SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0750 AM CDT Sun May 29 2022
Valid 291300Z - 301200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM CENTRAL
NEBRASKA TO CENTRAL MINNESOTA...
...SUMMARY...
Severe thunderstorm gusts of 60 to 85 mph, hail over 2 inches in
diameter, and a few tornadoes are possible this afternoon and
tonight from parts of Nebraska northeastward into southwestern and
central Minnesota.
...Synopsis...
The dominant mid/upper-level feature for this forecast period will
be a substantial, currently negatively tilted synoptic trough --
apparent in moisture-channel imagery from the BC coastal vicinity
southeastward over the inland Pacific Northwest, Great Basin and AZ.
A vorticity lobe now located over southeastern OR is forecast to
evolve into a closed 500-mb cyclone over southern ID in the next few
hours, then move slowly southeastward toward southwestern WY through
the remainder of the period. Several weak perturbations/vorticity
maxima will eject northeastward across the central/southern Rockies
and central/northern Plains today in the associated cyclonic flow,
which will become strongly difluent across the northern Plains
overnight.
At the surface, 11Z analysis showed a primary/occluded cyclone
centered over west-central ND, occluded front to southeastern ND,
warm front from there to western/southern WI, and slow-moving cold
to quasistationary front across eastern SD, northeastern through
south-central NE, northwestern KS, to a low in CO between LHX-LIC.
By 00Z, the northern low should move slowly eastward to
northeastward to northeastern ND, with front arching over the
eastern Dakotas to northeastern and south-central NE, then to
another low over northeastern CO.
This evening, the central High Plains low will shift/redevelop over
northwestern KS and move into south-central/central NE. By 12Z, the
main surface low should be over central or south-central NE, with
cold front extending southwestward across western KS and
southeastern CO, and moving southeastward again. A dryline --
initially drawn across western KS, the TX Panhandle, to the Big Bend
area of TX, should move eastward into western OK and west-central TX
this afternoon before retreating northwestward tonight. Capping and
lack of stronger lift should suppress substantial convective
potential on the dryline.
...Central Plains to parts of SD/MN...
Three primary convective episodes across this region cumulatively
will offer the great majority of severe-thunderstorm threats through
the period, and are covered chronologically below.
1. An ongoing, broken band of thunderstorms over central/southern
MN, with potential for damaging gusts and hail the next few hours.
See SPC severe-thunderstorm watch 286 and related/nearby mesoscale
discussions for near-term coverage of the wind/hail threat from this
activity.
2. Widely scattered to scattered thunderstorms should develop as
soon as midday to midafternoon over the higher terrain of
northwest/north-central CO and southern WY, as the strongest
large-scale ascent ahead of the deepening cyclone spreads over at
least marginal low/midlevel moisture and steep lapse rates in the
region. Isolated strong-severe gusts and hail will be possible with
this "early" activity as it continues to spread/build east-
northeastward onto the adjoining High Plains of northeastern
CO/eastern WY, western NE and perhaps southwestern SD. Upon leaving
the mountains, this regime will encounter a favorable environment of
upslope flow with a substantial headlong component relative to storm
motion, with the resultant strong storm-relative low-level winds
enabling optimized lift. These factors should help to sustain this
activity toward the Sandhills and Badlands into evening. The
southeastern part of this regime over NE and perhaps south-central
SD will be in the most-favorable low-level moisture and instability
north of the boundary, should last longer than farther north/
northwest, and may merge with the next process in NE.
3. Scattered thunderstorms should develop near the boundary late
this afternoon and this evening over central/northeastern NE, with
early-stage supercell mode possible. Convection should evolve
upscale to a clustered, bowing, probably cold-pool-driven complex
with time into parts of northwestern IA, southeastern SD and
southern/central MN, moving astride the instability/buoyancy
gradient related to the baroclinic zone. Damaging gusts, large to
very large hail, and a tornado or two may occur with any supercells,
especially along the boundary where low-level moisture, SRH,
hodograph size, and vorticity will be maximized. In the adjoining
warm sector, steep low/middle-level lapse rates, strong diurnal
mixing, and related favorable DCAPE will support wind potential.
2500-4000 J/kg peak/preconvective MLCAPE is expected near the front,
supported by surface dew points in the 60s. By 00-06Z, this
corridor also will be near the axis of the strongest 500-250-mb
layer flow, contributing to effective-shear magnitudes commonly in
the 50-70-kt range. Descending rear-inflow jet(s) also may
transport momentum downward from the strong flow aloft, augmenting
the cold pools and wind potential, until activity encounters
more-stable boundary-layer air late tonight across the upper
Mississippi Valley.
..Edwards/Mosier.. 05/29/2022
Read more