Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI
FXUS63 KDTX 221955
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
355 PM EDT THU SEP 22 2016
Afternoon observations support faster timing of the frontal passage
through SE Michigan tonight that has come in with the latest model
run. Mid afternoon surface analysis indicates a weak wave of low
pressure along the front near the straits that is a reflection of
the mature MCV over lower Michigan shown aloft in satellite imagery
and model analysis fields. Modest coverage of showers will be
associated with these larger scale features during the afternoon
into early evening. The upper jet nearby to the north will also
contribute support, along with dynamic forcing on the north flank of
the MCV, to help focus weak convection within and to the south of
the frontal zone before the wave moves east by mid evening.
Thunderstorm potential will be limited by surface based CAPE
hovering around 1000 J/kg feeding MLCAPE only around 500 J/kg, both
of which will continue to fade with the loss of daytime heating.
However, expect shower potential to linger through the night as the
frontal structure remains sharp above the surface with just enough
elevated instability for some weak convection. The otherwise
unorganized pattern of forcing suggests only entry level POPs.
Pressure rises trailing the MCV will apply a southward shove to the
front as it exits the region during the evening, then synoptic scale
subsidence over northern Ontario under strong northwest flow aloft
will do the rest to build high pressure and push the front into Ohio
by early Friday morning.
The main story behind the front will be clouds and cooler
temperatures over SE Michigan. A chance of showers will also linger
within the low to mid levels of the frontal zone as it remains well
organized under neutral to slightly cyclonic flow aloft. There is
actually good model agreement that keeps the 850-700 mb theta-e
ridge overhead through the day and into Friday evening. This raises
the question of how far south/downstream to allow for showers as the
upper level ridge axis builds strongly to our west Friday night.
Prefer guidance that offers minimal coverage near the Ohio border
and dry conditions over the rest of the area. The upper ridge should
continue to be a limiting factor for rain, if not clouds, through
Saturday as well. Lingering clouds and NE low level flow will
reinforce cool air and likely limit high temps to the mid 60s near
Lake Huron to around 70 inland, which are actually readings right
around normal for late September.
Apex of upper ridge looks to be directly overhead Sunday, and
despite a modest increase in midlevel moisture, expect another dry
and seasonable day. For next week, a complex interaction between the
upper low now over the Sierra Nevada and the wave now approaching
the Alaskan Panhandle leads to somewhat low predictability.
Regardless, precipitation potential will increase for early next
week as lower heights approach.
Moderate to fresh northeast wind will develop across area waters
tonight as a cold front slowly settles south. Prolonged onshore flow
may gust to 25 knots at times during the day Friday...especially in
Saginaw Bay. In addition...prolonged onshore flow will build
significant wave heights into the 3 to 5 foot range for the
nearshore zones of Lake Huron late tonight into early Friday night.
Moderate easterly wind will persist through the weekend.
Issued at 1220 PM EDT Thu SEP 22 2016
Widespread MVFR and IFR firmly in place behind a weak surface trough
extending from Iowa across Northern Lower Michigan. This boundary
will settle south late tonight into Friday morning bringing veering
winds to the NE and an increasing likelihood of IFR conditions
filling in from MBS around 06z to KDTW around 12z. Today`s upstream
trends and forecast soundings for tomorrow yield very low confidence
that cigs will mix out at any point early Friday.
For DTW...Wind shift to the NE will lead the arrival of borderline
IFR cigs by a couple of hours. Noise abatement concerns with NE wind
will exist from about 10z through the remainder of Friday.
Confidence in wind speed exceeding 7 kts is highest for the midday
//DTW Threshold Probabilities...
* High for cigs aob 5kft.
Lake Huron...Small Craft Advisory from midnight tonight to midnight EDT Friday
night FOR LHZ421-422-441>443.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
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