SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0250 PM CDT Sat Sep 17 2022
Valid 172000Z - 181200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
NORTHERN MINNESOTA...AND ACROSS PARTS OF THE MID MISSOURI VALLEY
AREA...
...SUMMARY...
Scattered severe hail, isolated damaging winds, and a tornado remain
possible across a portion of northern Minnesota during the late
afternoon to early evening. Scattered large hail, damaging winds,
and a brief tornado are also possible this evening across a portion
of the Mid-Missouri Valley.
...Discussion...
Though severe weather has yet to evolve in earnest, gradual
afternoon destabilization that is underway still appears likely to
result in development of late afternoon/early evening convection --
some of which may pose an all-hazards severe risk, consistent with
prior outlook areas and reasoning. As such, no appreciable changes
appear necessary at this time.
..Goss.. 09/17/2022
.PREV DISCUSSION... /ISSUED 1127 AM CDT Sat Sep 17 2022/
...Central to northern MN...
A low-amplitude shortwave trough approaching the Upper Red River
Valley will move across northern MN into northwest ON by this
evening. Partial cloud breaks are evident ahead of this wave mixed
with patches of persistent but thinning low-level stratus. The 12Z
NAM appears overdone with MLCAPE magnitude given its depiction of
mean mixing ratios from 14-15 g/kg later today when upstream 12Z
observed soundings sampled only 12-13 g/kg at most. With the EML
plume and attendant steep mid-level lapse rates also displaced south
of this region, MLCAPE will probably only peak towards 1500 J/kg.
Surface-based thunderstorm development will likely be focused in a
confined corridor near the evolving frontal wave, currently over
northeast SD, as it tracks east-northeast into northern MN. 12Z
guidance has generally trended toward a weaker depiction of
low-level mass response relative to the 00Z ECMWF, suggesting
low-level hodograph curvature may remain small except along the
surface warm front. Favorable elongation of the mid to upper
hodograph given speed shear with height amid southwest flow should
support a few discrete supercells. Severe hail will probably be the
primary hazard in coverage, but a couple tornadoes are possible if
activity can remain rooted where SRH is enhanced along the
west/east-oriented warm front. These threats will likely diminish
into late evening as activity spreads towards northeast MN.
...IA to central KS...
A weakening MCS persists across southern IA and northwest MO with
large-scale outflow analyzed from the I-70 corridor in northeast KS
arcing to the northwest in central NE. Air mass recovery will occur
across the Mid-MO Valley into this evening, but will clearly be
impacted by this morning's activity, which renders uncertainty in
just how intense redevelopment this evening will truly be.
A hot air mass will be prevalent from the southern High Plains into
central KS. Isolated high-based thunderstorms will probably develop
along the dryline to triple-point intersection with a threat for
isolated severe gusts and hail. More prevalent convective
redevelopment will occur atop the residual outflow/differential
heating zone this evening as a southwesterly low-level jet
intensifies. Forecast soundings differ, but given the presence of
the upstream EML and limited time for intense boundary-layer heating
it appears most probable that convection will be rooted from
elevated parcels, especially with time after dusk. This renders low
confidence in a greater tornado threat despite low-level hodographs
becoming highly enlarged. With weak changes in magnitude in winds
with height above 700 mb, a cluster convective mode should dominate.
This should subdue the large hail threat and the weak low-level
lapse rates deeper into IA should limit the overall severe wind
threat with northeast extent as well. Still with upscale growth into
a slow-moving MCS and embedded organized updrafts probable this
evening, will maintain a cat 2 severe risk delineation.
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