SPC AC 021729

   Day 2 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1229 PM CDT Tue Jun 02 2020

   Valid 031200Z - 041200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS WEDNESDAY INTO
   WEDNESDAY NIGHT ACROSS SOUTHERN PORTIONS OF THE GREAT LAKES
   REGION...THE NORTHERN MID ATLANTIC COAST REGION...THE OHIO
   VALLEY...THE LOWER MISSOURI VALLEY AND NORTH CENTRAL HIGH PLAINS...

   ...SUMMARY...
   Clusters of strong to severe storms are possible Wednesday into
   Wednesday night across southern portions of the Great Lakes region
   into the Ohio Valley and northern Mid Atlantic, as well as across
   parts of the lower Ohio into lower Missouri Valleys, and across
   northern portions of the central high plains.

   ...Synopsis...
   Amplified, negatively tilted mid-level troughing (currently east of
   the northern Atlantic coast) is forecast to pivot northward through
   the Canadian Maritimes, and consolidate with troughing over Quebec,
   where a deep embedded mid-level low may evolve by late Wednesday
   night.  To the south of this feature, mid-level flow appears likely
   to trend more zonal, but remain broadly cyclonic across the lower
   Great Lakes through much of the Northeast.

   To the west, stronger mid-latitude westerlies are forecast to remain
   zonal, and largely confined to the northern tier of the U.S, from
   the Pacific Northwest through the Upper Midwest.  As an embedded low
   amplitude wave progresses eastward along the central Canadian/U.S.
   border, the westerlies may begin to split downstream, with a weaker
   branch of cyclonic mid-level flow developing across the middle/lower
   Missouri Valley.

   Beneath this regime, models indicate that a plume of warm elevated
   mixed-layer air (emanating from the southern Rockies/Great Basin)
   will overspread much of the Great Lakes, Ohio Valley and Mid
   Atlantic region, before becoming suppressed southward Wednesday. 
   This will occur along and ahead of a weak cold front, which will be
   preceded by moistening west-southwesterly low-level flow.  It
   appears that a combination of evapotranspiration and moisture
   advection will result in boundary-layer dew points increasing into
   the mid 60s+ across the middle Ohio into portions of the Allegheny
   Plateau and northern Mid Atlantic, and perhaps near 70f across the
   lower Missouri into lower Ohio Valleys.  Upper 50s to lower 60s
   surface dewpoints may also be maintained near lee surface troughing
   across northern portions of the central high plains.

   ...Lower Great Lakes into northern Mid Atlantic Coast region...
   At least some model output indicates that a belt of enhanced flow
   (30-50+ kt) in the 850-500 mb layer, associated with a convectively
   generated or enhanced perturbation, may contribute to convective
   potential as it migrates east-southeast of the lower Great Lakes
   region by early Wednesday.  This impulse may be accompanied by
   remnants of overnight convection which could impact downstream
   destabilization.  However, there appears potential for
   re-intensification, and the possible evolution of an organized
   convective system which could pose a risk for damaging wind gusts,
   severe hail and perhaps a tornado or two.  Model spread concerning
   the extent of boundary-layer destabilization remains the primary
   uncertainty resulting in the maintenance of 15 percent severe
   probabilities.  If moderate boundary-layer CAPE is able to develop,
   severe probabilities will probably need to be increased.

   ...Middle Ohio Valley into lower Missouri Valley...
   Although low-level wind fields may be fairly weak, modest, broadly 
   cyclonic mid-level flow may contribute to an environment conducive
   to the evolution of scattered clusters of strong to severe storm
   development Wednesday afternoon into Wednesday night.  Thermodynamic
   profiles exhibiting steep mid-level lapse rates and sizable CAPE
   probably will be supportive of the potential for severe hail and
   wind in strongest activity.

   ...North central higher plains...
   Beneath steep lapse rates and modest northwest mid-level flow,
   sufficient CAPE is forecast to develop to support widely scattered
   strong to severe storm development Wednesday afternoon and evening. 
   This may include isolated supercells, generally focused near surface
   troughing, from near the Black Hills into northeast Colorado.

   ..Kerr.. 06/02/2020

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