Fire Weather Outlook Discussion
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FNUS21 KWNS 131653
FWDDY1

Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1052 AM CST Wed Dec 13 2017

Valid 131700Z - 141200Z

...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHERN CALIFORNIA...

...Central United States...
Some minor adjustments made to the Elevated delineation but overall
forecast scenario outlined in the previous discussion (below)
remains valid. High temperatures are expected to be 10 to 15 degrees
above-average across the entire region, ranging from the mid 50s
across the central High Plains to the low 70s across central TX.
These warm temperatures will be accompanied by a very dry airmass.
Regional 12Z sounding sampled PW values in the lowest quartile
(based on SPC sounding climatology). Some enhanced winds are
possible as well, particularly across KS and farther east across the
Mid-South. In these areas, some locally critical conditions are
possible for an hour or two this afternoon. Limited spatial and
temporal extent of the critical conditions precludes the need to
introduce any Critical delineations.

...Coastal Southern CA and southern Sierra...
Portions of southern CA were upgraded to critical based on the
expectation of critical conditions beginning late tonight and
continuing through the early morning Thursday. In this area, poor
overnight recovery is anticipated amidst a strengthening pressure
gradient, which, when coupled with very dry fuels, will support a
critical fire weather threat. Elevated conditions are anticipated
farther north in the southern Sierra where a prolonged period of
single digit RH values is expected. Some gusty winds are also
possible, supporting isolated critical conditions.

..Mosier.. 12/13/2017

.PREV DISCUSSION... /ISSUED 0104 AM CST Wed Dec 13 2017/

...Synopsis...
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.

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

$$



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