Severe Storm Outlook Narrative (AC)
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ACUS11 KWNS 270026
SPC MCD 270026

Mesoscale Discussion 1159
NWS Storm Prediction Center Norman OK
0726 PM CDT Mon Jun 26 2017

Areas affected...southeast WA...northern ID...far western MT

Concerning...Severe potential...Watch unlikely

Valid 270026Z - 270130Z

Probability of Watch Issuance...20 percent

SUMMARY...Scattered 45-60 kt gusts are likely this evening as a band
of strong to severe thunderstorms continues to move north-northeast
across southeastern WA, northern ID, and into far western MT.

DISCUSSION...Radar imagery over the past few hours has shown a
gradual upscale growth of convection over northeastern OR.  This
region is immediately downstream of an approaching upper-level PV
anomaly moving across northern CA/western OR with a 75 kt 300-mb
speed max nosing into eastern OR.  9-km CAPPI imagery over the past
several hours has shown scattered intense thunderstorm cores
associated with earlier reports of large hail across north-central
OR.  A 56-kt gust was observed by the Pendleton, OR ASOS at 2347Z
and a 47-kt gusts by the Walla Walla, WA ASOS at 2311Z.  Surface
analysis shows temperatures near 100 degrees F over southeastern WA
and into the lower 90s across northern ID and western MT.  Surface
dewpoints are in the upper 40-lower 50s---resulting in
temperature-dewpoint spreads in the 40-50 F range.

The very steep lapse rates from the surface through 500 mb will be
very favorable for evaporative cooling and the propensity of
scattered strong to severe gusts through the early evening.  There
was a 8.9 degrees/km 700-500 lapse rate on the 00Z BOI raob with
40-60 kt southwesterly mid- to high-level flow.  Likewise, the OTX
00Z raob exhibited steep lapse rates and was substantially moist
with a PW of 1 inch.  The combination of factors listed above
coupled with a fairly well organized cold pool/outflow suggests the
severe threat will persist into western MT and perhaps the Flathead
Valley later this evening.

..Smith.. 06/27/2017

...Please see for graphic product...


LAT...LON   46331991 47771808 48181497 47701367 46401363 46021498
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