Fire Weather Outlook Discussion
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FNUS28 KWNS 222158

Day 3-8 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0457 PM CDT Sun Oct 22 2017

Valid 241200Z - 301200Z

A mid/upper-level ridge is forecast to continue building over the
western United States on Day 3/Tuesday, while a surface high
gradually shifts farther southward/southeastward through the Great
Basin. The surface high is forecast to weaken Day 4/Wednesday, as a
mid-level trough -- and an associated surface low -- moves from
Canada into the Northern Rockies and northern/central Plains.
Mid/upper-level ridging is then expected to become re-established
across the west Day 5/Thursday into the weekend, as the mid-level
trough gradually shifts eastward across the East Coast.

...Southern CA...
Offshore Santa Ana wind event is expected to peak early Day
3/Tuesday, as aforementioned surface high moves farther into the
Great Basin and surface pressure gradient strengthens. The very hot
temperatures (e.g., triple digit heat), dry low levels (e.g.,
minimum RH values less than 15%), sustained surface winds in excess
of 20 mph, and receptive fuels will combine to promote likely
Critical fire weather conditions. Additionally, poor overnight
recoveries will keep the fire weather threat going through Tuesday
night. The 70%/40% probabilities were maintained to account for
these conditions.

Latest guidance suggests only a gradual weakening of the surface
high -- and associated pressure gradient -- over the Great Basin on
Day 4/Wednesday, with lingering offshore breeziness continuing into
the afternoon. RH values are also expected to remain low, as
overnight RH recoveries remain poor. Thus, 40% probabilities for
Critical fire weather conditions have been introduced. An upgrade
may be needed in future updates if trends in guidance suggest
Critical conditions continuing well into Wednesday.

...Central Plains...
Although gusty northwest winds are likely on Day 3/Tuesday, the
uncertainty regarding the degree of boundary layer drying/warming
and fuel receptiveness precludes introducing probabilities for
Critical fire weather conditions with this outlook. If guidance
trends drier/warmer, then areas could be needed in future updates.

...Northern High Plains...
Strong downslope westerly/northwesterly pre-frontal winds are
expected to develop Day 4/Wednesday, as a mid-level impulse
approaches the region. The strong winds coupled with forecast RH
values near Critical levels and receptive fuels lends enough
confidence in at least locally Critical conditions to introduce 40%
Critical probabilities. An upgrade may be needed for portions of the
area if trends in guidance indicate the potential for Critical
conditions on a more widespread basis.

..Elliott.. 10/22/2017

...Please see for graphic product...

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