SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0749 AM CDT Tue Jun 28 2022
Valid 281300Z - 291200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER CENTRAL
MONTANA...AND PARTS OF WISCONSIN AND UPPER MICHIGAN...
...SUMMARY...
Widely scattered severe thunderstorms are possible over parts of the
upper Midwest and Montana this afternoon and evening.
...Synopsis...
The mid/upper-level pattern will feature a large, complex cyclone
over central/eastern Arctic Canada and Hudson Bay. In the southwest
fringes of the related flow, a shortwave trough is evident in
moisture-channel imagery over southern portions of SK/MB. This
feature should move southeastward across northern/central MN to Lake
Superior and parts of WI by 00Z, then pivot eastward over parts of
ON tonight. Meanwhile, a synoptic ridge now over the northern
Rockies and Great Basin will shift eastward ahead of a progressive
cyclone currently situated offshore from the Pacific Northwest. The
associated 500-mb low should reach southwestern mainland BC by 00Z,
then pivot eastward to the Canadian Rockies near Banff by 12Z.
At the surface, a wavy cold front related partly to the SK/MB
shortwave trough was analyzed at 11Z this morning from far northern
ON through a low near Thunder Bay, then across northern MN, eastern
SD, and the NE Panhandle. By 00Z, the front should reach
northeastern ON, eastern Upper MI, north-central WI, western IA,
south-central NE, northeastern WY, and central/south-central MT. By
12Z tomorrow, the front should extend from southwestern QC across
Lake Huron, Lower MI, southern WI, becoming a warm front over
northeastern NE, western SD, and eastern MT as height falls ahead of
the northwestern mid/upper cyclone cross the northern Rockies. A
low-level cold front related to the latter perturbation should cross
the northern Rockies today, reaching east-central MT and
southeastern ID by 12Z.
...WI and vicinity...
An area of clouds and precip -- with widely scattered to isolated
embedded/non-severe thunderstorms -- is apparent in satellite and
radar-reflectivity imagery this morning across parts of the upper
Mississippi Valley region. This activity is expected to proceed
eastward to east-southeastward across the region, following an
eastward-shifting LLJ with veering orientation. This will delay but
not prohibitively limit destabilization supporting later,
surface-based convective/severe potential.
Scattered thunderstorms are expected to develop this afternoon
along/ahead of the front, including a southward-directed/lake-
reinforced boundary south of Lake Superior. Given the lack of
substantial EML and the DCVA/large-scale lift ahead of the shortwave
trough, only weak MLCINH is expected, as reasonably evident in
forecast soundings over the area. The boundary layer is expected to
destabilize favorably from a combination of diurnal heating (in a
narrow corridor behind the earlier clouds/convection) and low-level
warm advection supported by moist southwesterly flow. Moisture
yielding mid-50s to near 60 F surface dew points will contribute to
peak MLCAPE values around 500-1000 J/kg (locally/briefly greater).
Veered and modest near-surface winds will limit hodograph size and
SRH. Still, strong mid/upper winds should contribute to effective-
shear magnitudes of 35-40 kt, supporting a blend of organized
multicell and episodic supercell characteristics. Strong-severe
gusts and large hail are possible, with tornado potential more
isolated, conditional on low-predictability storm-scale effects and
boundary interactions. Overall convective coverage/intensity should
diminish during mid/late evening.
...MT...
Widely scattered thunderstorms are expected to develop this
afternoon near and ahead of the cold front, with severe gusts
becoming the main concern. Activity should develop in a field of
overlaid DCVA/cooling aloft, low-level warm advection along/
southeast of the warm front, and diabatic heating to yield a very
deep/well-mixed boundary layer. Though buoyancy mostly will be low
(MLCAPE generally under 500 J/kg, but locally approaching 1000 J/kg
in northern parts), strengthening flow aloft and large DCAPE related
to the well-mixed subcloud layer will promote downdraft acceleration
and downward momentum transfer. Increasing flow aloft also will
strengthen deep shear, particularly over northern/western portions
of the area farther from the mid/upper-level ridge. Effective-shear
magnitudes of 40-45 kt are possible over parts of west-central/
northwestern MT near the front.
..Edwards/Goss.. 06/28/2022
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