SPC AC 240716

   Day 2 Convective Outlook CORR 1
   NWS Storm Prediction Center Norman OK
   0216 AM CDT Mon Aug 24 2020

   Valid 251200Z - 261200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
   THE NORTHEAST...

   CORRECTED TEXT

   ...SUMMARY...
   A slight risk for severe storms Tuesday is evident over the
   Northeast.  More isolated risk will extend from the northwestern
   U.S. and northern Intermountain region to the Upper Great Lakes, and
   also across Arizona.  Risk for a brief/weak tornado or two may also
   develop as Laura nears southern Louisiana.

   ...The Northeast...
   A strong cold front is forecast to shift across the U.S./Canada
   border near the start of the period, and then will advance quickly
   eastward across New England, while progressing more slowly
   southeastward across the Mid Atlantic region and southward across
   the central Appalachians.  Convection will likely be ongoing ahead
   of the front at the start of the period, casting some uncertainty
   across New England with respect to how much destabilization will be
   able to occur ahead of the fast-moving boundary.  Still, with very
   strong flow aloft promoting rapid storm motions, risk for damaging
   winds will exist with any sustained convection as storms move
   quickly east-southeastward and approach/clear the coast by early
   evening.

   Farther south/southwest, greater destabilization is expected ahead
   of the sagging front, but flow aloft will progressively weaken with
   southward extent.  Still, ample CAPE/shear combination is expected
   southward across the central Appalachians and into the Mid-Atlantic
   region, supporting clusters of southeastward-moving storms
   accompanied by risk for damaging winds and hail through afternoon
   and evening. 

   ...Upper Great Lakes/Midwest region...
   Storms may be ongoing at the start of the period across portions of
   the Wisconsin/lower Michigan vicinity, with limited/lingering severe
   potential possible with one or two of the stronger convective
   clusters.  

   Meanwhile, with daytime heating supporting some destabilization
   along the trailing portion of the cold front crossing the Northeast,
   a few late afternoon storms may redevelop near the boundary,
   followed by potential for some increase in coverage expected after
   dark as warm advection increases in conjunction with a southwesterly
   low-level jet.  Given the anticyclonic belt of fast flow overhead, a
   couple of stronger storms will be possible, with attendant potential
   for locally gusty winds or marginal hail.

   ...Northern Intermountain region into the northern Plains...
   A series of cyclonic mid-level disturbances will continue to move in
   an easterly anticyclonic arc across the northern Intermountain
   region and northern Plains, embedded within a belt of fast flow
   around the northern periphery of the upper ridge.  

   Afternoon heating will support modest destabilization from portions
   of eastern Oregon/Idaho eastward across the northern Intermountain
   region, supporting isolated storm initiation over the higher
   terrain.  Given strong mid-level flow promoting fast-moving storms,
   and a rather deep mixed-layer adding some evaporative enhancement to
   downdrafts, locally gusty/damaging winds will be possible.

   Farther east into the northern Plains, a dry/capped boundary layer 
   is expected, that should act to substantially limit convective
   development though the afternoon.  Still, with fast flow aloft
   supporting potential for updraft organization, gusty/damaging winds
   would be possible with any sustained storm which could develop.

   Overnight, evolution of a southwesterly low-level jet may foster an
   increase in convection coverage from the Dakotas into the Great
   Lakes region, though storms would likely be primarily elevated above
   the capping layer.  Some risk for hail would likely exist given
   steep mid-level lapse rates supporting ample CAPE above the cap, and
   a locally strong wind gust cannot be ruled out.

   ...Arizona...
   Model forecasts continue to depict small mid-level cyclonic
   disturbances moving southwestward across Arizona Tuesday and Tuesday
   night, within a belt of enhanced northeasterly mid-level flow.

   As the airmass heats/destabilizes through the afternoon, storms
   should develop over higher terrain/the Mogollon Rim, and then shift
   southeastward into the lower deserts.  With a very deep mixed layer
   promoting evaporative downdraft acceleration, potential for locally
   damaging wind gusts is evident with a couple of the stronger
   storms/storm clusters.

   ...Central/Western Gulf Coast region...
   The latest National Hurricane Center forecasts continue to show
   Marco weakening with time as it moves westward along the Louisiana
   coast, followed by Laura expected to be moving northwestward across
   the eastern and central Gulf of Mexico as a
   strengthening/substantial hurricane.  With sufficient low-level
   shear expected across parts of Louisiana due to the presence of
   Marco, risk for a brief/weak tornado or two will persist through the
   day.  Meanwhile, with Laura expected to reach the north-central Gulf
   south of southeastern Louisiana overnight, additional strengthening
   of the low-level wind field is expected.  While questions persist
   regarding the forecast track of Laura, a continued risk for a couple
   of weak/brief tornadoes is expected across parts of the
   central/western Gulf Coast region through the evening and overnight
   hours.

   ..Goss.. 08/24/2020

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