92°F
Updated:
8/16/2025
3:07:31pm
SPC Severe Thunderstorm Watch 596
WW 596 SEVERE TSTM IL IN WI LM 161855Z - 170000Z
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 596
NWS Storm Prediction Center Norman OK
155 PM CDT Sat Aug 16 2025
The NWS Storm Prediction Center has issued a
* Severe Thunderstorm Watch for portions of
Northern Illinois
Far Northwest Indiana
Far Southeast Wisconsin
Lake Michigan
* Effective this Saturday afternoon and evening from 155 PM until
700 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...Thunderstorm cluster currently ongoing over far southeast
WI is expected to continue southeastward through northern IL and
northwest IN this afternoon and evening. The airmass in these areas
is very unstable and supportive of robust updrafts capable of large
hail and damaging gusts.
The severe thunderstorm watch area is approximately along and 50
statute miles east and west of a line from 40 miles north northeast
of Janesville WI to 45 miles west of Valparaiso IN. For a complete
depiction of the watch see the associated watch outline update
(WOUS64 KWNS WOU6).
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
1.5 inches. Extreme turbulence and surface wind gusts to 60 knots. A
few cumulonimbi with maximum tops to 500. Mean storm motion vector
29030.
...Mosier
Read more
SPC Severe Thunderstorm Watch 596 Status Reports
WW 0596 Status Updates
STATUS REPORT ON WW 596
THE SEVERE WEATHER THREAT CONTINUES ACROSS THE ENTIRE WATCH AREA.
..BENTLEY..08/16/25
ATTN...WFO...LOT...DVN...MKX...
STATUS REPORT FOR WS 596
SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS
ILC007-031-037-043-089-093-097-111-141-177-197-201-162040-
IL
. ILLINOIS COUNTIES INCLUDED ARE
BOONE COOK DE KALB
DUPAGE KANE KENDALL
LAKE MCHENRY OGLE
STEPHENSON WILL WINNEBAGO
INC089-127-162040-
IN
. INDIANA COUNTIES INCLUDED ARE
LAKE PORTER
WIC045-055-059-079-101-105-127-133-162040-
WI
. WISCONSIN COUNTIES INCLUDED ARE
GREEN JEFFERSON KENOSHA
MILWAUKEE RACINE ROCK
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SPC MD 1966
MD 1966 CONCERNING SEVERE THUNDERSTORM WATCH 596... FOR SOUTHEAST WISCONSIN...NORTHEAST ILLINOIS...AND NORTHWEST INDIANA
Mesoscale Discussion 1966
NWS Storm Prediction Center Norman OK
0234 PM CDT Sat Aug 16 2025
Areas affected...southeast Wisconsin...northeast Illinois...and
northwest Indiana
Concerning...Severe Thunderstorm Watch 596...
Valid 161934Z - 162100Z
The severe weather threat for Severe Thunderstorm Watch 596
continues.
SUMMARY...The severe weather threat is increasing through the
afternoon.
DISCUSSION...A cluster of supercells has developed across central
Minnesota. The MKX VWP is sampling around 45 knots of mid-level flow
which is resulting in around 40 knots of effective shear. Shear
decreases rapidly with southern extent to only around 15 to 20 knots
across northern Illinois. Therefore, storms may become less
organized and outflow dominant as they congeal and move south across
northern Illinois. However, greater instability (3000-4000 J/kg
MLCAPE) and near 2 inch PWAT values will support a damaging wind
threat as the storm cluster moves south this afternoon and evening.
..Bentley/Mosier.. 08/16/2025
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...IWX...LOT...MKX...DVN...
LAT...LON 42908961 43088920 43088827 42948766 42628728 42018704
41668691 41358689 41178707 41188772 41328848 41568885
42068936 42388951 42908961
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...1.00-1.75 IN
Read more
SPC MD 1965
MD 1965 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR NORTHEAST IOWA...SOUTHEAST MINNESOTA AND WESTERN WISCONSIN.
Mesoscale Discussion 1965
NWS Storm Prediction Center Norman OK
0205 PM CDT Sat Aug 16 2025
Areas affected...northeast Iowa...southeast Minnesota and western
Wisconsin.
Concerning...Severe potential...Watch unlikely
Valid 161905Z - 162030Z
Probability of Watch Issuance...20 percent
SUMMARY...Isolated severe storms are possible this
afternoon/evening. No watch is anticipated.
DISCUSSION...A cluster of storms has developed across southeast
Minnesota and western Wisconsin in the wake of the morning MCS.
These elevated storms are in a region with strong shear (50+ knots
per ARX VWP), but are somewhat removed from the better elevated
instability according to SPC mesoanalysis. Therefore, the current
location and storm motion favoring movement farther into the cold
air would suggest severe potential may be somewhat limited from this
activity. If additional storms can develop farther south (across
northeast Iowa), they may pose a greater severe potential, but
visible satellite trends do not support an imminent threat of
additional development in this area.
..Bentley.. 08/16/2025
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...GRB...MKX...ARX...MPX...DMX...
LAT...LON 44409206 44419092 44719027 44718994 44388950 43798922
43368939 43099022 42889121 42889230 43059311 43529328
44409206
MOST PROBABLE PEAK WIND GUST...UP TO 60 MPH
MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN
Read more
SPC Aug 16, 2025 1630 UTC Day 1 Convective Outlook
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1130 AM CDT Sat Aug 16 2025
Valid 161630Z - 171200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS EVENING AND
TONIGHT OVER PART OF SD...AND THIS AFTERNOON THROUGH TONIGHT OVER
SOUTHEAST MN...SOUTHERN WI...AND NORTHERN IL...
...SUMMARY...
Scattered strong/severe thunderstorms are possible today into
tonight across parts of the northern Great Plains into Midwest and
Great Lakes region.
...Upper Midwest into the Mid MS Valley and Upper Great Lakes
Region...
An expansive MCS continues to move eastward across the Upper
Midwest, with a well-defined MCV evident in radar imagery over the
central WI/MN border vicinity. This MCS has continued to gradually
weaken throughout the morning, but a few strong updrafts persist
along its southeastern periphery over central WI. This portion of
the MCS is on the far northeastern periphery of the plume of steeper
mid-level lapse rates that extends from the northern/central High
Plains across the central Plains and into the Mid MS Valley. This
plume is observable in the 12Z sounding from DVN and ILX, which
sampled 700-500 mb lapse rates of 7.8 and 7.2 deg C per km,
respectively. Dewpoints downstream across southern WI, northern IL,
and northern IN are in the low 70s, with upper 60s dewpoints also
covering much of southern Lower MI. The combination of ample
low-level moisture and steep mid-level lapse rates will result in
strong to very strong buoyancy to the south of the MCS from the
MN/IA border into northern/central IL.
Given the lack of a well-defined surface boundary and negligible
large-scale ascent, additional thunderstorm development will be
associated with outflow from with the MCS, which results in
greater-than-average uncertainty for the Day 1 period. Ample
moisture and buoyancy downstream of the leading edge of the MCS
suggests the greater severe potential this afternoon/evening will
likely be associated with redevelopment/reintensification of the
MCS. Additionally, even if reintensification does not occur along
the leading edge of the MCS this afternoon, most guidance suggests
redevelopment does eventually occur this evening along the southern
periphery of the MCV circulation as it moves into northern/central
WI. Increased severe-wind probabilities (i.e. 15%) were introduced
with this outlook to cover both of these potential scenarios. A
small 15% hail probability was introduce to cover potential for
later evening storms atop the outflow as well.
Storms are possible into northern IN and the Lower MI this afternoon
and evening as well, but the lower buoyancy should temper the
overall coverage and magnitude in these areas.
...SD and Vicinity...
A well-defined but rather weak shortwave trough is currently moving
through western CO/western WY, and will continue northeastward into
eastern WY/western Dakotas by this evening. Similar to yesterday,
high-based storms will develop ahead of the approaching shortwave
and intensify as they move eastward into a progressively more
moist/unstable air mass over west-central SD. Upscale growth into
another nocturnal MCS is forecast by most guidance, with the MCS
tracking northeastward across western/central SD tonight. Strong to
severe gusts are possible with this potential MCS across much of
western/central SD.
..Mosier/Wendt.. 08/16/2025
Read more
SPC Aug 16, 2025 2000 UTC Day 1 Convective Outlook
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0257 PM CDT Sat Aug 16 2025
Valid 162000Z - 171200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS EVENING AND
TONIGHT OVER PART OF SD...AND THIS AFTERNOON THROUGH TONIGHT OVER
SOUTHEAST MN...SOUTHERN WI...AND NORTHERN IL...
...SUMMARY...
Scattered strong/severe thunderstorms are possible today into
tonight across parts of the northern Great Plains into the Midwest
and Great Lakes regions.
...20Z Update...
The prior forecast reasoning remains valid. Severe probabilities
were reduced in parts of northern/central Wisconsin where prior
convection has stabilized the boundary layer. Elsewhere, only minor
changes were made to the general thunderstorm forecast based on
current observational trends. See the previous discussion as well as
MCDs 1965/1966 for additional information.
..Wendt.. 08/16/2025
.PREV DISCUSSION... /ISSUED 1130 AM CDT Sat Aug 16 2025/
...Upper Midwest into the Mid MS Valley and Upper Great Lakes
Region...
An expansive MCS continues to move eastward across the Upper
Midwest, with a well-defined MCV evident in radar imagery over the
central WI/MN border vicinity. This MCS has continued to gradually
weaken throughout the morning, but a few strong updrafts persist
along its southeastern periphery over central WI. This portion of
the MCS is on the far northeastern periphery of the plume of steeper
mid-level lapse rates that extends from the northern/central High
Plains across the central Plains and into the Mid MS Valley. This
plume is observable in the 12Z sounding from DVN and ILX, which
sampled 700-500 mb lapse rates of 7.8 and 7.2 deg C per km,
respectively. Dewpoints downstream across southern WI, northern IL,
and northern IN are in the low 70s, with upper 60s dewpoints also
covering much of southern Lower MI. The combination of ample
low-level moisture and steep mid-level lapse rates will result in
strong to very strong buoyancy to the south of the MCS from the
MN/IA border into northern/central IL.
Given the lack of a well-defined surface boundary and negligible
large-scale ascent, additional thunderstorm development will be
associated with outflow from with the MCS, which results in
greater-than-average uncertainty for the Day 1 period. Ample
moisture and buoyancy downstream of the leading edge of the MCS
suggests the greater severe potential this afternoon/evening will
likely be associated with redevelopment/reintensification of the
MCS. Additionally, even if reintensification does not occur along
the leading edge of the MCS this afternoon, most guidance suggests
redevelopment does eventually occur this evening along the southern
periphery of the MCV circulation as it moves into northern/central
WI. Increased severe-wind probabilities (i.e. 15%) were introduced
with this outlook to cover both of these potential scenarios. A
small 15% hail probability was introduce to cover potential for
later evening storms atop the outflow as well.
Storms are possible into northern IN and the Lower MI this afternoon
and evening as well, but the lower buoyancy should temper the
overall coverage and magnitude in these areas.
...SD and Vicinity...
A well-defined but rather weak shortwave trough is currently moving
through western CO/western WY, and will continue northeastward into
eastern WY/western Dakotas by this evening. Similar to yesterday,
high-based storms will develop ahead of the approaching shortwave
and intensify as they move eastward into a progressively more
moist/unstable air mass over west-central SD. Upscale growth into
another nocturnal MCS is forecast by most guidance, with the MCS
tracking northeastward across western/central SD tonight. Strong to
severe gusts are possible with this potential MCS across much of
western/central SD.
Read more
SPC Aug 16, 2025 1730 UTC Day 2 Convective Outlook
SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1227 PM CDT Sat Aug 16 2025
Valid 171200Z - 181200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS IN PARTS OF THE
NORTHERN CONUS...
...SUMMARY...
Isolated severe thunderstorms are possible, mainly during the late
afternoon and evening Sunday from the Upper Midwest to the northern
High Plains. Isolated damaging winds are possible on Sunday
afternoon to early evening across the Northeast and New England.
...Upper Midwest...
Decaying convective swaths will likely be ongoing at 12Z Sunday,
centered on the eastern Dakotas to southern MN. The eastern lobe of
this morning activity will aid in strengthening the quasi-stationary
baroclinic zone, as differential boundary-layer heating occurs
across it through the day. Presence of mid to upper ridging
emanating north-northeast from the southern Great Plains anticyclone
will remain a limiting factor to more robust severe potential.
Still, drifting MCVs across the Dakotas in a modest southwesterly
flow regime in conjunction with large buoyancy in the warm-moist
sector should aid in scattered late-afternoon thunderstorm
development. This appears most probable in the eastern SD to
southwest MN vicinity, with isolated coverage trailing into central
NE. A mix of isolated severe hail/wind initially should transition
to mainly sporadic strong to severe gusts through the evening as
slow-moving clusters/MCSs develop. A brief tornado is also possible
with any transient supercell structures near the front.
...Northern High Plains...
Primary severe potential should emanate out of late afternoon
convection initiating off the higher terrain of southern MT and
separately in the Black Hills vicinity. A modest combination of
deep-layer shear and large-scale ascent suggests mainly a strong to
isolated severe threat should be expected as high-based convection
spreads northeast across eastern MT. The presence of weak
surface/low-level should modulate the eastern extent of severe
potential on Sunday evening.
...Northeast/New England...
A shortwave trough will progress across the St. Lawrence Valley
towards the Canadian Maritimes and northern New England through
Sunday afternoon. A cold front will push southeastward through the
day with isolated to widely scattered thunderstorms expected along
it during the afternoon. Buoyancy appears likely to be weak and will
remain a limiting factor to more robust severe potential. More
favorable deep-layer shear will exist in New England where localized
damaging winds and small hail should be favored. Farther southwest,
multicell clustering should be dominant with isolated damaging winds
from sporadic strong gusts.
..Grams.. 08/16/2025
Read more
SPC Aug 16, 2025 1930 UTC Day 3 Severe Thunderstorm Outlook
SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0221 PM CDT Sat Aug 16 2025
Valid 181200Z - 191200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS IN THE NORTHERN
GREAT PLAINS TO THE CORN BELT...
...SUMMARY...
Isolated severe thunderstorms are possible across parts of the Corn
Belt and northern Great Plains, mainly during the late afternoon and
evening on Monday.
...Corn Belt to the northern Great Plains...
Large-scale pattern will feature retrogression of the mid/upper
anticyclone from the southern Great Plains into the Southwest. An
MCV should amplify as a result of D2 MCS development and act as a
low-amplitude shortwave impulse drifting across the Upper Great
Lakes. Ridging will build north towards the northern High Plains by
early Tuesday. This evolution will yield a generally modest zonal
mid-level flow regime over the North-Central States on Monday.
Extensive but decaying convection should be ongoing at 12Z Monday
from the Lake Superior/Upper MS Valley into IA and perhaps the Lower
MO Valley. Pockets of stronger boundary-layer heating will be
necessary for diurnal intensification with weaker mid-level lapse
rates relative to prior days. Confidence is low in just how unstable
the airmass will be in WI/IL on Monday afternoon. Still, will
maintain a level 1-MRGL with a risk for isolated damaging winds.
Farther west, steep mid-level lapse rates will foster moderate to
large buoyancy from NE into eastern MT/western ND. Guidance has
varying signals for widely scattered convective development, but it
appears most probable over the central High Plains and Black Hills
during the late afternoon and evening. Coverage is more nebulous in
MT/ND as mid/upper ridging gradually builds, but deep-layer shear
will be greater compared to farther south. A broad swath of
low-probability severe remains appropriate with a mix of wind and
hail possible.
..Grams.. 08/16/2025
Read more
SPC Day 1 Fire Weather Outlook
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1153 AM CDT Sat Aug 16 2025
Valid 161700Z - 171200Z
Current satellite imagery shows a broad cloud shield associated with
an influx of Pacific moisture along a cold front draped from
northwestern CA into the ID Panhandle. PWAT values of around 1.00
inch along with higher surface dewpoints and relative humidity near
and behind the frontal boundary will promote more wetting rainfall
within heavier shower and thunderstorm cores. This has shifted the
dry thunderstorm threat slightly southeastward where diurnal heating
is more accessible in conjunction with a drier sub-cloud layer,
supporting more limited rainfall within northeastward thunderstorm
motions of up to 30 knots expected this afternoon and evening. A
mid-level wind maxima of 30-40 knots and associated increased shear
stretching from eastern OR into western MT could aid in sustained
convection through tonight across eastern OR, central ID mountains
and western MT.
..Williams.. 08/16/2025
.PREV DISCUSSION... /ISSUED 0202 AM CDT Sat Aug 16 2025/
...Synopsis...
A broad mid-level trough over the Northwestern US is forecast to
consolidate and intensify today/tonight as it impinges on the
northwestern edge of a ridge of high pressure over the central US.
The tightening height gradient will bolster flow aloft, while at the
same time, a surface cold front will move in from the Northwest.
Monsoon moisture will support showers and thunderstorms along/ahead
of the front, while localized dry and breezy conditions are possible
over the Southwestern US.
...Northwest and Rockies Dry Thunder...
Across the Northwest and central Rockies, persistent monsoon
moisture will be in palace ahead of the upper trough and attendant
cold front. Increasing PWATs (0.8-1 inch) will favor a mix of wet
and dry storms across far northern CA into eastern OR and ID/MT from
the afternoon into the evening hours. While the air mass in the
low-levels will not be as dry as recent days, with increasing RH
ahead of the front, 30-40 kt of mid-level flow should support faster
northeastward storm motions of 25-30 kt. This will allow for less
wetting rainfall as storms track eastward over areas of very
receptive fuels supportive of lightning ignitions. Additionally,
gusty outflow winds are expected, potentially impacting existing
active fires across the area. The risk for lightning may continue
overnight as the upper trough and front shift eastward towards ID
and MT. IsoDryT highlights will remain, and have been expanded over
areas of the expected driest fuels and storms.
...Southern Great Basin...
As the mid-level trough continues eastward across the Northwest,
southwesterly flow aloft should continue to promote locally breezy
and dry conditions across portions of southern NV and western UT.
South-southwest winds of up to 15 mph, along with daytime relative
humidity as low as 15%, are expected in some valleys in the southern
Great Basin. Amidst dry fuels, some locally elevated fire-weather
conditions are possible. The lack of stronger winds for now
precludes elevated highlights.
...Please see www.spc.noaa.gov/fire for graphic product...
Read more
SPC Day 2 Fire Weather Outlook
SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0257 PM CDT Sat Aug 16 2025
Valid 171200Z - 181200Z
...Northern Great Basin, Southern Idaho and southwestern Montana...
No significant changes were needed for isolated dry thunderstorm
threat area across the northern Great Basin into far southwestern
MT. Pacific moisture plume with PWATs reaching up to 1.00 inch along
a cold front combined with higher terrain convection in the
afternoon will still support areas a mix of wet/dry thunderstorms
Sunday. With elevated mid-level flow remaining in place from
southeastern OR into southwestern MT, faster northeast storm motions
will limit overall rainfall where fuels remain drier, increasing
lightning ignition potential.
...Southern Nevada into western Utah...
Amplifying mid-level trough over the Northwest along with the
arrival a subtle mid-level wave should enhance south-southwesterly
surface flow across southern NV into western UT. Fuels remain very
dry and receptive to spread, with some record to near record high
ERC values remaining across portions of the Great Basin along with
minimal rainfall over the past several days. Southwest winds of up
to 15 mph with relative humidity falling to as low as 10 percent
will bring elevated fire weather conditions to southern NV and
western UT Sunday where Elevated highlights have been introduced.
..Williams.. 08/16/2025
.PREV DISCUSSION... /ISSUED 0204 AM CDT Sat Aug 16 2025/
...Synopsis...
Across the US, broad ridging is forecast to expand while troughing
consolidates over the West. As height aloft build, very warm surface
temperatures are expected over parts of the southern and
Southwestern CONUS. A belt of stronger flow aloft will impinge on
the northern Rockies as the trough and a weak surface cold front
approach. Monsoon moisture should support dry thunderstorms, while
light winds and dry conditions will persist elsewhere Sunday.
...Northern Rockies Dry Thunder...
Troughing should continue to intensify as it moves into the Great
Basin and Rockies Sunday, as a cold front moves in from the west.
This will allow for additional monsoon moisture to filter northward,
supporting scattered showers and thunderstorms through the
afternoon. Despite PWATs climbing to near 0.8 to 1 inches, a mix of
wet and dry thunderstorms is expected ahead of the front from
northern CA into the Northern Rockies. While not as dry as previous
days, stronger flow aloft is expected ahead of the deepening trough.
This should allow for a favorable alignment of drier/more receptive
fuels and faster northeast thunderstorm motions to limit rainfall
across northern NV into central ID and western MT. Thus, isolated
dry lightning and ignitions are likely to remain a concern across
the receptive fuels beds of the northern Great Basin and Rockies
Sunday.
...Southern NV into southwest UT
South of the western US troughing and stronger flow aloft, another
day of dry and locally breezy conditions is expected over parts of
the southern Great Basin. While displaced from the stronger flow,
localized 15 mph surface winds and low RH below 15% are likely
across southern NV and southwest UT. With area fuels very dry and
receptive, some locally elevated fire-weather conditions are
possible, though widespread occurrence is unlikely owing to the
modest winds.
...Please see www.spc.noaa.gov/fire for graphic product...
Read more
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