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FNUS28 KWNS 202021

Day 3-8 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0321 PM CDT Thu Jul 20 2017

Valid 221200Z - 281200Z

Mid-level heights will build across much of the western US this
weekend, with enhanced westerly flow generally confined to areas
near the Canadian border. A weak closed low will approach the
northern California/southern Oregon coast late this weekend into
early next week, increasing thunderstorm chances across parts of the
Pacific Northwest and northern Rockies (see below regarding the
dry-thunderstorm threat). Moreover, mid-level moisture will slowly
spread north across western portions of the Great Basin, further
enhancing the threat of thunderstorms next week. Through the middle
of the week, the aforementioned low will weaken as it advances
towards the northern Rockies and is absorbed by a belt of stronger
westerly flow near the Canadian border.

The dry-thunderstorm areas for D4/Sun and D5/Mon are maintained with
only minor adjustments. Guidance still indicates a monsoon-related
northward-surge of mid-level moisture across the western/northern
Great Basin and parts of the interior Pacific Northwest.
Additionally, with forcing for ascent associated with the
approaching low, mid-level instability will be further enhanced. The
greatest overlap of thunderstorms and favorably dry profiles still
appears to be late weekend into early next week. As finer-scale
details are resolved over the next several days, critical/40%
dry-thunderstorm areas could be introduced. After D5/Mon, guidance
differs on the speed of the incoming low and related moisture
profiles, suggesting uncertainty regarding the thunderstorm mode
(dry vs wet). As such, no area is introduced after D5/Mon, but could
be needed in later outlooks if higher moisture content is slower to
overspread the northern Rockies.

..Picca.. 07/20/2017

...Please see for graphic product...

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