132
FXUS63 KDTX 091958
AFDDTX

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

.KEY MESSAGES...

- Numerous showers and thunderstorms will impact southeast Michigan
  between now and 9 PM.

- Strongest storms will be capable of isolated wind gusts to 60 mph
  and small hail.

- Isolated flash flooding is possible with these storms, mainly for
  urban areas where 2 to 3 inches of rain already fell this morning.

- Drier conditions are expected Thursday with increasing shower and
  thunderstorm chances into the weekend.

- Warmer conditions this weekend with highs near 90 degrees on
  Saturday

&&

.DISCUSSION...

A weak cold front extends from roughly Saginaw Bay to South Bend and
has been the triggering mechanism for convection early this
afternoon. While SPC mesoanalysis now shows a broad plume of ~1500
J/kg MLCAPE across all of SE Michigan, there is still a 3-4 degree
difference in surface temperatures where clouds/showers lingered
this morning (south of I-96). Cumulus development is still
underperforming in these areas, but has initiated nonetheless
indicating that surface conditions are likely destabilizing. If any
storms can sustain an organized cold pool into this area, severe
weather will be possible. Further north, boundary layer conditions
are still more primed for surface-based convection. Lack of mid-
level flow and resultant shear profiles supports pulse to
disorganized multicellular behavior with potential for precipitation
loaded wind gusts of 40-60 mph. The higher end gusts will likely be
isolated in nature. Slow storm motion of 15-20 knots and the high
moisture environment will also be supportive of heavy rainfall, to
be discussed in the hydrology section.

Drier conditions are expected for Thursday as low amplitude ridging
builds in aloft. A diurnally-driven stray shower or two is not out
of the question (e.g. 12z HRRR) if east flow can draw in a boost of
Lake Huron moisture into the boundary layer. Otherwise, the strong
subsidence inversion keeps the environment capped.  The thermal
trough holds firmly in place across the northeast quadrant of CONUS,
keeping temperatures seasonable in the low to mid 80s.

Unsettled weather then returns Friday into this weekend, beginning
with a compact vorticity maximum that barrels across lower Michigan
on Friday. This wave slightly outpaces the warm front that lifts
into the area overnight Friday, which will be followed by a strong
Pacific wave that brings steeper mid-level lapse rates to the region
through the weekend. For daytime Friday, this equates to weak
instability profiles with light column flow to support general
shower and storm chances during peak heating. PoPs then increase
through the weekend as low pressure deepens over central Ontario,
driving a pre-frontal trough through the area during peak heating
Saturday followed by a cold front on Sunday. The stronger forcing
will capitalize on warm sector instability to generate more
organized thunderstorm potential alongside comparatively stronger
mid-level flow (30-35 knots). Nocturnal to morning timing of the
frontal passage looks to bring temperatures back toward the mid-80s
by Sunday, while isentropic downglide supports increasingly stable
conditions throughout the day. Ridging builds back into the region
early next week, with H5 mean ensemble heights building to 591 dam
and temperatures warming back into the upper 80s.

&&

.MARINE...

The ongoing passage of a cold front and initiation along lake
breezes and storm outflows will produce scattered to numerous
showers and thunderstorms throughout the afternoon and evening, with
the best coverage expected across the Saginaw Bay into southern Lake
Huron, Lake St. Clair, and Lake Erie. The stronger thunderstorms
will be capable of producing wind gusts at or above 35 knots, small
hail, and heavy downpours. Thunderstorm coverage is expected to wane
late tonight leading into early tomorrow morning. Otherwise outside
of thunderstorm coverage, the pressure gradient remains weak with a
building high pressure reinforcing this weak gradient through late
into the week. This brings calm to light winds through Friday. This
also bring dry weather tomorrow and Friday, with active weather
returning by the weekend.

&&

.HYDROLOGY...

Numerous thunderstorms have developed over western lower Michigan
and the Saginaw Valley/Thumb regions and are moving east to
southeast at around 15 to 25 mph. These will track across the area
between now and 9 pm. The 12z KDTX sounding sampled a moisture rich
environment with PWAT values in the 90th percentile (1.6 inches)
along with weak westerly column flow. Several localized spots
received 2 to 3 inches of rainfall this morning, with some of that
rain occurring in the Detroit metropolitan area. Additional rainfall
totals of 1 to 2 inches, especially in urban areas, may contribute
to flash flooding this evening. This would be most likely if a west
to east oriented line of training thunderstorms developed, which
would be capable of even higher localized totals.

&&

.PREV DISCUSSION...
Issued at 156 PM EDT Wed Jul 9 2025

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.


&&

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

$$

DISCUSSION...MV
MARINE.......AM
HYDROLOGY....MV
AVIATION.....DRK


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