SPC AC 260601

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0101 AM CDT Fri Jun 26 2020

   Valid 271200Z - 281200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM EASTERN OHIO
   TO THE MID-ATLANTIC AND SOUTHERN NEW ENGLAND COASTS...

   ...SUMMARY...
   Scattered afternoon thunderstorms may pose a risk for mainly
   damaging winds across much of Pennsylvania and portions of
   surrounding states on Saturday.

   ...Synopsis...
   Gradual amplification of the upper flow field over the U.S. is
   expected Saturday, as short-wave troughing digging southeastward out
   of the Gulf of Alaska leads to a large expansion of cyclonic flow
   over the western U.S. through the period.  As a result, downstream
   ridging will increase over the north-central U.S. and central
   Canada, still further east, some amplification of troughing is
   expected over eastern Canada and into the northeastern CONUS.  

   Meanwhile, several vorticity maxima are forecast to shift eastward
   in a train-like manner, from the central High Plains across the
   Midwest/Ohio Valley and into the Mid Atlantic region/southern New
   England through the period.

   At the surface, a very weak/ill-defined baroclinic zone is progged
   to extend from the lower Great Lakes region west-southwestward
   across the Midwest/Ohio Valley states and then westward to the
   central High Plains.  In the West, a strengthening cold front will
   shift southeastward across northwestern portions of the country,
   reaching as far east as the northern High Plains overnight.

   ...Eastern Ohio to Long Island...
   Convection is expected to be ongoing at the start of the period,
   which continues to complicate the forecast, with respect to
   diagnosing the thermodynamic quality of the airmass.  Still, given
   enhanced low- to mid-level flow across the area, and weak cold front
   moving across the Lower Great Lakes, scattered thunderstorms --
   possibly in multiple episodes -- will likely occur across the region
   through the evening.  Risk for locally damaging winds remains
   apparent, and thus will maintain 15%/SLGT risk for wind across this
   region.

   ...Ohio and Mid Mississippi/lower Missouri Valleys...
   As several mid-level disturbances embedded in moderate westerly
   mid-level flow traverse this region, scattered thunderstorms are
   expected to develop in a destabilizing afternoon airmass -- in the
   vicinity of a weak/diffuse baroclinic zone lying across the area. 
   An ample combination of CAPE and shear is expected across the region
   to suggest that a few stronger storms will be capable of producing
   locally damaging winds, and marginal hail, supporting the
   introduction of 5%/MRGL risk across this region.

   ...Central High Plains/central Plains...
   As weak disturbances aloft move out of the Rockies and across the
   High Plains, daytime heating/modest destabilization should result in
   isolated to widely scattered storm development -- initially near a
   lee trough, and then possibly spreading into Kansas with time.  With
   a relatively dry boundary layer suggestive of potential for
   evaporatively enhanced downdrafts, and moderate mid-level westerlies
   supporting potential for organized storms, will introduce 5%/MRGL
   risk across the area.

   ...Parts of Montana into southeastern Idaho...
   As a cold front shifts southeastward across the region ahead of the
   digging upper trough, daytime heating will yield weak
   destabilization -- hindered by a relatively dry low-level airmass. 
   Still, CAPE should be sufficient to foster isolated storm
   development by mid to late afternoon, initially over the higher
   terrain of southern Montana and vicinity, and then spreading
   eastward with time -- into eastern Montana by evening.  With an
   enhanced belt of southwesterly mid-level flow atop the region ahead
   of the digging trough, shear will promote organization with any
   sustained updrafts, along with fast storm motions.  Aided by
   evaporative enhancement, a few strong downdrafts exceeding severe
   levels are expected, with risk lasting well into the evening.

   ...Lower Mississippi Valley into the Southeast...
   A weak short-wave trough will cross the central Gulf Coast region
   and vicinity Saturday.  Afternoon heating/destabilization -- aided
   by a very moist low-level airmass -- will fuel development of
   scattered thunderstorms, though areas of potentially greater storm
   coverage remain difficult to narrow down at this time.  Still, with
   enhanced mid-level westerly flow atop the region, a few stronger
   storms/storm clusters -- capable of producing locally damaging winds
   and possibly marginal hail, can be expected, before weakening
   diurnally after dark.

   ..Goss.. 06/26/2020

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