In forecasting temperatures, insolation and terrestrial radiation are two very important factors. Low latitudes, for instance, receive more heat during the day than stations at high latitudes. More daytime heat can be expected in the summer months than in the winter months, since during the summer months the suns rays are more direct and reach the earth for a longer period of time. Normally, there is a net gain of heat during the day and a net loss at night. Consequently, the maximum temperature is usually reached during the day, and the minimum at night. Cloudiness will affect insolation and terrestrial radiation. Temperature forecasts must be made only after the amount of cloudiness is determined. Clouds reduce insolation and terrestrial radiation,

Figure 4-25.-Illustration of the location of the maximum snow area. The low center moved to Iowa in 24 hours, and the maximum snow area spread northeast along the area 50 to 75 miles either side of a line through Minneapolis to Houghton, Michigan.

causing daytime temperature readings to be relatively lower than normally expected, and nighttime temperatures to be relatively higher. The stability of the lapse rate has a marked effect on insolation and terrestrial radiation. With a stable lapse rate, there is less vertical extent to heat; therefore, surface heating takes place more rapidly. With an unstable lapse rate, the opposite is true. If there is an inversion, there is less cooling, since the surface temperature is lower than that of the inversion layer; that is, at some point the energy radiated by the surface is balanced by that radiated by the inversion layer.

One of the biggest factors affecting temperature is the advection of air. Advection is particularly marked in its effect on temperature with frontal passage. If a frontal passage is expected during the forecast period, the temperature must be considered. Advection within an air mass may also be important. This is particularly true of sea and land breezes and mountain breezes. They affect the maximum and minimum temperatures and their time of occurrence.

Vertical heat transport is a temperature factor. It is considerably affected by the windspeed. With strong wind there is less heating and cooling than with light wind or a calm because the heat energy gained or lost is distributed through a deeper layer when the turbulence is greater.

This information is now available on CD in Adobe PDF Printable Format

Privacy Statement - Press Release - Copyright Information. - Contact Us - Support Integrated Publishing