SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0256 PM CDT Sat Aug 27 2022
Valid 272000Z - 281200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
IOWA...SOUTHEASTERN MINNESOTA...AND FAR WESTERN WISCONSIN...
...SUMMARY...
Severe thunderstorm potential appears most concentrated today over
parts of Iowa, southeastern Minnesota, and far western Wisconsin.
...20Z Update...
The only substantial change to the outlook with this update was to
trim the northeastern extent of the Slight Risk across western WI.
Cloud cover has remained entrenched most of this area through the
day, which has limited destabilization and reduced severe chances
through this evening. Otherwise, convection is still expected to
gradually increase in coverage and intensity across parts of IA into
southern MN this afternoon and evening. Reference Mesoscale
Discussion 1728 for more information on the short-term severe threat
across these areas.
..Gleason.. 08/27/2022
.PREV DISCUSSION... /ISSUED 1126 AM CDT Sat Aug 27 2022/
...IA/MN/WI this afternoon/evening...
A midlevel shortwave trough over the central NE/KS border will
continue moving northeastward to western IA by this evening and the
upper MS Valley overnight. Clouds and ongoing convection within a
deep moisture plume over the central Plains will likewise spread
northeastward through the day. Surface heating to the east of the
thicker cloud band and relatively steep low-midlevel lapse rates
will contribute to MLCAPE of 1500-2500 J/kg, and the likelihood of
additional thunderstorm development this afternoon in the zone of
differential heating from IA into southern MN (along and south of a
warm front). Vertical shear profiles are forecast to be a bit
disjointed with substantially backed/weaker flow in the mid levels
across IA this afternoon. Low-level shear/clockwise hodograph
curvature will be larger this afternoon/evening closer to the warm
front across southeast MN/western WI, with a similar weakness in the
midlevel flow. Thus, the environment favors a mixed/messy storm
mode with clusters and some transient rotating updrafts, with a
primary threat for damaging winds and isolated large hail given the
moderately large buoyancy/precipitation loading and sufficiently
steep low-midlevel lapse rates (DCAPE near 1000 J/kg).
...TX Panhandle into KS this afternoon/evening...
Along the southern fringe of the residual monsoonal moisture plume
and the ejecting midlevel trough over northern KS, differential
heating and weak convergence along a lee trough will support
scattered thunderstorm development later this afternoon. Midlevel
lapse rates will not be steep, but surface heating/mixing will
steepen low-level lapse rates, and westerly flow aloft will
contribute to modest effective bulk shear of 25-30 kt. Somewhat
organized cells/clusters will be capable of producing isolated
strong-severe outflow gusts and marginally severe hail from mid
afternoon into this evening.
...Southern MT and vicinity this afternoon/evening...
Within the primary jet, an embedded speed max/shortwave trough over
southern BC and WA will progress eastward to MT later this afternoon
into tonight. An associated cold front will move into central MT by
this evening, with strong surface heating and deep mixing in advance
of the front. Some high-based convection is expected to form over
the higher terrain of southern MT later this afternoon, and storms
will spread eastward into this evening. Though low-level moisture
and buoyancy will be limited, deep inverted-v profiles will support
isolated strong-severe outflow gusts.
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