SPC AC 121248

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0748 AM CDT Sun Jul 12 2020

   Valid 121300Z - 131200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS
   AFTERNOON/EVENING ACROSS PARTS OF THE CENTRAL/SOUTHERN HIGH
   PLAINS...

   ...SUMMARY...
   Isolated to widely scattered severe thunderstorms are forecast this
   afternoon through the late evening across parts of the central and
   southern High Plains.  Severe gusts and large hail are the primary
   hazards.

   ...Southern/central High Plains this afternoon/evening...
   In the wake of a large overnight MCS across OK, moist upslope flow
   has established along and north of a surface front from the TX
   Panhandle into northeast NM.  Subtle midlevel perturbations moving
   across CO (around the northeast periphery of the Four Corners high),
   daytime heating and the aforementioned upslope flow will contribute
   to thunderstorm development along the Front Range by mid afternoon. 
   Moderate buoyancy and steep midlevel lapse rates, along  with
   straight hodographs and sufficient deep-layer shear, will support
   splitting supercells capable of producing isolated hail near 2
   inches in diameter.  Steep low-level lapse rates and a deep mixed
   layer will also support the potential for isolated severe outflow
   gusts as clusters of storms spread eastward onto the High Plains
   through late evening.

   ...Western/middle TN to AL/MS today...
   A cluster of storms is ongoing this morning across western/middle
   TN.  The convection is supported by weak low-level warm advection on
   the northeast edge of a corridor of mid 70s boundary-layer dewpoints
   and associated strong buoyancy (MLCAPE near 2500 J/kg).  This area
   is also downstream from a midlevel shortwave trough moving
   east-southeastward over IL.  It appears that some form of this
   cluster will persist through the day while developing southward, as
   the low levels destabilize with daytime heating and moisture
   advection occurs from west-to-east from MS into AL.  Though
   deep-layer vertical shear will tend to weaken with southward extent
   through the day, strong buoyancy and downdraft potential (DCAPE in
   excess of 1000 J/kg) will favor embedded microbursts and an
   attendant threat for at least damaging winds, and perhaps isolated
   large hail.

   ...OH Valley this afternoon...
   Scattered thunderstorms will be possible, mainly this afternoon,
   across the OH Valley, in advance of the shortwave trough moving
   east-southeastward from IL, and in the wake of a lead wave now over
   OH/northern KY.  The primary uncertainty this area is the degree of
   low-level moisture/destabilization this afternoon.  The ongoing
   cluster of storms in TN continues to reinforce a cold pool, and
   moisture to the north of this convection is substantially reduced
   compared to areas farther southwest.  The KY area will continue to
   be monitored for evidence of recovery north of the morning
   convection, but uncertainty is sufficiently high to maintain a
   Marginal outlook area in this update.

   ...Eastern MT/western ND this afternoon/evening...
   A midlevel shortwave trough will move eastward over the northern
   Rockies/MT through tonight, along with an associated cold front. 
   Modest low-level moisture advection (dewpoints in the mid-upper 50s)
   will occur from the south today, while surface heating/mixing
   deepens the boundary layer and reduces convective inhibition along
   the wind shift in eastern MT this afternoon.  There will be a narrow
   window of opportunity for surface-based thunderstorm development
   along the wind shift this evening (better chance northeast MT into
   northwest ND), in an environment conditionally favorable for
   supercells with large hail/damaging winds.  A few elevated storms
   with an isolated hail threat may also form overnight as the stronger
   forcing for ascent spreads eastward from MT to ND.

   ..Thompson/Broyles.. 07/12/2020

   CLICK TO GET WUUS01 PTSDY1 PRODUCT

   NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1630Z