SPC 1200Z Day 1 Outlook

Day 1 Outlook Image

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1240 AM CDT Sun Oct 11 2020

Valid 111200Z - 121200Z


Isolated strong to severe thunderstorms are expected late this
afternoon and evening across parts of the northern/central Plains
into the Upper Midwest, with marginally severe thunderstorms also
possible across parts of the Southeast and Mid-Atlantic.

...Northern/Central Plains...

00z models are in general agreement regarding the progression of a
short-wave trough over the northwestern US. This feature is forecast
to advance into the High Plains, extending from the western Dakotas
into eastern CO by 12/00z, then shifting to near 97W longitude by
the end of the period. Low-level moisture is currently a bit scant
across the northern/central Plains where surface dew points are in
the 30s/40s. However, strengthening LLJ across this region should
allow moisture across KS to begin advancing north. Latest
indications are this modified air mass will likely be drawn north
across the mid-MO Valley into portions of southwestern MN prior to
frontal passage.

Latest guidance suggests a narrow corridor of strong boundary-layer
heating will extend across the central Plains into southwestern MN
by mid afternoon. While surface parcels may struggle to reach their
convective temperatures, frontal convergence should easily assist
parcels to their LFC, and scattered thunderstorms are expected to
develop along the strongly forced high-latitude portions of the
boundary by 21z. Forecast soundings suggest adequate deep-layer
shear for potential supercells; however, strong forcing should
result in a squall line quickly. Greatest threat with this initial
activity will be hail/wind, evolving into more of a wind threat as
the squall line matures. Have extended severe probabilities
southwest along the front into portions of northern KS where
forecast soundings suggest inhibition will be very weak with MUCAPE
in excess of 2000 J/kg. Southern extent of large-scale forcing
should extend into this region which should be adequate for
scattered convection along the wind shift.


Remnants of TC Delta are quickly ejecting east-northeast across the
TN Valley/northern Gulf States. Substantial mid-level drying is
spreading across AL/GA early this morning and this drying should
progress downstream into the western Carolinas early in the period.
Overall, this system is gradually weakening with forecast soundings
across the southeastern US/Carolinas exhibiting substantially weaker
shear than the eastern Gulf States Saturday. Even so, adequate flow
and moistening profiles suggest there is some risk for organized
robust convection. The greatest risk is for locally damaging wind
gusts, or perhaps a few brief/weak tornadoes.

..Darrow/Moore.. 10/11/2020

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