Fire Weather Outlook Discussion
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FNUS28 KWNS 172135
FWDD38

Day 3-8 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0435 PM CDT Tue Oct 17 2017

Valid 191200Z - 251200Z

A large-scale upper trough should amplify while moving quickly from
the eastern Pacific to the Plains from Day 3/Thursday to Day
6/Sunday. An upper ridge is then forecast to develop over much of
the western CONUS from Day 6/Sunday through Day 8/Tuesday.
Subsidence beneath this upper ridge should promote a broad area of
surface high pressure across the Great Basin.

...Day 3/Thursday - Day 4/Friday: Portions of the Northern/Central
High Plains...
Enhanced southwesterly mid-level winds associated with the
previously mentioned upper trough will overspread parts of the
northern and central High Plains beginning on Day 3/Thursday and
continuing into Day 4/Friday. Some of these winds should reach the
surface through diurnal mixing of the boundary layer and overlap
with pockets of reduced RH values. Confidence has increased in a
sufficient overlap of strong/gusty winds with lowered RH values to
introduce 40%/marginal areas across parts of north-central MT and
central/eastern WY for Day 3/Thursday.

...Day 5/Saturday - Day 8/Tuesday: Portions of Southern CA...
A prolonged moderate to perhaps locally strong offshore wind event
should begin around Day 5/Saturday and continue through the end of
the forecast period across parts of southern CA. Latest medium-range
guidance is in good agreement that the surface pressure gradient
will strengthen to near-critical thresholds by Saturday night, and
the potential for critical fire weather conditions continuing
through next Tuesday across this region has increased.

The surface pressure gradient and resultant strong/gusty offshore
wind potential appears to be maximized in the Day 6/Sunday to Day
8/Tuesday time frame. Therefore, 70%/critical probabilities have
been introduced for the mountains/foothills of southern CA for Day
6/Sunday and Day 7/Monday, as well as some adjacent valley areas.
40%/marginal probabilities have been expanded to the coast for these
days and included for Day 8/Tuesday. RH values will likely be
critically lowered through the period owing to hot/dry daytime
conditions and poor overnight RH recoveries. Fuels are also expected
to remain very dry, supporting a likely critical fire weather
threat.

..Gleason.. 10/17/2017

...Please see www.spc.noaa.gov/fire for graphic product...

$$



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