130
ACUS01 KWNS 191300
SWODY1
SPC AC 191258

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0758 AM CDT Sun May 19 2024

Valid 191300Z - 201200Z

...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS IN PORTIONS OF
KANSAS...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
EAST-CENTRAL/SOUTHEASTERN FLORIDA...

...SUMMARY...
An organized swath of severe thunderstorm wind (potential derecho)
is expected mainly across parts of Kansas this afternoon and
evening, possibly extending into northern Oklahoma.  Gusts of 75-100
mph are possible, along with large hail and a few tornadoes.

...Synopsis...
A broad fetch of westerly to southwesterly flow will cover most of
the central CONUS.  This will persist downstream from a synoptic-
scale trough over the Pacific Northwest that should amplify into the
Great Basin region through the period.  The downstream flow field
contains several embedded shortwaves, including a convectively
generated perturbation now over parts of KS/NE.  This feature should
eject northeastward over the upper Mississippi Valley this evening,
and away from the main threat area.  However, an upstream shortwave
trough -- apparent in moisture-channel imagery over the Four Corners
region -- will move east-northeastward and influence convective
potential over the central Plains this afternoon and evening.

Elsewhere aloft, a persistent trough was evident across portions of
VA, the Carolinas, GA, and AL, with cyclonic flow downstream over
the southern Atlantic Coast and as far south as most of the FL
Peninsula.  This trough should reach the NC/SC/GA coastlines and
northwestern FL by 00Z, and south FL by 12Z tomorrow.

The 11Z surface analysis showed a cold front from northeastern ON
across Lower MI, western IL, west-central MO and east-central KS,
where it is being overtaken by an outflow boundary arching
southwestward across south-central KS to the OK Panhandle. The
outflow boundary is expected to stall in the next few hours, then
shift northward over southern and central KS through the day.  A
dryline extended from eastern CO across the western TX Panhandle to
near LBB, MAF and northern Coahuila.  The dryline should mix
eastward slightly today, reaching near the KS/CO line and eastern TX
Panhandle by mid/late afternoon.  Elsewhere, a weak cold front was
drawn from a low offshore from NC southwestward over northern FL,
and should move slowly southward into central FL today.

...Central Plains...
Thunderstorms are expected to develop during mid/late afternoon
behind the dryline over the eastern Raton Mesa region, as well as
along the dryline itself, and move east-northeastward to eastward
into increasing moisture and instability.  As they do, some of the
activity should aggregate into clusters as smaller-scale outflows
combine and enlarge.  With supportive internal feedback of an
organizing cold pool, associated forced ascent at the front and
rear-inflow jet, and supportive midlevel winds for downward momentum
transfer, as well as the residual and diurnally destabilized outflow
boundary, the overall meso-alpha-scale pattern appears quite
suitable for an organized, potentially significant-severe
convective-wind swath to result.  The most probable corridor for
such growth still appears to be across KS in and near the "moderate
risk" corridor, driven by wind probabilities.

Initially separate dryline development over the northeastern TX
Panhandle and northwestern OK may blend into (or even get undercut
by outflow from) the broader event as well, after a few hours`
discrete time to its south, with a threat of large hail, locally
severe gusts and perhaps a tornado or two.  Other afternoon
development, along the dryline, in the mountains of northern CO and
southeastern WY, and over the Black Hills, may move east-
northeastward across a narrow moist sector and produce severe gusts
and hail into parts of the adjoining High Plains of western NE and
the Dakotas.

Near and behind the KS-to-Panhandles dryline segment, the storm-
initiation environment will be characterized by increasing
large-scale ascent and upper divergence ahead of the ejecting Four
Corners shortwave trough, as well as strong diurnal heating, mixing
and deepening of the boundary layer.  Superposition of these effects
will lead to nearly 9 deg C/km lapse rates throughout the lower/
middle troposphere, supporting 2000-3000 J/kg MLCAPE just east of
the dryline.  A deep subcloud layer conducive to strong-severe
downdrafts will be available to storms over western KS from the
beginning, and should support growth/merger of resultant outflows
before activity moves into greater moisture.  Forced ascent of the
moist boundary layer should help to sustain the forward-propagating
complex into strengthening nocturnal MLCINH at least across eastern
KS, and perhaps into parts of the lower Missouri Valley, before it
weakens tonight.

...FL...
Scattered thunderstorms should develop this afternoon near the I-95
corridor and roughly between MIA and the Space Coast, along and
south of a weak cold front.  Organized multicells and a few
supercells are possible, offering large hail and damaging to locally
severe gusts before they move offshore.  An active Atlantic
sea-breeze pattern will be augmented by mid/upper support preceding
the trough aloft.  Strong diurnal heating, a deep troposphere and
rich low-level moisture (with dewpoints commonly in the 70s F and
16.5-18.5 g/kg mean mixing ratios) will support 2000-3000 J/kg peak
MLCAPE.  Though weak near-surface winds will limit hodograph size,
30-45 kt effective-shear magnitudes and potential boundary
interactions will support storm organization, including supercell
potential.

..Edwards/Goss.. 05/19/2024

$$