SPC Apr 27, 2025 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0745 AM CDT Sun Apr 27 2025

Valid 271300Z - 281200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR MUCH OF THE
GREAT PLAINS...

...SUMMARY...
Isolated to scattered severe thunderstorms are possible on Sunday
evening into early morning Monday across parts of the Great Plains.
Large hail, severe gusts, and a few tornadoes are all possible.

...Synopsis...
Early morning satellite imagery shows modest upper ridging between 
a pair of well-defined cyclones, one centered over NV and the other
centered over northern NY/VT. The NV cyclone forecast to shift
slightly eastward throughout the day as a shortwave trough, and
associated jet streak, rotate through its base. Moderate to strong
southwesterly flow associated with this shortwave will spread
northeastward from the Southwest into central Plains and Mid MO
Valley. 

Recent surface analysis reveals an expansive area of high pressure
centered over the Upper Great Lakes covering much of the eastern
CONUS. A broad area of low pressure exists over the intermountain
West, with several embedded lows. A tight surface pressure gradient
exists between these two features across the Plains, and the
resultant moderate low-level flow will contribute to northward
moisture advection throughout the period.

Any large-scale forcing for ascent associated with the shortwave
progressing around the NV cyclone will remain west of this better
low-level moisture (and associated buoyancy) until later tonight,
when it reaches the northern High Plains. Ample buoyancy and
moisture will exist across the central and southern High Plains, but
the lack of stronger large-scale forcing for ascent will result in a
more conditional severe thunderstorm potential.

...Southeast MT...Western Dakotas...
A deepening lee trough is forecast to result in surface cyclogenesis
in the far eastern MT/WY border vicinity by late this afternoon.
Strong boundary-layer mixing is anticipated across the region,
promoting airmass destabilization but also likely keeping dewpoints
in the 40s across much of the region. Convergence along several
boundaries across the region, including a surface trough extending
across southeast MT and the lee trough along the eastern WY border
vicinity, amid this destabilized airmass will result in thunderstorm
development, particularly during the late afternoon/early evening as
increasing large-scale ascent complements the low-level convergence.

An eastward storm motion should take any storms that develop in
better low-level moisture over time, with a strengthening low-level
jet helping to maintain favorably moist low-level inflow. Even with
this modest improvement in thermodynamics, nocturnal stabilization 
should result in storms becoming more elevated over time. Primary
threat across this region are large hail and damaging gusts. 

...Central/Southern High Plains...
Mid 60s dewpoints are already in place across the Permian Basin and
the general expectation is for low-level moisture to increase
throughout the day. 60s dewpoints will likely be in place across all
but far western KS by 21Z and into much of central NE by 00Z. Strong
heating is anticipated across this region as well, resulting in an
area of moderate to strong buoyancy from southwest NE into west TX
by the late afternoon. 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 and convection-allowing guidance has limited
utility. Dryline circulations will likely be strongest across the TX
Panhandle/West TX where temperatures west of the dryline will be
warmest, but low-level coverage 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
today. 

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. Strong downdrafts are possible as well. A
westward shift of the dryline and strengthening low-level jet will
support an increase tornado threat during the evening with any
storms that persist (or develop along the retreating dryline). The
kinematic environment improves notably across the TX Panhandle,
western KS, and western NE between 00Z and 06Z, so any storms that
are ongoing may be able to organize considerably before eventually
weakening due to nocturnal stabilization.

..Mosier/Broyles.. 04/27/2025

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