863
FXUS63 KDTX 231115
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
715 AM EDT Sat Aug 23 2025

.KEY MESSAGES...

- Scattered showers and thunderstorms are possible this afternoon.
Severe weather is not anticipated.

- Below normal temperatures Sunday through Wednesday with highs in
the upper 60s to 70s and periodic chances for light showers.

&&

.AVIATION...

Lower level southwest flow ahead of an advancing cold front has
carried in some extra moisture and is supporting BKN to OVC skies at
around 4.5-6kft this morning. There is currently a thin strip of
radar returns crossing Lake Michigan. Expectation is for this to have
minimal impact to terminals this morning with maybe a brief VFR
shower. Forcing along the front during peak heating will then bring
scattered shower and thunderstorm chances this afternoon. Relatively
weak forcing with a lack of strong instability will be a limiting
factor today for more widespread and strong activity. Will maintain
PROB30 for thunder with this issuance. Timing is mainly between 17Z
to 01Z across southeast Michigan with MBS and FNT seeing activity in
the earliest part of this window. Southwest winds become gusty to
around 20 knots with the front late morning through the afternoon.
Decreasing coverage of clouds tonight in the wake of the front as
winds veer westerly.

For DTW/D21 Convection...Scattered showers and storms along a NE to
SW oriented line are forecast to move across the D21 airspace, mainly
between 19Z and 01Z Saturday afternoon/evening. Anticipate non-
severe thunderstorms given the lack of instability.

THRESHOLD PROBABILITIES...

* Low in thunderstorms this afternoon and evening.

* Low for ceilings at or below 5,000 feet.

&&

.PREV DISCUSSION...
Issued at 344 AM EDT Sat Aug 23 2025

DISCUSSION...

A mid-level ridge is retreating this morning as steady height falls
commence with the arrival of a broad low pressure system over
northern Ontario. This system will usher in a narrow ridge of low-
level theta-e ahead of the cold front set to track through later
this afternoon. There will be a chance for a pre-frontal band of
showers along the inbound instability gradient this morning as the
residual cap gradually erodes - will hold PoPs at around 30% or
below based on latest hi-res output. Slightly higher (40-50%)
probability for showers and thunderstorms mid to late afternoon as
frontal passage coincides with peak diurnal instability.

Weak convergence along the front and displacement of upper jet
forcing suggests mainly disorganized and scattered convection, while
warm mid-levels will limit instability to around 1000 J/kg or less.
A core of 0-6 km bulk wind shear of around 30 kt will pass through
the Thumb which may allow for a few stronger cells between 4 and
9pm. A few gusts to 40 mph seem plausible in the strongest storms
but the severe threat is low today. High temps reach the lower 80s
with a slightly muggier feel today as dew points creep into the mid
to upper 60s ahead of the front.

The upper low over Ontario stalls near James Bay Sunday through
Tuesday, sending a series of vorticity lobes over the Great Lakes.
This establishes an early taste of fall in a cool and unsettled
pattern with periodic chances for showers and drizzle. A wave
rounding the base of the trough passes overhead Sunday afternoon
which should be sufficient to support scattered showers. This wave
reinforces the cool advection and is followed by 850mb temps falling
to 5-7 C by Monday. Highs will struggle to reach 70 degrees both
Monday and Tuesday with lows in the 40s and 50s each night. Another
chance of showers occurs on Monday with an additional upper
shortwave passing through.

The stalled upper trough begins to ease eastward midweek which
should allow the thermal trough to follow suit, and high
temperatures are progged to moderate back into the 70s. Evolution of
the trough and timing of additional shortwaves carries increasing
uncertainty by late week, but overall, ensemble guidance maintains
negative height anomalies in the vicinity through next weekend. This
favors temperatures near or below normal through the end of
meteorological summer.

MARINE...

Vicinity high pressure breaks down and dislodges this morning as a
low pressure systems tracks across central Ontario. This drags a
cold front through the central Great Lakes during the second half of
the day, and perhaps into the early overnight hours. Expect some
shower/storm development ahead of the boundary, but uncertainty
exists regarding the degree of coverage. Cannot rule out a couple
strong to severe thunderstorms capable of generating locally higher
winds and/or waves. Cooler conditions settle in behind the front for
Sunday and the first half of next week. This leads to better mixing
potential amidst stronger flow aloft, therefore gusts might approach
Small Craft Advisory conditions at times. Chances exist for shower
and isolated waterspout development over parts of Lake Huron, mainly
Monday and Tuesday.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...None.
Lake St Clair...None.
Michigan waters of Lake Erie...None.
&&

$$

AVIATION.....AA
DISCUSSION...TF
MARINE.......KGK


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