SPC AC 150554

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1254 AM CDT Fri May 15 2020

   Valid 151200Z - 161200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PORTIONS
   OF NY INTO SOUTHERN NEW ENGLAND...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
   THE CENTRAL AND SOUTHERN PLAINS AND THE NORTHEASTERN STATES...

   ...SUMMARY...
   Severe thunderstorms are forecast across portions of the Northeast
   States this afternoon. Severe thunderstorms are also expected across
   the southern Plains while isolated strong/severe thunderstorms are
   possible across portions of the central High Plains.

   ...Northeastern States...

   Water-vapor imagery depicts a strong short-wave trough over the
   upper Great Lakes early this morning. This feature is forecast to
   eject across southern ON/QC by 16/00z as a 75kt 500mb speed max
   translates along the international border then into southern New
   England later tonight. A weak surface low should develop along the
   cold front over lower MI by sunrise then track toward western NY by
   early afternoon. This evolution favors strong boundary-layer heating
   from the central Appalachians into upstate NY where surface
   temperatures are expected to warm into the mid 70s prior to frontal
   passage. Latest thinking is convection will reintensify along the
   wind shift across southern ON by 17-18z then spread east within a
   westerly flow regime that should favor updraft organization. This
   activity will develop along southern influence of aforementioned
   short wave, and surface-6km shear is more than adequate for possible
   supercells, though a mixed storm mode is the most likely scenario.
   Damaging winds, hail, and a few tornadoes can be expected with
   severe thunderstorm clusters that spread from west to east across NY
   toward southern New England by early evening.

   ...Southern Plains...

   Frontal convection is gradually expanding across MO/southeast KS as
   the wind shift sags slowly south. Latest CAMs suggest a substantial
   complex of storms will surge south along the OK/AR border with
   outflow likely surging southwest across portions of OK during the
   mid-late morning. Cold-pool density will dictate the northern extent
   of potentially more significant daytime convection across the
   southern Plains. While the early-morning complex could produce some
   hail/wind, afternoon convection will have a chance to take advantage
   of a very unstable air mass. It's not entirely clear where the
   outflow boundary will be draped when surface parcels reach their
   convective temperatures; however, forecast soundings suggest MLCAPE
   values on the order of 5000 J/kg south of the wind shift from
   southern OK into northwest TX. There was some consideration for
   increasing severe probabilities across this region but weak
   deep-layer shear does not favor long-lived supercells. Even so, very
   large hail may be noted in the early life cycle of thunderstorms
   that develop across this region. Damaging winds are also possible,
   especially if another significant cold pool manages to develop with
   this activity.

   ...Central High Plains...

   A zone of low-level convergence is expected to remain oriented
   north-south across eastern CO into the NE Panhandle as dominant
   surface high settles into the MS Valley. While low-level moisture is
   not particularly high across the central High Plains, adequate PW
   should be in place for robust convection along this boundary ahead
   of a short-wave trough. Strong heating west of the wind shift should
   aid parcel buoyancy and strengthening wind fields suggest isolated
   supercells will be the primary storm mode. Hail/wind are the main
   threats.

   ..Darrow/Moore.. 05/15/2020

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