703
FXUS63 KDTX 051022
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
622 AM EDT Sat Jul 5 2025

.KEY MESSAGES...

- Hot and muggy conditions through this weekend with highs in the
lower 90s today into Sunday.

- Next chance for showers and thunderstorms on Sunday, then drier
with less humidity starting Monday.

&&

.AVIATION...

Lingering pockets of shallow fog/haze this morning will lift within
the next 1-2 hours as mixing improves with time. Otherwise, warm and
humid environment entrenched this period will support a standard
coverage of high based VFR diurnal cu today. Despite accompanying
increase in low level instability, less favorable conditions exist
for thunderstorm development given the capping evident under a warm
mid level profile. Prevailing winds from the southwest. Benign
weather with mostly clear skies tonight. Attention turns to
convective potential Sunday as a slow moving front enters the area.
Greater probability likely to reside at mainly MBS early in the day,
before potential increases across all of the area into the afternoon
and evening.

For DTW/D21 Convection... Thunderstorms are not forecast through
tonight.

THRESHOLD PROBABILITIES...

* None.

&&

.PREV DISCUSSION...
Issued at 405 AM EDT Sat Jul 5 2025

DISCUSSION...

A 500mb ridge axis marches across the Great Lakes today with hot and
muggy conditions held in place beneath. 850mb temp of 17C observed
in the 00z DTX sounding increases toward 18 to 19C this afternoon
which supports highs into the upper 80s to lower 90s today. Morning
fog resulting from a combination of firework smoke from last evening
and marine moisture from Lakes Erie and St. Clair should clear up
this morning as light wind organizes out of the southwest after
sunrise. Dew point currently in the mid 60s to near 70 gains a
slight boost from this flow, but then mixes back downward into the
mid to upper 60s this afternoon. This will keep heat index
relatively in check, but we can still expect a few hours of heat
index in the mid 90s today.

Can`t rule out a stray shower or rumble of thunder this afternoon,
but overall the environment will tend to suppress convection. Mid-
level lapse rates will be extremely poor as 500mb temps peak near
-4C - near climatological max - which should cap convective chances
for most of the area. Highest chances (~15%) exist in the Thumb and
near Saginaw Bay where HREF guidance hints at a weak pool of SBCAPE
owing to dew points that are slower to mix out. This paired with
subtle height falls working in late in the day may be sufficient to
trigger a few weak updrafts.

The ridge begins to break down on Sunday but the heat and humidity
will hold on for another day around Metro Detroit. After lows dip
only into the 70s Sunday morning, highs there are forecast to again
reach the lower 90s, with dew points around 70 holding heat index in
the mid 90s. Across the northwest forecast zones, earlier arrival of
clouds and showers/storms with the inbound cold front will dampen
the heating potential - highs mainly in the 80s there.

The front will be driven in by a positively tilted 500mb trough
arriving from the west by midday, which then washes out overhead by
Sunday night. As a result, the front will lose some forward momentum
and definition by the time it works in during the day Sunday. Still,
ample moisture pooling ahead of it should support scattered to
numerous showers and thunderstorms. Mid-level lapse rates are again
weak but model soundings indicate tall skinny SBCAPE of 1000 to 2000
J/kg is attainable. Relatively weak unidirectional wind through the
column holds deep layer wind shear at around 20 kt which precludes
an organized severe threat. The main hazard with storms will be
lightning and localized heavy downpours given PWAT nearing 2.00",
slow storm motion, and deep warm cloud layer. HREF LPMM guidance
suggests a few pockets of 1"+ rainfall will be possible but with
little confidence on location. WPC has included most of SE MI in a
marginal outlook for excessive rainfall. The front looks to stall in
the vicinity Sunday night with additional shortwave energy arriving
from the Midwest to maintain at least a chance of continued
shower/thunderstorm activity into early Monday.

Northerly post-frontal flow brings relief from the heat on Monday
with highs in the 70s/80s and notably lower humidity. The daytime
precip forecast carries lower confidence given uncertainty with
frontal placement, but eventually high pressure looks to favor dry
conditions into Tuesday. The next disturbance in the low amplitude
zonal flow pattern looks to arrive on Wednesday offering the next
opportunity for rain chances. Temperatures in this pattern are
likely to stay near seasonal norms through next week with highs in
the 80s and lows in the 60s.

MARINE...

Low pressure ejecting out of the northern Plains leads to a
tightening of the local gradient and strengthening southwest winds
today. Strongest gusts, around 20kts, occur over the central
portions of Lake Huron. Due to shoreline effects, the Saginaw Bay
has the potential to reach/exceed 25kts this afternoon-evening with
waves, particularly in the outer portions of the Bay, being able to
approach 3-5ft. While borderline to meet Small Craft Criteria, given
the holiday weekend and the rougher waters even if winds/waves come
up a bit short, Small Craft Advisories have been issued for these
waters. A cold front sagging south from the aforementioned low now
sliding over the northern Great Lakes gradually crosses late tonight
through Sunday. In advance, scattered to numerous showers and storms
are expected. Severe storms not generally expected however an
isolated strong storm can`t be ruled out. A few showers/storms look
to linger into Monday for the southern Great Lakes as the front is
slow to fully vacate. High pressure then briefly follows late Monday
through Tuesday before unsettled weather returns midweek.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory from 2 PM this afternoon to 10 AM EDT Sunday
     for LHZ421-422.

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

$$

AVIATION.....MR
DISCUSSION...TF
MARINE.......KDK

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