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SPC Convective Outlook

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 Forecast Discussion

  
000
ACUS01 KWNS 221609
SWODY1
SPC AC 221608

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1108 AM CDT Sat Jul 22 2017

Valid 221630Z - 231200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OH VALLEY TO
MID-ATLANTIC...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS UPPER MIDWEST...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISKS TO THE CENTRAL GREAT PLAINS...

...SUMMARY...
Scattered wind damage is possible from parts of the Ohio Valley
eastward into the Mid-Atlantic through this evening, with scattered
severe hail possible across parts of the Upper Midwest late this
afternoon and evening.

...Mid-Atlantic States...
A lead MCV is progressing east across northwest PA with a short
convective line segment farther south across the MD/eastern WV
Panhandles. Surface wind gusts with this leading-line convection
have remained modest amid a minimal cold pool. Robust diabatic
heating downstream across the Piedmont and Coastal Plain should
result in convection expanding in coverage and intensifying during
mid/late afternoon. With area RAOBs sampling 700-500 mb lapse rates
of 5.5-6.0 degree C/km, setup should favor damaging winds as the
main hazard. On the periphery of 700-mb winds at or above 30 kt
along with an ill-defined surface pattern, wind damage should
primarily be produced by scattered strong wind gusts.

...OH Valley/Midwest...
Primary change this outlook is to expand Slight Risk west.
Destabilization is well underway with south to southwest surface
winds in the wake of leading-line convection over the central
Appalachians. More pronounced outflow has been established from
decaying convection over east-central IL and this should mark the
western edge of organized severe potential. Weak confluence
boundaries and low-level WAA atop the remnant outflow across parts
of southern IL/IN/OH should aid in multiple rounds of scattered
storms through this evening. Large buoyancy to the south amid a
swath of 30-40 kt 700-mb flow will offer a primary risk of damaging
winds and secondary risk of severe hail. 

...Upper Midwest...
A compact shortwave trough over southern MB should reach Lake
Superior tonight. Widely scattered storms are expected downstream
and south of this trough first across northern MN and later into WI.
A nearly unidirectional mid/upper-level profile with robust speed
shear will favor elongated hodographs supportive of splitting
supercells. Overall intensity should be stymied by ongoing light
northerly surface winds and swaths of stratus evident from the MN
Arrowhead into southern WI. But on the northeastern periphery of an 
air mass that should become moderately unstable, the setup should
yield risks of severe hail and locally damaging winds.

..Grams/Bunting.. 07/22/2017

$$