Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 161235

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
835 AM EDT SUN OCT 16 2016


An update was issued to the forecast to increase coverage of
showers/thunderstorms through mid day, mainly south of Saginaw.
Mid level frontogenetical forcing is acting upon an axis of deep
moisture, triggering widespread showers and scattered
thunderstorms. This mid level fgen and axis of deep layer moisture
will push south across the rest of the forecast area between now
and early afternoon. Some enhanced upper divergence within the
exit region of an upper jet max nosing into nrn Illinois/srn
Wisconsin will sustain the mid level forcing through early
afternoon before it weakens and moves southeast of the area. Given
the expected coverage of rain, forecast afternoon highs have been
taken down a couple degrees across metro Detroit and points south.
The sfc cold front will slow as it slides into the Saginaw Valley
and thumb this afternoon. Recent model guidance suggest some weak
sfc based instability developing along this boundary by mid-late
afternoon. This will be enough to support a chance of additional
convection across the north later today.


Issued at 715 AM EDT Sun OCT 16 2016


Surface trough and weak cold front sinking through Southeast
Michigan will provide a good chance of showers with embedded thunder
at the terminals today. Deeper plume of moisture currently spreading
into Southeast Michigan will have a bigger impact on FNT and MBS
this morning before sliding southward through the remainder of Lower
MI. As this occurs, forcing along the front will weaken and this
should provide a lower coverage of convection (especially TS) than
currently seen from PTK south. Deeper pool of moisture will slide in
behind the front gradually dropping ceilings north to south to MVFR
and then IFR. Slight southerly gradient will remain overnight
lending some uncertainty to whether moisture will settle in as low
stratus or fog. There is good potential for conditions to fall to
LIFR or even VLIFR overnight and early Monday. The potential will be
greatest from PTK north, with Detroit-area terminals more uncertain
as the front settles closer to this area and then lifts back through
early Sunday morning.

For DTW...First batch of showers shown on radar should brush DTW
between 11-13Z with dry air most likely dropping conditions to high-
end MVFR at the worse. Next area of showers/tstorms near the Chicago
area are timed to arrive around 16Z. Deeper moisture will be sliding
down into the area from the north at this time, allowing ceilings to
drop below 5000 feet with higher confidence for MVFR conditions in
showers/tstorms. Forcing should weaken as the front drops into the
area, and confidence with tstorms is not high. Fog/stratus then the
main concern overnight as deeper moisture resides over the area on
the north side of the front. Some uncertainty whether threat will be
low stratus or fog, and may see LIFR conditions develop overnight.

//DTW Threshold Probabilities...

* Medium in ceilings below 5000 ft late morning and afternoon. High
  during the evening and overnight.

* Low for thunderstorms today

* Low for ceilings below 200 feet or visibility below 1/2 mile

Issued at 326 AM EDT Sun OCT 16 2016


Area of showers and embedded thunderstorms should continue to expand
along/south of frontal boundary from southern Wisconsin into lower
Michigan as right entrance region of jetlet extending south of main
jet over Ontario/Quebec lifts along front early this morning. Will
increase precipitation chances to 80-100 percent over the northern
forecast area during this time frame as widespread showers and some
thunder shifts into locations along/north of I-69 especially. This
jetlet shifts to the east of the area by midday, so south/southeast
expansion of precipitation is a bit in question from mid morning
into the afternoon as the front sags into southern lower Michigan
and stalls with the loss of this upper support.

Will graduate rain chances down to about 50 percent by midday south
of M-59 or so given uncertainty of coverage along front by this
time. This basically maintains the going forecast. Thunder has been
widespread within the initial expansion of activity to the west
given decent elevated instability and jet support/upper divergence.
While coincidence of these factors fade gradually this morning, see
no reason that some thunder will not remain possible area-wide
today as higher theta-e airmass continues to funnel into area and
sub-zero Showalter Indices persist into afternoon.

Shower/embedded thunder chances then persist into this evening and
overnight, but shift quickly to the north on Monday morning as
forcing from next shortwave trough to the west pulls front north.
A bigger concern associated with this front will be expansive area
of low level moisture along/north of the boundary. With dew points
forecast in the lower 60s at 2M and near surface soil temperatures
roughly in the upper 50s, fog may become something of an issue. At
the very least, low stratus deck with areas of fog will be likely.

A very warm period (even compared to the 70ish degree readings over
the weekend) then sets up Monday into Tuesday as south/southwest
gradient flow increases from midday Monday into midday Tuesday.
While the aforementioned fog and/or stratus may hamper temperatures
Monday afternoon over northern portions of the forecast area, it
seems likely that a solid 1/3 of the area will push/eclipse 80 by
afternoon (much above the average in the upper 50s). The same
airmass is in place Tuesday, but mid/upper level clouds and late day
cold air advection may cap temperatures somewhat in the afternoon.
Again, southeastward forecast area will be the warmest and likely
see some 80+ degree readings. Monday night will be an exceptionally
mild night with lows in the mid/upper 60s (some 25-30 degrees above
the average mid October low temperatures in the upper 30s).

Mean upper trough over the western CONUS shifts into area from mid
to late week as this forecast period ends. While the evolution of
this features remains elusive, there will be a shift to cooler and
rather unsettled conditions from Wednesday on into next weekend.


Modest southwest flow will continue through late morning ahead of a
surface trough. Speeds will be strongest over the central and
southern portions of Lake Huron (including Saginaw Bay), where
sustained speeds will reach 15 to 20 knots with gusts around 25
knots. While rain showers will be the predominant form of
precipitation, a few thunderstorms will also be possible. Weak
ridging will then provide much lighter winds this evening and
tonight which will allow some areas of fog to form as a warm and
moist airmass remains in place. Southerly flow will begin to
increase again on Monday as low pressure starts to lift into the
Great Lakes. Speeds look to peak late Monday night and Tuesday as
the low lifts from Lake Superior to northwest Quebec while
intensifying. Top wind speeds and potential for any headlines (gale
watches and/or small craft advisories) are a little uncertain this
far out as forecast models struggle with how deep the area of low
pressure will get and as warmer air arriving over the cooler lake
waters will create a stable profile and limit gust potential. This
will need to be watched closely, especially for central and
northern portions of Lake Huron.


Showers and a few thunderstorms will develop today as a plume of
deep layer moisture surges into the area ahead of a surface trough.
Activity over northern and western Lower Michigan will slowly drop
through Southeast Michigan during the morning and afternoon. This
will provide the best chance for precipitation today, although
additional showers and thunderstorms may pop up during the evening
and even overnight as the front stalls near the Ohio border and then
begins to lift back northward. Rainfall amounts are expected to
average between one-quarter and one-half inch north of the M-59
corridor, with lesser amounts expected along and south of there. Any
thunderstorms would provide a brief period of heavy rainfall, and
bring locally higher amounts to those locations.


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



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