WW 547 SEVERE TSTM IN MI OH LM 091705Z - 092300Z
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 547
NWS Storm Prediction Center Norman OK
105 PM EDT Sun Aug 9 2026
The NWS Storm Prediction Center has issued a
* Severe Thunderstorm Watch for portions of
Northern Indiana
Southwest Lower Michigan
Northwest Ohio
Lake Michigan
* Effective this Sunday afternoon and evening from 105 PM until
700 PM EDT.
* Primary threats include...
Scattered damaging wind gusts to 70 mph possible
Isolated large hail events to 1 inch in diameter possible
SUMMARY...A line of thunderstorms will track across southern Lake
Michigan into the watch this afternoon. The stronger cells along
the line will pose a risk of damaging wind gusts.
The severe thunderstorm watch area is approximately along and 55
statute miles north and south of a line from 45 miles west northwest
of Benton Harbor MI to 10 miles east of Jackson MI. For a complete
depiction of the watch see the associated watch outline update
(WOUS64 KWNS WOU7).
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 546...
AVIATION...A few severe thunderstorms with hail surface and aloft to
1 inch. Extreme turbulence and surface wind gusts to 60 knots. A few
cumulonimbi with maximum tops to 500. Mean storm motion vector
29030.
...Hart
WW 0547 Status Updates
STATUS REPORT ON WW 547
SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 45 SSE RAC
TO 35 NNW BEH TO 15 SW MKG TO 20 NNE MKG.
FOR ADDITIONAL INFORMATION SEE MESOSCALE DISCUSSION 1879
..WENDT..08/09/26
ATTN...WFO...IWX...GRR...
STATUS REPORT FOR WS 547
SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS
INC033-039-087-091-113-141-151-092040-
IN
. INDIANA COUNTIES INCLUDED ARE
DE KALB ELKHART LAGRANGE
LA PORTE NOBLE ST. JOSEPH
STEUBEN
MIC005-015-021-023-025-027-037-045-059-065-067-075-077-081-121-
139-149-159-092040-
MI
. MICHIGAN COUNTIES INCLUDED ARE
ALLEGAN BARRY BERRIEN
BRANCH CALHOUN CASS
CLINTON EATON HILLSDALE
INGHAM IONIA JACKSON
KALAMAZOO KENT MUSKEGON
OTTAWA ST. JOSEPH VAN BUREN
WW 0546 Status Updates
STATUS REPORT ON WW 546
SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 40 ESE RFD
TO 20 S RAC TO 35 E RAC.
..WENDT..08/09/26
ATTN...WFO...LOT...MKX...
STATUS REPORT FOR WS 546
SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS
ILC031-043-097-091940-
IL
. ILLINOIS COUNTIES INCLUDED ARE
COOK DUPAGE LAKE
LMZ675-740-741-742-777-091940-
CW
. ADJACENT COASTAL WATERS INCLUDED ARE
LAKE MICHIGAN FROM WIND POINT WI TO WINTHROP HARBOR IL 5NM
OFFSHORE TO MID LAKE
WINTHROP HARBOR TO WILMETTE HARBOR IL
WILMETTE HARBOR TO NORTHERLY ISLAND IL
NORTHERLY ISLAND TO CALUMET HARBOR IL
LAKE MICHIGAN FROM WINTHROP HARBOR TO WILMETTE HARBOR IL 5NM
OFFSHORE TO MID LAKE
MD 1881 CONCERNING SEVERE THUNDERSTORM WATCH 546...547... FOR NORTHWEST INDIANA
Mesoscale Discussion 1881
NWS Storm Prediction Center Norman OK
0349 PM CDT Sun Aug 09 2026
Areas affected...Northwest Indiana
Concerning...Severe Thunderstorm Watch 546...547...
Valid 092049Z - 092215Z
The severe weather threat for Severe Thunderstorm Watch 546, 547
continues.
SUMMARY...A locally greater wind threat is evident in northwest
Indiana.
DISCUSSION...KLOT and TMDW/TORD radar velocity data suggest a
locally greater wind threat developing in northwest Indiana. Two
small bowing segments are evident with around 50 kt outbound
velocities. Given the strong heating and large buoyancy ahead of
these storms, they will likely pose a locally greater severe wind
threat over the next 1-3 hours. Depending on the persistence of
these storms, additional extensions of WW 547 may become necessary.
..Wendt.. 08/09/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...IWX...LOT...
LAT...LON 40898601 41158705 41288738 41488761 41898689 41528585
41268572 40918591 40898601
MOST PROBABLE PEAK TORNADO INTENSITY...UP TO 90 MPH
MOST PROBABLE PEAK WIND GUST...55-70 MPH
MOST PROBABLE PEAK HAIL SIZE...UP TO 1.25 IN
MD 1880 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR SOUTHEAST LOWER MICHIGAN INTO NORTHWEST OHIO
Mesoscale Discussion 1880
NWS Storm Prediction Center Norman OK
0339 PM CDT Sun Aug 09 2026
Areas affected...Southeast Lower Michigan into northwest Ohio
Concerning...Severe potential...Watch possible
Valid 092039Z - 092245Z
Probability of Watch Issuance...40 percent
SUMMARY...The threat for wind damage will eventually spread eastward
into parts of western Ohio and southeast Lower Michigan. A watch is
possible for parts of these areas later this afternoon.
DISCUSSION...Airmass destabilization continues in portions of
northwest Ohio into southeast Lower Michigan. An upstream line of
convection may impact portions of these areas later this afternoon
into the evening. Cloud cover ahead of the convection has slowed the
northward progress of the more favorable airmass and the northern
portion of the convection has trended downward in the last hour. It
is possible that the strongest activity may track farther south
where buoyancy is much larger. The greatest risk for damaging winds
will probably exist where dewpoints are 70+ F. However, at least
isolated wind damage will remain possible along the instability
gradient into the evening. A watch is possible for portions of these
areas later this afternoon.
..Wendt/Hart.. 08/09/2026
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...CLE...ILN...DTX...IWX...GRR...
LAT...LON 42358410 42178321 41648237 41058253 40488321 40428390
40548457 40608470 41198482 42358410
MOST PROBABLE PEAK WIND GUST...UP TO 60 MPH
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0259 PM CDT Sun Aug 09 2026
Valid 092000Z - 101200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FOR PORTIONS OF
THE MIDWEST INTO THE OHIO VALLEY...
...SUMMARY...
Scattered damaging winds are possible today into this evening from
southern Wisconsin eastward across parts of northern Illinois,
southern Lower Michigan, northwest Ohio, and northern Indiana.
Damaging wind and hail may also occur across portions of the Dakotas
tonight.
...20Z Update...
The main changes made to the outlook were to remove the Slight Risk
and more broadly expand Marginal Risk severe probabilities across
the central/northern Plains. CAM guidance has shown appreciable
uncertainty regarding storm coverage in this region, and trends in
model output continue to show sparse coverage. Nonetheless,
widespread 2000+ J/kg MLCAPE amid 50+ kts of effective bulk shear
may support a couple of severe multicells or supercells should any
storms manage to become sustained this afternoon or evening. The
Slight Risk along/south of the Great Lakes was expanded slightly
eastward into northern OH to account for some boundary layer
destabilization ahead of an approaching MCS, where a few damaging
gusts are possible.
Otherwise, the previous forecast remains on track, with only minor
changes made to the severe/thunder probabilities to account for the
latest observations and guidance consensus.
..Squitieri.. 08/09/2026
.PREV DISCUSSION... /ISSUED 1056 AM CDT Sun Aug 09 2026/
...Midwest...
A persistent cluster of thunderstorms over southern WI appears
likely to continue southeastward through much of the day into parts
of IL/MI/IN and eventually OH. This activity will track near a
NW-SE oriented baroclinic zone, with dewpoints in the lower 70s to
the south. Eventually, low-level lapse rates will become
sufficiently steep to support damaging wind gusts along the leading
edge of the storms. Later tonight, strengthening southwesterly
low-level winds will enhance warm advection and lift over parts of
IL/IN, potentially leading to another round of strong/severe storms
capable of damaging winds and hail after 06z.
...Dakotas...
12z model guidance continues to decrease the confidence in overnight
severe storms, with some CAM solutions showing no thunderstorms.
Therefore have made the SLGT area smaller and focused where there is
highest confidence in isolated storms. Forecast soundings continue
to indicate steep mid-level lapse rates and strong deep shear,
providing a conditional risk of supercells if convection can be
sustained.
...AZ...
Thunderstorms are once again predicted to form along the Rim and
track westward toward the PHX metro area this evening. The strength
of the steering flow, instability, and mid-level moisture all appear
favorable for a severe risk. However, mesoscale details of the
evolution of the storms over high terrain will dictate the eventual
risk.
SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1237 PM CDT Sun Aug 09 2026
Valid 101200Z - 111200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ROUGHLY FROM
ILLINOIS EASTWARD INTO PENNSYLVANIA...
...SUMMARY...
Thunderstorms with severe wind gusts will be possible Monday
afternoon and evening from northern Illinois eastward into western
Pennsylvania. Isolated severe gusts and hail will also be possible
from parts of the central and northern Plains into the Midwest, with
scattered strong storms over southern Arizona.
...From northern IL eastward into PA...
A leading shortwave trough may support early day thunderstorms over
portions of NY and PA, though probably not immediately severe. Some
chance exists for re-development from southern New England into NJ
during the afternoon as a surface trough develops, and at least
isolated severe activity is possible. Additional afternoon storms
may develop across the remainder of NY and PA as instability
develops behind the initial wave with areas of strong gusts and
marginal hail.
While isolated wind/hail may occur during the early to mid afternoon
as the air mass becomes uncapped, a greater coverage of severe
storms is expected during the late afternoon and into the evening
from southern WI/IL into IN and OH. Here, a large area of strong
instability will develop, with a persistent/deepening boundary layer
theta-e plume out of the southwest. The high PWAT, relatively steep
midlevel lapse rates, and deep layer shear of 40-50 kt will support
supercell development, with possible bowing structures with time.
Large hail, perhaps an isolated tornado, and damaging winds will be
possible.
...Northern Plains...
Southeast surface winds will maintain 60s F dewpoints into NE and SD
during the afternoon as strong heating occurs near a surface trough
over the High Plains/Black Hills. This will occur beneath moderate
westerly flow aloft, which will elongate hodographs and produce
favorable deep-layer shear for long-lived cells or bows. Storm
coverage is uncertain, but the conditional risk for large damaging
hail and wind is high. At least isolated cells are expected to form
near the Black Hills and into western NE where heating will be
strong, with perhaps greater storm chances increasing after 00Z into
the central Dakotas with the aid of a modest nocturnal low-level
jet.
...Southern AZ...
Substantial moisture will remain over the area Monday, with PWAT
over 1.25" and areas of 60s F dewpoints. Westerly surface winds are
forecast to develop during the afternoon over southern AZ, which
when combined with the deep easterlies aloft, will support
westward-propagating cells. Storms should form near the Rim and over
the higher terrain of southeast AZ, with locally severe gusts as
activity moves across the lowlands. A storm or two could potentially
produce small hail as well as deep-layer effective shear will be
over 30 kt.
..Jewell.. 08/09/2026
SPC 1930Z Day 3 Outlook
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0233 PM CDT Sun Aug 09 2026
Valid 111200Z - 121200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM ILLINOIS TO
THE APPALACHIANS...
...SUMMARY...
Thunderstorms with severe wind gusts will be possible on Tuesday
over parts of the Ohio Valley and central Appalachians. Isolated
severe gusts and hail will also be possible from parts of the
central and northern Plains into the Midwest.
...From IL into western VA/NC...
Bouts of strong to severe thunderstorms are expected Tuesday, though
timing and position of the greatest threat corridor is uncertain.
Areas of thunderstorms may be ongoing early on Tuesday across parts
of the OH Valley region, and strong gusts cannot be ruled out at
that time. Daytime heating and a weak surface trough may aid
re-development across the Appalachians and into VA/NC, with
deep-layer mean winds supporting mobile clusters of storms producing
damaging gusts.
Late afternoon and evening development should occur farther west as
west/southwest boundary layer winds maintain a warm and unstable air
mass into IL/IN/OH. The greatest threat of a damaging wind corridor
appears to be in these areas, with MUCAPE over 3000 J/kg, and
potentially 40-50 kt deep-layer shear. Depending on how mesoscale
factors resolve, supercells will be possible, but the primary risk
is expected to be potentially widespread damaging winds.
Predictability is currently low, but categorical risk upgrades
cannot be ruled out in later outlooks.
...Northern Plains...
Storms are expected to develop late in the day over the western
Dakotas near a surface trough over the High Plains. Southeasterly
surface winds and 60s F dewpoints will yield moderate instability,
and favorable 40-50 kt deep layer shear. The elongated mid to upper
hodographs should aid supercell and hail potential, with bowing
structures producing damaging wind during the evening.
...AZ...
An easterly flow regime will persist on Tuesday, with scattered
afternoon storms over the higher terrain moving generally westward.
Locally damaging gusts may occur with the stronger outflows.
..Jewell.. 08/09/2026
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1133 AM CDT Sun Aug 09 2026
Valid 091700Z - 101200Z
The forecast remains on track for an expansive isolated dry
thunderstorm threat extending from the Great Basin to the central
Plains, and elevated fire weather conditions across much of the
Pacific/Intermountain West and a portion of the southern Plains.
Satellite imagery depicts dense smoke over portions of the northern
Great Basin and Intermountain West, and mixed mid/high-level clouds
due to deeper monsoonal moisture advecting northward. With more
sufficient instability in place this afternoon (as compared to
yesterday), a greater coverage of mixed wet/dry thunderstorms are
expected throughout the dry thunderstorm risk area, in the exception
of a few areas where denser plumes of smoke may inhibit more
efficient vertical mixing. A prolonged dry boundary layer will
continue to limit precipitation efficiency; however, slower storm
motions and areas that see multiple rounds of thunderstorms could
encounter localized accumulating rainfall up to 0.5". On the
periphery of much desired precipitation, lightning ignitions will
remain a concern as a result of drought-stressed fuels and an
exceptionally dry environment. See the previous discussion for more
information.
..Elizalde-Garcia.. 08/09/2026
.PREV DISCUSSION... /ISSUED 0114 AM CDT Sun Aug 09 2026/
...Synopsis...
Elevated fire weather conditions are expected across a broad swath
of the western CONUS for today, stretching from northern California
into the northern Great Basin and central Rockies. Additionally,
isolated dry thunderstorms are possible across portions of the Great
Basin and into the southern High Plains.
...California into the Great Basin and Wyoming...
Early morning water-vapor imagery continues to depict a broad upper
ridge over the Southwest. This feature is expected to linger over
the region for the next several days, and will act to modulate any
low-level mass response associated with weak perturbations embedded
within northern stream of the ridge axis. Consequently, surface
winds today will mainly be driven by orographic influences through
terrain-favored locations. Most high-res guidance depicts sustained
winds generally around 15 mph for most locations from northern CA
into the northern Great Basin and portions of WY. However, deep
mixing within a very dry environment will facilitate downward
transport of stronger flow near the top of the boundary layer, which
should manifest as 15-25 mph gusts at the surface. Given the
antecedent dry air mass (which should yield afternoon RH minimums in
the teens to single digits) and very limited rainfall over the past
1-2 weeks, areas of elevated fire weather conditions appear likely.
Sustained elevated conditions appear most likely across northwest NV
and eastern WY where more focused corridors of downslope flow will
promote sustained 15-20 mph winds.
Further west into central CA, an onshore flow regime should promote
downslope off the coastal terrain and into the Central Valley.
Sustained winds near 15 mph coupled with 15-20% RH minimums should
support areas of elevated fire weather conditions, especially in
close proximity to terrain features.
...Southern High Plains...
Hot and dry conditions will prevail across the Southern Plains this
afternoon where high temperatures will likely exceed 100 F. Weak lee
troughing juxtaposed with high pressure over the mid/lower MS Valley
will yield a swath of 15-20 mph gradient winds from the TX Panhandle
into southwest KS. The combination of hot/dry conditions and breezy
winds will support a swath of elevated fire weather conditions.
While the primary fire weather concern will be focused across the
OK/TX Panhandles, fire weather conditions may extend well into
central KS; however, recent rainfall over the past 72 hours should
modulate fuel status to some degree with east/northeastward extent.
...Dry Thunderstorms...
00 UTC RAOBs from the Southwest/Great Basin sampled very steep
mid-level lapse rates with sufficient mid-level monsoonal moisture
for 250-500 J/kg MUCAPE. Additionally, soundings from the Great
Basin sampled very dry boundary-layer conditions, which is reflected
in surface observations by poor overnight RH recoveries. MRMS QPE
and lightning activity over the past 24 hours suggests dry
thunderstorms occurred across portions of the Great Basin/Four
Corners yesterday afternoon, and similar thermodynamic conditions
should prevail today. However, the dry thunderstorm risk will be
displaced further north compared to yesterday due to continued
northward advection of monsoonal moisture on the western edge of the
ridge. Regardless, the potential for dry lightning over dry fuels
will pose a risk for additional lightning ignitions this
afternoon/evening.
...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
0210 PM CDT Sun Aug 09 2026
Valid 101200Z - 111200Z
Only minor adjustments were made to the risk areas based on updated
guidance. A narrow region of locally critical fire weather
conditions are possible across portions of western Nevada where
stronger downslope winds of 15-25 mph and 8-15% RH values overlap
very dry fuels (and several new fire starts, including the larger
Bug Fire northwest of Reno). The rest of the forecast remains on
track, please see the previous discussion for more information.
..Elizalde-Garcia.. 08/09/2026
.PREV DISCUSSION... /ISSUED 0143 AM CDT Sun Aug 09 2026/
...Synopsis...
Another day of elevated fire weather conditions is expected across
the northern Great Basin into the central/northern Rockies as well
as portions of the southern High Plains. Isolated dry thunderstorms
will also pose a fire weather concern for parts of the Great Basin.
...Northern Great Basin...
As with today, a persistent upper-level ridge will modulate any
low-level mass response across the western CONUS, resulting in weak
gradient winds for most locations Monday afternoon. However, deep
mixing and localized orographic enhancements will promote areas of
15-20 mph winds (gusting to 20-25 mph at times). Little moisture
recovery is expected across the central to northern Great Basin,
which will promote another day of single digit to low teen RH
minimums by mid-afternoon. Widespread areas of elevated fire weather
conditions are expected, but hot, dry, and windy conditions may be
more prolonged/widespread in the lee of the northern Sierra Nevada
in northwest/western NV, through the Snake River Valley, and across
east-central WY in proximity to a weak surface low.
...CA Central Valley...
An onshore flow regime is expected to persist into Monday. Downslope
westerly flow off the coastal terrain should promote 15-20 mph winds
into western portions of the Central Valley. Dry conditions (RH
values in the teens to low 20s) coupled with preceding days of
dry/windy conditions should support some fire weather concern.
...Southern High Plains...
A modest deepening of the lee trough along the central to northern
High Plains will maintain modest pressure gradient winds across the
southern and central Plains on Monday. Another day of afternoon high
temperatures in the 100s will promote very dry conditions across
western OK into the Panhandles and southwest KS. A combination of
15-20 mph gradient winds (gusting to 20-25 mph) and RH minimums in
the teens should support a swath of elevated fire weather
conditions.
...Dry Thunderstorms...
A plume of monsoonal moisture will continue to shift northward over
the next 24-48 hours. Weak ascent - largely driven by orographic
lift - will promote isolated thunderstorms across much of the Great
Basin and Southwest/Four Corners. However, drier conditions on the
northern fringe of the returning moisture (characterized by PWAT
values of 0.45 to 0.75 inches), coupled with antecedent dry
low-level conditions, should support favorable thermodynamic
profiles for dry thunderstorms. With dry fuels already in place
across much of the region, lightning ignitions will be possible.
...Please see www.spc.noaa.gov/fire for graphic product...
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