WEATHER FORECASTING

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CHAPTER 14 WEATHER FORECASTING
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• Extra Credit Opportunity (5 pts.)
• Pick a historical hurricane
• Not Allison, Not Ike
• One page summary of storm
• Lifecycle, max winds, wind at landfall, impacts,
  etc.
• Print a plotting chart. Hand plot track, use
  correct symbols.

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Favorable conditions for tornadoes

• In addition to moisture, instability, and
  lifting, we need strong wind shear
• At low levels, southerly winds bringing warm,
  moist air into the area
• Aloft, advection of dry air adds to instability
• Upper-level divergence leads to low-level upward
  motion

Example from book
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And, especially for South Plains
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What do we need to forecast?

• Temperatures (high/low/average/changes)
• Precipitation (will it rain or snow, and how
  much?)
• Wind (speed and direction)
• Cloud cover
• Severe/hazardous weather (tornadoes, hurricanes,
  floods, etc.)
• Fire weather
• Marine weather (forecasts for ships at sea)
• Pollution/smog/air quality
• Much more

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Timescales of forecasts

• Short-term forecasts (aka nowcasts) minutes to
  a couple hours in advance
• What time will the severe storm affect my area
  and how intense will it be?
• Short-range forecasts 6 to 60 hours in advance
• How likely is it to rain tomorrow?
• Mid-range forecasts 3-10 days in advance
• Will it be warm or cold next weekend?
• Climate predictions months or seasons in advance
• Will we have above normal or below normal
  precipitation for the next ski season?

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Who makes forecasts?

• National Weather Service
• 122 weather forecast offices (WFOs) located
  around the country
• NWS issues a variety of forecasts, warnings, and
  other products for a local area
• We are covered by the WFO in League City (south
  of Houston)
• http//weather.gov
• http//www.srh.noaa.gov/hgx/

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Who makes forecasts? (contd)

• National Centers for Environmental Prediction
• NCEP headquarters collects observations and runs
  numerical models to make forecasts
  http//www.ncep.noaa.gov
• Storm Prediction Center, Norman, OK (Severe
  thunderstorm and tornado watches)
  http//www.spc.noaa.gov
• National Hurricane Center/Tropical Prediction
  Center, Miami, FL (official hurricane forecasts,
  watches and warnings) http//www.nhc.noaa.gov
• Hydrometeorological Prediction Center, Camp
  Springs, MD (precipitation and flood forecasts)
  http//www.hpc.ncep.noaa.gov
• Climate Prediction Center, Camp Springs, MD
  (seasonal outlooks, El Niño predictions)
  http//www.cpc.noaa.gov
• Private Companies
• TV and radio stations, The Weather Channel,
  AccuWeather, WeatherNews, many others

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What is a good forecast?

• Depends on the user/customer
• For the general public, getting the high/low
  within a few degrees is probably good enough
• For an energy company, an error of a few degrees
  can be very costly
• Transportation departments need very accurate
  snowfall forecasts will plows need to be
  deployed? Should highways be closed?
• Aviation industry needs to know cloud cover,
  where storms are moving, turbulence, etc.
• Human forecasters need to provide skill
• Anyone could forecast 80 and sunny every day of
  the year in LA and be pretty close 90 of the
  time
• Its the other 10 where a skilled forecaster
  earns his/her salary

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Manual forecasting techniques

• Before computers, forecasts were mainly limited
  to predicting the movement of existing weather
  (It snowed yesterday in Minnesota, so it will
  snow today in Wisconsin)
• Pattern recognition was (and still is) used by
  experienced forecasters after looking at the
  weather every day, you gain an instinct for
  certain weather patterns
• Ingredients-based forecasting
• Will there be moisture, instability, and lift?
• Rules of thumb
• If air temperature is 14C colder than water
  temperature, lake effect snow is possible
• For high temperature (in summer) take forecast
  850-mb temperature at 0000 UTC, add 15C

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Weather forecast models

• North American Mesoscale (NAM, previously called
  Eta) Primary model used for forecasting in the
  U.S.
• Run every 6 hours (00, 06, 12, 18 UTC) out to 84
  hours, 12-km horizontal grid spacing
• Global Forecast System (GFS) Covers the entire
  globe
• Run every 6 hours, 35-km horizontal grid spacing
  to 180 hours, 70-km grid to 384 hours (16 days)
• Rapid Update Cycle (RUC)
• Run every hour out to 12 hours for short-term
  forecasts
• Mesoscale models Weather Research and
  Forecasting (WRF), Regional Atmospheric Modeling
  System (RAMS), Mesoscale Model version 5 (MM5)
• Run by forecast offices, universities, etc., on a
  regional basis
• Climate Prediction Models

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The 4-panel map look at multiple levels at once
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Where to get numerical forecasts?

• http//www.rap.ucar.edu/weather/model/
  (National Center for Atmospheric Research)
• http//www.nco.ncep.noaa.gov/pmb/nwprod/analysis/
  (National Centers for Environmental Prediction)
• http//hdwx.tamu.edu/wxdata.php (if on campus
  network this site is still under construction!)
• But, interpret this information with caution
  until you have a good sense for how it works
  for official forecasts and warnings, use
  weather.gov (theyre experts in interpreting
  numerical forecasts!)

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A super-outbreak, right during your 201 Class
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Fig. 14.1, p. 415
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Table 12.4, p. 345
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Table 12.5, p. 346
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http//vimeo.com/22970879Gets a little shaky
for a bit around 545 while he adjusts
camerahttp//www.youtube.com/watch?vT0FHTG9VETY
http//www.youtube.com/watch?vsA7TKSHJ_wMfeatu
rerelatedhttp//www.youtube.com/watch?vNjVW0Du
2ZIofeaturerelatedhttp//www.youtube.com/watch
?vEv2bZRV8eOofeaturerelmfuPhotos of the
Damagehttp//www.time.com/time/photogallery/0,29
307,2067604,00.html http//www.chron.com/news/ph
otogallery/Severe_weather_across_the_country.html

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PREDICTING LONG-TERM WEATHER AND CLIMATE PATTERNS

• El Niño, La Niña and Southern Oscillation
• ENSO is a combined atmosphere and ocean
  phenomenon.
• Originally, referred to unusually warm waters off
  of NW coast of S. America.
• Reverse of pressure difference between Tahiti and
  Darwin is SO, Walker Cell reversal
• This was found to be part of a large system which
  also includes shift of convective max, changes in
  the upper ocean structure and currents.
• All together - ENSO
• Weather all over planet impacted -
  teleconnections
• Asia
• Australia
• South America
• Caribbean
• North America

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Fig. 14.13, p. 418
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Fig. 14.14, p. 419
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Fig. 14.15, p. 420
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Fig. 14.16, p. 421
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http//www.cpc.ncep.noaa.gov/products/analysis_mon
itoring/lanina/enso_evolution-status-fcsts-web.pdf
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Fig. 14.18, p. 422
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Also, Atlantic hurricane season modulation. El
Niño years tend to be less active seasons, La
Niña enhanced.
Fig. 14.17, p. 421
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PREDICTING LONG-TERM WEATHER AND CLIMATE PATTERNS

• The other oscillations
• Pacific Decadal Oscillation (PDO)
• Similar to ENSO, 20-30 cycles, W. Coast impacts
• North Atlantic Oscillation (NAO)
• Large impact on European weather, some on E. U.S.
• Affects tropical storm tracks
• Arctic (AO)
• Close cousin of NAO

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Fig. 14.19, p. 423
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Fig. 14.20, p. 424
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Fig. 14.21, p. 425