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FNUS21 KWNS 171655

Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1154 AM CDT Thu Aug 17 2017

Valid 171700Z - 181200Z

Isolated dry thunder introduced for portions of northeast MT into
far western North Dakota. Otherwise, no changes needed to Day
1/Thursday forecast.

...Montana into the far western Dakotas...
Recent satellite imagery depicts shortwave trough digging into the
northern Rockies, while radar/lightning data show a small cluster of
thunderstorms with occasional CG lightning progressing southeastward
near the Canadian/MT border.

Afternoon forecast soundings across eastern MT show a deep mixed
boundary layer, moderately-strong mid-level flow, PWs generally less
than 0.75", and marginal instability. While CAM solutions generally
suggest thunderstorm coverage might be rather sparse, combination of
very dry fuels, dry sub-cloud layer, and gusty outflows will
increase the potential for new fire ignitions from CG lightning
outside of any heavier rain cores.  The best chance for isolated
thunder is likely across northeastern MT this afternoon out ahead of
aforementioned thunderstorm cluster starting to enter MT. Further
south across southeast MT, isolated dry thunder potential appears
lower owing to extensive cloud cover and light rain showers across
the area, which should limit destabilization this afternoon.

In addition, forecast of elevated fire weather conditions this
afternoon continues across a larger portion of Montana (east of the
continental divide) into the far western Dakotas as relative
humidity drops below 20% and post-frontal sustained winds approach
15-20 mph in a area of very dry fuels.

..Elliott/Jirak.. 08/17/2017

.PREV DISCUSSION... /ISSUED 0304 AM CDT Thu Aug 17 2017/

As one mid/upper trough shifts eastward into the northern Plains and
another trough approaches the British Columbia coast, a mid/upper
ridge is expected to briefly build into portions of the Northwest
today. A cold front is expected to move through portions of the
northern Rockies and northern High Plains, resulting in some
increase in the fire weather threat.

...Montana into the far western Dakotas...
A relatively dry and breezy post-frontal regime will result in a
threat of elevated fire weather conditions across much of Montana
east of the Continental Divide, potentially spreading eastward into
the western Dakotas. Sustained winds of 15-20 mph are possible as RH
values drop to near or below 20% during the afternoon. While locally
critical conditions are possible, especially from central into
southeast MT, confidence in sustained winds exceeding 20 mph is too
low for an upgrade at this time.

Locally elevated conditions will be possible across portions of
central/eastern WA/OR in the lee of the Cascades, and also across
portions of the Snake River Valley in Idaho. RH may fall to near
critical thresholds across these areas, though wind speeds are
expected to remain relatively light outside of localized
terrain-favored locations.

...Please see for graphic product...

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