EAS 380 Fall 2008 August 28, 2008 - Temperature Forecasting

Material Covered:

• Practice METAR decoding
• Practice plotting station models
• Forecasting high/low temperatures

• Forecasting High Temperatures	Technique	Theoretical Basis
  	Sunny, breezy "Perfect day"	Well-mixed lower atmosphere; temperature profile will be dry adiabatic (Note: Depth of mixed layer will change during the year due to change in solar radiation) Use 850 mb temperature and temperature forecast to approximate depth of mixed layer (700 mb temperature for elevated stations)
  	Amount of cloudiness	Clouds absorb and reflect some incoming solar radiation (Note: cloudy days tend to be warmer during cold season due to weak solar radiation intensity tend to be colder during warm season since solar radiation loss is significant)
  	Snow cover vs. no snow cover	Fresh snow cover has albedo of 85-95%
  	Wet ground	More solar energy used to evaporate water, rather than to heat air. More likely to form clouds. Falling precipitation will produce the same effect.
  	Presence of low-level inversion	Inhibits mixing Warm-air advection day will have a shallower mixed layer than cold-air advection day
  	Advection	Find area where surface air comes from. Use trajectory (actual path of air parcel) rather than streamline (parallel to winds at a given time; isobar or height contour). Make sure to note if air mass characteristics (elevation, change of cloud cover, evaporate surface water, etc.) may change during time of travel. (Note: NGM Trajectory Forecast useful)
  	Normal Temperature Range	Normal difference between high and low temperature reflects average effect of sunny days, clear night (works best when conditions not extreme, i.e., partly cloudy, light to moderate winds, no air mass change)
  Computer Forecasts (MOS) Source of MOS Forecasts	Tend to be best with "medium conditions." Trouble with near records. Will have problems if the forecast scenario is wrong.
  Forecasting Low Temperatures	Will hit dew point temperatures on radiational cooling "perfect night"	Cooling beyond the dew point will result in latent heat release, offsetting the cooling
  	Amount of cloudiness	Clouds absorb and reradiate outgoing earth IR radiation back to earth's surface (enhanced greenhouse effect)
  	Wind	Lighter winds allow cooling to distributed through a narrower layer, producing a colder low temperature.
  	Advection	Find area where surface air comes from. Use trajectory (actual path of air parcel) rather than streamline (parallel to winds at a given time; isobar or height contour). Make sure to note if air mass characteristics (elevation, change of cloud cover, evaporate surface water, etc.) may change during time of travel. (Note: NGM Trajectory Forecast useful)
  	Normal Temperature Range	Normal difference between high and low temperature reflects average effect of sunny days, clear night (works best when conditions not extreme, i.e., partly cloudy, light to moderate winds, no air mass change)

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Last updated: Thursday, September 4, 2008 1:21 PM

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