SPC AC 131242

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0742 AM CDT Mon Jul 13 2020

   Valid 131300Z - 141200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS
   AFTERNOON/EVENING FOR EXTREME EASTERN CO AND WESTERN KS INTO CENTRAL
   NE...

   ...SUMMARY...
   Severe thunderstorms are possible from the central High Plains into
   parts of the Upper Midwest this afternoon into tonight.  Severe
   gusts, possibly significant, large hail and a couple of tornadoes
   are the threats with the stronger storms.

   ...Central High Plains this afternoon into early tonight...
   A deepening lee cyclone is expected this afternoon across extreme
   northeast CO, downstream from the southern fringe of the 35-50 kt
   midlevel westerly flow with the northern Rockies shortwave trough. 
   Meanwhile, low-level moisture (boundary-layer dewpoints in the upper
   60s to lower 70s) will return northwestward from OK to western KS,
   around the southern/western periphery of a lingering MCS across
   central OK this morning.  This moisture will then spread northward
   across central NE toward eastern SD, east of the lee cyclone and
   ahead of the northern Plains cold front.  The moistening will occur
   beneath midlevel lapse rates in excess of 8.5 C/km, which will
   support strong buoyancy (MLCAPE of 2500-4000 J/kg).

   Initial storm development is expected in the deeper mixed
   environment near the lee cyclone/trough from extreme southeast WY
   into eastern CO, and storms will subsequently intensify once they
   reach the richer moisture/larger CAPE to the east.  Deep-layer shear
   will be sufficient for supercells capable of producing isolated very
   large hail.  However, the environment will be favorable for strong
   downdrafts (steep lapse rates and DCAPE of 1500-2000 J/kg), and
   upscale growth into a couple of clusters appears likely by this
   evening as storms progress into western KS and central NE.  By this
   time, damaging winds will become a more substantial threat, with a
   few significant (75+ mph) outflow gusts possible.  Storms will also
   develop northeastward along the front toward southeast SD/southwest
   MN by late evening/early tonight, and persist overnight across
   southern SD on the immediate cool side of the front, as an embedded
   speed max ejects eastward. 

   ...Eastern ND into MN through this evening...
   A midlevel shortwave trough over MT will progress eastward today
   toward the Dakotas, as an associated surface cold front likewise
   moves eastward to eastern SD and northwestern MN by this evening. 
   Loosely organized convection is ongoing across central/north central
   ND this morning just ahead of the cold front, in a zone of low-level
   warm advection and immediately east of an embedded speed max
   ejecting east-northeastward over southeast SK/southwest MB.  Some
   form of this morning convection could persist through the day across
   northeastern ND and eventually northwestern MN.  As the convection
   spreads eastward, the low levels will warm and moisten from the
   south, such that surface-based thunderstorm development will become
   more probable later this afternoon along the southern edge of the
   remnant morning convection.  There could be a narrow zone of overlap
   of the richer low-level moisture from the southwest, and the
   stronger low-level shear to the east, such that supercells rooted at
   the surface would pose a tornado threat, in addition to large
   hail/damaging winds.  

   ...Eastern NC and vicinity this afternoon...
   A weak midlevel trough will move eastward over VA/NC today, and a
   surface trough will help focus thunderstorm development as the low
   levels destabilize in the wake of weak morning convection.  Though
   low-midlevel flow/shear will be weak, MLCAPE will increase to in
   excess of 2000 J/kg with PW values approaching 2", and a few storms
   could produce wet microbursts.

   ...Southeast New England this afternoon...
   Similar to areas in NC, and embedded/subtle shortwave trough will
   move over southeast New England today.  Though MLCAPE is unlikely to
   exceed 1000 J/kg and vertical shear will be rather modest below the
   500 mb level, the stronger storms could still produce isolated
   strong outflow winds and perhaps some minor wind damage across
   southeast New England this afternoon.

   ...Texarkana area southeastward into LA this afternoon/evening...
   A remnant MCS in central OK, and an associated MCV, will continue to
   move east-southeastward toward southeast OK/southwest AR by
   midday/early afternoon.  By this time, surface heating will begin to
   weaken convective inhibition, and additional thunderstorm
   development will be possible with the MCV, as well as farther
   southeast along a diffuse front into LA.  Afternoon surface
   temperatures in the low-mid 90s with mid-upper 70s boundary-layer
   dewpoints, beneath the east edge of the steeper midlevel lapse
   rates, will result in large buoyancy (MLCAPE in excess of 3000 J/kg)
   along the stalled boundary.  This environment could support a few
   storms with isolated damaging outflow winds, as well as isolated
   large hail.

   ..Thompson/Broyles.. 07/13/2020

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