391
FXUS63 KDTX 171004
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
604 AM EDT Sat May 17 2025

.KEY MESSAGES...

- Much cooler this weekend with westerly wind gusts of 30 to 35 mph
today.

- Below average daytime temperatures persist into next week.

&&

.AVIATION...

Cold air circulating around an upper low forecast to track across
the northern lakes today will deepen the low level mixing depth.
With 30 knots within the top of the mixed layer, gusty WSW winds
will result. The peak winds are forecast during the afternoon and
evening hours. Ample low level moisture is also circulating around
the upper low and will advance across Se Mi late this morning into
tonight. This combined with daytime mixing will likely resulting in
fluctations in ceilings heights between low end VFR and MVFR
throughout the afternoon and evening.

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

THRESHOLD PROBABILITIES...

* High in ceilings aob 5000 feet from late morning through Sunday
  morning.

&&

.PREV DISCUSSION...
Issued at 400 AM EDT Sat May 17 2025

DISCUSSION...

A cold front passing through early this morning ushers out the last
vestiges of the summer-like weather felt over the past few days. The
parent low pressure, its mid-level closed circulation now tracking
directly into Lower MI, ushers in a much cooler air mass through the
day. 850mb temps analyzed near 11C will fall to around 4C by late in
the day with diurnal heating dampened by opaque stratus wrapping
around the system. The result will be highs only reaching the lower
to mid 60s - some 20 degrees lower than yesterday. A dry slot keeps
the area dry and cloud free in the pre-dawn hours, but post-frontal
moisture is quickly filling in from west MI with low clouds and
spotty showers arriving over the next few hours. Weak daytime
instability in the moist cyclonic flow allows for additional light
showers at times through the day. With the surface low tracking
across northern MI, a tight pressure gradient will produce gusty
winds to around 30 to 35 mph that taper off this evening.

The upper low slowly peels off to New England on Sunday but leaves
us beneath a lingering moist cyclonic northwest flow pattern that
maintains cool and mostly cloudy conditions through the day. Far
southern areas stand the best chance to see more prolonged intervals
of sun, so highs there may be able to climb into the upper 60s. A
shortwave emerging from the Canadian Prairie then tracks through the
northern Lakes Sunday night into Monday morning, sending a backdoor
cold front across the area. Northeast wind over the cool waters of
Lake Huron reinforces the cool pattern through the mid-week with
highs each day limited to the upper 50s and lower 60s.

A closed upper low develops over the Plains early in the week and
slowly meanders toward the Ohio Valley. Confidence is increasing for
this system to interact/merge with a lobe of vorticity stalled north
of Lake Huron on Wednesday. This evolves into a broad, stalled low
that lingers in the vicinity through the end of the week.
Instability and thunderstorm chances are likely held south of the
area, but a period of wet and cool weather is becoming increasingly
likely from Tuesday night into Friday.

MARINE...

Moderate west-southwest winds follow last night`s frontal passage
with the strongest winds (20-30kts) still expected over the southern
half of the region where the gradient is strongest. Small craft
advisories remain in effect for all nearshore waters through this
evening. Low fully departs Sunday shifting winds to the northwest.
Gusts peak near 20kts during the day before weakening overnight as
weak high pressure slides overhead. Winds gradually shift to the
northeast early next week in response large low pressure moving out
of the Plains towards the Ohio Valley. Strongest flow looking to
occur Wednesday as the surface low moves across the Ohio River. Some
showers are possible with this system but the region is too far
removed from the current favored track to support much in the way of
thunderstorm chances.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory until 10 PM EDT this evening for LHZ421-422-
     441>443.

Lake St Clair...Small Craft Advisory until 10 PM EDT this evening for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 10 PM EDT this evening for LEZ444.

&&

$$

AVIATION.....SC
DISCUSSION...TF
MARINE.......KDK


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