164
FXUS63 KDTX 091756
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
156 PM EDT Wed Jul 9 2025

.KEY MESSAGES...

- Numerous showers and thunderstorms are likely this afternoon and
evening with highest confidence north of M-59. The strongest storms
will be capable of producing isolated wind gusts around 50 to 60 mph
and small hail. Isolated flooding is also possible through this
evening.

- Dry conditions are favored Thursday and Friday with a warm-up
expected Friday into Saturday.

- The next chance of thunderstorms arrives Saturday, with some
strong storms possible.

&&

.AVIATION...

Just as the early day convection has pushed east of the area, the
next round of storms has already initiated. Areas north of M59
stayed fairly clear today leading to increased instability and thus
stronger storms will be possible this afternoon across MBS and FNT.
Storms have initiate across western MI and are already impacting
MBS as of 18Z and scattered storms will continue through the next
few hours eventually drifting southward across FNT and PTK. Storms
have also initiated just north of the state line and will continue to
advance toward the Detroit taf sites but are a few hours away. Most
of the convection should end or push east between 8-10pm. Attention
then turns toward fog development tonight as moisture left behind
from the storms, elevated dewpoints, and clearing skies lead to
favorable conditions for fog.

For DTW/D21 Convection...Potential remains for period of
thunderstorms this afternoon into the evening ending around 8-10pm.
Gusty thunderstorm outflow winds will be possible with any stronger,
more organized clusters of storms along with brief heavy downpours.

THRESHOLD PROBABILITIES...

* Medium for thunderstorms this afternoon and evening.

* Low for cigs aob 5000 ft this afternoon through tonight.

* Low for ceilings/visibilities to drop below 200ft or 1/2SM
  tonight.

&&

.PREV DISCUSSION...
Issued at 1157 AM EDT Wed Jul 9 2025

UPDATE...

Deformation axis responsible for localized heavy rainfall this
morning has shifted south and is dissipating in response to inbound
subsidence/mid-level drying. Still seeing some convective
enhancement to the broader region of showers which brings hourly
rainfall rates above 1 inch per hour, but should continue to see a
gradual decrease in coverage/intensity over the next few hours.

Focus for this afternoon shifts to convective redevelopment as a
weak cold front drops through the area. The morning discussion is
still valid regarding potential for 40-60 mph wind gusts as cores
collapse, heavy rainfall, and small hail. This update refines
confidence in convective redevelopment as a density gradient has
developed between the I-96 and I-69 corridors due to differences in
diabatic heating. Plenty of sunshine north of the boundary (Tri
Cities/Thumb) has afforded diurnal cumulus development and
temperatures already in the upper 70s-low 80s. Radar echoes are
already observed upstream between Grand Rapids and Big Rapids, and
will slowly track east at 15-20 mph. This suggests time of arrival
between 2pm-4pm to the Tri Cities. Diurnal recovery is much more
muted near the Detroit Metro region where cloud cover and showers
have persisted longer than models depict. Less confidence exists in
convective redevelopment and intensity on this cool side of the
boundary, where cooler temperatures hinder destabilization.

PREV DISCUSSION...
Issued at 353 AM EDT Wed Jul 9 2025

DISCUSSION...

A moist environment within a sfc-850mb theta-e tongue has supported
blossoming elevated convection overnight with radar derived rainfall
estimates so far reaching 0.75 to 1.25" in the heaviest slow-moving
storms. These have been driven along the nose of a weak LLJ beneath
ascent tied to upper jet entrance region. The LLJ weakens and upper
jet forcing eases east through the mid morning hours which should
bring a relative lull in precip coverage mid to late morning. The
plume of instability holds in place through the day to continue to
support convective chances, gradually becoming surface based with
1000 to 2000 J/kg SBCAPE this afternoon. A weak cold front working
into the area should be sufficient to trigger numerous showers and
storms this afternoon and evening. Weak flow through the column
limits deep layer wind shear to around 20 kt which keeps storms
disorganized into a pulse or multicell mode.

The probability for severe weather is low in this setup but precip
loaded downbursts will be a threat, capable of isolated wind gusts
of 40 to 60 mph. Small hail is also possible in the strongest
updrafts. Compared to recent similar setups, PWAT will be slightly
lower at around 1.50" but still supportive of localized heavy
downpours - especially given slow storm motion around 15 to 25 mph.
SE MI is highlighted in a Marginal Risk for severe weather and
excessive rainfall today with the greatest threat expected between
2pm and 10pm. Highs in the lower to mid 80s with dew point near 70F
maintains a muggy feel through the day.

Confluent northwest mid to upper flow follows passage of the trough
axis, allowing the cold front to gradually settle south of the area
on Thursday. Post-frontal thermal advection will be relatively weak,
just a degree or two drop in 850mb temp, but dew point will settle
into a slightly more comfortable range in the mid 60s. Can`t rule
out a stray lake boundary triggered shower in the far southeast
where some weak instability lingers into tomorrow afternoon, but the
subsidence in place and strong dry advection at 700mb should support
overall dry conditions and clearing skies.

Relatively high forecast uncertainty exists for the Friday period as
a ridge attempts to amplify overhead but contends with one or more
embedded shortwaves working beneath it. The bulk of shortwave energy
arriving initially will be generated by convection over the Northern
Plains tonight - the strength and timing of this activity will
influence moisture return and the cloud/precipitation forecast
Friday. There is a camp of solutions, dominated by the Canadian
ensemble, that produce a stronger trough over the Canadian Prairie
and Great Plains that appears to propel this shortwave activity in
to offer a higher chance for precip. For now, given the governing
ridge setting up and dominant signal for lower precip chances among
ensemble solutions, no reason to deviate from the NBM forecast that
carries just a slight chance of showers and storms.

Stronger signal exists for a low pressure system to track through
the region on Saturday in response to the aforementioned Plains
trough taking on a negative tilt as it pivots over the upper Great
Lakes. This period bears watching for stronger storms given higher
wind shear and potential for organized forced ascent along the
height fall center. Assuming the warm sector passes overhead during
daylight hours, highs in the upper 80s and lower 90s are achievable.
Chances for additional showers and storms carry into the weekend as
low amplitude prevailing flow offers opportunity for several
disturbances to pass over the region.

MARINE...

A weak surface low/trough drifts over Lake Huron this morning while
gentle winds organize out of the SE. This draws more humid and
increasingly unstable air into the region while the governing upper
low tracks across eastern Ontario into western Quebec. The
combination of forcing and instability ensure periodic thunderstorms
this afternoon and evening, with later rounds tied to the passage of
the system`s cold front. Ambient dynamics are rather weak which
should keep prevailing conditions below Small Craft Advisory
criteria, but locally higher winds/waves are possible with some
stronger storms that might develop. Shortwave ridging slides east
Thursday allowing surface high pressure to build in from the Upper
Midwest which facilitates mainly dry conditions across the
waterways. A more robust low moves in late Friday into Saturday with
renewed potential for showers and storms.

HYDROLOGY...

Scattered to numerous showers and thunderstorms are forecast today,
mainly during the afternoon and evening. Storms will be relatively
disorganized, but with humid conditions and slow storm movement east
at around 15 to 25 mph, storms will be capable of producing
torrential downpours. Localized areas may receive near 1 inch per
hour rainfall rates, with isolated rainfall totals ranging from 1 to
3 inches possible. The higher totals will be most likely for any
areas that see training or repeated thunderstorm activity. Isolated
instances of flooding of urban areas, small streams, and otherwise
poorly drained areas will be possible, especially if storms track
over locations that already received heavy rain early this morning.
The main threat for flooding will be between 2pm and 10pm.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

AVIATION.....DRK
UPDATE.......MV
DISCUSSION...TF
MARINE.......KGK
HYDROLOGY....TF


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at www.weather.gov/detroit.