Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 181834

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
234 PM EDT Mon Sep 18 2017


Extremely messy setup across southeastern Michigan as old frontal
boundary coasted into the central Great Lakes from the west with
virtually zero upper level forcing remaining. Models show this old
surface trough stalling out over far southeastern sections of the
cwa at least for the next 24 hours all the while large scale
trajectories aloft become increasingly anticyclonic. As a result,
will continue to impacted by the amount of pre-existing clouds and
saturation that will hold on in a neutral advection regime. First
item will be watching afternoon showers re-initiate across the far
southeastern cwa. This is currently happening and thus far as
remain southeast of the DTW. Given these showers activated along the
800-675mb theta e gradient and data supporting some sight drift
eastward of the boundary will leave out of the TAF forecast this
afternoon. Second item of interest for aviation forecast is the
eventual northward movement of main theta e gradient as a pseudo
warm front tonight. Cloud from today is not expected to erode out
completely which should lead to reestablishment of ceilings again
after sundown. Easterly gradient flow is expected to remain high to
discourage fog formation.

For DTW...Postfrontal stratus will be slow to erode this afternoon
with front now stalling out. Main midlevel frontal boundary
providing focus for showers is pushing east. Question for late
tonight distills down to potential for low stratus or fog. Given
persistent light easterly gradient flow, preference was to err with
status. Otherwise, potential does exist for a shower late tonight as
moisture begins to lift back northward. Introduced a Prob30 group
late tonight.


* Moderate in ceilings below 5000 ft today.


Issued at 337 AM EDT Mon Sep 18 2017


A cold front continues to slowly work eastward through SE MI through
the early morning hours. The front continues to weaken as the parent
low is well removed over northern Ontario thus shearing out whatever
remains of the frontal forcing. Isolated to scattered showers will
accompany the front during the rest of its passage across the area
through the morning hours. Cold advection with northerly flow behind
the cold front will result in a low stratus deck which should hold
through the afternoon hours before drier air and mixing can scour
out the moisture trapped beneath the subsidence inversion from
building high pressure. Highs should reach into the low/mid 70s
today, but if the stratus holds longer across the north, could very
well see highs only in the 60s.

The high pressure system sliding through the Great Lakes will lead
to dry conditions for Monday once morning showers move east. Tuesday
is the next chance of precipitation as an upper level wave lifts
northeast toward southern MI. There is a slight chance or low chance
of seeing some rain on Tuesday from this system. High pressure will
still reside over the region with the remnant cold front draped just
south of MI. Models show a bit of overrunning as the system
interacts with the front, resulting in some rain over southern MI.
There could be some right entrance region jet forcing over the area
for a short time before it lifts north as well. Not very confident
in this outcome as the ridge could over power the weakening system
and keep the front too far south. Will hold with low pops for now,
but could see a dry forecast for most locations.

Story for the rest of the forecast is sun and warmth as a deep
trough setting up over the west coast resulting in downstream
amplification of the ridge already in place over the eastern conus.
The steering currents around the mid level ridge, building to 590
dam by the end of the week, will keep any shortwaves to our west
through the weekend. Increased southwest flow will eventually push
the thermal ridge into the region where 850mb temps will then hover
in the upper teens (C) for several days. This combined with clear
skies and full sun, will lead to high temperatures in the mid 80s
for the latter half of the week into the weekend. This will be
around 10 degrees F above normal for mid September.


High pressure will track across the northern Great Lakes today. This
high will drive a secondary cold front into the southern Great Lakes
region later this morning. Modest northerly winds will prevail
through the day in the post frontal environment. Wind gusts over much
of Lake Huron will approach 20 knots today within the post frontal
cool air. Winds will veer toward the northeast tonight into Tuesday
as the high slides into Quebec. A slight uptick in the gradient will
sustain northeast winds generally in the 10 to 20 knot range on
Tuesday. Persistent high pressure is forecast to take hold across
the eastern Great Lakes during the latter half of the weak,
supporting generally light and variable winds across the region.


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



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