SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0241 PM CDT Wed Apr 26 2023
Valid 262000Z - 271200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
CENTRAL TEXAS AND THE CENTRAL FLORIDA PENINSULA...
...SUMMARY...
A few tornadoes (possibly some strong), very large/destructive hail,
and severe thunderstorm gusts are expected over parts of central
Texas this afternoon and evening. Very large hail and damaging winds
remain a threat over parts of Florida into far southeast Georgia
this afternoon and early evening.
...20Z Update...
Adjustments were made to the Category 3/Enhanced risk area (and
associated probabilities) in central TX to align with the warm
sector along and just south of an outflow boundary which is behaving
like an effective warm front. Storms that form just ahead of the
dryline and can traverse the outflow boundary area will likely
become supercells capable of very large hail, hurricane-force wind
gusts, and a couple of tornadoes. Any storms that can traverse the
boundary for a long enough period of time may ingest locally higher
amounts of streamwise vorticity, which may support the development
of a strong tornado. Please see MCD #0623 for more information.
The Category 2/Slight risk across northern FL was extended northward
to include portions of far southeast GA, where supercell structures
have produced reported golfball size hail, and where MRMS MESH
suggests that significant severe hail may be occurring. Given the
presence of steep lapse rates and adequate deep-layer shear, the
severe hail threat may continue into the early evening hours.
Finally, the Category 2/Slight risk in Texas was expanded farther
east into central LA. Here, a cluster of storms may persist into the
overnight hours and support short bowing structures capable of
damaging gusts.
..Squitieri.. 04/26/2023
.PREV DISCUSSION... /ISSUED 1125 AM CDT Wed Apr 26 2023/
...Texas into the Lower Mississippi Valley...
Elevated convection is ongoing late this morning across
north-central TX and far southern OK. This activity is related to
low-level warm advection and ascent preceding an upper trough over
the southern High Plains. Recent surface observations show a warm
front draped across north-central into east TX. Most 12Z guidance
continues to suggest that this warm front will attempt to lift
northward this afternoon as the upper trough/low ejects slowly
eastward across the southern Plains. A surface dryline is also
forecast to mix eastward across parts of west into central TX, and
provide a focus for robust convective development this afternoon.
Convective evolution across north/central TX this afternoon will be
somewhat complicated by the ongoing convection near the Red River.
These thunderstorms will probably tend to limit the northward
advance of the warm front. Still, moderate to locally strong
instability appears likely to develop by peak heating this afternoon
south of the warm front and east of the dryline as steep mid-level
lapse rates/an EML overspread the warm sector, and as surface
dewpoints generally increase into the mid to upper 60s. Current
expectations are for multiple surface-based supercells to initiate
along/near composite the outflow/warm front/dryline intersection
early this afternoon, probably no later than 19-20Z. Given the
presence of steep mid-level lapse rates and 40-50 kt of deep-layer
shear, this initially semi-discrete convection will pose a threat
for very large hail (2-3+ inch diameter) as it spreads
east-southeastward this afternoon across north TX. The threat for a
few tornadoes will also exist, as low-level flow will strongly veer
from east-southeasterly at low levels to westerly at mid levels,
enhancing the low-level hodograph and effective SRH. Strong tornado
potential should remain focused with any supercell that can remain
anchored along the warm front.
The initially semi-discrete supercells will likely grow upscale into
a bowing complex/MCS by early evening. As this mode transition
occurs, the threat for severe/damaging winds will increase, with
some potential for significant (75+ mph) gusts across north-central
into east TX. 12Z guidance shows this MCS continuing into LA and
parts of central/southeast TX this evening/overnight. While some
decrease in updraft intensity may eventually occur, there will
probably be a continued threat for scattered damaging winds given a
reservoir of favorable buoyancy. Some chance for a couple of
supercells may also exist over central TX this afternoon, driven by
modest low-level warm advection. If robust thunderstorms can form,
they would pose a threat for all severe hazards, including very
large hail. Have therefore expanded the Slight Risk southward to
include more of central/southeast TX to account for this severe
potential. An isolated severe threat should also persist tonight
into portions of the lower MS Valley, as generally linear convection
spreads eastward from TX.
...Florida...
Based on recent visible satellite imagery, mostly clear/sunny
conditions are present over the FL Peninsula. The eastern extent of
a remnant EML, shown in the fairly steep 700-500 mb lapse rates on
the 12Z TBW/15Z XMR soundings, has overspread much of the FL
Peninsula. Robust diurnal heating of a rich low-level airmass will
contribute to a moderately to strongly unstable airmass, with MLCAPE
generally around 2000-2500+ J/kg. Even with low-level winds expected
to remain fairly weak, enhanced mid/upper-level flow will foster
40-50 kt of effective bulk shear and updraft organization. Compared
to the past two days, it appears likely that multiple supercells
capable of producing both very large hail and strong/damaging winds
will develop this afternoon over the northern/central FL Peninsula
along both sea breezes and residual outflow boundaries, and
subsequently spread southward through the early evening.
Read more
