Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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229
FXUS63 KDTX 260715
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
315 AM EDT Tue Sep 26 2017

.DISCUSSION...

One more day with high temperatures topping out at 90 degrees, as
the trend of the cold front looks to be a bit slower. With 850 MB
temps progged to reach and slightly exceed 18 C this afternoon, high
confidence in maxes reaching 90 degrees or even slightly better based
on upstream observations yesterday and with the favorable light
southwest low level flow today, which should lead to fairly uniform
temperatures across southeast Michigan, +/- 2 degrees from 90.

Still favoring a dry or mainly dry frontal passage with little to no
upper level support/PV advection, as local probabilistic SREF
weighted guidance indicating pops under 30 percent. Instability
looks to be limited to a couple hundred J/KG of MUCape, and if there
is any activity, looks to be north of I-69, in the tail of the 850
MB/low level jet.

With the surface cold front looking to come through Wednesday
morning, should allow Detroit to hit 80 degrees on Wednesday before
the deeper cool air can become established. 925-850 mb temps then
falling into the mid single numbers Wednesday night, as pronounced
surface ridging arrives Thursday morning. Max temperatures
potentially coming up just short of 70 degrees on Thursday, as 850 mb
temps look to only recover to around 6 C.

Seasonably strong upper level wave/trough coming out of the Gulf of
Alaska will encompass the Great Lakes Region on Friday, but remain
progressive, with the trough axis moving off the East coast by 00z
Sunday already, per 00z Euro. Upper level northwest confluent flow
over the weekend will lead to dry conditions as the large area of
high pressure is slow to slide eastward. If the center of the high
remains parked over over the Central Great Lakes Saturday Night,
could see min temperatures dip into the upper 30s across the normally
colder spots. Fog could turn out to be an issue as well. With the
chilly airmass and limited mixing depths, looking at daytime temps
holding in the 60s. Forecast is mostly sunny for the weekend, but
always have to be leary of good diurnal CU up.

Building heights and increasing southwest flow early next week will
support another significant warm up, with 80 degrees not out of the
question by the time we get to Tuesday, but still big differences in
the position of the strong upper level ridge, based off the 00Z
Euro/GFS/Canadian solutions.

&&

.MARINE...

After one more day of warm conditions and light wind, a cold front
will cross the central Great Lakes late tonight through Wednesday
morning. The front will drop temperatures back down to readings more
typical for late September and produce a low chance of showers and
thunderstorms. Winds behind the front will turn northwest at
moderate speed, especially over the open waters of northern and
central Lake Huron where gusts around 30 knots will be possible
through Wednesday evening. Part of the forecast to monitor remains
wave height trends in the nearshore areas which are expected to
remain below criteria for small craft advisories due to the
northwest fetch. High pressure will settle over the region Thursday
followed quickly by another low pressure system and cold front due
Friday. This system will bring a reinforcement of colder air and
unstable marine conditions Friday and Friday night before rapid
improvement occurs with high pressure during the weekend.

&&

.PREV DISCUSSION...
Issued at 1223 AM EDT Tue Sep 26 2017

AVIATION...

Other than patchy MVFR fog around sunrise, expect VFR conditions
with mainly clear skies as high pressure holds sway. A bit of a
theta-e surge along a pre-frontal trough late in the day on Tuesday
may lead to some enhanced sct cumulus in the 5-6kft range. Light
and variable winds will become south southwest, but will do no
better than 8-10 knots during peak afternoon mixing.

//DTW THRESHOLD PROBABILITIES...

* None.


&&

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

$$

DISCUSSION...SF
MARINE.......BT
AVIATION.....DG


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