ACUS02 KWNS 271749
SWODY2
SPC AC 271748
Day 2 Convective Outlook CORR 1
NWS Storm Prediction Center Norman OK
1248 PM CDT Fri Jun 27 2025
Valid 281200Z - 291200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS SATURDAY INTO
SATURDAY NIGHT ACROSS CENTRAL AND SOUTHERN MINNESOTA...WEST CENTRAL WISCONSIN...MUCH OF SOUTH DAKOTA AND ADJACENT PORTIONS OF NORTHERN
NEBRASKA...
CORRECTED FOR NDFD THUNDER GRID
...SUMMARY...
Scattered strong to severe thunderstorms, perhaps including one or
two organizing clusters, will pose a risk for severe hail, wind and
perhaps a couple of tornadoes across parts of the middle Missouri
Valley into Upper Midwest Saturday afternoon into Saturday night.
...Discussion...
Models indicate that the stronger westerlies will remain confined to
the northern mid-latitudes. There may be some amplification in the
flow across the northeastern Pacific into British Columbia and the
Pacific Northwest by the end of the period. However, a zonal regime
is likely to generally persist near the Canadian/U.S. border, along
the northern periphery of modest mid-level ridging encompassing the
subtropics through much of the southern mid-latitudes of the U.S.
One embedded short wave trough is still forecast to progress east of
the lower Great Lakes vicinity, through the St. Lawrence Valley and
northern New England, Saturday through Saturday night. Models
indicate that this will be accompanied by an initially modest, but
weakening, surface cyclone, with a trailing intrusion of cooler,
drier boundary-layer air spreading southeast of the lower Great
Lakes region toward northern Mid Atlantic coastal areas, while
relatively cool/dry air associated with a prior intrusion is slow to
lose influence across northern New England.
Upstream, low-amplitude larger-scale mid-level troughing is forecast
to progress eastward along the central Canadian/U.S. border
vicinity, with at least a couple of embedded shorter-wavelength
perturbations. One notable convectively generated or augmented
perturbation may be overspreading portions of north central
Minnesota into northern Wisconsin at the outset of the period, near
the southern leading edge of this regime. The convectively
reinforced trailing flank of the Great Lakes cold front may be slow
to modify/retreat eastward across the Upper Midwest, as another
upstream cold front advances south of the international border.
...Upper Midwest into northern Great Plains...
There appears a better consensus within model output that a
low-level baroclinic zone, generated or reinforced by convective
outflow, may be initially stalled across the west central through
southeastern Minnesota vicinity, in the wake of a dissipating
cluster of storms. Thereafter, it may slowly retreat
northeastward/eastward through the day, while also becoming a focus
for strengthening differential heating.
There remains at least some spread among the latest model output
concerning the warmth of temperatures around 700 mb, near the northern/northeastern periphery of a plume of elevated mixed-layer
air, which may continue to increase mid-level inhibition across
South Dakota through southern Minnesota, before gradually becoming
suppressed southward by late Saturday night. However, a belt of
convectively augmented (30-50 Kt) southwesterly to westerly flow in
the 850-500 mb layer is forecast to slowly overspread the low-level
baroclinic zone through and beyond peak diurnal destabilization.
Supported by surface dew points around or above 70 F, moderate to
large mixed-layer CAPE appears likely to develop, coincident with a
corridor of strong shear, including sizable clockwise curved
low-level hodographs along the boundary. If forcing for ascent and
heating, beneath broadly difluent mid/upper flow overspreading the
Upper Midwest, is able to overcome inhibition, supercells posing a
risk for severe hail and a couple of tornadoes appear possible
across parts of central Minnesota, before perhaps growing upscale
into an organizing cluster while propagating into west central
Wisconsin by late Saturday evening.
Upstream, potential convective developments remain more unclear.
However, there appears a general signal within the model output that convection, emerging from the more deeply mixed environment across
the high plains, could intensify while acquiring more moist and
potentially unstable updraft inflow, along/north of a remnant
outflow boundary or front across southern South Dakota or far
northern Nebraska Saturday evening. Generally becoming focused
along the periphery of the increasingly suppressed, more strongly
capping elevated mixed-layer air, thermodynamic profiles
characterized by steep lapse rates and large CAPE may become
supportive of an organizing convective system, aided by forcing for
ascent associated with warm advection.
...Northern Mid Atlantic into Champlain Valley vicinity...
There remain mixed signals within the model output, including
convection allowing guidance, concerning the extent of the
convective potential within deepening pre-frontal surface troughing
across the region by Saturday afternoon. The more substantive
destabilization may remain focused across the northern Mid Atlantic,
to the south of the better deep-layer shear. However, it still
appears that the environment will probably become conducive to at
least widely scattered vigorous storms accompanied by a risk for
potentially damaging wind gusts.
..Kerr.. 06/27/2025
$$
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