SPC AC 131953

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0253 PM CDT Thu Jun 13 2019

   Valid 132000Z - 141200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
   INTO EARLY TONIGHT OVER PARTS OF THE SOUTHERN HIGH PLAINS...

   ...SUMMARY...
   The greatest concentration of severe thunderstorms today should be
   over parts of the south-central High Plains, with damaging wind and
   hail expected.

   ...Discussion...
   Only 2 changes were made to the outlook this update.
   1)  Removed low-wind probabilities over the central/southern FL
   Peninsula due mostly to the stabilizing influence of convective
   overturning on the boundary layer.  
   2)  Minor eastward adjustment of the western edge of the 5-percent
   wind probabilities over the central Appalachians.

   ..Smith.. 06/13/2019

   .PREV DISCUSSION... /ISSUED 1130 AM CDT Thu Jun 13 2019/

   ...Southern High Plains this afternoon into early tonight...
   Low-level moisture is returning northward from southwest TX into
   eastern NM, and low-mid 50s boundary-layer dewpoints should reach as
   far north as the Raton Mesa by mid-late afternoon.  Though only
   subtle/embedded speed maxima may traverse the southern Rockies to
   the southern High Plains, surface heating and deep mixing should
   support thunderstorm development this afternoon in the immediate lee
   of the Raton Mesa, as well as southward across NM to the Sacramento
   Mountains.  Inverted-v profiles with steep low-midlevel lapse rates
   and effective bulk shear around 40 kt will support high-based
   supercells capable of producing large hail the first few hours after
   initiation.  Some clustering of storms is possible from northeast NM
   into the TX Panhandle this evening into early tonight, and
   convection could be maintained by (and develop into) a 30-40 kt
   southerly low-level jet along the corridor of richer low-level
   moisture.

   ...East central/southeast FL this afternoon...
   Outflow with pre-frontal convection has sagged southward into
   central FL as of midday, and to its south, diurnal/sea breeze
   convection is developing across the southern and western parts of
   the peninsula.  Given weak deep-layer southwesterly flow, convection
   should spread toward the Atlantic coast this afternoon, with
   multiple storm/boundary interactions possible.  The strongest storms
   could produce isolated strong/damaging outflow gusts.

   ...Central Appalachians/northern Mid Atlantic through this
   evening...
   A pronounced midlevel trough will continue eastward from the OH
   Valley to the Mid-Atlantic/NY by tonight.  A surface cyclone will
   move northeastward across southwestern ON, as an associated cold
   front moves eastward from OH to the Mid-Atlantic coast by late
   tonight.  The magnitude of low-level moisture is limited in advance
   of the cold front as a result of a secondary low just off the
   Mid-Atlantic and southern New England coasts now, and 12z soundings
   revealed modest midlevel lapse rates of 6.5-7 C/km.  These factors
   will tend to limit pre-frontal buoyancy and updraft intensity. 
   However, some increase in deep-layer flow/shear is expected with
   eastward progress of the midlevel trough, and isolated
   strong/damaging outflow gusts cannot be ruled out with stronger
   storms along and in advance of the cold front.

   ...Northern Great Basin and vicinity this afternoon/evening...
   A series of subtle/low-amplitude midlevel shortwave troughs will
   continue to move slowly eastward over the northern Great Basin
   through this evening. Low-midlevel moisture is sufficient for at
   least weak surface-based buoyancy, once afternoon temperatures warm
   well into the 70s/80s.  Resultant inverted-v profiles will favor
   strong outflow gusts with the more intense/persistent storms, within
   a broader corridor of expected thunderstorm development across the
   northern Great Basin.

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