442
FXUS63 KDTX 181423
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1023 AM EDT Sat Oct 18 2025

.KEY MESSAGES...

- Widespread rainfall totals 1 to 2 inches expected through Sunday.
A narrow band of greater than two inches will be possible, mainly
towards the Tri-Cities. Record setting daily rainfall likely on
Sunday at Flint and Saginaw.

- Marginal Risk for severe weather this afternoon/evening and late
  tonight. Isolated damaging winds will the main threat.

- Northwest winds gusts of 35-45 mph expected Sunday afternoon into
  Sunday evening.

- Rain showers expected Monday night into Tuesday along with breezy
conditions once again with even colder air settling into the region
mid to late week.

&&

.UPDATE...

The axis of showers and embedded thunderstorms now extending from SW
Lower Mi into northern Lake Huron will continue to lift northeast
over the next several hours. The main region of ascent, tied to a
short wave feature, will exit northeast early this afternoon leaving
a trailing ribbon of weakening mid level fgen to push into Se Mi.
This will result in an overall decreasing trend of the these showers
over the next few hours. An influx of warm and weakly unstable air
will be advected into at least the southern half of Se Mi this
afternoon with enhanced boundary layer convergence noted along a
surface trough. Warm mid level temps suggest some degree of capping,
which model soundings suggest will erode late in the afternoon/early
evening. This will open the door to a chance for convection. 0-6km
bulk shear values of 40-45 knots and model soundings indicative of
weak downdraft cape will remain supportive of the marginal/isolated
risk of severe thunderstorms. The weak CAPE values (under 1k J/kg)
will maintain the low severe storm risk despite the shear values.
Shower and thunderstorm coverage will increase later this evening as
large scale dynamic ascent begins to intensify low to mid level
frontogenetical forcing across Se Mi. Overall, a forecast update was
issued to reflect current trends for precipitation chances this
afternoon and evening.

&&

.PREV DISCUSSION...
Issued at 627 AM EDT Sat Oct 18 2025

AVIATION...

Seasonably warm and moist conditions exist today under a modestly
gusty southerly wind. A narrow axis of higher moisture will ease
into the region during the afternoon and evening hours. This will
provide the focus for some scattered showers and isolated
thunderstorms over Se Mi. Confidence in occurrence at any one
location remains low given limited overall coverage and duration.
Otherwise, VFR through the evening within a mix of higher based
diurnal cu and thicker mid cloud. A widespread region of rain
expands north into the region ahead of a low pressure system
tonight. High probability of moderate intensity rain with
accompanying reduction of cigs at MBS/FNT/PTK given the trajectory,
with the Detroit corridor along the eastern fringe of this initial
surge. Potential for some embedded thunderstorms with this activity.
Arrival of the low directly across the area by mid morning Sunday
brings a period of gusty southerly winds to the Detroit airspace,
with north/northwest gusts at MBS/FNT.

For DTW/D21 Convection...Potential exists for isolated thunderstorms
to develop this evening. Embedded thunderstorms will remain possible
as rain increases in coverage overnight into Sunday morning ahead of
a cold front.

DTW THRESHOLD PROBABILITIES...

*  Low for ceilings below 5kft this afternoon through early tonight.
   Moderate late tonight into Sunday.

*  Low for thunderstorms this evening and overnight into Sunday
   morning.

PREV DISCUSSION...
Issued at 416 AM EDT Sat Oct 18 2025

DISCUSSION...

Southeast Michigan will begin the day in the warm sector between a
departing mid level ridge and slowly moving cold front across the
western Great Lakes. Deep southwest flow and a 30-40 knot low level
jet will ramp up moisture advection this morning into the afternoon.
PWATs of greater than 1.25 inches will arrive and support increasing
shower potential within the southwest to northeast oriented moisture
axis. This targets the Tri-Cities with the likely PoPs this morning
before expanding southeast towards Detroit metro this afternoon into
this evening. The morning activity should be rather weak and
elevated. Moving into the afternoon/early evening, better diurnal
instability will try and develop with MUCAPEs increasing to around
500 j/kg while 0-6km bulk shear increases to 30-40 knots supportive
of some organized convective potential. Rather weak mid-level lapse
rates to around 6.0 C/km and skinny CAPE profiles will be factors
working against any strong convection. Given the stronger low level
wind profiles, any storm that can get even slightly organized may be
able to produce damaging winds. RAP parameters favor areas south of
I-69, especially closer to the southern MI border through about 8 pm
this evening with this initial wave of showers and thunderstorms.
Daytime mixing heights today will also be capable of producing gusts
of 20-25 mph, which will peak early to mid afternoon. One more warm
day is also expected today with highs to around 80 degrees across the
south and around 70 degrees across the far north.

Rapid cyclogenesis will occur tonight into tomorrow along the
frontal zone with the consolidation of a southern stream wave into
the Canadian trough. Low level shear (0-1 km) will increase
dramatically over southeast Michigan during the 11 pm Saturday to 8
am Sunday as the 0-6 km shear increases to 50 knots. Latest machine
learning tools still want to highlight a low end tornado (2%) and
wind (5%) threat during this time, but overnight stability should
limit this potential. This potential is now highlighted with a
Marginal Risk of severe weather up to the I-96 corridor, which also
encapsulates the wind threat this evening.

This dynamic low pressure system will also bring heavy rain
potential. Greater moisture advection on the north end of this low
will push PWATS towards 1.50 inches. The associated strong
FGEN/deformation along and northwest of the low will yield QPF
amounts of 1 to 2 inches with a narrow band(s) of greater than 2
inches. Bulk of rainfall will fall over the course of a 24 to 36
hour period Saturday afternoon to Sunday evening. Confidence
increasing for the stripe of higher totals to focus from southwest
Michigan through the Saginaw Valley/Tri-Cities as the low tracks
across central Michigan. Though, subtle adjustments of the low track
remain possible, which in turn would slide the heavy rain axis
slightly north or south. Strongest low level wind fields with 850mb
jet winds of 45-50+ knots will be over southeast Michigan around 12Z
Sunday morning. Local wind probability guidance is highlighting a
peak in gusts around this time. Given the shallow mixing depths/low
level stability this early in the day on Sunday, it may be tied to
convection which could result in scattered wind gusts of 40 mph or
greater. Lower confidence exists at this time with respect to the
Sunday morning wind potential.

Rain chances begin to wane as low pressure lifts to the north late
Sunday afternoon into the evening, which will open the door for cold
air advection to surge across Michigan in northwest winds. Winds in
the lowest 3kft drop to around 30-40 knots into Sunday evening, but
can still expect occasional wind gusts of 35-45 mph during the late
afternoon and early evening hours.

Monday will see daytime high temperatures fall to around 60 degrees
with high pressure bringing mostly dry conditions before another
potent low pressure system arrives late Monday night into Tuesday
leading to gusty winds and more rain. Cold cyclonic flow will take
hold mid to late week leading to daytime highs in the 50s. The
overlake delta t`s will support fair amount of lake clouds along
with periodic light rain showers throughout that period.

MARINE...

Small Craft Advisories around the Thumb drop off this morning as
south-southeast winds gradually weaken through the day. Lull is
shortlived as rapidly developing low pressure system forms over mid-
Mississippi river before tracking over lower MI Sunday. Low center
is still expected to track directly over Lake Huron (from roughly
the Saginaw Bay to Manitoulin Island) first half of the day. This
results 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. A ~50kt LLJ jet develops mainly over the
southern half of the region Sunday morning-early as the low nears
peak strength which opens the door to see a period of southerly
gales particularly over the southern waters of Lake Huron. The
complicating factor however is strong accompanying warm air
advection which sets up a solid stable near-surface layer greatly
inhibiting momentum mixing down to the ground. Confidence is still
low for consistent enough gusts to warrant a headline so have erred
on not expanding the current gale watch to cover this timeframe with
the running forecast mentioning more sporadic gusts to entry-level
gales.

Higher confidence in the better gale potential Sunday evening
through much of the night once the low tracks into northern Ontario
ushering in colder northwesterly flow. The Gale Watch remains in
effect from 3PM Sunday to 4AM Monday. Strongest flow looks to occur
over northern Lake Huron where 40-45kt flow aloft supports potential
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.

HYDROLOGY...

A strong low pressure system will lift across Michigan over this
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 is leans 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 the more likely higher
end rates. Though, rainfall rates greater than 0.50" per 3 hours
will be possible with any stronger thunderstorm. Heaviest rainfall
is expected to occur tonight 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)

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory from 5 AM Sunday to 5 AM EDT Monday for LHZ443.

     Gale Warning from 2 PM Sunday to 2 AM EDT Monday for LHZ361-362.

     Gale Warning from 8 AM Sunday to 2 AM EDT Monday for LHZ363-462-463.

     Small Craft Advisory from 8 AM to 3 PM EDT Sunday for LHZ421-422-
     441-442.

     Gale Warning from 3 PM Sunday to midnight EDT Sunday night for
     LHZ421-422-441-442.

Lake St Clair...Small Craft Advisory from 5 AM Sunday to 5 AM EDT Monday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from 5 AM Sunday to 5 AM EDT Monday for LEZ444.

&&

$$

UPDATE.......SC
AVIATION.....MR
DISCUSSION...AA
MARINE.......KDK
HYDROLOGY....AA
CLIMATE......SF


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