886
FXUS63 KDTX 091901
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
301 PM EDT Thu Oct 9 2025

.KEY MESSAGES...

- Frost Advisory is in effect through 9am Friday for much of
Southeast Michigan outside of Wayne and Monroe Counties.

- Area of low pressure will bring rain chances to Southeast Michigan
Friday evening through Saturday night. It remains highly uncertain
what the duration of rain activity will be for any one location
across Southeast Michigan. Low confidence exists in the forecasted
rainfall amounts for this system particularly in the Thumb and Metro
Detroit areas.

&&

.DISCUSSION...

The center of 1034mb polar surface anticyclone will push from
northern Lake Huron this afternoon to New England by 12Z Friday
morning. Surface dewpoints, currently in the mid 30s, and persistent
influence of the surface ridging will allow temperatures to quickly
cool into the 40s this evening. Concern for tonight and Friday
morning is frost potential despite possible limiting factors, high
cloud and easterly gradient wind). Per the latest NBM guidance,
decided on a Frost Advisory for the majority of Southeast Michigan
with lows in the middle 30s. Locations immediately downwind of Lake
Erie and Lake Huron will likely not see any frost formation and kept
Wayne and Monroe counties out of the Advisory.

Main weather driver for the Friday and Saturday period is a compact,
vigorous absolute vorticity maximum that will dig directly into
Southeast Michigan Friday evening/night before slowing and possibly
stalling for Saturday. First thing to note is the amount and degree
of ridging occurring both in advance and behind the vorticity
maximum. This is important as it likely suggests that sensible
weather impacts will be limited to those areas directly under the
vorticity center. Increasing model confidence that precipitation
chances will begin after 21Z Friday for portions north of I 69 as a
band of rain showers pushes into the area from the northwest.
Primary mechanism for precipitation appears tied to a band of
relatively shallow, below 7.0 kft agl, thetae advection streaming
northward directly ahead of the vorticity maximum. System relative
progs show little to no upglide/upward frontal motion so showers
could low rainfall rate/spotty particularly north of I 69 Friday
evening. Hiresolution model data suggests very little precipitation
06-12Z Saturday which matches with plan view isentropic progs of
sharp dry slotting. Lowered Pops late Friday night and first part of
Saturday into the lower chance category.

Confidence then decreases substantially for midday Saturday through
Saturday night regarding precipitation potential. The reason for the
low confidence is that given the tight circulation of the vorticity
maximum, where exactly the center resides and how various moisture
channels converge matters. What will the depth of the moisture be
for any one location is of low confidence and becomes more of a
Period 1 forecast. There is a model solution or two that suggests a
meridional moisture transport axis will be possible immediately east
of the vorticity maximum that will be in vicinity of Lake Erie or
Southeast Michigan. While some solutions suggest it could miss
Southeast Michigan altogether it remains possible that a longer
duration Lake Erie enhanced rain event (Saturday and Saturday night)
occurs over portions of Southeast Michigan. Did prefer to go with
higher chance PoP for the diurnal boost of daytime heating Saturday
afternoon mainly the Thumb and city of Detroit. All indications
suggest wind speeds will remain manageable with this low pressure
system.

&&

.MARINE...

High pressure over southern Ontario gradually shifts toward the
Northeast tonight ahead of the next low pressure system dropping out
of northern Canada. For the central Great Lakes, strengthening south-
southwest winds develop as a result with peak gusts occuring daytime
Friday. Given the direction, the northern half of Lake Huron and the
Saginaw Bay are favored to see the strongest winds with gusts
generally between 20-25kts expected- southern half of the region
likely stays closer to the 15-20kt range. Aforementioned low weakens
as it becomes a closed low while crossing the Great Lakes late
Friday-Saturday keeping winds under 30kts. Scattered showers
accompany this low as will waterspout chances as the cooler airmass
is reinforced. A weak area of ridging, induced by low pressure
systems over the northern Plains and Atlantic seaboard, then expands
over the local area Sunday-Monday.

&&

.PREV DISCUSSION...
Issued at 150 PM EDT Thu Oct 9 2025

AVIATION...

High pressure centered near Toronto maintains favorable aviation
conditions for the terminal airspace through the rest of today with
ENE winds AOB 10 knots. Diurnal/lake-augmented VFR cloud field
dissipates this evening with a period of SKC likely. Some signal
exists for borderline MVFR stratus off Lake Erie early Friday which
may affect the Metro terminals. However, modeled saturation lends
some uncertainty in the generation of BKN-OVC skies. Otherwise, low
cloud fraction emerges through the first half of Friday with light
winds organizing out of the SSW with generally light speeds.

For DTW/D21 Convection...No convection expected through the TAF
period.

DTW THRESHOLD PROBABILITIES...

* None


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Frost Advisory from midnight tonight to 9 AM EDT Friday for
     MIZ047>049-053>055-060>063-068>070-075-082.

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

$$

DISCUSSION...CB
MARINE.......KDK
AVIATION.....KGK


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