Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1130 AM CDT Sun Apr 27 2025
Valid 271630Z - 281200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR MUCH OF THE
GREAT PLAINS...
...SUMMARY...
Isolated to scattered severe thunderstorms are possible mainly this
evening into early morning Monday across parts of the Great Plains.
Large hail to very large hail, severe gusts, and a few tornadoes are
all possible.
...Synopsis...
Water-vapor imagery this morning shows a mid- to upper-level low
over NV. A belt of strong southwesterly mid to high-level flow will
extend from the base of the western U.S. trough through the
southern/central High Plains later today into tonight. A pair of
smaller-scale disturbances are forecast to eject east-northeastward
into the central High Plains and Black Hills vicinity during the
mid-late evening. Concurrently, an upper ridge over the eastern
half of the Great Plains states will shift eastward over the MS
Valley towards daybreak Monday.
Late morning surface analysis shows a developing low centered over
southeast WY with a lee trough/dryline extending southward through
the southern High Plains. The cyclone will deepen near the WY/NE/CO
border through early evening before developing northeast into
central SD late tonight.
...Southeast MT...Western Dakotas...
A sharpening lee trough is forecast by late this afternoon amidst
appreciable heating and moistening, especially across western SD.
Model guidance shows a narrow plume of 500-2000 J/kg MLCAPE (highest
over SD) developing by mid-late afternoon as large-scale ascent
begins to overspread the region. Isolated to widely scattered
thunderstorms are forecast to develop from the northern NE Panhandle
to the Black Hills, and north of the developing low over southeast
MT by late afternoon. The stronger storms will gradually move into
richer moisture with an accompanying risk for mainly large hail and
severe gusts. Gradual cooling during the evening will favor a
transition to elevated storms evolving with time as a LLJ
strengthens tonight. A severe risk will probably develop farther
east in association with WAA into parts of the eastern Dakotas and
MN late.
...Central/Southern High Plains...
Visible-satellite imagery indicates a very moist boundary layer with
a mix of a cumulus field across central and north TX and eastern
NM/CO and stratus from the TX Caprock northward through OK to NE.
The depth and quality of moisture sampled by the 12z Midland,
Amarillo, and Dodge City raobs is considered seasonably moisture
rich, and is located beneath an elevated mixed layer. Additional
moistening through advection and evaporation will contribute to 60s
dewpoints east of a dryline/lee trough by late afternoon. Strong
heating is forecast near the dryline from western NE southward
through West TX, which will result in a weakly capped but moderate
to very unstable airmass by 21z. Large-scale forcing for ascent
across the region will be nebulous, but low-level convergence along
the dryline amid little to no convective inhibition may result in
convective initiation.
With dryline convergence as the mechanism for convective initiation,
predictability is low. Dryline circulations will likely be
strongest across the TX Panhandle/West TX where temperatures west of
the dryline will be warmest, but low-level convergence will likely
maximize in the CO/NE/KS border intersection vicinity near a
developing surface low. As a result, these two areas may have a
greater risk for thunderstorms (isolated, widely spaced storm
coverage) late this afternoon into the evening.
The overall environment will be very supportive of supercells with
any storms that do form, with large to very large hail as the
primary risk initially. If any storms manage to develop and become
sustained, a strengthening low-level jet will support a tornado
threat during the evening with any storms that persist (or develop
along the retreating dryline). Nocturnal cooling and increased CINH
by mid to late evening will act to eventually weaken storm activity
in this region.
..Smith/Wendt.. 04/27/2025
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