Record High Temperatures When a record high temperature occurs, often the following will occur: dry soil, clear skies, dry weather for many days if not weeks, light wind, and sometimes manmade influences that increase temperature. A record high temperature is almost always going to occur during the daylight hours. When the soil is drier than usual there will be less evaporation. Evaporation is a cooling process and moderates high temperatures. When less moisture is present then more of the solar energy will go into heating the ground and this in turn increases the air temperature. When the air is dry and the sky is clear this will let the maximum amount of solar radiation in to heat the ground. A light wind will help confine the warm air right at the surface and will reduce the amount of mixing with cooler air aloft. Manmade influences such as urbanization, heat generate from industry and warming from pollutants can contribute to a warmer temperature at a reporting station. Record Lows Temperatures When a record low temperature occurs, often the following will occur: dry soil (if no snow cover), clear skies, dry weather for many days if not weeks, light wind, snow cover, unusual penetration of cold air toward the south. A record low temperature is almost always going to occur at night. Dry soil, dry air and clear skies allow for the maximum amount of longwave radiation to escape from the surface at night. When this combines with light wind the greatest cooling will be confined right near the surface. Snow cover is a strong emitter of longwave radiation and insulates away heat energy and this further helps the cooling process. A record low temperature in winter is common a couple of days after a strong cold front that has snowfall with it. Once the cold dry air settles in and the winds slacken at night then there will be a significant amount of cooling. Very cold air masses form in the polar regions. When this air is allowed to penetrate quickly and penetrate deep toward the south then record lows can occur once the coldest air settles in. |