687
ACUS01 KWNS 031930
SWODY1
SPC AC 031929

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0229 PM CDT Thu Jul 03 2025

Valid 032000Z - 041200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR NORTH DAKOTA
AND MUCH OF THE NORTHEAST...

...SUMMARY...
Scattered severe thunderstorms capable of producing severe/damaging
winds and large hail are forecast across parts of the Northeast and
northern Plains today.

...20z Updates...
Minor adjustments were made to the 20z outlook to remove
probabilities behind convection in western New York. The Marginal
Risk was expanded westward to include portions of northwestern New
York where severe storms are crossing the international border from
Quebec. See MCD1549 for more information.

Otherwise, the outlook remains on track with no changes needed at
this time. See previous discussion below for more information.

..Thornton.. 07/03/2025

.PREV DISCUSSION... /ISSUED 1120 AM CDT Thu Jul 03 2025/

...Northeast...
Recent satellite imagery shows a well-defined cyclone over northern
QC and a shortwave trough embedded within the southern periphery of
this cyclone progressing through the Lower Great Lakes. An attendant
cold front is in place just ahead of this shortwave. Expectation is
for this shortwave to continue quickly eastward into the Northeast,
with the cold front progressing eastward/southeastward as well. The
leading edge of the stronger large-scale forcing for ascent has
already reached ME and NH, contributing to thunderstorm development
where the preceding airmass has already destabilized. Continued
destabilization is anticipated, likely resulting in a nearly
continuous line  of storms. In addition to moderate buoyancy,
moderate vertical shear is in place as well. This combination of
buoyancy and shear is expected to result in organized storms capable
of large hail (more probable during the early-stage cellular mode)
and damaging gusts (more probable later with later-stage linear
modes).

This ongoing development is well ahead of the primary cold front, so
the potential exists for additional development across NY this
afternoon, continuing into southern New England during the late
afternoon and evening. Environmental conditions will be similar to
those farther north and east, with large hail and damaging gusts
possible with these storms as well.

...Northern Plains...
Low-level moisture will continue to advect northwestward into the
region today, helping to offset some of the anticipated mixing and
keeping dewpoints in the upper 60s/70s later this afternoon/evening.
This favorable low-level moisture beneath steep mid-level lapse
rates will promote a very unstable airmass, with MLCAPE from 2000 to
3000 J/kg across ND this evening. Subtle ascent attendant to a
modest vorticity maximum rounding the northwestern periphery of the
central CONUS upper ridging will begin interacting with the
westernmost edge of this moist and unstable airmass around 21Z-00Z.
Initial cellular development is anticipated across northeast WY and
far southeast MT, before expanding northeastward into more of ND
over time.

A risk for very large hail and perhaps a tornado would accompany
initial supercells before storm outflow and mergers lead to upscale
growth into an eastward-moving cluster during the evening. Once this
upscale growth occurs, a quick northeastward progression is
anticipated across ND with some severe wind gusts possible. An
instance or two of gusts around 75 mph are possible.

...Southeastern ND/Northeast SD into the Upper Midwest...
Recent regional radar imagery shows an MCV tracking
east-northeastward over south-central ND. The airmass downstream
from southeast ND/northeast SD into southern MN and northern IA is
destabilizing amid strong heating and ample low-level moisture. As a
result, there is a low-probability chance for thunderstorm
redevelopment/reintensification early this afternoon in the vicinity
of the MCV. If this occurs, isolated damaging gusts are possible.

A more probable scenario is for this MCV to continue rounding the
ridge and provide the impetus for thunderstorm development farther
east across the Upper Midwest later this evening. Weak warm-air
advection could augment ascent across the region as well. Moderate
to strong buoyancy and moderate deep-layer vertical shear will be in
place, supporting strong updrafts capable of large hail,
particularly with initial development. Storms should continue
throughout much of the night, with an isolated hail risk.

$$