Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 151643

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1243 PM EDT SAT OCT 15 2016


Good moisture surge lifting through southeast Michigan Late this
morning supported high IFR/low MVFR deck of clouds, but
mixing/clearing already has made inroads past Wayne county, and
suspect southern TAF sites (dtw-det-yip) to be VFR/ceiling free
below 5000 Feet through Tonight. Moisture axis holding back across
Western Michigan and approaching cold front makes for difficult call
across MBS and FNT/PTK. Higher confidence with MVFR/LOW VFR clouds
holding across MBS, with showers and possible thunderstorms
developing late Tonight. FNT/PTK look to be muddled in the middle,
both in terms of showers overnight and in between MVFR/low VFR
ceilings vs NO Ceilings. South-Southwest winds generally in the
8-16 knot range through much of the TAF period.

For DTW...Partly cloudy skies expected to persist into early evening
hours at least, and probably much of the night before clouds and
possible showers return by Morning.

//DTW Threshold Probabilities...

* Low in ceilings below 5000 ft through Tonight, medium tomorrow.

* Low for thunderstorms during Sunday.


Issued at 1014 AM EDT Sat OCT 15 2016


Low stratus has been slowly but steadily inching its way into Se
Mi from the southwest. These low clouds represent the lead edge of
a low level moisture plume which has been advecting northward from
the Ohio Valley within the low level sw flow. The stratus should
extend across much if not all of Se Mi by early afternoon. Strong
warming above the low level inversion and a mid October sun angle
will be a limiting factor in eroding these clouds this afternoon.
Considering the strength of the winds above the shallow stable
layer, there is likely to be partial if not total erosion of the
clouds later in the day across the eastern half of the forecast
area where the moisture looks to be more shallow. Farther
northwest across the Saginaw Valley, the low stratus deck may be
too thick for total cloud erosion, warranting a more pessimistic
cloud forecast. An update will be issued to account for latest
cloud trends. Afternoon temps will also be adjusted accordingly,
mainly lowered across the northwestern sections of the forecast
area where afternoon cloud cover is likely to be more persistent.

Issued at 251 AM EDT Sat OCT 15 2016


Large area of stratus to the south and southwest of the area will
funnel into lower Michigan later this morning within increasing
southerly gradient flow between high pressure to the east and a cold
front impinging on the upper midwest and northern Great Lakes. This
trend to mostly cloudy skies in the late morning to early afternoon
will cap afternoon high temperatures to some degree despite having a
notably warmer airmass in place. Still, expect temperatures to climb
to around 70 most locations during the afternoon.

Aforementioned cold front will sag southeast into the area late
tonight into Sunday as shortwave disturbance and related surface low
pressure system lift east/northeast across Ontario into Quebec.
Forecast timing of this frontal. As the main forcing with the upper
wave shifts northeast of the area, cold front will gradually take on
west to east orientation before stalling over lower Michigan on
Sunday. Moisture along the front will actually be pretty substantial
for the middle of October with precipitable water values on the
order of 1.50 inches and double digit H85 dew points.

So, even with the loss of upper support, anticipated a decent
coverage of showers working into the area late Saturday night into
Sunday morning. Will maintain likely pops in the 60-70 percent range
during this time frame with initial activity dropping into the
Saginaw Valley 06-12z and then reaching metro Detroit and points
south by 12z or shortly thereafter. Will maintain a mention of a few
thunderstorms as elevated instability (Showalter indices on the
order of 0/-2C) increases within axis of higher theta-e airmass that
funnels into area along frontal boundary. That said, low level
instability appears negligible, so any thunderstorm should remain
limited despite an increasingly sheared environment.

After stalling Sunday, expect the front to lift back north Sunday
night into Monday in response to forcing from next shortwave that
ejects from main upper trough over western NOAM into the Canadian
Prairie Provinces. The front should basically exit the forecast area
by Monday morning and focus remain shower activity further and
further north during the day.

Mean upper trough to the west then ejects eastward and brings a cold
front through area Tuesday evening/night. So, after pushing 80
degrees on Monday and Tuesday, temperatures are expected to settle
back into the 50s to around 60 during the latter half of next week.
Medium range models have been quite erratic the the exact evolution
of this upper trough as it shifts to the Mississippi Valley and
points east late in the forecast period. While confidence is pretty
low, it does appear that a more unsettled period will develop with a
varying degree of showers across the area, particularly by Thursday
and Friday.


Two low pressure systems will pass north of the area through early
next week, bringing periods of unsettled weather and a predominantly
strong southerly flow. The first low will lift through Ontario and
into St James Bay by tonight, tightening the surface pressure
gradient and increasing southerly winds over the area. Winds will
remain sustained at 20 to 25 knots with gusts to 30 knots over
northern and central portions of Lake Huron through tonight, with
speeds also increasing to between 10 and 20 knots with gusts to 25
knots over the remainder of the marine area. A small craft advisory
remains in effect for Saginaw Bay today and tonight. The passage of
the cold front will also bring a good chance for showers, and
potentially a few thunderstorms tonight and Sunday. Winds will
decrease dramatically on Sunday as a ridge of high pressure briefly
builds into the Central Great Lakes.

The slow passage of a second low pressure system through the
northern Great Lakes will bring a another period of increased
southerly winds late Monday into Tuesday, and provide a high
likelihood of showers and thunderstorms over Lake Huron.


A plume of deeper moisture will work up into Southeast Michigan
Saturday night and Sunday ahead of a weak cold front. This will
provide showers and even a few thunderstorms across the area, with
rainfall amounts expected to run on average around one-quarter of an
inch. Locations that experience thunderstorms or heavier showers
will receive a brief period of heavy rainfall however, allowing
rainfall totals to reach around one-half inch.


Lake Huron...Small Craft Advisory until 6 AM EDT Sunday FOR LHZ421-422.

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



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