Fire Weather Outlook Discussion
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FNUS21 KWNS 130705

Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0104 AM CST Wed Dec 13 2017

Valid 131200Z - 141200Z

Persistent ridge-trough pattern across the contiguous United States
will persist on Wednesday. The ridge across the western United
States will maintain cool, dry air across the Great Basin and a
surface-pressure gradient favoring offshore flow across Southern
California. Additionally, the eastern trough will maintain generally
equatorward flow across areas east of the Rockies, which will
maintain the dry, continental airmass in place.

...Southern California and the southern Sierras...

The long-duration Santa Ana event will continue for yet another day.
The persistent downslope, offshore flow has resulted in very low
relative humidity (single digit to low teens) with very little if
any overnight recovery across the area. Therefore, despite a weaker
surface-pressure gradient than last week, elevated to locally
critical conditions will remain on Wednesday.

Farther north, elevated fire-weather concerns will exist for
portions of the Sierras. This will stem from very low relative
humidity (single digits) being advected westward from the Great
Basin. Additionally, winds around 10 mph will be possible.

...Central United States...

A very dry airmass remains in place across much of the eastern
two-thirds of the United States. This dry airmass, coupled with
little precipitation this fall and curing fuels, will set the stage
for elevated to locally critical fire-weather conditions through the
day on Wednesday.

The dry airmass, full sunshine, and adiabatic warming associated
with a southward moving cold front will combine to allow
temperatures to warm into the 50s and 60s across the region.
Generally, southern and western areas (western Kansas, Oklahoma,
Texas, and southwest Arkansas) within the highlighted area will be
warmer, with the stronger winds across the northern and eastern
areas (Kansas, much of Missouri, northeast Arkansas, western
Tennessee, and western Kentucky). This will result in two different
regimes for elevated fire-weather concerns.

(1) North and East: Here, slightly cooler temperatures will result
in modestly higher relative humidity as compared to areas farther
south. The slightly higher relative humidity (20-35%) will be offset
somewhat by stronger/gustier surface winds (20-30 mph).

(2) South and West: Warmer temperatures will allow for relative
humidity to fall into the teens. However, surface winds are expected
to be only in the 10-20 mph range.

There will be the potential for a few hours of near-critical
fire-weather conditions across western Kansas. Here, relative
humidity will fall into the upper teens to low twenties in the
presence of winds gusting between 20-30 mph. However, concerns
regarding the duration of the stronger winds preclude an upgrade to
critical at this time.

..Marsh.. 12/13/2017

...Please see for graphic product...

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