LIVE MAP (ABOVE) ... SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1240 AM CDT Tue Apr 18 2023
Valid 181200Z - 191200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF
THE GREAT PLAINS REGION INTO WYOMING...
...SUMMARY...
Isolated severe thunderstorms are possible from parts of the
southern Great Plains northward into the Mid Missouri Valley and
westward into Wyoming. Severe gusts and large hail will be the
hazards with the stronger storms Tuesday afternoon into Tuesday
night.
...Discussion...
Upper ridge is forecast to shift across the Great Plains into the MS
Valley by 19/00z as a significant short-wave trough ejects across
the Great Basin to a position from eastern ID-western CO by early
evening. In response to this feature, lee surface low should migrate
from southeast WY into central NE Tuesday evening before tracking
into northeast NE by sunrise Wednesday. LLJ is forecast to
strengthen in a couple of segments before focusing over the central
Plains Tuesday night with speeds in excess of 60kt.
Large-scale pattern appears favorable for dryline convection shortly
after peak heating and overnight convection within the
warm-advection corridor. One concern regarding the prospect for more
widespread convection is the limited moisture currently observed
across the Plains, especially the southern Plains. Early this
morning, lower 60s surface dew points were suppressed into deep
south TX while leading surge of 50F dew points extended as far north
as Fort Stockton/Pecos in west TX. Latest model guidance suggests
60s dew points will advance across western OK prior to sunset and
strong surface heating west of the dryline should allow surface
parcels to reach their convective temperatures by late afternoon. In
the absence of meaningful forcing, convection should remain quite
isolated along this boundary from KS into west TX. Slow-moving
supercells that materialize could produce damaging winds/hail.
During the latter half of the period, increasing low-level moisture
should advance into a corridor of strong low-level warm advection
(mostly north of I80). Latest guidance suggests elevated convection
should easily develop along/north of a warm front as it advances
across NE/IA toward the MN border ahead of the aforementioned
surface low late in the period. Hail is the primary risk with
elevated storms and while gusty winds may also accompany
near-surface-based storms across the warm sector.
Additionally, strong forcing ahead of the short wave should enhance
scattered convection across WY by mid afternoon. Forecast soundings
exhibit very steep lapse rates through 8km with strong southwesterly
flow through a deep layer. While PW values are quite low, vertical
mixing may contribute to wind gusts with this activity as it spreads
toward the Black Hills region.
The lack of significant moisture across the Plains is the main
limiting factor for potentially more widespread/organized severe.
For this reason will maintain MRGL Risk.
..Darrow/Squitieri.. 04/18/2023
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