Warm and/or moist wait encroaching top top a massive of cooler or drier air outcomes in a warmth front. Warm and also moist air is naturally less dense than cold and also dry air and will conveniently "ride" end the height of cool air. Accordingly, a heat front go not represent an abrupt or sudden contrast, together does a cold front (Figure 9.29).




You are watching: What is the first sign of an approaching warm front

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Fig. 9.29 heat moist air conveniently rides over colder air as soon as impinging upon it.

Warm fronts are stood for on weather maps as a red line through "half suns" top top the top edge (Figure 9.30).


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Fig. 9.30 explicate of heat front in a mid-latitude cyclone.

The top edge of a heat front may have a 30,000 foot or better altitude and also be numerous miles in advancement of the heat at soil level separating warm and also cold. Together the heat air lifts end the cool air, it also cools and also at part level condensation begins. The very first indication of one approaching heat front might be cirrus clouds (or persistent contrails) complied with in time by altostratus and then stratus clouds (Figure 9.31), and also possibly widespread and general rain (or snow). Back not considered as violent together weather events connected with a cold front, warmth fronts room usually the reason of glaze or freeze rain that have the right to cripple activity of traffic and also break trees and also power lines. Also, heavy basic rains that can occur may result in extensive flooding, together opposed to extreme flash flooding frequently caused by a thunderstorm.


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The wind change around a heat front goes native easterly or southeasterly front of the front to southerly the southwesterly behind it. Unequal the cold front, advance notice of a warm front is an extremely apparent. Cirrus clouds portend the advance of a warm from 24-36 hours ahead. This clouds are developed by the heat air gift lifted to an extremely high levels in the atmosphere. Behind the warm front the dew point and temperature rise as the waiting mass alters from a cP wait mass to a mT waiting mass. Precipitation have the right to occur, but is more showery form as opposed to the thunderstorm form of the cold front. The considerable cloudiness ahead of the warm front quickly gives means to clean skies. The elevator disappears after ~ the former passes. Push is commonly falling till the prior passes, climate it may rise slightly together the warmth sector of the cyclone overcome over.




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Fig. 9.32 A heat front is illustrated from southern Canada across the Dakotas. Click image to enlarge.


Usually, the contrast throughout the heat front is no as to mark as throughout a cold front. But changes deserve to be seen. Ahead of this warmth front there is some cloudiness, but not as comprehensive as commonly occurs. This is probably due to the fact that the air below is really dry ~ coming turn off the mountains. The fronts on this map are attracted from 2 hours prior to this observations. Therefore, areas of the eastern Dakotas are probably behind the heat front.