869
FXUS63 KDTX 160408
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1208 AM EDT Wed Jul 16 2025

.KEY MESSAGES...

- Shower and thunderstorm chances begin Wednesday and increase
  Wednesday late afternoon-evening through Thursday with potential
  for heavy rainfall.

- A cold front sweeps through the area early Thursday night followed
  by cooler and less humid air to end the work week and start the
  weekend.

&&

.AVIATION...

A weak shortwave slowly migrating northeast across MO/IL/IN will
lift across far southeast Michigan on Wednesday. This lead pocket of
energy aloft will help mid-level cloud spread into the area, but it
may not be enough to overcome the drier air in place over the area
late this evening. Thus confidence is waning as to whether or not
this first round of showers and storms will develop or maintain
itself later this morning. Later this afternoon, instability is
expected to build and should support widely scattered shower and
storms. Late Wednesday night, the delaying area of storms moving
across central Michigan may hold together enough to bring a few
storms to MBS/FNT.

For DTW/D21 Convection...Confidence is waning regarding the initial
round of showers and storms moving into the D21 airspace between 10-
15Z. Still expect scattered slow moving showers and storms around
during the afternoon and evening hours after 18Z.

THRESHOLD PROBABILITIES...

* Low to Moderate for thunderstorms after 18Z Wednesday.

&&

.PREV DISCUSSION...
Issued at 310 PM EDT Tue Jul 15 2025

DISCUSSION...

Southern lower MI has remained under the influence of surface high
pressure maintaining sunny skies and light winds thus far today.
This has also kept lingering wildfire smoke over the area though
what wind we have in addition to diurnal mixing has aided in
decreasing the worst of the haze. Said high vacates to the east late
this evening as a weak shortwave embedded within deeper layer
southwest flow lifts out of the mid-Mississippi. Wave is progged to
slide to our south, towards central OH resulting in the bulk of
forcing likewise holding south of the state line. That said, with
the northern fringe of the PV anomaly glancing the south and the
attendant theta-e gradient lifting into the state, a few showers
creeping north into southern SE MI (south of I-96/696) are expected.
Scattered to numerous convection then develops over the CWA during
the afternoon as moisture advection fully establishes 70F+ surface
dewpoints over the area allowing diurnal heating to build 1500J/kg
of SBCAPE (bullish solutions reach or exceed 2000J/kg). Despite the
ample instability, the overall wind field is abysmal with column
wind aob 20kts up through 400mb yielding minimal shear. Main hazard
tomorrow will be heavy rainfall any under storm as PWAT`s climb to
around 1.75" (right around the 90th daily climo percentile) with
warm cloud layers 10-14kft. Slow storm motion, given the weak wind
field, supports longer duration rainfall over locales as well
increasing locally heavy rainfall/flooding chances. For the
Wednesday afternoon-evening period, isolated water-laden downbursts
as pulse storms collapse would be the potential severe hazard-
region remains under a Day 2 marginal risk from SPC.

Additional storm chances arrive late evening-early Wednesday night
as some manner of convective complex crosses Lake Michigan into
lower MI. Late timing, after 04Z, limits the magnitude of lingering
instability with MLCAPE falling sub 1000J/kg. Should this organized
convection sufficiently survive to this side of the state a few
strong wind gusts can`t be completely ruled out. Worth noting there
are a notable subset of CAM solutions, like the HRDPS, that
advertise convection effectively dying on our doorstep resulting in
only spotty showers.

Surface low pressure tracks across the upper Great Lakes Thursday
morning with its attendant cold front sinking through the state over
the course of the day. Some scattered shower/t-storm redevelopment
occurs along the front with greatest chances/coverage likely south
of I-69 as these areas have a longer duration of diurnal
heating/destabilization compared to north given the faster frontal
speed. Front looks to clear the region by the first half of Thursday
night ushering in a cooler, much less humid airmass for Friday.
850mb temps fall to around 10C yielding seasonably cool highs in the
upper 70s to 80 as PW falls sub 1". High pressure holds over the
area through early Saturday morning before another weak shortwave
arrives over the Great Lakes/Ohio Valley. This system brings the next
chances showers and storms for both Saturday and Sunday.

MARINE...

Modest uptick in southerly winds this evening over northern Lake
Huron, with sustained winds reaching near 15 knots. Increasing low
level moisture tomorrow and daytime instability will produce
numerous showers and thunderstorms in the afternoon. Some of the
thunderstorms could be strong, producing localized wind gusts in
excess of 45 knots. Scattered-numerous showers and thunderstorms
likely persist Wednesday night, as low pressure and associated cold
front race east, passing through the Central Great Lakes Thursday
morning. North-northwest winds behind this system will likely top
out briefly in the 20-25 knot range over Lake Huron, which will
bring a chance of waves of 4 feet or greater to clip the nearshore
waters by Thursday evening. There may be just enough of an offshore
component to prevent small craft advisories however.

Winds veer around to the north-northeast Thursday evening, but
should be 15 knots or less by that time, with light and variable
winds for Friday as a large area of high pressure encompasses the
Great Lakes region.

HYDROLOGY...

Low pressure tracking into the Great Lakes/Ohio Valley brings
chances for scattered showers towards the Ohio border Wednesday
morning. Scattered to numerous showers and storms then develop
during the afternoon-evening as an increasingly humid airmass
settles over the region with surface dewpoints in the lower 70s and
PW values around 1.75". Overall setup is favorable for locally heavy
rain with any thunderstorm given this ample moisture as well as a
deep warm cloud layer increasing precipitation efficiency and a very
weak background wind field supporting slow moving pulse
thunderstorms. Rainfall rates of 1-2"/hr expected with these storms
which will lead to minor flooding in low-lying/flood prone areas.

&&

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

$$

AVIATION.....JA
DISCUSSION...KDK
MARINE.......SF
HYDROLOGY....KDK


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