SPC AC 031255

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0755 AM CDT Wed Jun 03 2020

   Valid 031300Z - 041200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS THE
   NORTHEAST/MID-ATLANTIC STATES...

   ...SUMMARY...
   Clusters of strong to severe storms are expected today and tonight
   from the central Plains through the Midwest and
   Northeast/Mid-Atlantic States. The most intense storms, capable of
   damaging winds and hail, are expected across Pennsylvania into New
   Jersey and the New York City metro area.

   ...Northeast/Mid-Atlantic States...
   Scattered storms have increased early this morning in the immediate
   lee of eastern Lake Erie across northwest Pennsylvania. See
   Mesoscale Discussion 792 for short-term details. This activity is in
   general association with an apparent MCV-enhanced mid-level impulse
   and outflow, byproducts of last night's Lake Michigan-crossing MCS.
   Enhanced mid-level winds (50+ winds between 4-6 km) are readily
   evident in early morning regional VWP data from Cleveland/Buffalo.
   These belt of stronger northwesterly winds will overspread
   Pennsylvania/New Jersey/southern New York today in tandem with a
   southward-spreading cold front.

   The aforementioned early day storms are likely a sign of what should
   be a steady increase in storm coverage/intensity southeastward
   across northern Pennsylvania/far southern New York through late
   morning and early afternoon. This corridor aside, additional
   surface-based development should occur generally by mid-afternoon
   near the front, including additional parts of Pennsylvania and
   northern portions of West Virginia/Maryland.

   Within the warm sector, low/middle 60s F surface dewpoints will
   contribute moderate buoyancy, with the strongest destabilization
   expected this afternoon across western/southern Pennsylvania where a
   greater pre-convective duration of heating should occur. The
   strength of the mid/high-level northwesterly winds will support
   relatively fast southeastward storm motions, including some initial
   supercells capable of severe hail, aside from more prevalent linear
   clusters/bowing segments capable of wind damage.

   ...Midwest including Missouri/Illinois to Indiana/Ohio...
   Strong/isolated severe thunderstorms have been occurring in the
   predawn hours across southern Iowa. At least some severe risk in the
   form of hail/possibly locally severe wind may continue this morning
   as storms develop south-southeastward into far northern Missouri and
   northern Illinois. The air mass ahead of this activity and a
   southeastward-moving cold front will steadily destabilize into the
   afternoon, owing to ample heating under limited/high-level cloud and
   east-northeastward pre-frontal moisture transport. By mid-afternoon,
   MLCAPE in excess of 3000 J/kg is likely particularly across
   northern/central Missouri into central Illinois, with as much as
   2000-3000 J/kg MLCAPE eastward across central portions of
   Indiana/Ohio where mid-level winds and deep-layer shear will be
   somewhat stronger (25-30 kt effective). 

   While the severe risk should initially be focused along the
   Iowa/Missouri border into northern Illinois early day, a steady
   increase in coverage and intensity is likely to occur into
   mid-afternoon, with scattered storms filling in generally between
   the I-70/I-80 corridors. Strong/sustained multicellular clusters
   will be the prevalent mode, with severe hail and damaging winds
   expected. Storm intensity will gradually wane into the mid/late
   evening hours as storms develop south/southeastward toward the Ohio
   River and Ozarks.

   ...Northern High Plains/Central Plains...
   A low-amplitude impulse over the northern High Plains this morning
   will continue east-southeastward today within a belt of 40-50 kt
   west-northwesterly mid-level winds that will be located roughly I-80
   and northward. A few strong storms could occur over the western
   Dakotas early today, but a somewhat greater severe risk should
   initially develop beginning around mid-afternoon across western
   South Dakota/southwest North Dakota into the Nebraska
   Panhandle/northern Nebraska. While low-level moisture will not be
   robust, 50s/lower 60s F surface dewpoints beneath very steep
   mid-level lapse rates will support moderate buoyancy. 

   In the presence of 35-40 kt effective shear, at least widely
   scattered severe storms/supercells capable of large hail are
   expected. Severe-caliber wind gusts can also be expected,
   particularly within a corridor of stronger heating/destabilization
   across southern Nebraska/northeast Colorado/northwest Kansas.
   Furthermore, there is some concern that storms may cluster/grow
   upscale into a southeastward-moving MCS this evening across
   southwest/south-central Nebraska and northern Kansas. If so, the
   potential for severe wind/some hail would continue through late
   evening, and possibly into the overnight.

   ..Guyer/Gleason.. 06/03/2020

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