Fire Weather Outlook Discussion
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FNUS28 KWNS 102153

Day 3-8 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0352 PM CST Sun Dec 10 2017

Valid 121200Z - 181200Z

Upper ridging will remain in place across the Intermountain West for
the first half of the period before finally weakening some as a
stronger jet stream migrates southeastward across the northern
Rockies.  Downstream, longwave troughing will be reinforced by
multiple waves migrating southeastward towards the general vicinity
of the Great Lakes.

At the surface, high pressure will continue to persist across
portions of the Great Basin and maintain an offshore pressure
gradient in dry areas of southern California.  This offshore
gradient will finally weaken some after about D6/Fri - with surface
flow slackening and a weak onshore flow providing some reprieve to
the high-impact fire weather conditions that have plagued the region
over the past several days.  Farther east, periods of downslope flow
will be enhanced by surface cyclogenesis in the Great Lakes around
D4/Wed and also in the lee of the Rockies on D6/Fri, prompting fire
weather concerns there.

...Southern California...
The long-duration Santa Ana event should continue through at least
D5/Thu - although in a somewhat weaker state compared to previous
periods.  Elevated to locally critical fire weather conditions are
expected in southern California as a very dry airmass should
continue to reside across the region amidst areas of gusty
easterly/northeasterly winds.  This region will be monitored for any
potential strengthening of the offshore pressure gradient beyond
currently depicted in model guidance, which would necessitate
categorical/probabilistic upgrades.

Beyond D5/Thu, models suggest that the pressure gradient across the
region will weaken substantially due to weakening high pressure in
the Great Basin.  Slightly higher RH values and weaker surface flow
will be the likely result, although fuels will remain dry as
precipitation potential appears negligible for the foreseeable

...D4/Wed - Central High Plains...
An area of gusty northwesterly surface flow will develop on the
western periphery of a deepening low over the Great Lakes.  RH
values appear to be a bit borderline for critical fire weather
conditions, although dry fuels and high ERC values suggest potential
for rapid fire spread across the region.  40%/elevated probabilities
have been added to address this threat.

...D6/Wed - Portions of the Central and Southern High Plains...
Models suggest that a couple of corridors of strengthened downslope
flow will develop as a result of a sharpening lee trough - one
across southeastern Wyoming, western Nebraska, and northeastern
Colorado and another from eastern New Mexico into the Texas and
Oklahoma Panhandles.  These areas of increased surface flow will
occur amidst dry low-level conditions, near-critical RH values, and
dry fuels/high ERCs - highest in portions of the central Plains.
Subtle differences in depiction of key synoptic features in model
guidance preclude higher probabilities and or larger spatial
highlights at this time.  These areas will likely be readjusted in
later outlooks.

..Cook.. 12/10/2017

...Please see for graphic product...

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