SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0246 PM CDT Sat May 07 2022
Valid 072000Z - 081200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS LATE THIS
AFTERNOON AND EVENING ACROSS PARTS OF SOUTH DAKOTA AND NEBRASKA...
...SUMMARY...
Scattered strong thunderstorm development is possible late this
afternoon and evening, particularly across parts of the northern
Great Plains, where a few may become severe and capable of producing
large hail and potentially damaging wind gusts.
...20Z Update...
Based on the progression of synoptic and sub-synoptic features, and
ongoing trends concerning instability, the risk for thunderstorms
through the remainder of this period appears increasingly negligible
in a number of areas. Some adjustments to the categorical
thunderstorm lines have been made to account for this (reducing
thunderstorm probabilities below 10 percent).
Some initial attempts at deep convective development are evident
across parts of the Texas Hill Country/Edwards Plateau vicinity.
However, due to the presence of warm and capping elevated
mixed-layer air beneath mid-level ridging, the risk for sustained
thunderstorm development near the sharpening dryline is also
appearing increasingly questionable. Even so, with potential
instability becoming quite large across this region in the presence
of modest shear, if a storm can initiate and be maintained, the
evolution of a supercell or two does still appear possible. Given
little change to the degree of the conditional severe threat, the
previous outlook across this area will be maintained.
..Kerr.. 05/07/2022
.PREV DISCUSSION... /ISSUED 1136 AM CDT Sat May 07 2022/
...Nebraska/Dakotas...
Increasingly prevalent/strengthening cyclonic upper-level flow will
influence the region through tonight. Initial strong/severe
thunderstorm development is expected across central portions of
South Dakota/North Dakota near the eastward-shifting boundary, with
a bit later (hour or two) development expected southward into
west-central/north-central Nebraska by evening. Large hail will be
possible with this initial supercellular development, prior to an
upscale transition which will likely include an increasing potential
for severe-caliber wind gusts during the evening.
Low-level moisture will be limited in both magnitude and lateral
extent, with a narrow corridor of mainly 50s F surface dew points
extending from central Kansas 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. 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 South Dakota, 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.
Farther south, scattered thunderstorms also are forecast to develop
over portions of western into central Nebraska -- but this evening,
generally as the front overtakes the dryline, and a combination of
height falls and shots of DCVA occur in midlevels. Supported by the
southerly LLJ, and its associated combination 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 Florida...
Scattered thunderstorms will continue near a west-east front across
the Florida Peninsula, with outflow/sea breeze being additional
developmental influences. A moist air mass and moderate buoyancy,
with upwards of 2000-2500 J/kg MLCAPE, will yield some
strong/sustained multicells in the presence of 25-35 kt effective
shear. A few instances of locally damaging winds and/or hail are
possible this afternoon.
...Portions of central/north-central Texas...
Some potential will exist for isolated but intense thunderstorm
development near the dryline late this afternoon. The region will be
influenced the near-crest portion of the southern/central upper
ridge, with most available short-term guidance suggestive of limited
prospects for deep convective development. However, robust
heating/mixing in the post-dryline environment and sufficient
near-dryline convergence in the presence of upper 60s/near 70F
surface dewpoints could result in isolated storm development.
If/where storms develop, a storm or two capable of localized large
hail and/or severe-caliber wind gusts would be possible in the
presence of 3500+ J/kg MLCAPE and low/mid-tropospheric that is weak
but veers with height. Any such severe risk would likely gradually
diminish shortly after sunset.
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