Fire Weather Outlook Discussion
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FNUS21 KWNS 170700

Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0159 AM CDT Tue Oct 17 2017

Valid 171200Z - 181200Z


A mid/upper-level ridge that is centered over the Desert Southwest
will become suppressed/flattened today as an area of enhanced zonal
flow -- with embedded subtle impulses -- ejects from the Pacific
Northwest into the Northern Rockies and northern High Plains. At the
surface, a cold front will move onshore across the Pacific Northwest
then progress eastward into the northern High Plains.

...Eastern Wyoming and Western Nebraska...
Lead subtle shortwave trough -- with an associated compact mid-level
speed maximum -- is forecast to pass over WY later today. Despite
cool surface temperatures, steep-low level lapse rates are expected
to foster efficient deep-layer mixing, which will allow for
sustained easterly downslope surface winds of 15-25 mph (with higher
gusts). Additionally, modest warming of a dry low-level airmass will
allow for minimum afternoon RH values near 15% atop receptive fuels.
The ongoing Elevated/Critical fire weather areas were maintained
with only minor adjustments. The Critical area over southeastern WY
is where the greatest confidence in overlapping strong winds,
reduced RH values, and receptive fuels exists.

...Central/Eastern Montana...
Strong west-southwesterly pre-frontal winds around 15-40 mph (with
higher gusts) are expected over MT later today in response to
deepening surface low over Alberta/Saskatchewan. Despite cool
surface temperatures, downslope warming of an antecedently dry
low-level airmass is expected to allow afternoon RH values to fall
to around 15-25%. Additionally, the lack of recent precipitation
coupled with long-term drought have rendered fuels -- especially
fine fuels -- sufficiently receptive to large fire starts.
Confidence regarding the overlap of sustained surface winds greater
than 20 mph, RH values less 20%, and sufficiently receptive fuels
has increased enough that a Critical fire weather area was
introduced over north-central MT. While near critical conditions are
possible in the surrounding Elevated fire weather area, confidence
in stronger winds overlapping sufficiently lowered RH values and/or
critical fuel receptiveness is less. RH values should increase by
evening in the wake of the cold frontal passage, but a rapid change
in wind direction to westerly/northwesterly is expected.

...Central/Southern California...
A mid-level impulse is expected to move onshore this afternoon in
the vicinity of Santa Barbara/San Luis Obispo Counties. While recent
lightning data indicate a modest amount of lightning associated with
the impulse, the expectation is for the lightning activity to
diminish later today as the impulse encounters an increasingly
stable atmosphere near land. If lightning is able to develop, then
the very dry low levels would tend to limit the amount of
precipitation reaching the surface. While there is a chance for a
few lightning strikes, it currently appears that coverage will
remain below the 10% threshold for the introduction of dry thunder

..Elliott.. 10/17/2017

...Please see for graphic product...

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