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FNUS21 KWNS 241625
FWDDY1

Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1124 AM CDT Mon Jul 24 2017

Valid 241700Z - 251200Z

...CRITICAL FIRE WEATHER AREA FOR PARTS OF THE PACIFIC NORTHWEST TO
THE NORTHERN ROCKIES...

The only significant change with the ongoing forecast is the joining
of the two previous scattered dry-thunderstorm areas into one
corridor stretching from northeast California to southwest Montana.
While the potential exists for a relative minimum in activity across
parts of Idaho, recent satellite/lightning data, and some high-res
guidance, suggest pockets of scattered thunderstorm activity may
evolve across this region through the day and into tonight.
Considering the relatively brisk storm motions, favorable
upper-level flow for strikes downstream (i.e., outside precipitation
cores), and presence of dry fuels, portions of Idaho are now
included in a scattered dry-thunderstorm highlight.

Elsewhere, the previous forecast reasoning remains valid. See below
for more details.

..Picca.. 07/24/2017

.PREV DISCUSSION... /ISSUED 0314 AM CDT Mon Jul 24 2017/

...Synopsis...
An upper trough off of the northern California coast is expected to
remain nearly stationary or drift slowly eastward today, while a
stronger upper trough and associated surface low/cold front move
eastward across the southern Canadian Prairies and northern High
Plains.

...OR/Northern CA northeast into MT - Dry Thunderstorm Threat...
Scattered thunderstorms are expected across a broad zone from
Oregon/northern CA northeast into portions of MT, as the slow-moving
upper trough gradually moves inland and smaller-scale features ahead
of the primary trough move from the Great Basin into the northern
Rockies. Thermodynamic profiles will favor a mix of wet and dry
thunderstorms, though with coverage expected to be relatively high
in an area where fuels are quite dry, this activity is expected to
pose a substantial fire weather threat.

Two critical areas were delineated - one across southern OR/northern
CA/southwest ID, in closer proximity to the primary upper trough,
and also from eastern ID into southwest MT, where a smaller-scale
embedded trough and terrain-enhanced circulations may favor the
development of a forward-propagating thunderstorm cluster this
afternoon/evening. An isolated dry-thunderstorm threat will extend
potentially as far east as eastern MT, depending on the timing of
convection moving in from the southwest. Strong and erratic outflow
winds may accompany any of the thunderstorm activity across the
region, especially across portions of southwest into central MT.

...Portions of Montana into the western Dakotas - Elevated Wind/RH
Threat...
Somewhat cooler temperatures are expected across portions of MT and
eastern ID into the western Dakotas compared to Sunday. However, dry
westerly/northwesterly post-frontal flow will allow for low RH
(potentially down to critical levels) to develop during the
afternoon. In conjunction with these low RH values, anticipated
sustained wind speeds of 15-20 mph (with locally higher gusts) will
result in the potential for elevated to locally critical conditions.
Confidence in the development of critical wind speeds remains too
low for a critical upgrade (for wind/RH concerns) at this time.
However, erratic thunderstorm outflow winds will also be possible
across primarily southern portions of the elevated area (see section
above for discussion of thunderstorm potential) during the late
afternoon and evening.

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

$$



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