SPC Jun 23, 2025 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook

Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1122 AM CDT Mon Jun 23 2025

Valid 231630Z - 241200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS AFTERNOON
THROUGH LATE EVENING FROM THE CENTRAL PLAINS TO THE UPPER GREAT
LAKES...

...SUMMARY...
Storms with occasional damaging outflow gusts and marginally severe
hail will be possible today from the southern and central Plains
northeastward into the Great Lakes.

...Upper Great Lakes to the Plains this afternoon/evening...
A surface cold front will make slow southeastward progress from WI
to IA and KS, in the wake of a primary shortwave trough moving over
western ON.  Surface heating is ongoing ahead of the front, where
boundary-layer dewpoints range from the upper 60s to lower 70s
beneath midlevel lapse rates of 7-8 C/km, which will drive MLCAPE of
2000-3000 J/kg.  Convective inhibition will likewise weaken by
early-mid afternoon, when thunderstorm development is likely along
the front and differential heating zone in the SLGT risk corridor. 
Deep-layer flow will be a little stronger toward WI in closer
proximity to the main belt of westerlies, where a mix clusters/line
segments and transient supercell structures will be possible.  The
primary severe threat will be damaging outflow winds (60-70 mph)
from roughly 20z-03z, though isolated large hail of 1-1.5 inches in
diameter may also occur with the strongest storms.

More loosely organized storm clusters are expected this afternoon
through this evening into the southern High Plains, where
thermodynamic profiles will favor isolated severe downbursts.
 
...Northern Maine later this evening...
Around the northern periphery of a closed midlevel high over the
Appalachians, a series of embedded speed maxima will move over ON/QC
through tonight.  Boundary-layer dewpoints in the 60s beneath
midlevel lapse rates near 7 C/km, in combination with daytime
heating, will boost MLCAPE to 1500-2000 J/kg with minimal convective
inhibition by late afternoon.  Thunderstorm development is expected
upstream across QC in association with an embedded speed max/surface
wave, and this convection will approach northern ME by late
evening/early tonight.  Though buoyancy will slowly weaken with the
loss of daytime heating, low-level hodograph curvature and
deep-layer westerly shear should be sufficient for an organized
storm cluster to reach ME before weakening overnight.  Isolated
damaging winds will be the main threat with these storms.

..Thompson/Squitieri.. 06/23/2025

Read more