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Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0753 AM CDT Sat May 07 2022

Valid 071300Z - 081200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PORTIONS OF
WESTERN/CENTRAL NEBRASKA TO THE CENTRAL SOUTH/NORTH DAKOTA BORDER
AREA...

...SUMMARY...
Scattered severe storms capable of large hail and isolated severe
gusts are possible across western and central Nebraska, mainly this
evening and tonight.  Other isolated severe storms are possible
across parts of North Dakota, north and central Texas, and the
Florida Peninsula.

...Synopsis...
Two substantial, slow-moving cyclones will be the dominant
mid/upper-level features this period, for convective purposes:

1.  A vortex now appears over the eastern WV/southern PA/northern VA
area, with troughing south-southwestward to the northwestern Gulf. 
The 500-mb low should move slowly eastward to the Delmarva Peninsula
through the overnight hours, with trough across eastern NC,
central/southern FL and intervening Atlantic waters by 12Z tomorrow.

2.  A very large, co*plex gyre will arise from two initially well-
separated cyclone centers now apparent in moisture-channel imagery
over northern AB and over the northeast Pacific near 50N148W.  The
Pacific portion will approach coastal OR by 12Z, while vorticity
maxima consolidate around the erratically drifting AB center. 
Cyclonic flow and height falls will expand across most of the
western half of the CONUS, as a series of vorticity maxima pivot
from the Great Basin to the northern Plains.

In between those cyclones, a high-amplitude mid/upper ridge --
initially from the southern High Plains to Lake Superior and far
northern ON -- will pivot slowly to near a HOU-LIT-MKE-James Bay
axis by the end of the period.

At the surface, 11Z analysis depicted an occluded low over WV,
nearly stacked with the mid/upper low, and a triple-point low over
Atlantic waters east of the Hampton Roads region.  A cold front was
drawn from there across northern FL to extreme southeastern LA,
beco*ing a warm front across southeast and central TX.  Another cold
front was drawn from a low in the JDN/GGW area across central WY and
northwestern CO.  The eastern cold front will proceed slowly
southeastward down the FL Peninsula, while beco*ing quasistationary
from northeastern Gulf to LA, and moving back northward as a warm
front over east TX and into western/southern OK by 00Z.  To its
southwest and west, a dryline should develop and mix eastward to a
maximum late-afternoon extent (minimum longitudes) in an arc from
near DRT-SEP-SPS-CDS, then northward over the eastern TX/OK
Panhandles, western KS and western NE.  In western NE, the dryline
will be overtaken by a cold front that will move eastward/
southeastward across the northern Plains and central High Plains
through the period.  By 00Z, the cold front should reach the central
Dakotas, western NS and extreme northern CO.

...Dakotas, Nebraska...
Scattered strong-severe thunderstorms are expected, initially late
this afternoon over portions of SD and perhaps ND, then this evening
and tonight across parts of western/central NE.  The greatest
concentration of convective/severe potential should be in the SD/NE
corridor, where large hail will be possible from early, relatively
discrete and potentially supercellular activity.  A transition to
upscale clustering with some severe-wind threat also exists this
evening before the foregoing boundary layer stabilizes too much.

Being well north of the southern Plains warm front, moisture will be
limited in both magnitude and lateral extent, with a narrow corridor
of mainly 50s F surface dew points extending from central KS to the
central Dakotas, east of the dryline and cold front.  Still, this
and insolation will foster enough late-afternoon/early evening
mixing/drying of the boundary layer to boost DCAPE and weaken MLCINH
substantially, supporting the gust potential beneath 500-1500 J/kg
MLCAPE values.  Time series of forecast soundings suggesting an
"inverted V" subcloud thermodynamic profile in the short time window
before deep convective initiation.  Veering and strengthening of
flow with height, from surface through midlevels, will support
45-55-kt effective-shear vectors aligned nearly orthogonal to the
front in SD, with initial discrete/semi-discrete modes until some
mergers and cold-pool processes occur.  Activity should transition
from a hail-dominant to wind-dominant threat before shifting east
and weakening in greater stability this evening. 

Scattered thunderstorms also are forecast to develop over portions
of western into central NE -- but this evening, generally as the
front overtakes the dryline, and a co*bination of height falls and
shots of DCVA occur in midlevels.  Supported by the southerly LLJ,
and its associated co*bination of increasing moisture and favorable
storm-relative winds above the surface, elevated supercells and
organized multicellular clusters are expected to offer a large-hail
threat.  Isolated severe gusts may occur as well, where sufficient
downward momentum and cold-pool forcing from mesobeta-scale upscale
growth can allow downdrafts to penetrate a near-surface stable layer
locally.  Continued eastward movement of activity atop progressively
more-stable boundary-layer conditions should reduce storm intensity
overnight.

...Central/south FL...
Widely scattered to scattered thunderstorms are expected to
continue, predominantly south of the cold front, offering sporadic,
marginally severe hail and damaging gusts to near severe limits.
Away from small-scale boundaries (outflows, sea breezes), warm-
sector flow generally will be nearly unidirectional from the
southwest or west-southwest.  While this will limit low-level shear
and convergence, convective potential will be supported increasingly
by strong surface heating and favorable boundary-layer moisture
(with surface dewpoints co*monly in the 70s F).  MLCAPE of 2000-2500
J/kg should be co*mon, amidst 25-35-kt effective-shear magnitudes,
for a dominant, sporadically organized multicellular mode. 
Convection should weaken by evening as low-level thermodynamic,
frontal, and prefrontal-boundary lift all diminish.

...Portions of central/north-central TX...
Although this area will be under, or very close to, the upper ridge,
an isolated intense thunderstorm or two may erupt by late afternoon
with a conditional risk for severe gusts and large hail.  Intense
diabatic surface heating on both sides of the broad dryline bulge
may be sufficient to remove most or all EML-related capping for a
few hours, in the presence of roughly 70 F surface dew points, and
additional lift support from the dryline.  With a deep troposphere
and steep low/middle-level lapse rates expected, MLCAPE should
exceed 4000 J/kg -- much of that in suitable hail-growth layers with
no shortage of inflow-layer moisture for precip generation.  A
well-mixed subcloud layer also will enable strong-severe downdrafts
to the surface in any storms that can develop.  Lack of greater mid/
upper-level winds will limit deep shear (e.g., effective-shear
magnitudes generally 20-30 kt expected), though flow will veer well
with height in the low levels.  Any severe threat should wind down
quickly this evening as the boundary layer cools, the dryline
retreats, and MLCINH increases.

..Edwards/Gleason.. 05/07/2022