Fire Weather Outlook Discussion
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FNUS21 KWNS 121547
FWDDY1

Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0946 AM CST Tue Dec 12 2017

Valid 121700Z - 131200Z

...Montana...
The elevated area has been expanded across parts of central/eastern
Montana. Recent observations and high-res guidance suggest
west/northwesterly downslope flow around 15-25 mph will combine with
dry fuels and RH values below 20% to promote elevated to locally
critical conditions in the lee of the Rockies this afternoon.

...Southern California...
Morning observations indicate pockets of elevated/locally critical
conditions ongoing across terrain-favored areas. Winds may weaken
slightly during the day, but very dry conditions will maintain
higher fire-weather concerns. The current elevated area captures the
risk area well, and no changes are needed.

..Picca.. 12/12/2017

.PREV DISCUSSION... /ISSUED 0128 AM CST Tue Dec 12 2017/

...Synopsis...
The overall mid-level pattern across the United States continues to
be a general west-to-east ridge-trough pattern. This will maintain a
very dry airmass across most of the United States. Additionally, the
pattern will maintain surface ridging across the Great Basin and a
generally favorable pattern for offshore winds across Southern
California.

...Southern California...

The long-duration offshore-wind event will continue on Tuesday. Peak
wind gusts should be in the 20-40 mph range as compared to the 60-80
mph range last week. This continued offshore flow will maintain a
very dry airmass across the region, with very poor overnight
recovery. Thus another day of elevated-to-locally critical
fire-weather conditions is expected.

One note, even though the overall large-scale surface-pressure
gradient will be weakening with time, forecast soundings indicate
mid-level-lapse rates will be on the order of 7.5-8.0 C/km. These
lapse rates will support plume-dominated fires. Any fire plume
would likely modify/enhance low-level winds in the vicinity of the
fire.

...North-central to Southeast Montana...

Strong westerly downslope flow will contribute to afternoon
temperatures warming to around 60F across the area. Surface
dewpoints will be in the teens across the region and then should
fall during the day. The combination of warm temperatures and
falling dewpoints will result in minimum afternoon relative humidity
at or below 20% across much of the area, with local areas even
lower. Additionally, the lack of appreciable precipitation in recent
weeks has allowed fuels to cure and ERC percentiles to rise. Thus,
given the dry, receptive fuels, strong, gusty winds, and the warm,
dry airmass, elevated fire conditions are likely.

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

$$



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