846
FXUS63 KDTX 171909
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
309 PM EDT Fri Oct 17 2025

.KEY MESSAGES...

- Widespread rainfall totals in excess of 1 inch over the weekend.
Record setting daily rainfall likely on Sunday at Flint and Saginaw.

- Northwest winds gusts of 35-40 mph expected Sunday afternoon into
Sunday evening.

- Reinforcing shot of cold air and showers Monday night into
Tuesday, along with breezy conditions once again.

&&

.DISCUSSION...

Upper level jet (~130 knots at 250 MB) energy currently tracking
through southern British Columbia/Pacific Northwest. This will
establish an active pattern over North America heading into the
weekend, with phasing and amplification occuring over Central North
America on Saturday. This setup will allow for near record moisture
to stream up from the Southern Plains through southeast Michigan.
Precipitable water (PW) values are forecast to top out near 1.5
inches.

The first wave of moisture tracked through Lower Michigan this
afternoon, triggering showers over Lake Huron and nearby locations.
A second moisture axis, carrying higher moisture content, will
arrive tomorrow. This is associated with an upper level wave
currently over southern Manitoba lifting northeast. With the
moisture advection and a southwest low level jet of 35-40 knots,
showers/isolated thunderstorms are likely with the slightly negative
showalter indices and MUcapes < 1000 j/kg. Tri-cities region appears
to have the best coverage/chance of activity, situated closet to the
upper level jet forcing and the highest surface dew pts (lower 60s).
Due to the limited instability, skinny cape profile, and weak mid
level lapse rates, and we remain in just general thunder per latest
SPC day 2. With the rapid deepening of the low, low level wind shear
will become high Saturday evening/night. This raises a slight
concern for rotation/tornado (2%) and wind (5%) per machine learning
tools, given the strong low level jet (50-60 knots). However, a
surface-based inversion is ultimately expected to be in place,
mitigating the threat.

Merging height falls over the Midwest Saturday evening. The
consolidated maximum height fall center (~120 M at 500 MB) looks to
be tracking through the southern Ohio Valley/along the Ohio River
with a northern extension up through the Central Great Lakes.
Cyclogensis/deepening surface low progged to track from the Western
Ohio Valley northeast through central Lower Michigan. The exact
track will be critical in determining where the heaviest rain axis
sets up Saturday night into Sunday, likely along and northwest of
the low level circulation track, aided by favorable
deformation/frontogensis (FGEN) response. (See hydro section for
additional thoughts and potential amounts.)

As rain coverage diminishes on Sunday, wind will become the weather
story. It appears a 6 hr rise/fall pressure couplet of 20 MB will
work through the region. This is assuming the low deepens into the
986-988 MB range as it exits the northern Great Lakes. Cold
advection late in the afternoon/early Sunday evening looks good as
850 MB temps reach around 1 C, with 50 knots of flow forecasted.
Current expectations are for a brief wind pop, with gusts of 35-45
mph in the late afternoon/early evening hours.

Yet another strong upper level wave and assocaited strong height
fall center is projected to track across the Great Lakes region
Monday night, bringing even colder air and windy conditions into
Tuesday. Cyclonic flow, steep low level lapse rates, and lake
enhancement should be supportive of numerous showers.

&&

.MARINE...

Warm front tied to low pressure lifting through northwestern Ontario
has cleared the central Great Lakes this afternoon setting up
moderate south-southwest winds in its wake. Gradient gradually
tightens through the night as the trailing cold front begins to sag
into the western Great Lakes. Ongoing warm advection however keeps
the overlake thermal profile stable capping peak wind gusts aob
30kts. Small Craft Advisories remain in effect around the Thumb into
Saturday morning as a result.

Rapidly developing low pressure system forms along the cold frontal
boundary over mid-Mississippi river before tracking over lower MI
Sunday. While some uncertainty still exists in the exact low track,
model guidance has been to largely converge on tracking the low
center directly over Lake Huron (from roughly the Saginaw Bay to
Manitoulin Island). This track would result in strengthening
southerly flow over the bulk of the central Great Lakes save for far
northern Lake Huron which would see more north/northeast flow.
Forecast soundings advertise a ~50kt LLJ to develop only 2-3kft agl
in the southerly flow Sunday afternoon. Strong warm advection
however leads to a solid stable near-surface layer greatly limiting
mixing potential. While a few periodic gusts to entry-level gales
are possible given the strength of the jet, confidence is not high
enough at this point for sufficient duration to issue a Gale
Watch- for that timeframe.

Better gale potential arrives Sunday evening through much of the
night once the low tracks into northern Ontario ushering in colder
northwesterly flow. Strongest flow expected over northern Lake Huron
where 40-45kt flow aloft will support surface wind gusts in the 35-
40kt range. Winds aloft are slightly weaker over the southern
portions of the lake (closer to 35-40kts) however this will still
support a chance to see 35kt gales over most of these waters. As
such, a Gale Watch has been issued from 3PM Sunday to 4AM Monday.

&&

.HYDROLOGY...

A dynamic autumn system will lift across Michigan over the weekend
bringing basin average rainfall totals ranging between 1.25" to 2.5"
across southeast Michigan. The best chance for isolated totals in
excess of 2.50 inches looks to be across the Tri-Cities region and
Flint Vicinity. Rainfall rates are expected to reside in the low to
moderate range for most of the event, but may become briefly heavy
at times, especially in any thunderstorms. Rainfall rates of 0.25"
to 0.50" per 3 hours will be most common. Heaviest rainfall is
expected to occur Saturday night through Sunday afternoon.
Significant flooding is not expected as 6 hr flash flood guidance is
running high, with most locations around 3 inches. Even if rainfall
reaches 2-3 inches, rivers should remain in their banks due to the
current drought/low river levels. Localized flooding of urban, low-
lying, and poor draining areas will be possible however, especially
if fallen leaves clog storm drains. Daily record precipitation
amounts for October 19 will likely be broken at Flint and Saginaw
(see climo section).

&&

.CLIMATE...

The daily record precipitation amounts for Sunday October 19th.

Detroit: 2.02 inches  (Set in 1985)
Flint:   1.15 inches  (Set in 2011)
Saginaw: 1.37 Degrees (Set in 2011)

&&

.PREV DISCUSSION...
Issued at 205 PM EDT Fri Oct 17 2025

AVIATION...

Upper level ridging will remain in control tonight and throughout
much of the daytime on Saturday. Very low potential for elevated
shower activity to develop and impact DTW 7-10z. Did leave out of
the forecast at this time with the expectation that showers will
impact areas to the east. Persistent dry air and subsidence between
6.0 and 12.0 kft agl is expected to limit vertical motion and
saturation until later in the day on Saturday. Based on model trends
did favor a more optimistic/dry forecast initially.

For DTW/D21 Convection...Thunderstorms are not expected through
middle of the day Saturday.

DTW THRESHOLD PROBABILITIES...

*  None.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Gale Watch from Sunday afternoon through late Sunday night for
     LHZ361>363-421-422-441-442-462-463.

     Small Craft Advisory from 10 PM this evening to 4 PM EDT Saturday
     for LHZ421-441-442.

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

$$

DISCUSSION...SF
MARINE.......KDK
HYDROLOGY....SF
CLIMATE......SF
AVIATION.....CB


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.