090
FXUS63 KDTX 181942
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
342 PM EDT Fri Sep 18 2026

.KEY MESSAGES...

- Increasing clouds into this evening.

- Several rounds of showers and embedded thunderstorms are likely
  Saturday, Saturday night, and Sunday.

- A cool and cloudy pattern is expected through early next week.

&&

.DISCUSSION...

Cooler north-northeasterly flow on the south end of a surface high
pressure migrating across Ontario and into Quebec tonight will
ensure more stable conditions locally. Limited cloud cover exists
this afternoon with the flow supplying a good amount of lower level
dry air. The quiet weather expected for the remainder of the
afternoon with seasonal afternoon high temperatures.

Upstream over the western Great Lakes states, showers and isolated
thunderstorms have developed on the leading edge of the theta-e
ridge and monsoonal moisture plume and at the nose of the low level
jet. Increasing cloud cover will arrive locally into the evening and
tonight before greater rain chances begin to increase around 12Z
tomorrow morning. Deeper moisture will be characterized by PWAT
values climbing to 1.5 inches and above and will be focused along
the warm frontal slope over the course of the weekend. This supports
a good soaking rain and some isolated thunder potential Saturday
morning with additional rounds of heavy rain potential and isolated
thunder Saturday night into Sunday.

The first round moving through Saturday morning with QPF amounts
generally at 0.25" to 0.75" through 00Z Saturday evening. CAPE depth
will be lacking in a weak lapse rate environment with some hi-res
guidance pointing toward a lull in heavier precipitation potential
by mid afternoon Saturday given the showers moving across this
weaker instability environment. Though, could still see scattered
light shower activity continue during the afternoon. MUCAPE will be
minimally supportive of embedded thunder potential with isolated to
scattered coverage that becomes lesser in the afternoon. Highest QPF
axis is focused across southwest portions of the CWA in the latest
HREF.

The next surge of monsoonal moisture along the frontal zone is
driven into the area Saturday after 00Z into Sunday morning. This
presents the next chance for heavier precipitation potential with
FGEN that could lead to areas of banded precipitation. Forecast QPF
from 00Z Saturday to 12Z Sunday carries the highest 12 hour QPF
potential with 0.75" to 1.00" or greater with the higher totals
covering smaller footprints based on where any focused banding sets
up along the frontal slope.

Latest NBM has trended toward a more broad area of 1+ inches of
storm total precipitation over the course of Saturday and Sunday
generally across the Tri-Cities east towards the Port Huron area as
a camp of models have moved this direction as opposed to a focused
swath of higher precipitation across southeast portions of the CWA.
Still lean towards the look of the HREF with highest precipitation
focused across southwest/southern portions of the CWA. Given the
high end moisture and potential for repeated rounds, there will be
at least a low chance for localized amounts of 2.00 to 2.50 inches
over the 24 to 36 hour period. Given the spaced out nature of
precipitation and weak thunderstorm activity, widespread flooding
potential looks limited, but will come with the typical urban
flooding potential if repeated heavier rounds of precipitation do
occur over these areas.

Another high pressure moves into central Ontario and then into
Quebec late Sunday into Monday. This allows northeasterly flow to
push bulk of any lingering showers activity to the southern MI
border or south. Cooler airmass with a tightening pressure gradient
will bring breezy conditions with temperatures dropping down into the
low to mid 60s for all of southeast Michigan for Monday and Tuesday.
Developing trough mid-week will bring a return to more widespread
rain precipitation chances early Wednesday.

&&

.MARINE...

High pressure is building southward across the Great Lakes today in
the wake of a cold front that has about cleared the area to the
south. Northeasterly winds behind the front gusting to around 20
knots have built waves enough to continue the current Small Craft
Advisory for the southern Lake Huron nearshore zones. Weaker
gradient with the incoming ridge will decrease winds and waves
through the evening allowing the headline to end this evening. A low
pressure system will then ride along the front on Saturday nudging
the front back northward into southern MI through the day.
Widespread showers and scattered thunderstorms are possible, mainly
focused over the southern half of the region. Tightening of the
gradient on the backside of the exiting low will ramp northeast
winds back up on Sunday reaching 25 to 30 knots. These increased
winds will carry into Monday as well which may necessitate
additional headlines.

&&

.HYDROLOGY...

A low pressure system approaching from the Plains with increasing
deep moisture will bring showers and isolated embedded thunderstorms
to the area this weekend. Forecast rainfall totals have trended
toward a broader area of higher total rainfall amounts across the
Saginaw Valley towards Port Huron area. Relatively high confidence
still exists for total rainfall ranging between a half inch to two
inches, but the highest amounts are more likely to occur mainly
south of a line from Lansing to Detroit. A period of light to
moderate rainfall Saturday morning will may be followed by a lull in
heavier precipitation potential Saturday afternoon. Then moderate
rainfall rates and potential for training/repeated showers is more
favored to occur from Saturday night into Sunday morning, especially
for areas south of M-59. The longer duration rainfall event will
mitigate widespread flooding concerns, but ponding will be possible
where any repeated rounds of showers lead to localized totals in
excess of 1 inch, especially in urban areas.

&&

.PREV DISCUSSION...
Issued at 1210 PM EDT Fri Sep 18 2026

AVIATION...

Dry mid-levels and subsidence are in place over southeast Michigan.
Northeast winds off Lake Huron are helping to moisten the low levels
just enough to produce scattered low clouds (2500-5000 feet) early
this afternoon. Low clouds are expected to mix out by early evening,
with increasing mid to high clouds this evening and tonight. Higher
based light showers/sprinkles are possible at MBS/FNT overnight, but
dry low level easterly winds will attempt to dissipate activity. A
much better surge of moisture and showers is expected on Saturday,
spreading from southwest to northeast. As showers become numerous to
widespread Saturday afternoon, cigs/visibilities will settle into
MVFR. Although, with easterly flow trending southeast off Lake Erie,
it`s possible an MVFR deck of clouds tracks through the southern
TAFS during the morning hours.

D21/DTW Convection...Thunderstorms are not forecast through the TAF
period.

DTW THRESHOLD PROBABILITIES...

* Medium for ceiling at or below 5000 ft Saturday morning, high for
  Saturday afternoon.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 4 PM EDT this afternoon for LHZ421-441.

     Small Craft Advisory until midnight EDT tonight for LHZ442-443.

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

$$

DISCUSSION...AA
MARINE.......DRK
HYDROLOGY....AA
AVIATION.....SF


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