RSS Mesoscale Discussions from Storm Prediction Center
WW 520 SEVERE TSTM IL IN MI LM 271645Z - 280000Z
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 520
NWS Storm Prediction Center Norman OK
1245 PM EDT Mon Jul 27 2026
The NWS Storm Prediction Center has issued a
* Severe Thunderstorm Watch for portions of
Northeast Illinois
Northern Indiana
Western Lower Michigan
Lake Michigan
* Effective this Monday afternoon and evening from 1245 PM until
800 PM EDT.
* Primary threats include...
Scattered damaging winds and isolated significant gusts to 75
mph likely
Scattered large hail and isolated very large hail events to 2
inches in diameter possible
A tornado or two possible
SUMMARY...Clusters of thunderstorms will track southeastward through
the afternoon across the watch area. Damaging winds, large hail,
and even a tornado or two are possible.
The severe thunderstorm watch area is approximately along and 70
statute miles east and west of a line from 70 miles north of
Muskegon MI to 60 miles south southeast of Valparaiso IN. For a
complete depiction of the watch see the associated watch outline
update (WOUS64 KWNS WOU0).
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.
&&
OTHER WATCH INFORMATION...CONTINUE...WW 519...
AVIATION...A few severe thunderstorms with hail surface and aloft to
2 inches. Extreme turbulence and surface wind gusts to 65 knots. A
few cumulonimbi with maximum tops to 500. Mean storm motion vector
31030.
...Hart
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WW 519 SEVERE TSTM MI WI LM 271340Z - 272000Z
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 519
NWS Storm Prediction Center Norman OK
840 AM CDT Mon Jul 27 2026
The NWS Storm Prediction Center has issued a
* Severe Thunderstorm Watch for portions of
Western Upper Michigan
Northeast Wisconsin
Lake Michigan
* Effective this Monday morning and afternoon from 840 AM until
300 PM CDT.
* Primary threats include...
Scattered damaging wind gusts to 70 mph possible
Scattered large hail events to 1.5 inches in diameter possible
SUMMARY...A cluster of intense thunderstorms along the
Wisconsin/Michigan border will track southeastward through the late
morning, posing a risk of damaging winds and hail.
The severe thunderstorm watch area is approximately along and 55
statute miles east and west of a line from 55 miles north northeast
of Rhinelander WI to 20 miles east southeast of Manitowoc WI. For a
complete depiction of the watch see the associated watch outline
update (WOUS64 KWNS WOU9).
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.
&&
OTHER WATCH INFORMATION...CONTINUE...WW 518...
AVIATION...A few severe thunderstorms with hail surface and aloft to
1.5 inches. Extreme turbulence and surface wind gusts to 60 knots. A
few cumulonimbi with maximum tops to 500. Mean storm motion vector
31030.
...Hart
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WW 0520 Status Updates
STATUS FOR WATCH 0520 HAS NOT BEEN ISSUED YET
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WW 0519 Status Updates
STATUS REPORT ON WW 519
SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 10 ESE AUW
TO 25 NNE GRB TO 50 WNW TVC.
..LEITMAN..07/27/26
ATTN...WFO...MQT...GRB...
STATUS REPORT FOR WS 519
SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS
WIC009-015-061-071-087-115-271740-
WI
. WISCONSIN COUNTIES INCLUDED ARE
BROWN CALUMET KEWAUNEE
MANITOWOC OUTAGAMIE SHAWANO
LMZ522-541-542-543-563-565-567-271740-
CW
. ADJACENT COASTAL WATERS INCLUDED ARE
GREEN BAY SOUTH OF LINE FROM OCONTO WI TO LITTLE STURGEON BAY WI
ROCK ISLAND PASSAGE TO STURGEON BAY WI
STURGEON BAY TO TWO RIVERS WI
TWO RIVERS TO SHEBOYGAN WI
LAKE MICHIGAN FROM ROCK ISLAND PASSAGE TO STURGEON BAY WI 5NM
OFFSHORE TO MID LAKE
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MD 1763 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR SOUTHERN IOWA INTO FAR NORTHERN MISSOURI
Mesoscale Discussion 1763
NWS Storm Prediction Center Norman OK
1249 PM CDT Mon Jul 27 2026
Areas affected...Southern Iowa into far northern Missouri
Concerning...Severe potential...Watch unlikely
Valid 271749Z - 271945Z
Probability of Watch Issuance...5 percent
SUMMARY...An isolated hail threat may materialize through
mid-afternoon across southern Iowa into far northern Missouri. In
general, this activity is expected to remain sufficiently weak to
negate the need for a watch.
DISCUSSION...Convection has been gradually deepening per MRMS VIL
and echo top imagery over the past hour across southwest to
south-central IA. This activity appears to be largely driven by
modest ascent along a weak frontal zone draped across the Plains,
and is maturing within an environment featuring ample buoyancy
(MUCAPE of around 3000 J/kg) and sufficient deep-layer wind shear
for organized convection based on the KDMX VWP (which sampled a 0-6
km BWD of just under 25 knots). Given this environment, loosely
organized convection appears possible and may pose a threat for
sporadic large hail - most likely 1.25 inch or less. The primary
modulating factor to overall storm longevity and intensity is
increasing inhibition with southward extent and a lack of stronger
synoptic forcing for ascent. Consequently, storms will most likely
begin to weaken as they track south/southeast (this behavior has
already been observed with a few leading cells) and will mainly pose
an isolated/transient severe threat through the afternoon.
..Moore/Hart.. 07/27/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LSX...DVN...DMX...EAX...OAX...
LAT...LON 41929527 41749319 41639261 41419211 40829147 40539143
40309158 40259208 40319453 40469490 40749514 41659562
41859552 41929527
MOST PROBABLE PEAK WIND GUST...UP TO 60 MPH
MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN
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MD 1762 CONCERNING SEVERE THUNDERSTORM WATCH 520... FOR NORTHEAST IL/NORTHWEST IN
Mesoscale Discussion 1762
NWS Storm Prediction Center Norman OK
1224 PM CDT Mon Jul 27 2026
Areas affected...northeast IL/northwest IN
Concerning...Severe Thunderstorm Watch 520...
Valid 271724Z - 271900Z
The severe weather threat for Severe Thunderstorm Watch 520
continues.
SUMMARY...A favorable environment supporting large to very large
hail and a tornado risk will develop across portions of northeast IL
into northwest IN over the next 1-2 hours.
DISCUSSION...A supercell located over northeast IL will develop
south/southeast across the southern greater Chicago metro vicinity.
The downstream airmass is very moist (mid/upper 70s dewpoints) and
unstable (3000-4000 J/kg MLCAPE). Favorable vertical shear with 50+
kt effective shear magnitudes and 0-1 SRH near 125 m2/s2 is noted
from the KLOT VWP. Effective STP values have increased to 3-5 as
well. This environment will continue to support supercell structures
with a continued risk for very large hail to around 2.5 inches,
strong wind gusts, and possibly a strong tornado over the next 1-2
hours.
..Leitman.. 07/27/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LOT...
LAT...LON 42018782 41528726 41138721 40998753 41038799 41228829
41718827 41928825 42058811 42018782
MOST PROBABLE PEAK TORNADO INTENSITY...100-125 MPH
MOST PROBABLE PEAK WIND GUST...65-80 MPH
MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN
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MD 1761 CONCERNING SEVERE THUNDERSTORM WATCH 519... FOR EAST-CENTRAL WI
Mesoscale Discussion 1761
NWS Storm Prediction Center Norman OK
1216 PM CDT Mon Jul 27 2026
Areas affected...east-central WI
Concerning...Severe Thunderstorm Watch 519...
Valid 271716Z - 271845Z
The severe weather threat for Severe Thunderstorm Watch 519
continues.
SUMMARY...Very large hail and tornado potential may persist the next
1-2 hours as a cell near Winnebago and Calumet counties continues
southeast.
DISCUSSION...A supercell over far northeast Winnebago and Calumet
counties likely produced a damaging tornado recently based on strong
rotation and TDS from KGRB radar. The downstream airmass remains
very unstable with effective layer STP approaching 4 to 6 in a
corridor southeast of ongoing storms. Given steep lapse rates,
favorable thermodynamics and strong effective shear greater than 50
kt supporting continued supercell structures, a risk for very large
hail up to 2.5 inches and a continued risk of strong tornadoes may
continue for another 1-2 hours.
..Leitman.. 07/27/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...GRB...MKX...
LAT...LON 44028760 43758746 43498751 43438780 43528823 43998868
44308875 44358815 44348807 44298798 44028760
MOST PROBABLE PEAK TORNADO INTENSITY...100-125 MPH
MOST PROBABLE PEAK WIND GUST...65-80 MPH
MOST PROBABLE PEAK HAIL SIZE...1.50-2.50 IN
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SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook CORR 1
NWS Storm Prediction Center Norman OK
1149 AM CDT Mon Jul 27 2026
Valid 271630Z - 281200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE MIDWEST...
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER THE CENTRAL
HIGH PLAINS...
CORRECTED FOR THUNDERSTORM LINES
...SUMMARY...
Severe storms capable of strong to severe wind gusts and large hail
are expected across the Great Lakes and Midwest through tonight.
More sporadic occurrences of damaging wind are possible in the
Mid-Atlantic, Tennessee Valley, central High Plains, and southeast
Arizona.
...Midwest/Ohio Valley...
A large upper ridge remains present today over the central
Plains/Rockies, with moderately strong northwest flow aloft from the
Midwest into the OH Valley. A very moist and unstable low-level air
mass resides from WI/IL into MI/IN/OH, where mostly clear skies will
result in hot afternoon temperatures and MLCAPE values over 3000
J/kg. Multiple clusters of intense thunderstorms are ongoing over
parts of WI tracking southeastward. These storms will move through
this reservoir of high CAPE, leading to the potential for an active
severe weather event today. However, details of how these clusters
evolve are uncertain.
Vertical shear across this region will support supercell structures,
capable of damaging winds, hail, and isolated tornadoes this
afternoon. However, the greater concern is if storms can congeal
into a southeastward bowing system and that sweeps across Lower MI,
eastern IL, IN, and western OH. Several morning CAM solutions
indicate that risk, with storms spreading into KY overnight before
weakening. Unfortunately, this synoptic pattern does not lend
itself to a high-confidence convective forecast.
...High Plains...
Widespread clouds are affecting parts of western NE this morning.
However, strong heating will occur north and south of these clouds,
leading to afternoon thunderstorms. The most active area will
likely be over the Black Hills region where damaging winds and hail
are possible. Farther south, widely scattered high-based
thunderstorms will affect eastern CO/western KS with a risk of
damaging wind gusts.
..Hart/Moore.. 07/27/2026
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SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1234 PM 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 PARTS OF THE APPALACHIANS...
...SUMMARY...
Severe thunderstorms capable of damaging winds and isolated hail are
possible from the southern Mid-Atlantic into the Carolinas and parts
of the Appalachians Tuesday into Tuesday evening. A tornado threat
may develop from southeast Virginia into eastern North Carolina.
Isolated severe wind gusts and large hail may occur in the central
High Plains.
...Southern Mid Atlantic / Appalachians / Carolinas...
An upper trough will gradually deepen and move southeastward across
the Mid Atlantic, with the left-front quadrant of the upper jet
moving across VA and NC. At the surface, low pressure will deepen
ahead of a cold front, with wind shift roughly from eastern PA into
central VA and NC during the afternoon.
A moist and unstable air mass will develop across the region, and
shear profiles will become increasingly favorable for supercells.
The most favorable combination of shear and instability looks to be
from parts of eastern VA into east-central/northeast NC. Here, 850
mb winds will increase out of the southwest to around 30 kt, with
effective SRH possibly into the 200-300 m2/s2 range. A tornado or
two is possible, with perhaps a transition to bows producing
damaging winds. This area will be watched closely into the Day 1
period.
Farther north and also within the surface trough, shear will be
weaker aloft. However, favorable low-level shear may yield a brief
tornado as well into eastern PA/NJ.
Otherwise, additional storms are likely across the Appalachians as
surface heating occurs beneath the relatively cool temperatures
aloft. Low-level winds will be more veered in these areas, but long
hodographs and substantial instability will still favor hail and
locally damaging winds.
...Central High Plains...
Strong heating will occur under the upper ridge, with a weak lee
trough developing. Surface winds will back to easterly late in the
day and evening, which will increase upslope-flow and yield a
moderately unstable environment by afternoon with MLCAPE of
1500-2500 J/kg. This will support scattered thunderstorm development
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. Generally mixed-modes
should persist into the evening into eastern CO and far western NE
with locally strong gusts.
..Jewell.. 07/27/2026
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SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1146 AM CDT Mon Jul 27 2026
Valid 271700Z - 281200Z
The forecast remains on track for elevated fire weather conditions
across portions of the northwestern CONUS. Poor to marginal
overnight humidity recoveries and daytime heating will contribute to
critical RH values of 10-15% this afternoon amid southwesterly winds
of 10-15 mph (gusts up to 25 mph). Meteorological conditions will
overlap a very dry, drought-stressed fuelscape (80-95th percentile
ERCs) with multiple ongoing large wildfires. Any lightning holdovers
from thunderstorms last week/weekend may also emerge as a result of
hot, dry, and breezy conditions.
..Elizalde-Garcia.. 07/27/2026
.PREV DISCUSSION... /ISSUED 1124 PM CDT Sun Jul 26 2026/
...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.
...Please see www.spc.noaa.gov/fire for graphic product...
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