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 Forecast Discussion

  
000
ACUS01 KWNS 260543
SWODY1
SPC AC 260542

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1242 AM CDT Wed Jul 26 2017

Valid 261200Z - 271200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER A PORTION OF
THE UPPER MIDWEST...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM A PORTION
OF THE CENTRAL PLAINS INTO THE UPPER GREAT LAKES...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER A PORTION
OF NEVADA INTO SOUTHERN OREGON...

...SUMMARY...
Scattered thunderstorms, a few capable of producing locally strong
to severe wind gusts, are expected over portions of the Upper
Midwest region this afternoon and evening. Storms may also produce a
few locally strong to damaging wind gusts from a portion of Nevada
into southern Oregon.

...Synopsis...

Belt of modest westerlies will persist over the northern and central
Plains through the Great Lakes. Embedded within this regime, an MCV
currently over South Dakota will continue east through the upper MS
Valley.  Farther west the cutoff upper low over northern CA will
deamplify as it begins to shift northeast through northwest NV and
southeast OR in response to an approaching upstream trough.  At the
surface a cold front will move southeast through the upper
Mississippi Valley and Great Lakes region with southwestern
extension of this boundary continuing through the central Plains.
Warm front will shift slowly eastward through the middle and upper
MS Valley region ahead of the cold front.

...Upper Midwest through central Plains regions...

Thunderstorms now over the central Plains will develop east into the
upper MS Valley supported by a southwesterly low-level jet and MCV,
but will probably undergo some decrease in coverage later this
morning. Downstream from this activity an extensive cirrus plume may
delay or slow diabatic warming of the moist warms sector, but the
atmosphere should become moderately unstable with 1500-2000 J/kg
MLCAPE from northern KS through southern half of IA into northern
IL. Storms will likely redevelop along residual outflow boundaries
along and ahead of the cold front as atmosphere destabilizes. Some
mesoscale enhancement in the winds aloft and vertical shear might
occur in association with the MCV/shortwave trough, with effective
bulk shear generally from 25-40 kt. However, tendency will be for
storms to evolve into clusters and line segments with damaging wind
the primary threat, though some hail will also be possible with the
stronger storms.  

...Western Nevada through southeast Oregon...

High-based storms will likely once again develop in this region in
association with upper low circulation as the atmosphere
destabilizes during the afternoon into the evening. Deeply mixed
inverted-V boundary layers will support a risk for a few downburst
winds through early evening.

..Dial/Dean.. 07/26/2017

$$