SPC AC 061932
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0232 PM CDT Tue Jun 06 2023
Valid 062000Z - 071200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
THE NORTHEAST...NORTHERN CALIFORNIA TO NORTHERN UTAH/SOUTHERN
IDAHO...NEW MEXICO/TEXAS TRANS-PECOS...SOUTH FLORIDA...AND THE SOUTH
Isolated severe thunderstorms with threats of damaging winds and
large hail will be possible through this evening across several
portions of the country: the South Carolina vicinity, the Northeast,
northern California to northern Utah/southern Idaho, New
Mexico/Texas Trans-Pecos, and south Florida.
Overall forecast outlined in the previous outlook remains valid.
Thunderstorms remain possible across a large portion of the CONUS,
with stronger storms anticipated in a few areas, including portions
of the Northeast, northern CA into the Great Basin, and southern
High Plains. Each of these areas are addressed in the previous
discussion. Additional details for the Northeast can be found in
recently issued MCD #941, and for portions of northern California,
north and central Nevada, and western Utah in MCD #942. In all,
generally modest buoyancy and the lack of stronger flow aloft is
expected to preclude a more widespread severe-thunderstorm threat.
.PREV DISCUSSION... /ISSUED 1123 AM CDT Tue Jun 06 2023/
A plume of moderate buoyancy with MLCAPE of 1000-2000 J/kg centered
on north GA will shift east into SC later this afternoon. Isolated
to scattered thunderstorms will develop along and just ahead of a
weak surface trough shifting slowly south across NC to upstate SC.
The region will lie within the gradient of weak to moderate
mid-level northwesterlies, well to the southwest of a deep upper low
over the Canadian Maritimes. While low-level flow will remain weak
and veered to the west-southwest, 15-25 kt effective bulk shear
should support some multicell clustering and a threat for isolated
damaging winds and severe hail.
A secondary mid-level impulse embedded within the larger-scale
trough on the backside of the deep upper low over the Canadian
Maritimes should aid in isolated to scattered higher-based
convection. MLCAPE will remain weak owing to surface dew points only
in the mid 40s to around 50 F. But moderate speed shear through the
cloud-bearing layer should foster small to marginally severe hail
growth in the deeper cores. This combined with an inverted-v
thermodynamic profile will support a threat for locally damaging
winds. Refer to the SPC Fire Weather Outlook for additional
...Northern CA to northern UT/southern ID...
An upper low will wobble over the San Joaquin Valley through
tonight. A belt of modest buoyancy with MLCAPE of 600-1200 J/kg
should develop at peak heating within a largely west/east-oriented
arc across northern CA to northern UT/southern ID. Scattered
thunderstorms are expected within this buoyancy plume by late
afternoon. While moderate mid-level flow will generally be displaced
to the south, 20-30 kt southeasterlies around 500 mb will support
some multicell clustering and a primary threat of isolated severe
wind gusts. Small to marginally severe hail will also be possible in
...NM and the TX Trans-Pecos...
Downstream of the CA upper low, scattered thunderstorms will develop
within a modest buoyancy plume characterized by MLCAPE of 700-1400
J/kg. The bulk of stronger mid-level flow should remain displaced
west of the buoyancy/higher PW plume in AZ, as a low-amplitude
mid-level ridge tries to hold over central NM. As such, convection
will likely struggle to initially organize with sporadic severe
gusts and small hail being the main threats. Somewhat greater
effective shear should occur from the TX Trans-Pecos to the Raton
Mesa during the early evening, where isolated marginally severe
storms may occur.
Morning convection along the southeast FL coast has yielded outflow
that has pushed inland over the Everglades. Later afternoon
convection will probably be focused along this boundary into
southwest FL. While a 50-kt speed max at 500 mb was sampled in the
12Z Miami sounding, guidance is consistent with weakening mid-level
winds through the afternoon. It still should remain sufficient for a
transient cell or two with mid-level rotation, and supportive of a
brief threat for severe wind/hail.
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