

Overshooting top

When convection and updraft are strong, the rising air may intrude into the stable stratosphere.

Gust front

Represent the leading edge of the cold outflowing air, and this front is formed when the cold downdraft pushes outward on Earth’s surface. Causes dust/roll clouds and the lifting needed for new thunderstorms.

Straight line winds

High winds behind a strong gust front to distinguish them from the rotating winds of a tornado, and these winds can inflict damage.

Shelf cloud

Forms as warm/moist air rises along the forward edge of the gust front, and is prevalent when the atmosphere is stable and near the thunderstorm’s base.

Roll cloud

Clouds that appear to slowly spin about a horizontal axis.

Outflow boundary

Gust fronts may combine into a huge gust front, and along this boundary air is forced upward sometimes creating thunderstorms.

Downbursts

Strong localized downdrafts that may form beneath thunderstorms.

Microburst

Downbursts with winds extending 4 km or less., and if strong enough can create straight line winds over 100 knots (115 mi/hr).

Heat bursts

Sudden warm downbursts.

Squall line

Line of multicell storms that might form along a cold front and extend for hundreds of kilometers, and can form in warm air 100-300 km out ahead of the cold front-linear features.

Bow echo

Squall line shaped like a bow, and the strongest winds usually occur at the bow’s center which is where the sharpest bending occurs, and tornadoes can form near the bow’s left (northern) end.

Derecho

The windstorm created if straight line winds gust over 50 knots (58 mi/hr) persist along a minimum 400 km (250 mi) squall line path.

MCCs

Multiple thunderstorms organized into one large circular cluster, can cover an area of 100,000 km and last for 12 hours or more. Usually form in the Great Plains from afternoon air mass storms, and requires a strong low level flow of warm/moist air.

Supercell

Intense long-lasting storm with a rotating updraft, and can form tornadoes. Has diameters between 20 km-50km and lasts several hours.

Mesocyclone

Vertical cylinder of rotating air about 3-10 km’s across the storm’s southside and occurs in the updraft of a severe storm. Depends on vertical wind shears, with strong winds aloft and weak surface winds.

Wall cloud

This rotating cloud may descend from the storm’s base if humid low-level air is reeled in the updraft.

Cap

Serves as a rising thermal lid, allows small cumulus cloud formation, when its weak storms develop vice versa, and rising air may break through it at isolated places which causes rapid cloud formation.

Flash floods

Form rapidly with little to no advance warning, and tend to form when storms move slowly causing intense rainfall over small areas.

Lightning

Electricity discharge, occurs in mature storms/clouds, its stroke can heat the air to 30,000 C*/54,000 F*= 5x hotter than the Sun’s surface.

Thunder

The result of the explosive air heating by lightning as a booming sound wave.

Sonic boom

Mistaken for thunder, produced when aircrafts exceed the speed of sound at any altitude (the speed of sound at sea level =761 mi/hr or 661 knots but decreases with height).

Stepped leader

Invisible to the human eye, the voltage per meter increases as its tip reaches the ground while a positive charged current forms from the ground to meet it.

Return stroke

a bright electric current that. transfers positive charges up into a cloud when the downward flow of electrons (stepped ladder) meet the upward surge of positive charges.

Dart leader

Moves from the cloud along original stepped leader’s channel, but moves down quicker due to the lowered path of the electrical resistance.

Heat lightning

Lightning that isn’t heard but seen that usually occurs during hot summer nights when the sky is clear.

Dry lightning

Starts forest fires in dry timber regions, and forms when ground-to-cloud lightning with storms don’t produce rain.

St Elmo’s fire

Tends to for above pointed objects, when visible a thunderstorm is nearby, and this electric discharge is named after the patron saint of sailor’s.

Tornado

Extend downward from a cumulonimbus cloud and blows around low pressure small areas with ground reaching circulation. Strong versions of these tend to form near the hail boundary.

Funnel cloud

30% of these clouds become tornadoes, and form when rapidly spinning vortexes emerge from the wall cloud’s base. Considered as a tornado if it touches the ground.

Tornado Alley

Tornado belt where the greatest amount of tornadoes occur.

Suction vortices

Smaller whirls that rotate within tornadoes that exceed 180 knots, and are 10 m (330 ft) in diameter.

Tornado watch

Issued to alert the public that tornadoes may develop within a specific area during a certain time usually a few hours long.

Tornado warning

Covering parts of one/multiple counties and lasts from 30-45 minutes.

Tornado emergency

Rarely issued except when a strong tornado threaten a populated area.

Fujita scale

Based on tornado/storm damage, and is used for classifying tornadoes according to their rotational wind speed. F0-F5

EF Scale

The combo of the 28 damage indicators/damage degree gives a range of probable wind speeds/EF rating for the tornado.

How is the EF scaled?

EF0:65-85 MI/HR=56-74 KNOTS

EF1: 86-110 MI/HR= 75-95 knots

EF2:111-135 MI/HR=96-117 knots

EF3: 136-165 MI/HR=118-143 knots

EF4: 166-200 MI/HR=144-174 knots

EF5: > 200 MI/HR= >174 knots.

Tornado outbreak

When 6 or more tornadoes develop within a weather system and can extend over multiple days.

Supercell tornadoes

Tornadoes that form with with super cell thunderstorms.

Hook echo

When rotating precipitation unveils itself in the shape of a hook while the precipitation is drawn into a cyclonic spiral around the mesocyclone. On the Doppler radar

Tornado genesis

Formation of a tornado when the rear-flank downdraft strikes the ground it may interact with the forward-flank downdraft beneath the mesocyclone.

Non-supercell tornadoes

Tornadoes that don’t occur in association with a supercell mid-level mesocyclone.

Gustnadoes

Tornadoes that form along gust fronts, and are short-lived and rarely damaging.

Land spouts

Tornado that formed over land due to the air rising/condensing into a cumulus congestus cloud along the converging wind boundary as the updraft draws the air up into the cloud.

Waterspout

Rotating column of air connected to a cumuliform cloud over a large body of water.

NEXRAD

The network of computers and 150+ Doppler radar units deployed at selected weather stations within the continental U.S., and its computers collect data, display them on monitors, while running algorithms. Detect storm cells, hail, mesocyclones, and tornadoes.

What is a thunderstorm?

Storm that creates lightning, winds, heavy rain, and hail. Form when warm/humid air rises in unstable environments.

How do downdrafts form in ordinary cell thunderstorms?

As clouds build over the freezing level, its particles get heavier and fall. Also, drier air surrounding the cloud is is being drawn in by entrainment, and entrainment evaporates some of the raindrops which chills the air. Finally, the air begins to descend as downdraft since its now colder/heavier than the air around the cloud.

Why do ordinary cell storms tend to form in the afternoon?

Air near the ground is most unstable in the afternoon.

Why do ordinary cell storms tend to dissipate much sooner than multicell storms?

Supercell storm=enormous rotating thunderstorm with a sufficient structured up/downdraft that allow the storm to hold itself together for hours.

How does the National Weather Service define a severe thunderstorm?

A thunderstorm having at least one of the following: large hail with a diameter of at least one inch, surface wind gusts of 50 knots (58 mph) or greater, or produces a tornado.

What atmospheric conditions are necessary for a multicell thunderstorm to form?

The process of a mature/dissipating storm’s cold downdraft causing warm/moist air to rise then condense, and build into a storm may repeat until new cells form making it possible for new storms to form in lines in different development stages.

Give a possible explanation for the generation of a pre-frontal squall-line thunderstorm.

Cumulus clouds growing along the cold front may cause the air aloft to develop into gravity waves, the rising motion of the wave may create cumulus clouds and a pre-frontal squall line out ahead of the cold front.

Describe the atmospheric conditions at the surface and aloft for the development of most supercell storms.

If the winds aloft gain stronger shears and move from a southerly to more westerly aloft height, the storm may prevent the downdraft’s outflow of cold air to undercut the updraft. The wind shear must be strong enough to form a horizontal spin and the formation of a supercell.

What are HP supercells?

High precipitation, and often make extreme downdrafts: downbursts, flash floods, and hail. Tornadoes usually form in these areas.

When thunderstorms are training, what are they doing?

Passing over the same area, like cars, tracks, or railroads after another.

Where does the highest frequency of thunderstorms occur in the U.S.? Why there?

In the southeastern states along the Gulf Coast with a maximum in Florida, because there is plenty of available moisture, unstable surface air, and convergence.

Why is large hail more common in Kansas than in Florida?

Dry air keeps the hail intact where humidity makes hail smaller.

Describe one process by which thunderstorms become electrified.

Hail falls/collides with droplets, then freeze on contact and release latent heat.

How does a cloud-to-ground lightning stroke develop?

Electricity builds up in the clouds base then shoots down to earths surface creating a cloud to ground lightning strike.