Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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056
FXUS63 KDTX 190742
AFDDTX

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

.DISCUSSION...

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.

&&

.MARINE...

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.

&&

.PREV DISCUSSION...
Issued at 1157 PM EDT Mon Sep 18 2017

AVIATION...

Late evening observations showed mostly low clouds within the
stalled frontal boundary near the Ohio border. Data also showed only
thin cirrus over the remainder of SE Michigan. This sets the stage
for fog development before the front begins to accelerate northward
during the late night through morning. The combination of fog and
advancing low clouds will produce MVFR trending to IFR, and possibly
LIFR north of the cloud edge, as the front progresses across the
terminal corridor. There remains a chance of showers later in the
night as well but coverage will be minimal compared to the
restriction already in place due to clouds and fog. The slow
westward and northward drift of the front is expected to keep the
area under at least MVFR ceiling/fog restriction with scattered
showers through most of the day.

For DTW... Low clouds will continue to solidify along the stalled
front and expand back northward over lower Michigan during the
night. This will ensure coverage of stratus and fog with borderline
MVFR/IFR restriction through the morning with only slow improvement
during the afternoon.

//DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 ft or less during the night through late
  afternoon.


&&

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

$$

DISCUSSION...DRK
MARINE.......SC
AVIATION.....BT


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at www.weather.gov/detroit.



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