SPC AC 271254

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0754 AM CDT Sat Jun 27 2020

   Valid 271300Z - 281200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS PARTS OF THE
   NORTHEAST AND SOUTH-CENTRAL MT...

   ...SUMMARY...
   Scattered damaging winds and a brief tornado are possible across
   parts of the Northeast this afternoon into early evening. Scattered
   large hail and isolated severe winds are possible across a portion
   of southwest to central Montana during the late afternoon and early
   evening. Isolated severe thunderstorms are also possible in the
   Central States and Southeast.

   ...Northeast...
   An MCV over western NY will track east into southern New England
   this afternoon. Stratiform rain is pervasive across much of
   western/central NY into northern PA and NJ. This will hinder the
   northeast extent of destabilization today. To the south and west of
   the ongoing precip shield, pockets of stronger boundary-layer
   heating will occur amid 60s surface dew points. Ascent tied to the
   MCV should aid in convection increasing towards midday as the air
   mass becomes weakly unstable. Poor mid-level lapse rates and
   relative early onset of forcing for ascent prior to peak heating
   should be limiting factors to a more robust severe threat.
   Nevertheless, enlarged low-level hodographs beneath a belt of 50-60
   kt 700-mb westerlies will foster an opportunity for a couple
   supercells consolidating into a fast-moving cluster in the eastern
   PA/NJ/southeast NY/Long Island vicinity. Damaging winds and a brief
   tornado will be the main threats.

   ...MT...
   A shortwave trough will amplify from British Columbia into the
   Northwest during the period. This should yield a swath of 500-mb
   southwesterlies strengthening to 50-60 kts from southern ID through
   central MT by evening. Robust boundary-layer heating ahead of an
   impinging surface cold front should yield modest buoyancy amid mid
   40s to low 50s surface dew points. Scattered thunderstorms will
   initiate towards mid-afternoon off the Sawtooths in central ID to
   the higher terrain of southwest MT. 40-50 kt effective shear will
   foster at least a few supercells with large hail as the primary
   threat centered on southwest to central MT. Some clustering
   potential is possible into eastern MT during the evening with a
   localized uptick in severe wind potential before convection wanes
   overnight.

   ...OH/Mid-MS/Lower MO Valleys...
   As multiple MCVs in moderate westerly mid-level flow traverse this
   region, isolated to scattered thunderstorms are expected to develop
   as the air mass destabilizes. Ample instability and at least modest
   deep-layer shear will contribute to mainly multicell clusters
   capable of isolated severe wind and hail. A somewhat greater severe
   threat this afternoon might evolve from the remnant MCV near the
   KS/MO/NE border area that should drift east into the Mid-MS Valley.
   Recent HRRR and HRRR-P runs do suggest better potential for severe
   coverage, which will be conditional on adequate destabilization to
   the north of a decaying but still ongoing MCS in eastern KS to
   western MO. Will defer to later outlooks for possible category
   2/Slight Risk upgrade if mesoscale uncertainties become better
   resolved.

   ...Central Great Plains...
   As weak disturbances aloft move out of the Rockies and across the
   central High Plains, daytime heating/modest destabilization should
   result in isolated to widely scattered storm development, initially
   near a lee trough. This activity may then gradually consolidate and
   spread east-northeast into western/central portions of KS/NE. Steep
   lapse rates will support risks for both severe hail and wind. At
   this time, overall coverage is expected to remain isolated, but an
   upgrade to Slight Risk may be warranted for parts of the region in
   later outlooks.

   ...Lower MS Valley into the Southeast...
   A low-amplitude upper trough will move east across the region today.
   Afternoon heating/destabilization, aided by a very moist low-level
   air mass, will fuel development of scattered thunderstorms. With
   enhanced mid-level westerly flow atop the region, a few stronger
   storms/storm clusters, capable of producing locally damaging winds
   and possibly marginally severe hail, can be expected before
   weakening in the early evening.

   ..Grams/Gleason.. 06/27/2020

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