WW 518 SEVERE TSTM MI MN WI LS 270630Z - 271400Z
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 518
NWS Storm Prediction Center Norman OK
130 AM CDT Mon Jul 27 2026
The NWS Storm Prediction Center has issued a
* Severe Thunderstorm Watch for portions of
Upper Michigan
Northern Minnesota
Northern Wisconsin
Lake Superior
* Effective this Monday morning from 130 AM until 900 AM CDT.
* Primary threats include...
Scattered large hail and isolated very large hail events to 2
inches in diameter possible
Scattered damaging wind gusts to 70 mph possible
A tornado or two possible
SUMMARY...Scattered thunderstorms will continue to increase in
coverage and intensity overnight as they moved southeastward
regionally. Large hail will the most common concern overnight,
although damaging wind potential could increase toward dawn and
beyond if storms begin to cluster and organize.
The severe thunderstorm watch area is approximately along and 80
statute miles north and south of a line from 80 miles west of
International Falls MN to 15 miles south southeast of Iron Mountain
MI. For a complete depiction of the watch see the associated watch
outline update (WOUS64 KWNS WOU8).
PRECAUTIONARY/PREPAREDNESS ACTIONS...
REMEMBER...A Severe Thunderstorm Watch means conditions are
favorable for severe thunderstorms in and close to the watch area.
Persons in these areas should be on the lookout for threatening
weather conditions and listen for later statements and possible
warnings. Severe thunderstorms can and occasionally do produce
tornadoes.
&&
AVIATION...A few severe thunderstorms with hail surface and aloft to
2 inches. Extreme turbulence and surface wind gusts to 60 knots. A
few cumulonimbi with maximum tops to 600. Mean storm motion vector
30025.
...Guyer
WW 0518 Status Updates
STATUS FOR WATCH 0518 HAS NOT BEEN ISSUED YET
MD 1756 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR PORTIONS OF CENTRAL VIRGINIA
Mesoscale Discussion 1756
NWS Storm Prediction Center Norman OK
0135 AM CDT Mon Jul 27 2026
Areas affected...Portions of central Virginia
Concerning...Severe potential...Watch unlikely
Valid 270635Z - 270730Z
Probability of Watch Issuance...5 percent
SUMMARY...A supercell moving southward near I-95 in central Virginia
may produce isolated wind damage and small to marginally severe
hail.
DISCUSSION...Convection continues in parts of central Virginia in
association with a passing shortwave trough. Despite some nocturnal
cooling, modified observed 00Z soundings from the Mid-Atlantic
suggest MLCIN is not overly large/prohibitive. A supercell with a
prominent mid-level mesocyclone continues southward near I-95. With
the KAKQ VAD showing around 50 kt of 0-6 km shear, this activity
should be able to persist for another hour or two before the
shortwave trough moves away from the region. Isolated damaging winds
and small to marginally severe hail will be possible as this storm
tracks near the Richmond metro.
..Wendt/Guyer.. 07/27/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...AKQ...LWX...
LAT...LON 37287711 37287729 37337737 37437754 37777777 37997780
38137775 38177754 38107731 37897718 37587700 37457694
37347699 37287711
MOST PROBABLE PEAK WIND GUST...UP TO 60 MPH
MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN
SPC 1200Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1252 AM CDT Mon Jul 27 2026
Valid 271200Z - 281200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS FROM PORTIONS
OF THE UPPER MIDWEST/UPPER GREAT LAKES INTO THE OHIO VALLEY...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS OF
SOUTHWEST SOUTH DAKOTA...WESTERN NEBRASKA...NORTHEAST COLORADO...AND
FAR NORTHWEST KANSAS...
...SUMMARY...
Severe storms capable of strong to severe wind gusts and large hail
are possible across the Great Lakes into the Ohio Valley Monday into
Monday night. More sporadic occurrences of damaging wind appear
possible in the Mid-Atlantic, Tennessee Valley, central High Plains,
and southeast Arizona.
...Upper Midwest/Great Lakes into the OH/TN Valleys...
A very moist airmass is in place from the Upper Midwest into the OH
and TN Valley. This airmass is exists south of a diffuse cold front
that extends from a surface low over far southeast Manitoba
southeastward to far eastern Upper MI. One thunderstorm is currently
ongoing near this boundary over eastern Upper MI. Most of the
thunderstorms are ongoing just northeast another surface boundary
demarcating the very moist (i.e. 70+ dewpoints) to it southwest. How
this warm-air advection activity evolves early this morning will
have a large impact on the severe potential farther downstream from
the Mid MS Valley into the OH and TN Valleys through the late
morning into the afternoon and evening.
Much of the guidance is beginning to suggest the warm-air advection
activity clusters early this morning over the MN Arrowhead vicinity
before then tracking southeastward within the moisture/buoyancy
gradient and organizing/intensifying significantly. Synoptically,
the overall setup matches many characteristics of scenarios with
strong, forward-propagating MCSs, including a surface boundary
parallel to the deep-layer shear, at least modest mid-level warm
advection, and very strong to extreme buoyancy. Given the trend
within the guidance and favorable synoptics, confidence in the
development of a strong forward-propagating MCS is high enough to
adjust the 30% wind probabilities westward while also introducing a
CIG1 area. There is a chance that both higher wind probabilities and
a CIG2 may be needed, but predictability regarding convective
evolution is too low at this time.
...Central High Plains into western/central NE and SD...
Moist, post-frontal surface flow is expected across much of NE and
SD, shifting from northerly early in the day to more easterly by the
afternoon. Dewpoints will initially be in the mid to upper 70s,
although strong boundary-layer mixing will likely result in
dewpoints ranging from the upper 50s/low 60s across the NE Panhandle
to the low 70s across eastern NE. This reservoir of low-level
moisture coupled with strong heating and steep mid-level lapse rates
will result in a corridor of moderate to extreme buoyancy from
eastern WY/northeast CO/southwest SD eastward across south-central
SD and much of NE.
Most of the guidance indicates a subtle, convectively augmented
vorticity maximum will progress eastward through the northern
periphery of the Four Corner upper ridge. This should contribute to
thunderstorm development across the high terrain, which would then
progress downstream into a more moist and unstable airmass. One or
more clusters could evolve, but the overall predictability of the
convective evolution is low. That being said, environmental
conditions support the potential for strong to severe gusts,
including the potential for some over 75 mph. Eastern extent of the
wind threat will likely be limited by building convective inhibition
associated with nocturnal cool, unless a more coherent and
organized MCS were to evolve. If that occurs, the wind threat could
extend farther east into more of eastern NE and north-central KS,
and 5% wind probabilities were expanded eastward/southeastward to
account for this potential.
Depending on the strength of the MCS, the wind threat could extend
eastward into more of OH and PA, and also farther southward into
more of TN, during the late afternoon/evening.
...Mid-Atlantic States...
Some wind threat could exist during the afternoon/evening across the
Mid-Atlantic, where marginal buoyancy and deep-layer shear could
support a few stronger updrafts.
...Southeast Arizona...
Isolated severe gusts are possible over southeast AZ as mid-level
moisture and daytime heating leads to scattered storms over
the higher terrain, particularly far southeast AZ. Cells are
expected to move westward into warmer temperatures and deeper
boundary-layer mixing, with PWAT over 1.25" and steep low-level
lapse rates supporting strong outflows.
..Mosier/Squitieri.. 07/27/2026
SPC 0600Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1220 AM CDT Mon Jul 27 2026
Valid 281200Z - 291200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE SOUTHERN
MID-ATLANTIC INTO THE CAROLINAS AND CENTRAL AND SOUTHERN
APPALACHIANS...
...SUMMARY...
Severe thunderstorms capable of damaging winds and isolated hail are
possible from the southern Mid-Atlantic into the Carolinas and
central and southern Appalachians Tuesday into Tuesday evening.
Isolated severe wind gusts and large hail may occur in the central
High Plains.
...Synopsis...
Considerable trough amplification is forecast over the eastern CONUS
this period, aided by the propagation of the mid/upper-level jet
streaks from the Great Lakes and OH Valley through VA and NC. A
series of vorticity maxima is forecast on the cyclonic side of the
jet streaks, which will enhance forcing for ascent over the central
Appalachians into the Mid-Atlantic. At the surface, the primary low
pressure is expected to deepen over the Delmarva with a secondary
cyclone over western NY. A lee trough will extend from the Delmarva
low south-southwest along the Piedmont, ahead of a cold front moving
through the TN Valley and central and southern Appalachians.
...Mid-Atlantic into the Southern Appalachians...
Showers and thunderstorms (some potentially severe with damaging
winds) are expected to be ongoing Tuesday morning from the lower
Great Lakes into the central Appalachians. The longevity and areal
extent of the early-day storms will be a determinant in where more
robust air mass destabilization will take place during the
afternoon. The 00Z HREF calibrated thunder probabilities suggest the
most likely areas for persistent morning storms will be from NY and
PA into the Delmarva and WV. To the south of those locations,
stronger daytime heating appears more probable, which, combined with
boundary-layer dewpoints in the upper 60s to mid 70s, will yield
moderate to potentially strong afternoon instability with MLCAPE of
1500-2500+ J/kg.
Thunderstorms are expected to increase in coverage and intensity
during the afternoon along and ahead of the cold front and lee
trough as background forcing for ascent strengthens in the left exit
region of the approaching upper-level jet streak. The presence of
the mid/upper-level wind maxima will yield long hodographs with
sufficient vertical shear for supercells and bowing structures. The
strengthening shear combined with cooling mid-level temperatures
will be supportive of large-hail production with any supercells that
form. Otherwise, damaging winds will be the primary hazard,
especially with any storm clusters or bowing line segments. Some
tornado threat could also materialize Tuesday afternoon into evening
near and south of the Delmarva surface low where slightly stronger
low-level shear is forecast.
...Central High Plains...
Strong heating of a moist, upslope-flow air mass is expected to
yield a moderately unstable environment by afternoon with MLCAPE of
1500-2500 J/kg. Isolated to widely scattered thunderstorm
development appears possible by mid- to late afternoon along the
high terrain within a kinematic environment featuring 30-35 kt
westerly deep-layer shear. Transient supercell structures appear
possible, which suggest some marginally severe hail potential,
despite the warm mid-level temperatures. There is some model signal
for storm clustering over the adjacent High Plains by evening, at
which point the threat for isolated severe wind gusts would
increase.
..Mead.. 07/27/2026
SPC 0730Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0200 AM CDT Mon Jul 27 2026
Valid 291200Z - 301200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS IN THE SOUTHEAST
AND NORTHERN AND CENTRAL HIGH PLAINS...
...SUMMARY...
Isolated severe storms capable of mainly damaging winds appear
possible in the Southeast and northern and central High Plains
Wednesday afternoon into evening.
...Synopsis...
A short-wave trough will move through the Canadian Prairie
Provinces, effectively flattening the northern extension of the
upper ridge in those areas. There is some model signal for a
lower-latitude disturbance to progress from the northern Rockies
into the northern High Plains. Elsewhere, an upper low over the
Mid-Atlantic will evolve into an open wave with the broader-scale
trough slowly shifting east. At the surface, a cool front will
settle south through the Southeast, while a lee trough deepens over
the northern High Plains.
...Southeast...
A hot and very moist air mass is expected ahead of the front, with
moderate to strong instability developing by afternoon. The models
suggest the stronger mid-level winds and resultant vertical shear
will be displaced to the north of the frontal zone, which should
limit the organizational potential of the storms developing along
the boundary. Nonetheless, the degree of instability and high
precipitable water content will favor locally intense wet
microbursts capable of damaging winds, especially with any storm
clusters that may evolve.
...Northern and central High Plains...
A hot and deeply mixed boundary layer is forecast east of the lee
trough Wednesday afternoon with steep low/mid-level lapse rates
contributing to moderate instability. Diurnally enhanced storm
coverage along the boundary remains uncertain due to the absence of
any appreciable forcing mechanisms, except perhaps the weak
disturbance mentioned above. Nonetheless, the presence of the steep
lapse rates and latent cooling potential in the sub-cloud layer
suggests a threat for severe wind gusts and perhaps large hail with
any storms that develop.
..Mead.. 07/27/2026
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1124 PM CDT Sun Jul 26 2026
Valid 271200Z - 281200Z
...Synopsis...
An upper ridge will remain in place over the western CONUS today,
with modest mid-level flow poised to pivot around the ridge during
the afternoon hours, when a deep and dry boundary layer will
encourage downward momentum transport of the stronger flow aloft.
The most likely location for boundary-layer mixing and associated
stronger surface winds will be across the northern Sierra into the
northern Rockies, where southwesterly surface winds may occasionally
exceed 15 mph amid 20 percent RH and dry fuels. As such, Elevated
highlights have been maintained.
..Squitieri.. 07/27/2026
...Please see www.spc.noaa.gov/fire for graphic product...
SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1125 PM CDT Sun Jul 26 2026
Valid 281200Z - 291200Z
...NO CRITICAL AREAS...
...Synopsis...
Another day of mid-level ridging will characterize the upper-air
pattern for the western CONUS tomorrow (Tuesday). As in the past
couple of days, upper flow pivoting around the ridge should continue
to weaken in intensity, supporting a weaker surface wind field in
turn. Widespread dry conditions are expected across western portions
of the Great Basin toward the Pacific Northwest and northern
Rockies. Nonetheless, the lack of a stronger surface wind field
precludes fire weather highlights at this time.
..Squitieri.. 07/27/2026
...Please see www.spc.noaa.gov/fire for graphic product...
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