ACUS01 KWNS 071927
SWODY1
SPC AC 071925
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0225 PM CDT Fri Aug 07 2026
Valid 072000Z - 081200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS MUCH OF IOWA...NORTHERN WISCONSIN INTO THE UPPER PENINSULA OF MICHIGAN...AND
THE MID-ATLANTIC...
...SUMMARY...
Isolated to scattered severe thunderstorms are possible across parts
of the Upper Midwest/Great Lakes this afternoon and evening, with
large to very large hail and severe winds the main threats.
Thunderstorms capable of scattered damaging winds may also occur
over portions of the Mid-Atlantic.
...20z Update...
Adjustments were made to the D1 Convective Outlook to trim
probabilities behind the cold front across Minnesota/Iowa and behind morning/early afternoon convection across Kansas/Oklahoma. The
Marginal Risk was shifted southward across Oklahoma/Arkansas to
account for recent trends in storm/outflow evolution and resulting
increasing potential for damaging wind downstream.
A Marginal Risk was added across portions of southwestern New Mexico
into far western Texas. Across this region, a very deeply mixed and
hot boundary layer will support outflow dominant storms. Hi-res
guidance suggests that storms may produce strong to severe outflow
winds across this region later this afternoon.
See previous discussion below for more information.
..Thornton.. 08/07/2026
.PREV DISCUSSION... /ISSUED 1106 AM CDT Fri Aug 07 2026/
...Upper Midwest/Great Lakes...
Thunderstorms are ongoing along/ahead of a cold front late this
morning from the MN Arrowhead southwestward into southern
MN/northern IA. While there are still uncertainties regarding
convective evolution this afternoon and evening, it appears
increasingly probable that two mesoscale corridors of greater severe
potential will exist: one across southern MN into IA, and another
across northern WI into the U.P of MI. In general, the severe risk
today will be aided by a mid/upper-level trough advancing
east-southeastward across these regions in tandem with a 35-50 kt west-northwesterly mid-level jet.
Thunderstorms are expected to further increase in coverage and
intensity along the eastward-advancing cold front this afternoon
across parts of northern WI into the western U.P of MI. While latest
NAM/RAP forecast soundings across this area suggest low-level
moisture remains fairly shallow/limited, mostly clear conditions are
noted on recent visible satellite imagery. Resultant moderate
instability and gradually strengthening deep-layer shear with the
approach of the mid/upper-level trough will aid in thunderstorm
organization. Small clusters/bowing line segments will probably be
the dominant mode given the linear forcing of the cold front, with
enhanced low/mid-level flow aiding the risk for scattered
severe/damaging winds. A Slight Risk has been added for parts of
northern WI into the U.P of MI given increased confidence in this
scenario occurring.
Farther south, generally elevated convection is ongoing across
southern MN into northern IA. The 12Z observed sounding from MPX
showed fairly steep low/mid-level lapse rates in the 850-530 mb
layer, which along with 35-40 kt of effective bulk shear and around
2000 J/kg of MUCAPE may continue to support a threat for severe hail
with this activity in the short term. Even though cloud cover
remains prevalent across these areas late this morning, a corridor
of moderate to locally strong instability is still forecast to
develop this afternoon across parts of eastern NE into IA ahead of
the cold front. Current expectations are for multiple surface-based
supercells and/or bowing clusters to develop along/ahead of the
front in southern MN, and then spread southeastward across IA
through the late afternoon/early evening. A threat for both large
hail and damaging winds should exist with this activity, and a
Slight Risk has been introduced where confidence is greater that
robust convection will occur. 2+ inch diameter hail and perhaps a
tornado also appear possible with any surface-based supercell, even
though low-level flow will not be overly strong.
...Ohio Valley into the Mid-Atlantic...
Between upper troughing over central Canada/the Upper Midwest and
upper ridging over the western Atlantic, around 20-30 kt of
southwesterly mid-level flow will exist today from the OH Valley
into the Mid-Atlantic and Northeast. Greater destabilization and
steepening of low-level lapse rates are anticipated this afternoon
across the Mid-Atlantic, where recent visible satellite imagery
shows generally clear skies. Loosely organized cells/clusters that
initially develop across the higher terrain of the central
Appalachians should spread into the Mid-Atlantic coastal plain
through the afternoon/evening, while posing a threat for scattered
damaging winds up to 50-60 mph and perhaps marginally severe hail.
Across the OH Valley, somewhat weaker mid-level flow may tend to
limit updraft organization. Still, some potential for clustering and
isolated damaging winds may exist downstream of ongoing convection
where greater destabilization can ocur. Have therefore expanded the
Marginal Risk across much of the OH Valley to account for this
possibility.
...Southern/Central Plains into the Ozarks...
Elevated thunderstorms posing an isolated hail threat in southeast
KS late this morning should further diminish into the early
afternoon as a southwesterly low-level jet gradually weakens. To the
south and east of this activity, a hot and unstable airmass will
exist this afternoon across OK into parts of southern MO and AR.
Although details regarding convective evolution remain unclear, it
is possible that robust thunderstorms develop/continue on the
outflow from this morning's activity, or near multiple MCVs present
from earlier convection. Isolated strong to severe winds appear
possible, even though deep-layer shear should remain weak. The
Marginal Risk has been expanded eastward and connected to the risk
area in the OH Valley. Other isolated thunderstorms posing some
severe wind threat may develop this afternoon farther west across
eastern NM into the OK/TX Panhandles.
...Arizona...
Modest east-southeasterly mid-level flow will persist today over AZ
to the south of a mid/upper-level anticyclone centered over the Four
Corners. Widely scattered convection should develop over the
Mogollon Rim and the higher terrain in southeast AZ this afternoon,
and gradually spread into the lower deserts this evening. Given the
very well-mixed boundary layer and weak to locally moderate
instability expected to be in place ahead of these thunderstorms,
have maintained low severe wind probabilities.
...Northern Nebraska/Southern South Dakota...
Elevated thunderstorms may develop across parts of northern NE and
southern SD late tonight/early Saturday morning as isentropic ascent
increases in tandem with modest strengthening of a southerly
low-level jet. Low-level moistening beneath steepening mid-level
lapse rates should support sufficient MUCAPE for robust updrafts,
although confidence in overall coverage remains low due to
weak/nebulous large-scale ascent. Regardless, strong shear in the
cloud-bearing layer across this area should promote organized
convection capable of producing isolated severe hail.
$$
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