Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1255 AM CDT Tue Jun 30 2026
Valid 301200Z - 011200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS NORTHERN
WISCONSIN AND THE UPPER PENINSULA OF MICHIGAN...PARTS OF NEW YORK
AND VERMONT...AND PORTIONS OF THE CENTRAL/SOUTHERN PLAINS......
...SUMMARY...
Severe thunderstorms will be possible from parts of the central High
Plains into the Upper Midwest, and across parts of the Northeast on
today.
...Synopsis...
An upper-level low will move into Saskatchewan/Manitoba today, with
west southwesterly flow aloft overspreading portions of northern
Minnesota into northern Wisconsin and the Upper Peninsula of
Michigan. A frontal boundary will extend from a surface low across
Manitoba southward across the Upper Midwest into the Central Plains,
with a dryline extending southward into the Southern Plains. Across
the Northeast, enhanced northwesterly flow aloft will impinge upon
the northeastern periphery of a high amplitude ridge across the
eastern US.
...Upper Midwest/Great Lakes...
A southwesterly low-level jet is set to increase across
central/northern Wisconsin by late afternoon. This in combination
with forcing for ascent from the upper-level trough should support
convection developing near the surface boundary across northern
Wisconsin into the Upper Peninsula of Michigan. To the south/east of
the boundary, a very moist air mass with 70s dewpoints is forecast.
Strong to extreme instability is forecast across this region amid
strong deep layer shear profiles, supporting initial supercells
capable of large hail, damaging wind, and perhaps a tornado. With
time, clustering may support potential for an increase in damaging
wind potential.
Guidance also suggests further development may occur by late evening
across portions of Nebraska into northern Iowa as the surface
boundary begins to shift northward with a short-wave impulse
rotating through the upper trough. This will pose some potential for
damaging wind and hail through the late evening/overnight period.
Forecast soundings suggests this activity may remain elevated,
leading to lower confidence in higher probabilities.
...Northeast...
A belt of 45 kt northwesterly flow aloft will overspread portions of
the Northeast this afternoon. Guidance suggests that thunderstorms
will develop across the region by the afternoon. Deep layer shear
around 35-40 kts and moderate instability thunderstorm development
is forecast across the region. This will support transient
supercells before one or more clusters/bowing segments develop and
spread south and eastward with damaging wind potential. A stronger
supercell or two may be capable of a tornado or two.
...Southern/Central High Plains...
A mid-level shortwave will eject across the central Plains this
afternoon, with widely scattered thunderstorm development expected
near the surface trough/dryline in the afternoon/evening. A
southerly low-level jet is progged to increase across the area
through the evening. Moderate to strong instability is progged amid
steep low to mid-level lapse rates. Initial high-based convection
will pose potential for large hail and damaging wind. With
clustering/consolidation along outflows, the damaging wind threat
will increase with potential for instances of significant winds
70-80 mph.
...Southeastern US...
Forecast guidance depicts 25-35 kt mid-level northeasterly flow on
the southern periphery of an upper high centered over the OH/TN
Valley. A very moist air mass will be present across much of the
region and strong destabilization is forecast amid strong daytime
heating. Forecast soundings depict around 20-30 kt effective shear
magnitudes, supporting some risk of organized cells/clusters.
Isolated damaging wind gusts are possible as activity develops
west/southwest through early evening.
..Thornton/Chalmers.. 06/30/2026
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