SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0744 AM CDT Thu Jun 30 2022
Valid 301300Z - 011200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM PARTS OF IOWA
TO UPPER MICHIGAN...
...SUMMARY...
Severe thunderstorm gusts and isolated large hail are most likely
today from parts of Iowa to Upper Michigan.
...Synopsis...
In mid/upper levels, a nearly zonal northern-stream belt is forecast
from the Pacific Northwest to New England, with gradual cyclonic
bend and height falls forecast across the Great Lakes as a strong
low digs southeastward close to the MB/ON Hudson Bay coastline. To
its south, a shortwave trough was evident in moisture-channel
imagery across parts of southern MB/SK to extreme north-central MT.
This perturbation is expected to maintain positive tilt as it moves
eastward astride the international border, reaching the Thunder Bay
region, MN Arrowhead, and southeastern ND by 00Z. Thereafter, the
shortwave trough will weaken considerably and accelerate east-
northeastward to southwestern QC by 12Z tomorrow. Ahead of that, a
weaker, convectively reinforced perturbation now over northeastern
to southern MN will move quickly across Lake Superior and Upper MI
this morning before weakening.
The 11Z surface analysis showed a primary cold front from
northwestern MN southwestward over southwestern SD and south-central
WY, with a weaker/preceding one across eastern SD and central NE.
These boundaries should merge today, with a low developing this
afternoon over northwestern KS, along the combined fronts'
intersection with the dryline. By 00Z the front should extend from
there northeastward to near OMA, MSP and CMX. By 12Z, the front
should extend from northern Lower MI across southern WI, eastern/
southern IA, and central KS, to northeastern NM.
...IA to Upper MI...
Through early afternoon, areas of clouds and widely scattered to
scattered showers and thunderstorms will move across the area from
southern MN and WI to Upper MI. Instability will be modest with
this activity, which should be predominantly elevated in nature,
though marginal/pulse-severe hail may occur in the most vigorous
cells.
As the boundary layer destabilizes diurnally (and through theta-e
advection) behind the early clouds/precip, weakening MLCINH and
increasing moisture along/ahead of the front should support
additional rounds of thunderstorms offering damaging to severe gusts
and isolated large hail. This activity should be mostly surface-
based, with forecast soundings suggesting a narrow corridor of
around 1000-1500 J/kg MLCAPE across WI, increasing to 2000-3000 J/kg
over portions of southern MN and northern IA, where a combination of
evapotranspirative moisture flux and the strongest, most sustained
surface heating should be expected. Convective coverage is more
uncertain with southwestward extent over the MN/IA area in
particular, given greater proximity to EML-related capping.
However, somewhat conditional potential exists for supercells, with
the southern rim of the stronger cyclonic flow in mid/upper levels
offsetting weak/veered surface flow enough to yield 40-50-kt
effective-shear vectors. A significant-hail threat may develop, but
is too conditional on storm coverage/longevity to insert in the
outlook at this time.
...Central Plains...
With southwestward extent, weaker moisture will contribute to less
MLCAPE than over the Upper Midwest/Upper Mississippi Valley region.
However, strong diabatic heating and increasing lift are expected
along the front as the surface low deepens. Post-frontal upslope
lift is expected over elevated terrain (High Plains and adjoining
mountains/foothills). These factors should weaken MLCINH enough to
support isolated to widely scattered thunderstorms. Isolated severe
gusts are the main concern, given the presence of deep/well-mixed
subcloud layers, large dewpoint depressions and DCAPE, and just
enough moisture to support MLCAPE in the 200-800 J/kg range over the
High Plains, and 500-1500 J/kg farther east. Low/middle-level flow
will be modest, with small hodographs. However, favorable upper-
level winds will exist for ventilation aloft and potentially
organized multicells. Additional convection may form tonight in
clusters over parts of KS/NE/IA near the front, with isolated severe
potential where potentially damaging downdrafts can accelerate
enough through a relatively dry subcloud profile to penetrate the
diabatically cooling near-surface layer.
...Upper TX/western LA coastline...
A broad, weak cyclonic circulation over the northwestern Gulf may
become a tropical depression before moving inland along the
mid/upper TX coast later today. See latest NHC tropical outlooks
for forecast details on this system. In any event, the main hazard
will be locally heavy/flooding rain, as discussed in WPC
excessive-rainfall outlooks. Because of the expected weak overall
kinematic structure and modest boundary-layer winds, with curved but
small hodographs forecast near the coast northeast of center,
tornado potential currently appears too minimal and conditional for
an outlook. Still, weak supercells may be detected sporadically,
especially over the coastal/offshore waters.
..Edwards/Goss.. 06/30/2022
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