SPC AC 120546

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1246 AM CDT Sat Aug 12 2023

   Valid 121200Z - 131200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM FAR
   EASTERN OHIO ACROSS PENNSYLVANIA AND INTO PARTS OF CENTRAL NEW
   YORK...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE OHIO
   VALLEY INTO SOUTHWEST NEW ENGLAND...OVER PARTS OF THE CENTRAL
   PLAINS...AND OVER THE TENNESSEE VALLEY...

   ...SUMMARY...
   Severe thunderstorms are likely across portions of the Ohio Valley
   and Northeast, parts of the central Plains region, and across the
   Tennessee Valley today. The most concentrated area of damaging
   storms appears to extend from northeast Ohio across parts of
   Pennsylvania and into central New York, where damaging hail, wind,
   and tornado or two will be possible.

   ...Synopsis...
   An upper ridge will be located over the southern Plains and lower MS
   Valley today, with moderate mid and high-level winds from the
   northern Rockies and Plains across the Great Lakes and into the
   Northeast. Embedded in this broad region of primarily cyclonic flow
   aloft, a shortwave trough will move from the upper Great Lakes
   eastward across OH, PA, NY by 00Z, with 500 mb speeds of 40-50 kt.

   At the surface, low pressure will move east across parts of
   southwest Ontario and toward northern NY by 00Z. Winds around 850 mb
   will increase out of the southwest, aiding the advection of an
   unstable air mass across OH, PA, and NY. Low-level shear will be
   maximized near the nose of the low-level jet and theta-e advection
   plume from northeast PA into parts of central NY. Deep-layer shear
   will overlap an unstable air mass extending westward into OH.

   Elsewhere, hot conditions will again prevail over the southern
   Plains, with a low developing across northwest TX/eastern Panhandle.
   North of the low, a boundary will stretch from northeast NM eastward
   across northern OK, with easterly winds over KS and southeast OK
   maintaining a moist and unstable air mass.

   Farther north, a weak trough will develop over western SD and NE,
   beneath moderate west/northwest flow aloft favoring hail.

   ...OH into southern New England...
   As the shortwave trough approaches the area, southwest low-level
   flow will help spread moisture northeastward ahead of a cold front,
   with 1500-2000 J/kg MUCAPE widespread by midday/late afternoon.
   Initial development is likely along the southern shore of Lake Erie
   and extending east/northeast across northwest PA and southwest NY
   just south of the stable lake shadow. Other storms are likely to
   develop around 19Z as well over northeast PA and across much of
   central NY as the air mass will be uncapped. Forecast soundings from
   several models all show shear and instability favorable for
   supercells, especially near the nose of the low-level heat plume.
   Effective SRH over 200 m2/s2 is forecast, with 0-1 values of 100-150
   m2/s2 which will support a tornado threat. Elongated hodographs in
   the mid to upper levels along with the cool air aloft will strongly
   favor damaging hail with the strongest cells. A few hail reports
   approaching 2.00" diameter will be possible through early evening,
   given supercell wind profiles and cool air aloft.

   ...TX Panhandle across western and northern OK and southern KS...
   Hot temperatures will easily uncap the air mass this afternoon, just
   south and west of a moist plume extending out of central OK and
   across the OK/northern TX Panhandles. Indications are that the moist
   upslope will yield activity forming near Pueblo CO, with hail and
   wind potential as it moves east along the instability axis. Storms
   will likely initiate over the TX Panhandle as well, and models
   indicate substantial outflow may be produced with forward
   propagation across northwest OK and into southern KS. Hail may also
   occur during the peak heating hours, given expected strong updrafts
   and as storms encounter the moist plume.

   ...Mid MS/Lower OH Valley southeastward across AL...
   A very moist and unstable air mass will again exist today with mid
   70s F dewpoints and strong heating. Midlevel temperatures will also
   be relatively cool, resulting in MLCAPE in the 3000-4000 J/kg range.
   This will conditionally favor damaging downbursts with storms that
   develop in the uncapped air mass. Further, models indicate that a
   remnant outflow, or perhaps rejuvenated MCS, may move across Middle
   TN into northern and eastern AL, which would enhance damaging-wind
   potential. As such, as Slight Risk has been introduced.

   ...Western SD into northern NE...
   Developing southeast surface winds will help bring mid to upper 50s
   dewpoints northwestward toward the Black Hills. Strong heating will
   result in steep lapse rates, and this along with elongated
   hodographs will conditionally favor storms producing hail, despite
   MUCAPE generally less than 1000 J/kg. Deeply mixed low levels will
   also favor evaporative cooling and downdraft potential, as storms
   form over the higher terrain after 21Z and move southeastward during
   the evening.

   ..Jewell/Lyons.. 08/12/2023

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