SPC AC 051946

   Day 1 Convective Outlook  
   NWS Storm Prediction Center Norman OK
   0246 PM CDT Mon Jun 05 2023

   Valid 052000Z - 061200Z

   ...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER DEEP SOUTH
   TEXAS...

   ...SUMMARY...
   Isolated severe thunderstorms with damaging winds and large hail are
   possible across several areas of the country this afternoon and
   evening. The most likely corridor for severe storms appears to be
   over Deep South Texas through this afternoon into the evening.

   ...20Z Update...
   Overall forecast outlined in the previous outlook remains valid.
   Thunderstorms remain possible across a large portion of the CONUS,
   with pockets of stronger storms possible over the southern
   Appalachians and Carolina Piedmont, the Sierra and central valley of
   CA, western MT, south FL and south TX. Each of these areas is
   addressed in the discussion appended below. Greatest severe coverage
   is still expected across south TX, where a few supercells have
   developed along the outflow boundary moving westward across the
   region.

   ..Mosier.. 06/05/2023

   .PREV DISCUSSION... /ISSUED 1126 AM CDT Mon Jun 05 2023/

   ...Deep South TX...
   Scattered thunderstorms are ongoing over the northwest Gulf to the
   Corpus Christi vicinity of the TX Coastal Plain near a minor
   mid/upper trough. On the backside of this trough, a belt of enhanced
   mid-level northwesterlies (near 40 kts at 500-mb per 12Z BRO
   sounding) will slacken through this afternoon. This flow regime
   should remain sufficient for potential supercell development towards
   the Lower Rio Grande Valley where low to mid 70s surface dew points
   and nearly full insolation are prevalent. With minimal MLCIN amid
   modest mid-level lapse rates, 12Z HREF members (outside of the HRRR)
   and the RRFS are fairly consistent in backbuilding convection across
   Deep South TX through late afternoon. A south-moving cluster with
   embedded supercells may develop with a threat for both severe hail
   and wind until convection spreads into Tamaulipas by early evening.

   ...Southern Appalachians/Piedmont...
   A deep upper low will persist off the New England Coast today.
   Peripheral influence of this low will maintain a belt of enhanced
   mid-level north-northwesterlies extending to the southern
   Appalachians through this evening. This will overlap with the
   eastern extent of the surface-based instability plume from the TN
   Valley/Deep South. 

   Pervasive low clouds adjacent to the high terrain should gradually
   decrease through the day, with convective initiation likely to begin
   over the high terrain where breaks are already evident. Isolated to
   scattered thunderstorms will develop and attempt to spread
   southeast, but may tend to weaken with southeast extent in the
   Carolinas and backbuild west given the orientation of the
   instability plume. This should result in a corridor of isolated
   damaging wind and severe hail during the late afternoon to early
   evening focused along the lee of the high terrain.

   ...CA...
   An upper low spinning off the southern CA Coast should gradually
   shift inland north of the L.A. Basin by early morning. While its
   attendant strong mid-level jet will remain confined south of the
   border over Baja CA, a belt of enhanced south to southeasterlies
   will curl around the east to northeast semi-circle of the trough.
   Isolated to scattered thunderstorms are most likely over the Sierra
   NV towards the higher terrain of northern CA and separately towards
   the western portion of the Transverse Ranges in southern CA where
   upslope flow will occur. Steep low to mid-level lapse rates will
   support an isolated threat for severe wind and hail, mainly during
   the late afternoon and evening.

   ...South FL...
   30-40 kt mid-level westerlies should persist across the southern
   third of the peninsula downstream of the minor mid/upper trough over
   the western Gulf. With generally northeasterly surface winds, weak
   flow through 3 km, and some backing of winds in the mid to upper
   levels, mid-level updraft rotation will probably remain relatively
   transient. Given the strength of the mid-level flow, a few of the
   stronger cells might produce marginally severe wind and hail during
   the late afternoon to early evening.

   ...Western MT...
   A minor mid-level impulse will continue to drift north from ID into
   northwest MT. Its attendant cloudiness this morning will slow
   diabatic heating immediately ahead of it near the ID/MT border, but
   more robust boundary-layer warming will occur farther downstream in
   parts of western to north-central MT. With just modest enhancement
   to mid-level southerlies, effective bulk shear will remain subdued
   from 20-30 kts. In addition, modest mid-level lapse rates will
   further temper updraft acceleration. Overall severe threat appears
   rather marginal, but a few severe wind and hail events may occur.

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