244
FXUS63 KDTX 181006
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
606 AM EDT Fri Sep 18 2026

.KEY MESSAGES...

- Dry weather today with increasing clouds late in the day.

- 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.

&&

.AVIATION...

High pressure anchored over the northern great lakes will maintain
dry and stable conditions locally today. This ensures widespread VFR
conditions with limited diurnal cu development, with prevailing
northeast wind holding at around 10 knots. High cloud thicken
tonight as mid level moisture increase downstream of low pressure
lifting into the midwest. This system will bring periodic rain
chances this weekend, with an initial round of showers likely
arriving Saturday morning. Associated lowering of cloud base
expected during this time.

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

.DTW THRESHOLD PROBABILITIES...

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

&&

.PREV DISCUSSION...
Issued at 421 AM EDT Fri Sep 18 2026

DISCUSSION...

A stalled frontal boundary remains active with convection across the
Ohio Valley this morning but SE MI will see increasing drying
influence from high pressure passing through northern Ontario today.
Northeast flow allows remaining stratus to push south of the
stateline with a good amount of sunshine for the area through
midday. Subtle negative thickness advection within the southern
extent of thermal troughing allows high temps to arrive right around
seasonal average in the lower 70s and upper 60s (downwind of Lake
Huron).

Low pressure emerges out of the High Plains today in response to a
shortwave and upper jet entrance region running the ridge axis in
place, bolstered by a feed of monsoonal moisture from the Four
Corners region. Will see the first signs of this system locally
later this afternoon as high cloud begins to spill in from the west.
Dry weather is most likely to prevail overnight as persistent
easterly flow maintains a dry pocket within the lowest 8 kft or so.
Upstream, organized moisture transport into the developing warm
frontal slope will produce a corridor of steady and at times heavy
rainfall. The LLJ driving this rain is shown to veer overnight
before beginning to target parts of Lower MI Saturday morning. There
are still some discrepancies noted in the strength and northeastward
extent of this feature among 00z guidance, which appears to govern
how far north and east the swath of rain reaches into the local area
on Saturday.

Model cross sections show a sharp 850-700mb frontal structure and
attendant fgen within deep layer saturation, suggestive of banded
precip with inherent uncertainty as to where the frontal slope will
activate and for how long at any given location. This is evidenced
by a 1+" spread between the 25th and 75th percentile QPF in LREF
grand ensemble membership. QPF output in coarser global model
solutions is likely overdone spatially and prefer the look of hi-res
solutions that can better account for the initial dry easterly flow
and some of the mesoscale processes involved. Overall flavor of
these solutions shows the heaviest rain sinking southeast across
Lake Michigan and Chicagoland into western Lower MI and northern IN
Saturday morning before the LLJ weakens and rates/coverage begin to
taper off midday. What`s left for SE MI is a cool, cloudy, and
showery pattern with amounts most probable to hold below a half inch
through 00z Sun. Rates could become moderate at times as PWAT rises
above 1.50", but the threat for widespread heavier rain is low. Weak
lapse rates and marginal elevated instability offer low potential
for an embedded thunderstorm or two in the south. Conversely,
portions of the area north of I-69 may see little to no rain given
the farther proximity from the feed of moisture and lift.

Additional showers are likely, especially south of M-59, Saturday
night into Sunday. The stalled frontal slope remains overhead while
additional moisture continues to feed along it. As the nocturnal LLJ
becomes active again over the northern Ohio Valley, this will be a
window for training showers that have potential to produce locally
over 1 inch of rain. Placement of the axis of heaviest rain still
carries high uncertainty and may yet be displaced south of the state
line. Additional clarity should come into focus today and tonight as
additional hi-res runs begin to include this period.

High pressure builds back into northern Ontario on Sunday, offering
another period of dry northeast flow that should shunt any lingering
showers southward by late in the day. A tightening gradient brings
breezy conditions with temperatures capped in the mid 60s. Cool and
mostly cloudy conditions carry into the early week as the stalled
front remains active over the Ohio Valley. Showers will be possible
at times, especially in the south. An upper low looks to develop
overhead midweek which brings higher likelihood for showers
Wednesday and Thursday.

MARINE...

A secondary cold front finishes clearing the region this morning
resulting in a modest uptick in northeasterly winds (toward 20-
25kts) over the southern half of Lake Huron. Small Craft Advisories
are in effect along the Thumb due to the moderate onshore flow. This
front stalls over northern Ohio before attempting to lift back north
Saturday as Plains low pressure arrives. Front looks to reach the
southern Great Lakes before the system tracks over lower MI
resulting in predominant east-southeast turning northeasterly winds
this weekend. Widespread showers and scattered thunderstorms are
possible, mainly focused over the southern half of the region. A
moderate gradient, supporting NE/E gusts 20-30kts, lingers behind
the low Sunday into the new work week as the area holds between the
stalled boundary over the Ohio Valley and high pressure over
northern Ontario.

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 decreased
with the latest guidance, but relatively high confidence still
exists for total rainfall ranging between a half inch and 1.5
inches. The highest amounts are likely to occur mainly south of a
line from Lansing to Detroit. A period of moderate rainfall rates
and potential for training/repeated showers is most 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.

&&

.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.
&&

$$

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

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