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
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.
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
.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.
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
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.
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.
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.
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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