992
FXUS63 KDTX 171008
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
608 AM EDT Sun Aug 17 2025

.KEY MESSAGES...

- Breezy NW to NE wind brings cooler and less humid air into SE
Michigan that is more noticeable by tonight.

- Dry weather Monday and Monday evening, then another round of
showers and storms is possible early Tuesday through Tuesday night.
Locally heavy rainfall is the primary concern with this activity.

- Cooler temperatures and dry weather move in and hold Wednesday
through Friday.

&&

.AVIATION...

Uniform northwest flow has emerged across the airspace in the wake
of this morning`s cold frontal passage. Cloud bases in the existing
post-frontal moisture axis range from 4.0 kft agl to 10.0 kft agl.
Some lowering of these bases is expected through the morning with
the addition of Lake Huron moisture and boundary layer mixing, but
any periods of MVFR should be brief and return to low VFR by early
this afternoon. A sharp intrusion of dry air then arrives late this
afternoon/early evening as high pressure surges overhead from
Canada. This advects a much drier airmass into the airspace which
effectively scours out clouds for the rest of the TAF period. Winds
trend toward the northeast gradually throughout the day, peaking
around 10-15 knots (gusts to 20 knots) this afternoon before
subsiding this evening/overnight.

For DTW/D21 Convection... thunderstorms are not expected in the TAF
period, although a stray shower will be possible through early
afternoon.

THRESHOLD PROBABILITIES...

* High for ceilings at or below 5000 feet through approximately 20z-
  22z this evening.

&&

.PREV DISCUSSION...
Issued at 357 AM EDT Sun Aug 17 2025

DISCUSSION...

Clusters of showers and thunderstorms have exited into Ontario at
forecast issuance leaving just a short time window for any new
development toward metro Detroit and the Ohio border leading up to
sunrise. A stray shower is also possible off the warm water of
southern Lake Huron while low level moisture depth is still adequate
during the morning. An overall decreasing trend is promoted by the
larger scale atmospheric environment becoming increasingly subsident
as the robust MCV and surface wave exit eastward while the front
moves southward. Showers end but clouds linger well into the
afternoon in a trapped boundary layer moisture profile that limits
temperatures to highs in the upper 70s to lower 80s with a lingering
humid feel through the day. Wind direction then turns more from the
NE with gusts around 25 mph as marker for the arrival of
sufficiently dry air to support decreasing clouds into this evening
and lower humidity through tonight.

Monday starts out with a broad area of high pressure centered along
the Ontario/Quebec border reaching down into Lower Mi. It is
reinforced by a larger scale 500 mb ridge centered over central
Canada and the Plains states to ensure dry weather in SE Mi into
Monday night. There is, however, a short wave/MCV hybrid embedded in
this larger scale ridge pattern that is forecast with good model
agreement to round the ridge and move into the upper Midwest and
northern Great Lakes Monday night. The associated surface low is
well organized and capable of pulling the Ohio valley front back
northward as a focus for a new round of showers/storms. More
important, the system is strong enough to support a low level jet
capable of meaningful moisture/instability transport from the upper
Midwest into Lower Mi late Monday night into Tuesday. It is a
favorable environment to sustain a convective system, however there
is a wide range of track outcomes suggested by model QPF at these
longer forecast time ranges. It does look like early day timing is a
limiting factor for severe potential while speed of the system eases
heavy rainfall concern.

A chance of showers/storms continues into Tuesday night as the low
pressure system and cold front sweep through the Great Lakes. It`s a
short time window ending before midnight as the 500 mb wave and
surface low exit eastward. Passage of the cold front brings another
round of cooler and less humid air with greater staying power during
the late week. The long wave ridge centered over the 4 Corners
reaches up into the Great Lakes to help maintain dry weather
Wednesday through Friday.

MARINE...

A cold front is clearing the southern Michigan border this morning.
Strong high pressure building over northwest Ontario and solid cold
advection (850 MB temps lowering into lower teens) over Lake Huron
will allow northeast winds to reach 20-25 knots, with brief gusts to
around 30 knots this afternoon. Small craft advisories already
issued for all of southern Lake Huron nearshore waters as waves
build in excess of 4 feet.

Winds become easterly on Monday as high pressure retreats and a warm
front lifts in from the Western Great Lakes. Channeling of the winds
over northern third of Lake Huron/near the Straights looks to
support wind gusts of 20 to 30 knots.

Periods of showers and thunderstorms Monday-Wednesday, particularly
on Tuesday as surface low pressure tracks through the Central Great
Lakes. Wind speeds mostly in the 15 to 25 knot range around the
circulation.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through this evening for MIZ048-049-055-063.

Lake Huron...Small Craft Advisory until noon EDT Monday for LHZ421-441.

     Small Craft Advisory from noon today to midnight EDT tonight for
     LHZ422.

     Small Craft Advisory from 10 AM this morning to 8 AM EDT Monday for
     LHZ442-443.

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

$$

AVIATION.....MV
DISCUSSION...BT
MARINE.......SF


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