SPC AC 220550

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1250 AM CDT Wed Jul 22 2020

   Valid 221200Z - 231200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
   THE CENTRAL APPALACHIANS...MID-ATLANTIC AND NORTHEAST...

   ...SUMMARY...
   Strong to severe thunderstorms capable of producing mainly damaging
   winds will be possible today across parts of the central
   Appalachians, Mid-Atlantic and Northeast. Other isolated severe
   storms will also be possible across parts of the central Plains and
   West.

   ...Central Appalachians/Mid-Atlantic/Northeast...
   An upper-level trough will move slowly eastward across the Great
   Lakes and Ohio Valley today. At the surface, a moist airmass will be
   in place from the Ohio Valley eastward to the Mid-Atlantic where
   surface dewpoints should be in the upper 60s and lower 70s F. In
   response, moderate to strong instability will be in place by midday
   from parts of the central Appalachians eastward to the Mid-Atlantic
   and northward into southwestern New England. Scattered thunderstorms
   are expected to develop early in the day across the Ohio Valley with
   a general increase in convective coverage taking place during the
   afternoon. Although deep-layer shear will be on the low side for
   storm rotation, severe multicells associated with wind damage will
   be possible as low-level lapse rates steepen in the afternoon. The
   greatest instability is forecast to develop from eastern West
   Virginia eastward to southern New Jersey during the mid to late
   afternoon. This corridor will be favored for a wind-damage threat
   especially if an organized line segment and cold pool can move
   eastward across the region.

   Further north into eastern Pennsylvania, New Jersey and southeast
   New York, an axis of moderate instability is forecast to be in place
   by afternoon. Thunderstorms that initiate in the higher terrain of
   the central Appalachians will move eastward into the lower
   elevations during the mid to late afternoon where instability will
   be greater. Although deep-layer shear should be mostly at or below
   30 kt, the moderate instability and steep low-level lapse rates
   should be enough for a wind-damage threat. The threat could also
   impact southwestern New England where instability is expected to
   become maximized in the late afternoon. 

   ...Central Plains...
   An upper-level ridge will move across the central and northern
   Rockies today as west-southwest mid-level flow remains in the
   central and northern Plains. At the surface, a corridor of maximized
   low-level moisture will be in place by afternoon from central
   Nebraska into southern South Dakota. Moderate instability will
   likely develop along the moist axis during the mid to late
   afternoon. In spite of this, capping should prevent thunderstorm
   development until early evening when the low-level jet will markedly
   increase. Thunderstorms are expected to form during the early
   evening in western Nebraska near the center of the low-level jet and
   move eastward across central Nebraska in the mid to late evening.
   Any severe threat is expected to be marginal, mainly due to the
   influence of the upper-level ridge and relatively weak deep-layer
   shear.

   ...Northern California/Northwest Nevada/Southeast Oregon...
   An upper-level low will move slowly eastward into north-central
   California today. Ahead of the upper-level low, a surface low will
   deepen in northwest Nevada. Surface temperatures should become
   maximized from near the surface low northward into southeast Oregon
   by afternoon. Due to this, a pocket of moderate instability may
   develop. Although deep-layer shear is expected to be relatively
   weak, lapse rates will become very steep. As cells initiate in the
   higher terrain and move into the moderate instability during the
   afternoon, a few marginally severe wind gusts will be possible.

   ..Broyles/Cook.. 07/22/2020

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