SPC AC 221557
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1057 AM CDT Tue Aug 22 2017
Valid 221630Z - 231200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS NY/PA...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OH VALLEY TO
WESTERN NEW ENGLAND...
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SOUTHERN HIGH
PLAINS TO NEW ENGLAND...
Scattered to numerous swaths of damaging winds are expected from the
Ohio Valley to western New England through this evening. A couple
tornadic storms are possible, mainly over parts of New York into
...OH Valley to western New England...
Minimal change necessary this outlook with numerous storms expected
to develop in the next few hours. A pronounced shortwave trough over
the Upper Great Lakes will continue to amplify while approaching
Quebec tonight. Associated surface cyclogenesis will drive a cold
front southeast across the Lower Great Lakes and OH Valley. Primary
focus for storm development will be along the remnant
outflow/differential heating zone ahead of the front. Strong
tropospheric winds will support effective shear of 30-40 kt
southwest to 40-50 kt northeast. In spite of poor mid-level lapse
rates, robust diabatic heating will contribute to MLCAPE of
1500-2500 J/kg southwest to 1000-2000 J/kg northeast. An initially
mixed mode should transition to line segments with swaths of
damaging winds expected, especially with bowing segments. Stronger
low-level shear and enlarged hodographs are expected across parts of
NY into northern PA. Although storm mode may limit the sustenance of
rotating updrafts, embedded QLCS mesovortices should support a
threat for a couple tornadoes.
For additional short-term discussion, please see MCDs 1547 and 1548.
...Southern High Plains to Mid-South...
Deep-layer flow and shear will be substantially weaker along a
southward-sagging cold front and pre-frontal outflow near the I-40
corridor. Loosely organized multicell clusters are expected
mid-afternoon to mid-evening with isolated downbursts and marginally
severe hail possible.
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