Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 191055

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
655 AM EDT Tue Sep 19 2017


The cluster of showers and thunderstorms slowly rotating across Sw
Lower Mi is associated with an upper level short wave, which will
gradually pivot into Se Mi this afternoon. Radar/satellite composite
suggest a slow diminishing trend, which is likely to persist during
the morning with the loss of nocturnal instability. Daytime heating
however may support an uptick in convective showers (isolated
thunder) this afternoon. A sfc trough south of the state will nudge
northward during the course of the day. Abundant low level moisture
lifting into the area north of this front will sustain stratus over
much of the area. There will however continue to be a wide array of
ceiling heights with these clouds.

For DTW...The cluster of thunderstorms over nrn Indiana should
largely remain south of the airport this morning as they continue to
decrease in coverage. Additional thunderstorm development is
possible during the afternoon, with the greater chances being across
far southern portions of the D21 airspace.


* High for ceilings below 5000 ft today and tonight.

* Low in thunderstorm potential today.


Issued at 342 AM EDT Tue Sep 19 2017


Today is our best, and possibly only, chance of seeing precipitation
in the coming week. A strong jet diving down the west coast will
deepen the trough along the coast resulting in downstream
amplification of the ridge over the eastern half of the country. The
ridge has been in place for some time now resulting in a stretch of
above normal temperatures and dry weather. The amplification of the
ridge will lead to mid level heights around 590 dam with 850mb temps
in the upper teens (C) and 950mb temps above 20C. All this should
lead to high temps in the mid to upper 80s for several days which is
around 15 degrees F above normal for late September, just a few
degrees below daily records. The strength of the ridge also looks to
keep the jet axis and train of shortwaves out to our west, keeping
up dry through the period.

Back to the near term part of the forecast now. A stalled frontal
boundary laid out just south of the MI border and up through Windsor
will aide in a period of showers and thunderstorms today and into
tonight as a shortwave lifting into the Ohio Valley begins to
interact with it. The shortwave trough, though primarily an open
wave breaking off the tail of the northern stream trough lifting
north into Canada, is producing a decent area of showers with
embedded thunderstorms. being in an area with weak flow, it will
only slowly drift into MI, pushing the stall front northward across
southern MI. Models show this wave weakening as it moves along, but
with the good appearance on regional radar mosaic, believe as it
interacts more with the front it should spread showers into lower
MI. Best chance of showers and thunderstorms will be along and south
of I94 which is where the front could stall again. Lesser chances
north as moisture rides up the frontal slope resulting in scattered
isentropic showers. Will limit pops to high chance this afternoon
when the center of the wave passes near. Could possibly go likely
but with the majority of guidance showing a strong weakening trend,
would like to see how it holds together through morning. Some
showers will continue overnight across our eastern counties as the
upper wave stalls and continues to interact with the front. Forcing
will continue to fade thus showers activity should end by morning.

The next strong system ejecting out of the west coast trough will
lift NE through the plains and will take the local boundary and pull
it back north through the Great Lakes late Wednesday as a warm
front. Looks like we`ll stay dry but this front will open the door
for strengthening southwesterly flow and the start of the near
record warmth across the area.


High pressure anchored to the northeast of Lake Huron and a weak
frontal boundary extending just south of the state will sustain
northeast winds through the day. Winds will peak around 15 knots
across the open waters of Lake Huron into Saginaw Bay. Winds will
veer to the southeast tonight into Wednesday as the high pressure
expands into the eastern Great Lakes. This high will reside across
the eastern Great Lakes through the weekend, causing a light south-
southeast wind to persist.


Lake Huron...NONE.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.



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