ACUS01 KWNS 201239
SWODY1
SPC AC 201238

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0738 AM CDT Wed Mar 20 2024

Valid 201300Z - 211200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS THIS
AFTERNOON/EVENING ACROSS WESTERN OK/NORTHWEST TX...AND EARLY
THURSDAY MORNING NEAR THE TX COAST...

...SUMMARY...
Isolated, marginally severe storms will be possible this
afternoon/evening across parts of western Oklahoma and northwest
Texas. Isolated large hail will be possible early Thursday morning
near the Texas coast.

...Western OK/TX Panhandle this afternoon/evening...
A midlevel shortwave trough will begin to move eastward from AZ/NM
toward west TX by tonight, with associated downstream cyclogenesis
occurring today across eastern NM and the TX Panhandle. Low-level
moisture return will be limited in the warm sector, with
boundary-layer dewpoints ranging from 40-45 F as surface
temperatures warm into the 70s this afternoon along a surface
trough/front across western OK and the eastern TX Panhandle.
Steepening low-midlevel lapse rates and cool midlevel temperatures
will support weak buoyancy, and weak ascent along the boundaries
could result in a few storms with the potential to produce
marginally severe hail and strong outflow gusts. There is also a
low probability of a non-mesocyclone tornado with developing
updrafts along the slow-moving front in northwest OK later this
afternoon, given steep low-level lapse rates/vertical vorticity
along the front.

...South central TX to the coastal plain late tonight...
Low-level moisture return will occur in earnest by tonight as a
maritime tropical air mass spreads northward from the Bay of
Campeche (along the prior stalled front) to the TX coast. Near the
end of the period, destabilization will become sufficient for
elevated thunderstorm development in the warm advection zone atop a
diffuse coastal front. MUCAPE could reach 1000-1500 J/kg as
moisture increase below midlevel lapse rates of 7.5-8 C/km, in an
environment with sufficiently long hodographs (and some low-level
curvature) for a conditional supercell/large hail threat mainly
09-12z.

...Southern New England this afternoon...
A deepening midlevel trough will move from ON to New England, as an
associated cold front moves across New England later today and
cyclogenesis occurs tonight near the ME coast. Moisture/buoyancy
will be scant at best ahead of the cold front across southern New
England, where some shallow/forced convection may occur along the
cold front this afternoon. The convection could be associated with
a few strong gusts, but the potential for convectively driven severe
gusts appears too low to warrant introduction of an outlook area.

..Thompson/Grams.. 03/20/2024

$$
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ACUS01 KWNS 271246
SWODY1
SPC AC 271244

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0744 AM CDT Wed Mar 27 2024

Valid 271300Z - 281200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
THE NEAR-COASTAL SOUTHEAST...AS WELL AS PORTIONS OF CENTRAL AND
NORTH TEXAS...

...SUMMARY...
Isolated severe hail and damaging winds are possible over parts of
the near-coastal Southeast, as well as portions of central and north
Texas.

...Synopsis...
A vast area of the CONUS begins the period with cyclonic mid/upper-
level flow, thanks to nearly phased northern- and southern-stream
synoptic troughs. The southern one is apparent in moisture-channel
imagery from eastern NM to the Big Bend region of west TX, then over
Coahuila, and should move eastward to AR, east TX and the
northwestern Gulf by 00Z. The northern one is anchored by a 500-mb
cyclone centered initially over northwestern MN, forecast to pivot
to near Thunder Bay, ON, by 00Z, then northeastward to between Lake
Superior and James Bay around 12Z. By then, phased troughing will
extend from there across Lake Michigan and the lower Ohio Valley to
the southern-stream perturbation over parts of AL, southeastern LA
and the north-central/west-central Gulf.

At the surface, 11Z analysis depicted an occluded low over northern
ON, with an occluded/cold front to near BUF, PIT, and BKW, to a
triple-point low near AGS. A cold front extended from there
southwestward across the AAF area to the central/southwestern Gulf.
A warm front was drawn from the southern low east-southeastward
between SAV-CHS. The warm front should shift northeastward across
coastal SC and the Low Country today. Another frontal-wave low may
form tonight over SC then move offshore. The cold front should move
slowly southeastward, reaching near an XMR-EYW line by 12Z tomorrow.

...Southeast CONUS...
An ongoing belt of precip, with embedded/scattered thunderstorms,
should continue to shift slowly eastward across the area, in step
with (and near the position of) the front. The most intense cells
will be capable of damaging gusts -- especially on and ahead of the
boundary -- as well as severe hail. That includes a semi-organized,
bowing storm cluster moving inland from the FL coastal bend, for
another hour or so until it encounters substantially more stable air
sampled by the 12Z TBW and JAX RAOBs.

The near-surface layer -- initially stable over land from prior
nocturnal cooling -- should undergo both gradual diabatic heating
through anvil-cloud cover, and warm/moist advection through the
afternoon. This will erode the morning stable layer and support
peak preconvective/prefrontal MLCAPE of 1500-2000 J/Kg over parts of
northern FL, and 1000-1500 J/kg over eastern GA and parts of SC.
Flow aloft will remain strongly parallel to the front and the
convective plume, continuing a messy convective character with
embedded thunderstorms. Forecast hodographs support a blend of
sporadic left- and right-moving supercells, and mainly organized
multicells, with stronger shear and buoyancy but somewhat weaker
lift over southern parts of the outlook area. As the threat appears
sporadic and spatially isolated -- not very well-focused in time or
within the broader precip swath -- probabilities are held at
marginal unconditional thresholds for now.

...Central/north TX...
Widely scattered thunderstorms are possible for a few hours this
afternoon into early evening, moving eastward to southeastward, with
isolated severe hail and strong to marginally severe gusts possible.

An area of surface low pressure over eastern NM -- initially tied to
lee troughing that extends well poleward into AB -- will split off
and move southeastward over northwest/north-central TX this
afternoon in response to the perturbation aloft, with a trough/
convergence zone to the south or south-southeast across central TX.
These features should provide enough lift for convection, amidst
minimal capping. As the mid/upper trough shifts toward and over the
area, very cold air aloft (500-mb temperatures at or below -25 deg
C) will contribute to steep midlevel lapse rates exceeding 8 deg
C/km. Despite being seemingly cool at the surface and well behind
the cold front, diabatic heating and residual moisture (dewpoints
generally mid 30s to mid 40s F) should erode MLCINH by mid/late
afternoon, with 300-700 J/kg MLCAPE possible. Though low-level flow
will be weak, enough deep shear should exist to support multicells
and at least transient supercell structures, atop a well-mixed
subcloud layer. The threat should wane by about 03Z as the
near-surface layer stabilizes and coverage/intensity of what had
been mostly diurnally driven convection diminishes.

..Edwards/Leitman.. 03/27/2024

$$
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