SPC May 15, 2025 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1128 AM CDT Thu May 15 2025

Valid 151630Z - 161200Z

...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS
EAST-CENTRAL MINNESOTA...MUCH OF WISCONSIN...SOUTHERN AND WESTERN
LOWER MICHIGAN...NORTHEAST ILLINOIS...NORTHERN INDIANA AND NORTHWEST
OHIO...

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PORTIONS OF
VIRGINIA AND NORTHEAST NORTH CAROLINA...

...SUMMARY...
Severe thunderstorms are expected across parts of the upper
Mississippi River Valley and Great Lakes this afternoon and evening.
Tornadoes, some of which could be strong, and very large hail and
damaging winds will be possible. Severe thunderstorms are also
expected through the lower Ohio River Valley, Ozarks and in parts of
the Mid-Atlantic.

...Mid to Upper Mississippi Valley/Great Lakes/Ohio Valley...
Recent satellite imagery shows an upper low over SD, with a
negatively tilted shortwave trough moving into the Mid MO Valley.
Surface analysis places an occluded surface low associated with this
system over southeast ND, with an occluded front extending
southeastward to a triple point over far southeast SD. A cold front
extends south-southeastward from this front across far western IA
and into far northeast MO before arcing more southwestward across
far western MO and more southwestward across western OK. A warm
front extends easterward from this triple point across southern MN
and then more southeastward across southwest WI and northern IL.
These boundaries, including the occluded front, will all act in
tandem with increasing large-scale forcing for ascent to force
thunderstorm development this afternoon and evening.

The ongoing storms from eastern SD into central MN are confirmation
of the buoyancy sampled in the 12Z MPX sounding. Expectation is for
instability to build across the region as heating and low-level
moisture advection occur amid steep mid-level lapse rates. Airmass
destabilization and thunderstorm development is anticipated first
from the eastern Dakotas into MN, the occluded front as it shifts
northward as both the primary surface low and triple point low shift
northwestward. Additional development is then anticipated farther
southeast along the warm front across WI. Storms that develop in the
vicinity of the occluded front will likely have elevated structures,
with large hail as the primary risk. Some isolated very large hail
(i.e. greater than 2" in diameter) is possible. Farther southeast,
the corridor along the warm front appears very favorable for
supercells capable of all severe hazards, including very large hail,
strong wind gusts, and tornadoes. A locally higher tornado potential
may exist from  central into southeastern WI from 18Z-22Z. Deeper
mixing is anticipated farther south into northern IL, but the
overall environment will still support robust, organized updrafts.
There may be some trend initially for these storms to quickly become
outflow dominant, but strengthening mid-level flow across the region
after 21Z should aid in maintaining a more organized mode. Upscale
growth into a organized MCS appears probable after 00Z, with the
potential for significant-severe gusts as this line moves eastward
in southern Lower MI. The threat for damaging gusts and isolated
hail will persist throughout the night across Lower MI and the
middle/upper OH Valley.

...Ozarks into the TN Valley...
Additional thunderstorm development is anticipated this afternoon
across AR as a cold front pushes eastward across the region.
Moderate to strong flow aloft should allow for storms to move off
this boundary quickly into a strongly buoyant airmass downstream.
Warm air aloft could limit overall storm longevity during the
afternoon/early evening, but the warm/dry mid-levels are conducive
for producing strong outflows capable of damaging gusts. Whether or
not organization will occur along these outflows is uncertain, but a
conditional risk for continued damaging gusts exists into TN. 

Additional thunderstorms are possible during the evening and
overnight in the wake of the front. Persistent steep mid-level lapse
rates and strong shear will support large hail with some of these
storms.

...Central Appalachians/Mid-Atlantic...  
Large-scale height rises are expected across the region, but
diurnal heating and orographic effects will aid in thunderstorm
development across the higher terrain this afternoon. Northwesterly
flow aloft will favor a southeastward storm motion within an
environment of moderate/locally strong instability. 35-45 kts of
northwesterly deep shear is anticipated, supporting supercell
structures and clusters, posing a risk for large hail and damaging
winds. The overall hodograph structure and resulting storm motion
appears favorable for some very large hail over 2" in diameter as
well.

..Mosier.. 05/15/2025

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