Severe Thunderstorm Warning 39, NWS Detroit, MI

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
300 PM EDT Tue Jun 24 2025

.KEY MESSAGES...

- Extreme heat warnings and advisories should expire on-schedule
this evening as conditions improve.

- Scattered to numerous thunderstorms continue until the late
evening hours with locally strong and damaging wind gusts
possible.

- Additional chances for thunderstorms will persist Wednesday
through Friday, including the return of heat indices in the mid 90s
Friday.

&&

.DISCUSSION...

After starting the day in the low to mid 70s, midday heat indices
are peaking in the upper 90s to lower 100s ahead of an approaching
front since surface dewpoints haven't really mixed-out and 2m
temperatures have stalled in the low to mid 90s. Modest relief is
pending after a multi-day stretch of +90F highs once the forecast
narrative transitions from heat and humidity focus to convective
impacts this afternoon as a cold front drops through Southeast
Michigan. GOES imagery shows pre-frontal convective initiation well
underway with precipitation echoes blossoming in KDTX reflectivity
products. Mesoscale environment remains favorable for scattered to
numerous thunderstorms amidst uncapped SBCAPE building into the 1500-
2500 J/kg through the remaining daylight hours. Per HREF, ensemble
minimum SBCAPE values, south of I-69, range from 750-1750 J/kg which
ensures the presence of necessary instability for storm development.
Main limiting factor will be the lack of meaningful shear, marked by
0-6 km magnitudes of 20-25 knots. Still, expect some heavy water-
loading in the most robust multicellular updrafts which could lead
to isolated severe gusts/microbursts, in addition to efficient
rainfall rates. At issuance time, several SPSs and one SVR were in
effect with the most productive initial storm activity, located
along the instability gradient. Early observational data (PTK
gusting to 25 knots) reinforces the belief in winds as the primary
threat. Outflow boundaries are already organizing which should lead
to additional pre-frontal convective development, especially at
intersecting boundaries and lake breeze interactions.

Current heat headlines (Extreme Heat Warning and Heat Advisory) will
be allowed to expire on-schedule (8 PM) given the reduction in
temperatures due to the transition in diurnal cycle, expected
rainfall, and FROPA. Storms gradually decrease in coverage and
intensity overnight as the surface front settles near/south of the
MI/OH border Wednesday morning allowing for the first reprieve of
overnight lows to less deviant levels (mid-upper 60s, and 70F near
the state-line).

Shift to a light ENE gradient wind develops in the wake of the
boundary with a comparatively cooler airmass filtering in. 850 mb
temperatures drop into the mid teens (Celsius) which caps highs AOB
80F for most locations, aided further by a higher cloud fraction
throughout the day. Synoptically, the 598 dam sampled 500 mb ridge
will continue to flatten and fill-in Wednesday as the upper level
jet streak presses through southeastern Canada. Did raise MaxTs a
bit as guidance hints at minor reversal of the cold front as a warm
front which could bring highs into the upper 80s south of I-94.
Minor height falls are forecast for the local area Wednesday which
sustains additional chances for thundershowers at times Wednesday.
Latest CAMs are notably drier than the coarser solutions suggesting
a narrower footprint, generally south of I-96/696. This coincides
with the better residual moisture and proximity to the surface
convergence axis. Not expected much in the way of severe potential,
but can't rule out an isolated marginally severe gust given a less
unstable airmass.

Lower Michigan set to reside between a northern stream ridge rolling
east across the Canadian Prairies and the decaying Southeast CONUS
mid-level anticyclone to close out the workweek. This keeps the
region positioned within a more perturbed/cyclonically active height
field. Meanwhile, the stalled boundary lifts north as a warm front
Thursday with a sensible uptick in surface dewpoints. This
environment favors fresh convective activity with renewed CAPE,
although weak capping will need to be overcome/eroded for surface-
based parcels. 850 mb temperatures creep back into the upper teens
Thursday and Friday, perhaps even into Saturday providing above
normal readings into the weekend. A weak surface low tracks into the
Great Lakes Friday dragging a decaying cold front with. Expect it.
This serves as the next focus for convection Friday into Saturday
with a low-end severe threat. However, dynamics should be
unimpressive, and the front eventually washes out, undercutting
advection of meaningfully cooler air. Shortwave ridging passes
through aloft Saturday into Sunday for a brief period of higher
confidence drying before the next longwave trough digs into The
Midwest early next week with more showers and storms to follow.

&&

.MARINE...

A warm and unstable airmass persists over the Great Lakes this
afternoon, which will be the catalyst for shower and thunderstorm
development through the evening. The greatest coverage of
thunderstorms will be south of Port Huron, in which stronger storms
will be capable of wind gusts over 34 knots, heavy downpours, and
cloud to ground lightning. Storms wane with loss of daytime heating
while high pressure builds over Lake Superior. This eases winds to
the north-northeast by Wednesday morning as the high takes hold. SE
Michigan will still reside on the northern fringe of a strong ridge
axis with warm and unstable conditions, which affords the
opportunity for both nocturnal and afternoon storms with low
predictability. A broad trough of low pressure then tracks into the
region to end the work week, bringing another round of shower/storm
potential and enhancements to the wind field.

&&

.HYDROLOGY...

Initial round of showers and thunderstorms are underway this
afternoon as a slow moving cold front capitalizes on a moist and
unstable airmass. Deep column moisture makes for efficient rainfall
rates that could briefly approach two inches per hour. This may
result in localized flooding, predominantly in low-lying and flood-
prone areas. Locations which receive repeated rounds of showers and
thunderstorms are most susceptible, but confidence in specific
locations is low. The humid airmass remains in place through the end
of the week offering several additional opportunities for more
showers and storms, some of which could produce further instances of
isolated flooding.

&&

.PREV DISCUSSION...
Issued at 103 PM EDT Tue Jun 24 2025

AVIATION...

A stalled frontal boundary is the initiation point for shower and
thunderstorm development. Radar and satellite presentation shows
initial development has and will continue to form along and between
I-94 to M59, or across the Metro terminals up to KPTK. The PROB30
group has been upgraded to a TEMPO to account for the higher
confidence of sustained thunderstorm development. Terminals to the
north also have chances of observing showers and storms, however,
confidence is much lower as any development would be triggered off of
outflow boundaries from prior thunderstorms and/or lake breezes. The
strongest thunderstorms will have the potential to produce wet
microbursts capable of brief wind gusts aoa 40 knots. Confidence in
cloud trends and mvfr potential is very low overnight as it will be
contingent on this afternoon and evening's activity. However, this
stalled front may produce additional rain showers overnight and
possibly some rumbles of thunder which will bring the potential for
mvfr cigs as flow veers to the northeast.

For DTW/D21 Convection...Satellite and radar presentation has
warranted a TEMPO group for TSRA. Rain showers and thunderstorm
presentation will be scattered to possibly numerous at times, with
the most likely timing for thunderstorms ranging from 18Z to 01Z.
However, 20 to 23Z presents the most likely time to see thunderstorm
development. Any strong storm development will be capable of
producing wind gusts aoa 40 knots.

 THRESHOLD PROBABILITIES...

* Moderate for thunderstorms 18z-01z.
* Low for cigs aob 5kft overnight.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Heat Advisory until 8 PM EDT this evening for MIZ060-062-063-068-
     075-082-083.

     Extreme Heat Warning until 8 PM EDT this evening for MIZ061-069-070-
     076.

Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

DISCUSSION...KGK
MARINE.......MV
HYDROLOGY....KGK
AVIATION.....AM

You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.

Hazardous Weather Outlook
National Weather Service Detroit/Pontiac MI
359 AM EDT Tue Jun 24 2025

MIZ047>049-053>055-250800-
Midland-Bay-Huron-Saginaw-Tuscola-Sanilac-
359 AM EDT Tue Jun 24 2025

This hazardous weather outlook is for southeast Michigan.

.DAY ONE...Today and Tonight

Scattered to numerous thunderstorms are expected this afternoon,
mainly between 1 PM and 7 PM. The strongest storms will be capable of
producing wind gusts to 60 MPH as they move to the east at 30 MPH.
Any thunderstorm that occurs will produce intense rainfall rates.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

There is a chance of thunderstorms Wednesday through Friday. Heavy
rainfall and localized flooding will be the main concern.

.SPOTTER INFORMATION STATEMENT...
Dispatchers...Please notify your emergency managers. Spotter
activation may be needed this afternoon.

MIZ060>063-068>070-075-076-082-083-250800-
Shiawassee-Genesee-Lapeer-St. Clair-Livingston-Oakland-Macomb-
Washtenaw-Wayne-Lenawee-Monroe-
359 AM EDT Tue Jun 24 2025

This hazardous weather outlook is for southeast Michigan.

.DAY ONE...Today and Tonight

Heat advisories and warnings remain in effect until . Please see the
latest urgent weather message for additional information.

Scattered to numerous thunderstorms are expected this afternoon and
evening, mainly between 2 PM and 11 PM. The strongest storms will be
capable of producing wind gusts to 60 MPH as they move to the east
at 15 MPH. Any thunderstorm that occurs will produce intense
rainfall rates. Localized flooding is possible, especially in more
urbanized areas.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

There is a chance of strong thunderstorms Wednesday through Friday.
Heavy rainfall and localized flooding will be a concern.

.SPOTTER INFORMATION STATEMENT...
Dispatchers...Please notify your emergency managers. Spotter
activation may be needed this afternoon.

LCZ460-LEZ444-LHZ361>363-421-422-441>443-462>464-250800-
Lake St Clair-
Michigan Waters of Lake Erie from Detroit River to North Cape MI-
Lake Huron from 5NM east of Mackinac Bridge to Presque Isle Lt
beyond 5 NM off shore-
Lake Huron from Presque Isle Light to Sturgeon Point MI beyond 5NM
off shore-
Lake Huron from Sturgeon Point to Alabaster MI beyond 5NM off shore-
Outer Saginaw Bay SW of Alabaster to Port Austin MI to Inner Saginaw
Bay-Inner Saginaw Bay SW of Point Au Gres to Bay Port MI-
Port Austin to Harbor Beach MI-Harbor Beach to Port Sanilac MI-
Port Sanilac to Port Huron MI-
Lake Huron from Port Austin to Harbor Beach beyond 5NM Off Shore-
Lake Huron from Harbor Beach to Port Sanilac beyond 5NM Off Shore-
Lake Huron from Port Sanilac to Port Huron beyond 5NM Off Shore-
359 AM EDT Tue Jun 24 2025

This hazardous weather outlook is for portions of Lake Erie, Lake
Huron and Lake St Clair.

.DAY ONE...Today and Tonight

Scattered to numerous thunderstorms are forecast this afternoon and
evening, mainly south of Sturgeon Point and across Lakes St Clair and
Erie. The strongest storms will be capable of producing wind gusts to
50 knots as they move to the east at 20 MPH. Intense rainfall will
occur with any thunderstorm.

.DAYS TWO THROUGH SEVEN...Wednesday through Monday

There is a chance of strong thunderstorms Wednesday through Friday.

.SPOTTER INFORMATION STATEMENT...
Dispatchers...Please notify your emergency managers. Spotter
activation may be needed this afternoon.

You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.

SC

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