SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0259 PM CDT Wed May 11 2022
Valid 112000Z - 121200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM EASTERN SD
ACROSS CENTRAL MN INTO WEST-CENTRAL WI...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS THE
SOUTHERN HIGH PLAINS...
...SUMMARY...
Severe thunderstorms are expected this afternoon/evening over the
north-central states. Very large hail, wind, and a threat for
tornadoes is expected. Additionally, widely scattered severe
thunderstorms are anticipated across the southern High Plains.
Wind/hail are the primary threats.
..Discussion...
Only change this outlook update is to reduce probabilities over
parts of eastern NE and IA to the latitudinal south of the MCV over
the mid MO Valley. Otherwise, the forecast remains unchanged.
..Smith.. 05/11/2022
.PREV DISCUSSION... /ISSUED 1126 AM CDT Wed May 11 2022/
...Synopsis...
Expansive upper ridging currently extended from eastern Mexico
through the Upper Great Lakes is expected to amplify throughout the
day today. This amplification will occur as a shortwave trough
embedded within the western CONUS mean troughing moves eastward
towards the central Rockies and a large cyclone retrogrades
westward/southwestward off the Atlantic Coast.
Despite the presence of these large-scale features, the severe
weather potential will be driven primarily by low-level and/or
mesoscale features today, most prominently the convectively induced
vorticity maximum moving northeastward out of KS. Severe
thunderstorm development is anticipated as this vorticity maximum
moves into the Mid MO Valley and Upper Midwest this afternoon and
evening. Severe thunderstorms are also possible this afternoon and
evening across the southern High Plains along the dryline and over
the northern High Plains later this evening and overnight.
...Mid MO Valley into the Upper Midwest...
A reservoir of 70 dewpoints is already in place from northeast
KS/southeast NE across southern IA and into southern WI. Mid 60s
dewpoints exist just north of this region. As the warm front lifts
northward, expectation is for this low-level moisture to
correspondingly advect northward/northwestward throughout the day.
By the early afternoon, upper 60s dewpoints are expected to cover
into southern MN and much of WI, with 70s dewpoints over eastern NE
and much of IA.
Steep mid-level lapse rates (sampled well by the 12Z OAX sounding)
coupled with this abundant low-level moisture will result in a very
unstable air mass downstream of the mesoscale convective vortex
currently over KS. Strong heating will remove any convective
inhibition and the expectation is for thunderstorm initiation across
eastern NE early this afternoon as the leading edge of the MCV. An
initially discrete mode is probable, with shear profiles supportive
of supercells, even though some mid-level southeasterly flow around
the MCV (as noted on the UEX VAD) does cast some uncertainty towards
overall storm structure. Even so, strong buoyancy will support
intense updrafts capable of large to very large hail and strong
water loaded downbursts. Low-level flow is also sufficient for
tornadogenesis, particularly if the southeasterly mid-level flow
around the MCV turns more southerly with time. Upscale growth also
appears probable after the initially discrete mode, with the
orientation of the line perpendicular to the vertical shear vector.
This results in the potential for some significant wind gusts over
MN.
...Southern High Plains...
Thunderstorms are expected to develop along the dryline this
afternoon as the air mass destabilizes amid strong heating and
modest low-level moisture. Mid to upper level flow will be rather
modest, but enough directional shear should exist for some updraft
organization. Higher dewpoints and buoyancy will exist across
southern portions of the region, contributing to higher potential
for all severe hazards, particularly very large hail.
...Southeast MT/Eastern WY into the Northern Plains...
Large-scale ascent will increase this evening and overnight across
the region, as the strong shortwave trough pivots out of the Great
Basin and approaches. At the same time, associated mid-level
moistening will help promote elevated thunderstorm development
across southeast MT and eastern WY. Though buoyancy will be meager
(MUCAPE generally 300-800 J/kg), favorable deep shear
(effective-shear magnitudes around 50-65 kt) will favor supercell
potential, with large hail as the primary threat.
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