Chapter 14: Weather Forecasting
Weather forecasting requires a knowledge of current weather.
Sources: >10,000 land based stations and ships. Vertical profiles by radiosonde, aircraft,
and satellite.
World Meteorological Organization – collection and distribution of weather data.
National Center for Environmental Prediction (NCEP) produces weather maps, analysis
and forecasts for distribution worldwide.
National Weather Service – provides weather maps and forecasts to local stations.
Forecasting Methods
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Persistence forecast: weather will not change! Good for a few hours.
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Steady state or Trend method: Project systems will move at constant speed and
direction. Good for a few hours – up to a day.
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Analogue method: Prediction based on past similar conditions.
Example: Hurricane Irene will turn eastward south of Lake Okeechobee.
A high pressure system and advancing front to the north usually causes
hurricanes to veer eastward near Florida.
•
Climatological forecast: Based on climate of region
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Numerical weather prediction:
Use atmospheric models to predict how atmospheric elements (temperature, pressure, and
precipitation) will change with time.
Computer forecast charts are “prognostic charts” or progs
Computers now plot weather data, do analysis and forecast based on models.
One model: medium range forecast model (MRF) – see Fig. 14.1
Try this weather site
http://weather.unisys.com/
Click on MRF 10-day forecast or click on upper air data.
Some forecasting rules of thumb:
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Lows move toward area of greatest pressure drop (isallobars)
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Lows move parallel to isobars in warm sector
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Systems move parallel to winds on 500 mb chart. Lows move at a little less than
½ speed of the wind at 500 mb (500-1200 km/day, 300-750 mi/day).
Anther weather link:
www.intellicast.com
Try going to unisys.com and looking at the following:
Surface map and loop
Upper level chart - Are there areas of cold/warm advection?
- Where is diverging/converging air?
- Can you determine the direction of storm movement?
Satellite data and loop IR {white = high and cold, gray = low and warm}
ETA model forecast (pressure/precipitation)