SPC AC 100559

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   1259 AM CDT Fri Jul 10 2020

   Valid 101200Z - 111200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER A PORTION
   OF THE NORTHERN AND CENTRAL PLAINS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM COASTAL NEW
   JERSEY INTO COASTAL NEW ENGLAND...

   ...SUMMARY...
   Several clusters of severe storms are expected over parts of the
   northern and central Plains this afternoon into tonight. Large to
   very large hail and damaging wind are likely, and a few tornadoes
   are possible.

   ...Northern through central Plains regions...

   The northern and central Plains will remain within belt of modest
   westerlies today. A low-amplitude shortwave trough currently moving
   through the Pacific Northwest will reach the northern High Plains by
   late afternoon and continue through the Dakotas this evening
   accompanied by a cold front. A minor impulse will precede this
   feature and move through SD during the morning. Warm front will
   become established and extend from a weak surface low over southwest
   SD southeastward through eastern NE and KS. Dryline will extend
   southward through western NE into eastern CO. A cold front will
   approach the western Dakotas by late afternoon.

   Easterly low-level winds will persist north of the warm front and in
   advance of the cold front across the Dakotas into northeast WY and
   eastern MT maintaining a corridor of surface dewpoints from the
   upper 50s to low 60s F beneath steep lapse rates. The atmosphere in
   this region will likely become moderately to strongly unstable as
   the boundary layer warms with 2000-3500 J/kg MLCAPE likely by mid
   afternoon. Storms are expected to develop along the cold front as it
   interacts with the destabilizing boundary layer across eastern MT
   and northeast WY. Other storms will develop farther south near
   triple point over southwest SD into northwest NE. Vertical wind
   profiles with veering in the lowest 2 km and 50+ kt effective bulk
   shear will support supercells capable of large to very large hail
   and damaging wind. A few tornadoes are possible, especially with
   storms developing near warm front across SD into northern NE. Some
   of the storms may eventually grow upscale into lines and clusters
   and spread east and southeast posing a risk for more widespread wind
   damage. Though some uncertainty remains, potential will exist for a
   longer lived severe MCS to organize across SD or NE and move
   southeast along instability gradient into the overnight, supported
   by a strengthening southwesterly low-level jet. Have expanded the
   SLGT risk southward for the possibility of this scenario and farther
   southward expansion through eastern KS and western MO might be
   necessary if more confidence is gained in later outlooks.

   ...Northeast and southern New England coastal areas...

   Tropical storm Fay is forecast by the National Hurricane Center to
   continue moving northward, and the center should be located near the
   central NJ coast by early this evening. Shear in the 0-1 km layer
   will increase from coastal NJ through coastal southern New England
   later today where near-surface dewpoints will reach the low 70s F.
   Best tornado threat with low-topped supercells will evolve during
   the afternoon into the early evening if some surface heating can
   occur between outer rainbands.

   ..Dial/Lyons.. 07/10/2020

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