SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0259 PM CDT Thu May 12 2022
Valid 122000Z - 131200Z
...THERE IS A MODERATE RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
NORTHEAST NEBRASKA...EASTERN SOUTH DAKOTA...SOUTHEAST NORTH
DAKOTA...AND WESTERN MINNESOTA...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE LOWER
MISSISSIPPI VALLEY...
...SUMMARY...
Scattered to numerous severe thunderstorm gusts (some 75+ mph),
large hail and a few tornadoes are expected over parts of the
eastern Dakotas, eastern Nebraska, western Iowa, and
central/southern Minnesota this afternoon into tonight. Other severe
storms are expected across the southern Plains and Lower Mississippi
Valley.
...Discussion...
Only two notable changes were made to the previous convective
outlook and are listed below.
1) Upgraded severe wind probabilities from 30% to 45% for northern
portions of NE and southeast SD immediately ahead of an evolving bow
that is forecast to quickly move north-northeast at 55 kt. Severe
gusts ranging from 60-100 mph are possible in the short-term over NE
into southeast SD over the next several hours. See MCD #737 for
short-term details.
2) Reduced hail probabilities from 30% to 15% for NE and focused the
significant hail area to be over eastern SD where supercell
convective mode is most likely.
..Smith.. 05/12/2022
.PREV DISCUSSION... /ISSUED 1156 AM CDT Thu May 12 2022/
...Northern/central Plains and Upper Midwest...
Have made spatial (westward) adjustments to the categorical Moderate
Risk along with some increased potential for initial severe-discrete
storms, which includes the potential for a strong tornado, across
South Dakota. In general, scattered to numerous thunderstorms are
expected to develop in an arc near the surface low and cold front by
mid/late afternoon, from central/eastern South Dakota southward
across central/eastern Nebraska and into at least northern Kansas. A
brief interval, early in the convective cycle, may support discrete
to semi-discrete supercells before the convection becomes
quasi-linear. The most common severe type should evolve quickly to
thunderstorm gusts through early evening -- some of which may be
significant (65+ kt) strength, especially from parts of eastern
South Dakota and southeast North Dakota into western Minnesota.
The warm sector is forecast to destabilize throughout the day, with
a combination of at least weak large-scale ascent (increasing
northward), diurnal heating and related lift from below, and
ultimately frontal convergence, eliminating a basal EML inversion
and supporting convection initiation. Activity is expected to
intensify quickly as it impinges on a narrow but very favorable
prefrontal corridor where 60s to near 70 F surface dewpoints
contribute to MLCAPE in the 3500-4500 J/kg range in and near the
"moderate" area, decreasing gradually with southward extent as more
low-level moisture is mixed out. Low-level and deep shear will be
greatest near the triple point and warm front across South Dakota,
with 300-500 m2/s2 effective SRH and 45-55-kt effective-shear
magnitudes. A substantial component of mid/upper winds parallel to
the axis of convective forcing indicates potential for fairly fast
merging of early discrete and sporadically supercellular convection.
Surges of wind from resulting LEWP/bowing segments will pose the
greatest overall severe hazard, with line-embedded mesovortices and
perhaps a few associated tornadoes also possible. With the warm
sector's not being very broad, the convective event should diminish
late this evening into early overnight hours as it outruns the most
favorable instability.
...Eastern Minnesota/northern Wisconsin/northern Michigan today...
An ongoing linear complex of storms may persist eastward today in
vicinity of the warm front and nearby moist/unstable air mass. For
additional details, see Mesoscale Discussion 733.
...Portions of Mississippi/Louisiana and western Alabama...
Have upgraded portions of the region to a categorical Slight Risk.
Morning upper-air data reflects moderately strong
north-northeasterly mid/high-level winds across the region to the
west of the low centered in the Atlantic off the coastal Southeast.
Ample insolation/heating is occurring in conjunction with a moist
air mass across the region. This will contribute to scattered
thunderstorm development this afternoon with gradual clustering and
some potential for upscale evolution into multiple
southwestward-moving semi-organized clusters. Isolated wind damage
is expected to the primary severe hazard.
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