SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0256 PM CDT Tue Apr 25 2023
Valid 252000Z - 261200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
TEXAS AND SOUTHWEST OKLAHOMA...
...SUMMARY...
Severe thunderstorms are possible mainly late this afternoon into
tonight over parts of the southern Plains, with a risk for large to
very large hail, damaging winds, and perhaps a couple of tornadoes.
...20Z Update...
...Southern Plains...
Recent surface analysis reveals a developing lee low over northeast
NM, with a strengthening warm front extending southeastward across
the OK/TX Panhandles and into southwest OK then eastward along the
Red River. Convective initiation has already occurred in the
vicinity of the lee low, with these storms expected to move eastward
in the TX/OK Panhandles over the next few hours. Low-level moisture
is meager but cold temperatures aloft will still support modest
buoyancy and a few stronger storms.
Mid 50s dewpoints have reached southwest OK, with the expectation
that convective initiation will eventually occur in this region this
afternoon/evening. Surface temperatures are cool, but mid-level
lapse rates are steep enough to support isolated severe
thunderstorms capable of hail.
As mentioned in the previous outlook, initiation farther south in
southwest TX remain uncertain due to strong capping. The cloud cover
has now dissipated and the surface temperature at SJT has climbed to
78, which is 6 degrees warmer than recent RAP forecast soundings.
Additional warming is likely, but the boundary layer will further
mix as well. Given the EML and moderate mid-level flow, a
conditional risk for very large hail exists.
...Florida...
Thunderstorms are expected to continue across FL for the next few
hours until nocturnal stabilization sets in. Environmental
conditions support storms capable of isolated hail and/or a few
stronger gusts. Refer to MCD #612 for additional information.
..Mosier.. 04/25/2023
.PREV DISCUSSION... /ISSUED 1124 AM CDT Tue Apr 25 2023/
...Southern Plains...
An upper trough/low centered over the Great Basin and central
Rockies this morning will advance south-southeastward towards the
Four Corners by this evening, and will eventually reach the southern
High Plains late tonight. A subtle, southern-stream perturbation
over northern Mexico will move eastward across west/central TX
through the day. At the surface, weak cyclogenesis should occur
across eastern NM this afternoon/evening. Low-level moisture,
characterized by generally low 50s to low 60s surface dewpoints,
will continue streaming northward today along/south of a warm front
and east of a dryline.
Convective potential and evolution across the warm sector this
afternoon through tonight remains unclear owing to weak/nebulous
large-scale ascent. Still, the best signal for thunderstorm
initiation appears to be across the higher terrain of southeastern
CO and northeastern NM this afternoon with weak low-level upslope
flow occurring and ascent from the approaching upper trough. This
activity should spread generally southeastward across the OK/TX
Panhandles and eventually northwest TX. Although low-level moisture
will remain rather limited, the presence of steep mid-level lapse
rates and 30-40 kt of deep-layer shear should prove sufficient for
thunderstorm organization, including the potential for multiple
supercells posing a threat for mainly large hail.
Confidence in greater coverage of intense convection has increased
enough to expand the Slight Risk farther northwest into parts of the
TX Panhandle. These thunderstorms should continue east-southeastward
towards northwest TX and southwestern OK this evening/tonight. The
activity in OK will probably tend to become elevated to the north of
the warm front, but it may still pose some threat for hail. Gusty
winds will be possible with any clusters that can persist with
eastward extent tonight from northwest into central TX.
The prospect for convective initiation along the dryline this
afternoon from northwest to central TX still appears rather
conditional, as a pronounced cap noted on 12Z soundings from MAF and
DRT will be slow to erode and potentially difficult to breach.
Widespread low-level cloud cover noted on morning visible satellite
imagery east of the dryline will need to mix out to some extent to
generate sufficient diurnal heating to support parcels being lifted
near/to their LFCs. A somewhat better chance for surface-based
convective development may be across northwest into western north
TX, where some cloud breaks and filtered daytime heating have
already been observed. If thunderstorms can form and be sustained
across this region, they will likely be supercells and pose a threat
for large to very large hail initially given the presence of
moderate instability, steep mid-level lapse rates, and sufficient
effective bulk shear. As a southerly low-level jet modestly
strengthens this evening, there may also be a narrow, 2-4 hour
window (from roughly 22-02Z) for a couple of tornadoes with any
supercell that can remain surface based.
The possibility of open warm sector development this afternoon also
remains apparent over portions of coastal/southeast TX. If this
activity forms, it would likely be tied to weak low-level warm
advection and daytime heating on the southern fringe of persistent
cloud cover. Any thunderstorms that can persist in this regime may
pose a threat for large hail and damaging winds. Based on signals in
12Z guidance on where this convection may develop, have expanded the
Slight Risk a little southeastward towards the middle TX Coast.
...Florida...
Generally zonal flow aloft will persist over the FL Peninsula today.
With robust diurnal heating expected, scattered thunderstorms should
once again develop along both the Atlantic and Gulf Coast sea
breezes this afternoon, and to the south of a remnant front draped
across the north/central FL Peninsula. While low-level winds will
remain weak, strengthening west-southwesterly flow at mid/upper
levels should support around 30-35 kt of deep-layer shear. This
should be sufficient for some updraft organization, including the
potential for a mix of multicells and perhaps marginal supercell
structures. With seasonably cool mid-level temperatures present,
some of these thunderstorms could pose an isolated threat for severe
hail and damaging wind gusts this afternoon and early evening.
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