Fire Weather Outlook Discussion
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FNUS21 KWNS 231614
FWDDY1

Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1114 AM CDT Wed Aug 23 2017

Valid 231700Z - 241200Z

...CRITICAL FIRE WEATHER AREA FOR SCATTERED DRY THUNDERSTORMS ACROSS
PARTS OF CENTRAL AND EASTERN OREGON...

...Portions of the Northern Great Basin/Rockies and Pacific
Northwest: Dry Thunderstorm Threat...
Only minor changes were made to the previous outlook. 12Z soundings
at MFR and BOI both sampled the mid-level moisture over the region
well and isolated to scattered thunderstorm coverage is still
anticipated this afternoon as a subtle lead shortwave trough
interacts with this moisture as it moves through the region ahead of
a larger shortwave trough currently off the Pacific Northwest coast.
A mix of wet and dry storms is expected. Thunderstorm coverage will
be highest during peak heating (i.e. between 21Z/14 PDT and 03Z/20
PDT) but some occasional lightning is also possible later this
evening and overnight across the ID Panhandle and adjacent southeast
WA and northwest MT.

...Portions of the Northern Rockies and Adjacent High Plains:
Wind/RH Threat...
Elevated fire weather conditions are still anticipated over the
region this afternoon/evening and no changes are needed to the
previous outlook.

..Mosier.. 08/23/2017

.PREV DISCUSSION... /ISSUED 0145 AM CDT Wed Aug 23 2017/

...Synopsis...
As an upper trough/low moves over BC by late tonight, the
large-scale upper ridge over much of the western CONUS will begin to
shift eastward through the period. A weak upper low off the coast of
CA is forecast to advance eastward over southern CA by early
Thursday morning. Mid-level moisture emanating from the Southwest
monsoon will develop farther northward into portions of the northern
Great Basin/Rockies and interior Pacific Northwest, supporting
isolated to scattered thunderstorms across these regions this
afternoon and evening as a shortwave trough approaches the Pacific
Northwest from the eastern Pacific.

...Portions of the Northern Great Basin/Rockies and Pacific
Northwest: Dry Thunderstorm Threat...
The glancing influence of large-scale ascent associated with the
previously mentioned shortwave trough from the eastern Pacific and
terrain-driven circulations will likely foster isolated to scattered
thunderstorms across portions of the northern Great Basin and
Pacific Northwest into the northern Rockies. While precipitable
water values are forecast to increase along and east of Cascade
crest this afternoon, they should still be sufficiently marginal
(0.7-1.0 inch), coupled with a dry/well-mixed sub-cloud layer, to
support dry thunderstorm potential. Mid-level southwesterly flow is
also forecast to modestly strengthen to around 20 kt across
central/eastern OR into southeastern WA and parts of ID, which
should promote northeasterly storm motions and limit substantial
wetting rainfall potential. A broad isolated dry thunderstorm area
has been continued across these regions to account for this
convective fire weather threat, as fuels remain very dry and
receptive to large fire starts. Confidence has increased in
scattered thunderstorm coverage across parts of central/eastern OR
today, and a scattered dry thunderstorm area has been introduced
across this area given the near-record dry/very receptive fuels
combined with abundant lightning expected.

...Portions of the Northern Rockies and Adjacent High Plains:
Wind/RH Threat...
A modest increase in westerly mid-level flow will occur today across
parts of northern MT along/east of the Rockies. Westerly downslope
winds around 15 mph will warm/dry the low levels, with RH values of
15-20% expected by this afternoon. Some locally stronger wind gusts
may also be possible along the higher terrain. With dry fuels in
place, an elevated area has been introduced for a small portion of
northern MT to account for this gusty wind/lowered RH threat.

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

$$



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