SPC May 1, 2017 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0247 PM CDT Mon May 01 2017

Valid 012000Z - 021200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
WEST VIRGINIA...WESTERN MARYLAND...PENNSYLVANIA AND NEW YORK...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OUTSIDE OF THE
ENHANCED RISK AREA ACROSS PARTS OF THE APPALACHIAN MOUNTAINS AND
ATLANTIC COASTAL PLAINS...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OUTSIDE OF THE
SLIGHT RISK AREA ACROSS PARTS OF THE ATLANTIC COASTAL STATES AND
APPALACHIAN MOUNTAINS...

...SUMMARY...
Scattered to numerous strong to severe storms are expected this
afternoon into this evening with damaging winds and a few tornadoes,
most likely from western and central New York southward across the
Virginias into the Carolinas.

Several changes have been made to the outlook for this issuance. The
first change is to add a 45 percent contour across parts of
Pennsylvania and west-central New York. A large concentration of
wind reports is expected beneath the core of the mid-level jet where
large-scale ascent and deep-layer shear is strong across parts of
Pennsylvania and New York. The second change is to move the southern
most slight risk contour northward into central South Carolina where
deep-layer shear appears strong enough for an organized severe
threat. The third change is to move the southern most marginal
contour northward to encompass east-central Georgia and southern
South Carolina. South of this line, deep-layer shear appears
insufficient for a severe threat. The final change is to align the
western edge of the thunder and adjacent severe probability contours
to the western edge of a line of strong to severe thunderstorms
ongoing in the central and southern Appalachian Mountains.

..Broyles.. 05/01/2017

.PREV DISCUSSION... /ISSUED 1116 AM CDT Mon May 01 2017/

...NY to the Carolinas...
Broken clusters of showers with embedded isolated storms are ongoing
along a cold front from the Upper OH Valley to GA. Given the
meridional flow pattern, mid-level lapse rates were weak in regional
12Z observed soundings. In conjunction with pronounced downstream
cloud coverage, buoyancy will remain limited with MLCAPE largely
below 750 J/kg north of SC. 

A mid-level vorticity maxima ejecting northeast across the Upper OH
Valley should decay through this afternoon, but provide sufficient
large-scale ascent to aid in increasing storm coverage across parts
of WV into western PA/NY. Nearly unidirectional and quite strong
wind profiles should support evolution to northeastward-accelerating
linear bands with embedded bows across the northern Appalachians
vicinity. Damaging wind swaths should be the primary hazard, but
50-60 kt 850-mb winds should foster the risk for a few tornadoes
from QLCS-related mesovortices and embedded supercells. 

While large-scale ascent will be weaker with southern extent towards
upstate/Piedmont regions of the Carolinas, the overall
thermodynamic/kinematic environment should be similar and yield a
mixed mode of a few semi-discrete supercells and linear clusters.
Scattered damaging winds and a couple tornadoes will be possible.
The eastern extent of the risk towards the coastal plains of the
Northeast/Mid-Atlantic should wane tonight owing to a lack of
greater warm-sector instability.

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