EAS 380 Fall 2008 August 28, 2008 - Temperature Forecasting
Material Covered:
| 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) |
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| Amount of cloudiness | Clouds absorb and reflect some incoming solar radiation (Note: cloudy days
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| 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. |
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| Presence of low-level inversion | Inhibits mixing
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| 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) |
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| 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) |
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) |
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| 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) |
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| 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) | |
Last updated: Thursday, September 4, 2008 1:21 PM
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