SPC AC 112000

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0300 PM CDT Sun Jun 11 2023

   Valid 112000Z - 121200Z

   ...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
   THROUGH TONIGHT ACROSS THE MID-SOUTH AND TN VALLEY REGIONS...

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
   INTO EARLY TONIGHT FROM THE CO FOOTHILLS INTO NORTHERN TX
   PANHANDLE...AND ACROSS NORTH TX...

   ...SUMMARY...
   Severe thunderstorms capable of damaging winds and hail are expected
   across a broad portion of the Tennessee Valley and Mid-South this
   afternoon and evening. Severe thunderstorms are also possible across
   the south-central High Plains and North Texas.

   ...20Z Update...

   ...Mid-South/TN Valley...
   Thunderstorm coverage is still expected to increase this afternoon
   across the region as ascent from the approaching shortwave trough
   interacts with the moist and buoyant air mass in place. Effective
   bulk shear around 30-35 kt will support a mix of multicell
   clusters/line segments capable of producing damaging winds and large
   hail. Additional information about this region is available in
   recently issued MCD #974.

   ...CO Front Range into the TX Panhandle...
   Cumulus continues to build across the higher elevations of
   north-central NM and south-central CO, with a few thunderstorms
   already in place. The expectation outlined in the previous
   discussion remains valid, with thunderstorms coming off the terrain
   into post-frontal upslope environment across the lower elevations.
   As mentioned in MCD #973, this environment will support high-based
   supercells with the potential for large hail (with instances near 2
   inches) and damaging winds. Weak low-level shear will limit tornado
   potential but any discrete supercells that become established could
   pose risk of a tornado as they track eastward into the better air
   mass across far eastern Colorado/Oklahoma Panhandle.

   ...TX Big Country into North TX...
   Thunderstorm development is still expected later this
   afternoon/early evening in the corridor from SJT northeastward into
   the Young/Stephens/Eastland county vicinity. Robust buoyancy and
   shear will support the potential for splitting supercells capable of
   very large hail and strong downbursts. 

   ...Great Basin...
   A few strong gusts remain possible across the Great Basin as
   clusters of high-based thunderstorms move northwestward this
   afternoon and evening.

   ..Mosier.. 06/11/2023

   .PREV DISCUSSION... /ISSUED 1129 AM CDT Sun Jun 11 2023/

   ...Mid-South/TN Valley region through tonight...
   Around the southern periphery of a closed midlevel low over the
   upper Great Lakes, embedded shortwave troughs will move eastward
   over the lower OH and TN Valleys through early tonight.  An
   associated surface cyclone will likewise develop eastward along and
   just north of the OH River, as a trailing pre-frontal trough and
   cold front move southeastward across the Mid-South and southern
   Plains through tonight.  Clouds are fairly widespread as of late
   morning from the southern Appalachians northward into the OH Valley
   and westward into the mid MS Valley.  A little south of the thicker
   clouds and surface cyclone track, there is a corridor of stronger
   surface heating from south central KY into the Mid-South, where
   temperatures will warm into the 80s with mid-upper 60s dewpoints. 
   These surface conditions beneath midlevel lapse rates of 7-7.5 C/km
   will drive MLCAPE of 1500-2500 J/kg with minimal convective
   inhibition.

   Scattered thunderstorm development is expected by early-mid
   afternoon in the zone of weak low-level confluence/convergence
   associated with an embedded midlevel speed max, along the edge of
   the thicker clouds from central KY into western TN and AR.  The
   moderate-strong buoyancy and midlevel flow near 40 kt will support a
   mix of multicell clusters/line segments capable of producing
   damaging winds and large hail.  There will be somewhat stronger
   deep-layer flow/shear and a little greater potential for supercells
   across the Mid-South later this afternoon/evening.  The convection
   will continue to spread eastward and southeastward across the TN
   Valley early tonight, with some continued damaging-wind threat.

   Other scattered thunderstorms could form this afternoon/evening to
   the west of the thicker clouds across the southern Appalachians. 
   The stronger wind profiles/vertical shear will be west and north of
   this area through the afternoon, so the primary severe threats will
   be damaging downburst winds and marginally severe hail this
   afternoon/evening.  Uncertainty increases with eastward extent due
   to the widespread clouds/rain from northeast GA into western NC and
   vicinity, and the primary increase in flow/shear will tend to occur
   after the muted diurnal cycle.  

   ...Southern High Plains through tonight...
   Post-frontal, upslope flow is established this morning from eastern
   CO into northeast NM.  Though not particularly large, buoyancy will
   be sufficient for supercells forming and moving eastward off the
   Raton Mesa, given easterly low-level inflow and relatively long
   hodographs.  Large hail in excess of 2 inches in diameter and severe
   outflow gusts of 60-70 mph will be the primary severe threats,
   though an isolated tornado could also occur.  Convection will likely
   persist into the overnight hours, immediately downstream from an
   embedded mid-upper speed max that will move east-northeastward from
   AZ to NM.

   Storm development is much less certain farther south into northeast
   NM and the TX Panhandle/South Plains.  If a storm were to form along
   the stalled front this afternoon, it would potentially become
   supercellular with a conditional large hail threat. 

   ...North TX late this afternoon into early tonight...
   Strong surface heating is underway to the south of a pre-frontal
   trough and weak cold front that are moving slowly southward across
   OK.  As surface temperatures warm well into the 90s, convective
   inhibition will diminish and MLCAPE will increase to 3000-4000 J/kg.
   Low-level flow will remain rather weak, but deep-layer flow will be
   strong enough to support the potential for a few splitting
   supercells (given relatively straight hodographs with effective bulk
   shear of 35-40 kt).  Isolated very large hail up to 2.5 inches in
   diameter and damaging gusts will be the main threat with these
   storms from late afternoon into early tonight.

   ...Great Basin this afternoon/evening...
   Embedded speed maxima will rotate northward around the eastern
   periphery of the midlevel low over southern CA.  The ascent
   attendant to the speed maxima, in concert with daytime heating, will
   support clusters of high-based storms capable of producing a few
   strong-severe outflow gusts.

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