Lassen – Modoc Unit - Board of Forestry and Fire Protection - State ...

Lassen County’s climate, with its warm and dry summers, contributes to low
relative humidity and low fuel moistures. When combined with high fuel loading,
the potential for a catastrophic fire event is significant.
There are three weather conditions specific to Lassen County that may cause the
ignition and/or impact the behavior of wildland fires: (Reference #6)
1. As high air pressure systems move eastward, unstable moist air from the
south can move north and northwest along the eastern crest of the Sierra
Mountains bringing thunderstorms. These systems occur when there is an
unstable southeastern or southern flow aloft, or a closed low pressure system
aloft, and most commonly in mid to late summer. The thunderstorms and
the associated lightning, with or without precipitation, is a significant source
of fire starts.
2. High winds out of the southwest that occur due to deep vertical air mixing
over the warm, high terrain. These winds can become steady up to 20 MPH
and gust up to 30-40 MPH if they are associated with an upcoming dry cold
front or trough. This occurs most commonly in late Spring, and in late
August to mid October.
3. Hot, dry conditions associated with high pressure systems. This most
commonly occurs in August and September due to diverging air and
compression that warm and dry the lower atmosphere, and particularly
hinder nighttime humidity recovery.
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Lassen County CWPP