758
FXUS63 KDTX 170800
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
400 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.

&&

.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.

&&

.PREV DISCUSSION...
Issued at 1157 PM EDT Fri May 16 2025

AVIATION...

Well-mixed and gusty SW surface wind has spread into Lower Mi in
warm sector fashion ahead of low pressure occluding into the
northern Great Lakes. The associated cold front sweeps remaining
thunderstorm potential into Ontario by the 06Z forecast issuance
leaving a few hours of VFR in the system dry slot during the late
night. This precedes MVFR ceiling as it expands eastward from the
Midwest where coverage is widespread around the SW flank of the
surface low center. Gusty wind also becomes a weather highlight late
tonight and especially as daytime instability builds by late morning
through the afternoon. West gusts well in into the 30 knot range are
expected which also helps ceiling break into low end VFR late in the
day and Saturday evening.

For DTW/D21 Convection... Thunderstorms move east of the DTW
terminal area from 06Z onward late tonight.

THRESHOLD PROBABILITIES...

* Low for ceiling 5000 feet or less late tonight the high in the
  morning through Saturday evening.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...None.
Lake Huron...Small Craft Advisory from 8 AM this morning to 10 PM EDT this
     evening for LHZ421-422-441>443.

Lake St Clair...Small Craft Advisory from 8 AM this morning to 10 PM EDT this
     evening for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory from 8 AM this morning to 10 PM EDT this
     evening for LEZ444.

&&

$$

DISCUSSION...TF
MARINE.......KDK
AVIATION.....BT


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