SPC Apr 18, 2025 1300 UTC Day 1 Convective Outlook

SPC 1300Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0700 AM CDT Fri Apr 18 2025

Valid 181300Z - 191200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF THE
SOUTHERN PLAINS INTO THE MID MISSISSIPPI VALLEY AND UPPER GREAT
LAKES...

...SUMMARY...
Scattered severe thunderstorms are possible from parts of the
southern Plains northeastward toward the upper Great Lakes, mainly
from late afternoon into early Saturday morning. Large to very large
hail and severe wind gusts should be the main hazards, especially
across the southern Plains where storms will be more concentrated. A
few tornadoes also appear possible.

...Upper Great Lakes to Mid Mississippi Valley...
Ongoing, mostly elevated thunderstorms aided by persistent low-level
warm/moist advection and steep mid-level lapse rates should continue
to pose a large hail and damaging wind threat as they spread quickly
eastward across southern WI this morning. This activity should
eventually weaken later this morning as it continues moving across
Lower MI into a less unstable environment. Behind this initial
activity, the surface warm sector will attempt to spread northward
across parts of the Upper Midwest and Great Lakes today, as longwave
troughing gradually develops eastward over the northern/central
Plains and Southwest. Given the positive tilt/orientation of this
upper troughing and enhanced southwesterly flow aloft expected to
persist through the period, a strong cold front should make only
slow southeastward progress.

A cap will likely inhibit surface-based convective development until
peak afternoon heating and frontal forcing can help lift parcels to
their LFC. Given nebulous forcing aloft, there is still a fair
amount of uncertainty regarding overall convective coverage this
afternoon/evening. Even so, any thunderstorms that can develop along
or ahead of the front could pose a threat for severe hail and
damaging winds, with strong deep-layer shear aiding updraft
organization. This severe threat may persist for much of the
evening, and perhaps continuing into the early overnight hours.

...Southern Plains to the Ozarks...
The southern portion of the cold front is forecast to decelerate and
eventually stall over parts of OK later today. A dryline will extend
southward from a weak frontal low across northwest to west-central
TX by late afternoon. Even with widespread mid/high-level cloudiness
present, robust daytime heating of the moist warm sector is
anticipated across the southern Plains today. The low-level cap
should eventually be breached by late afternoon/early evening
(around 22-00Z), particularly along/near the cold front, and perhaps
the front/dryline intersection as well. Strong southwesterly flow
aloft and related deep-layer shear will likely support organized
severe convection.

Initial supercell development should pose a threat for large to very
large hail, potentially up to 2-3 inches in diameter. With time,
upscale growth into multiple clusters/short line segments is
expected through the evening into early Saturday morning, as a
south-southwesterly low-level jet gradually strengthens. An increase
in the severe/damaging wind threat is anticipated as this mode
transition occurs. The threat for a few tornadoes remains apparent,
especially across parts of OK along/south of the front, as favorable
low-level shear will be present this evening where supercells may
still exist. Even with a higher concentration of thunderstorms
expected across the southern Plains, the messy convective mode this
evening and tendency for convection to be undercut by the cold front
currently limit confidence in delineating a corridor of greater
severe hail/wind potential.

..Gleason/Broyles.. 04/18/2025

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