Region 5 Fires
Synoptic Circulation, Temperature, and Moisture Patterns
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.
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
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
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