USDA Forest Service

North Central Research Station

Region 5 Fires

Synoptic Circulation, Temperature, and Moisture Patterns


Map of Region 5 -- South-central

Severe wildland fires (>1000 acres) in the South-central region of the US typically occur during the months of March and April.  Analyses suggest there are three synoptic circulation patterns associated with the onset of severe wildland fires in this region.  Each figure depicts the 500 mb height contour pattern (in meters) along with the 500 mb streamlines which portray wind directions.  Higher wind speeds occur in regions where the 500 mb height contours are more closely packed together.

 

Region 5/Circulation Pattern 1

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Circulation Pattern 1

500 mb ridge over the Western half of the US accompanied by a prominent trough over the Eastern half of the US or off the Eastern US coast, resulting in dry conditions and northwesterly flow over the South-central US.


Region 5/Circulation Pattern 2

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Circulation Pattern 2

500 mb trough over the Western States with a ridge over the Eastern US, resulting in a warm, dry southwesterly flow over the South-central US.


Region 5/Circulation Pattern 3

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Circulation Pattern 3

Relatively strong 500 mb zonal flow over most of the US.  Portions of the region can experience Chinook winds from westerly flow over the Eastern slopes of the Rockies.



Associated with these 500 mb circulation patterns are typical lower atmospheric temperature and moisture (relative humidity) patterns.  The figures below depict average 850 mb temperature anomalies (C) and lower atmospheric relative humidity anomalies (%) associated with each of the three circulation patterns that were present during past severe wildland fire episodes in Region 5 (1971-1991).

 
 


USDA Forest Service - North Central Research Station
Last Modified: January 26, 2005