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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0242 PM CDT Mon Sep 19 2022

Valid 192000Z - 201200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FOR PARTS OF THE
NORTHEAST...A PORTION OF THE UPPER MS VALLEY...SACRAMENTO VALLEY...

...SUMMARY...
Isolated severe thunderstorms are possible over parts of the
Northeast, the Upper Midwest, and the Sacramento Valley.

...Discussion...
Only minor modifications were made to the previous convective
outlook.  1) Removed low-severe probabilities across PA in wake of
ongoing storm activity moving east through the Delaware River
Valley.  2) Remove low-severe probabilities across ND and northwest
MN as the focus for storm development (i.e., low-level WAA) moves
northeast away from the region through the remainder of the
afternoon.  While the risk for a strong storm cannot be ruled out
late tonight, the paucity of a convective signal precludes the
maintenance of low-severe probabilities.

..Smith.. 09/19/2022

.PREV DISCUSSION... /ISSUED 1130 AM CDT Mon Sep 19 2022/

...Northeast...
12Z observed soundings sampled weak, moist-adiabatic lapse rates and
modest low to mid-level westerlies, downstream of a broad swath of
weak convection across western NY/PA. This suggests that
boundary-layer heating will be the primary mechanism required for
intensification of this ongoing activity, which appears most
pronounced from the Lower Hudson to DE Valleys. Still, MLCAPE will
likely remain weak from 500-1000 J/kg. While there will be some
increase in 850-500 mb winds, the bulk of stronger flow aloft will
largely remain relegated west of the Appalachians this afternoon in
the southwest flank of the shortwave trough shifting east across
southeast ON and the Upper Saint Lawrence Valley. Lower-level flow
should largely peak from 30-35 kt with the convection that spreads
east, suggesting that strong but predominately sub-severe gusts
should dominate as convective intensities peak in the late
afternoon. These will still be capable of producing isolated to
perhaps even scattered tree damage, but the threat for severe gusts
appears too marginal to warrant an upgrade. Late morning CAM
guidance suggests that the Upper Hudson Valley vicinity will have
the greatest relative potential for multicell clustering, but
observational data suggests boundary-layer heating will likely be
stronger to the south.

Colder mid-level temperatures attendant to the shortwave trough will
overspread the region downstream of the Lower Great Lakes during the
early evening, as a mid-level jetlet spreads into western NY.
Despite the increasingly unfavorable time of day with respect to the
diurnal heating cycle, this setup could support a second round of
convective development that may produce a 2-3 hour period of
marginally severe hail and locally damaging gusts until convection
wanes tonight. 

...Eastern ND vicinity...
Low-level WAA-driven convection persists and will likely spread
northeast towards the international border while further decaying
this afternoon. In the wake of this activity, a pronounced EML and
attendant MLCIN appears likely to mitigate surface-based development
along a weakly convergent surface trough in central ND this
afternoon. Another round of low-level WAA-driven elevated
thunderstorms might occur in the early morning tomorrow, similarly
centered on central to eastern ND. While guidance differs greatly on
this scenario, favorable speed shear through the cloud-bearing layer
will support a conditional threat for isolated severe hail.

...Western WI vicinity...
A corridor of elevated convection driven by low-level WAA along the
eastern periphery of the north-central states EML appears probable
overnight. Ample elevated buoyancy and some cloud-bearing shear
could support isolated severe hail in the early life-cycle of the
convective development. Convection will likely evolve into a broad
cluster and temper individual updraft intensity towards 12Z.

... Sacramento Valley...
A few low-topped storms should develop during the late afternoon
within the left-exit region of a broad mid-level southwesterly jet
centered across central CA into NV. Favorable elongation of the mid
to upper-level hodograph could support small to marginally severe
hail in the strongest updrafts amid weak mid-level lapse rates and
MLCAPE of 500 J/kg or less.