Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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403
FXUS63 KDTX 020909
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
409 AM EST Fri Dec 2 2016

.DISCUSSION...

Lake Michigan remains activated this morning within deep, persistent
cyclonic flow. Drizzle, with isolated light rain showers have been
fairly consistent in a corridor focused between M 59 and I 96.
Activity may be waning some or transitioning more into pockets of
lighter drizzle with the collection of 07Z surface observations void
of prevailing precipitation. Convective depths are really not that
squatty as model soundings continue to advertise inversion heights
at upwards of 6000 ft agl or so. This is on the backs of the 00Z DTX
sounding which showed neutral lapse rates from the surface to 10.0
kft agl. KGRB and KDVN raobs both signaled inversion heights of 5.0
to 6.0 ft agl, which provides some confirmation to the nam trends.
Given some secondary mesoscale banding that has organized just south
of Saginaw Bay into the Thumb region and continued shower activity
streaming inland, decided to carry a low end chance for light shower
or drizzle right through the morning to 18Z. Difficult to go with any
-sn mention with saturation warmer than -8 C.

The low level wind profile is shown to veer at midday in the wake of
the U.P. shortwave as it tracks through southeastern Michigan. The
introduction to more organized NW flow with subsidence trailing the
shortwave is shown to lower inversion heights to less than 4.0 kft
agl at midday. Combine this with the low level convergence axis
being pushed south of the MI-OH stateline and the persistent lake
effect activity will end. Stratus will persist during the afternoon
which should set up daytime temperatures today exactly at average
for the 2nd of December.

Upper level flow will become increasingly zonal this weekend in
direct response to high amplitude shortwave energy digging into
northern Mexico. Southeastern Michigan will remain on the cold side
of the upper level jet which keeps steeper lapse rates locked in
below 900 mb. As a result, preference is for a cloudier forecast
both Saturday and Sunday. There is some potential for breaks late
Saturday but confidence is low. Higher sky fraction forecast for
opaque midcloud on Sunday. Colder temperatures Sunday morning and
low insolation will keep temperatures in the middle 30s a few
degrees below average.

The next potential for widespread precipitation will come Sunday
evening as a midlevel trough pushes through the northern stream and
pushes directly through the central Great Lakes. A little bit of a
messy solution as bulk of the dynamics will be directly tied to the
anticyclonically curved exit region to a strong +120 knot jet axis
over the PacNW. Midlevel trough and main shortwave is forecasted to
push directly across southeastern Michigan just after 00Z Monday.
Uncertainty exists as models suggests both a substantial change in
shortwave tilt as it arrives and also in the acceleration in the
shortwave while it passes overhead. With that stated both the cold
thermodynamic profile and depth of saturation suggests a higher
confidence in more widespread precipitation. It appears to be a good
synoptic scale ascent system with good moisture. Confidence is
moderate that minor accumulations of light snow will fall across the
area. Limitations for accumulations will be smaller flake size, more
neutral lapse rates, lack of strong frontal circulation forcing and
thus lower precipitation rates. Relying on QPF for the larger scale
ascent, it appears that 1 to 2 inches of snowfall may be possible.
Lower confidence is what the impact will be on area roadways. Time
window for the event is expected to be 21Z Sun ending by 06z Monday.

&&

.MARINE...

Cold cyclonic flow will continue over the eastern Great Lakes
resulting in winds gusts around 30 knots across Lake Huron. Westerly
winds will keep gusts near shore slightly tempered but still at
small craft criteria. The westerly winds will veer more
northwesterly through the afternoon as high pressure builds in from
the west. This will continue the elevated waves near the tip of the
Thumb through this evening hours with the northerly fetch. Winds
will drop below 10 knots on Saturday as the high drifts overhead
before re-emerging out of the southwest on Sunday ahead of the next
system.

&&

.PREV DISCUSSION...
Issued at 1245 AM EST Fri Dec 2 2016

AVIATION...

Conditions will continue to fluctuate between MVFR and VFR through
the overnight as lake effect clouds stream across the state into the
area. Increasing subsidence will lower the inversion through the
rest of the night which will lock the low level moisture in
resulting in persistent stratus deck. The convergence band of light
rain across southern MI will linger over the Detroit TAFs for a few
more hours before shifting south. Winds will be south of west
through this morning before veering to the northwest with decreased
flow after 12Z.

For DTW...Low level convergence will focus periodic rain showers off
southern Lake Mi over the next few hours. Mid level subsidence will
reduce convective cloud depths during the course of the night,
likely causing remnant showers to transition toward drizzle.
Temperatures will remain above freezing keeping precipitation in
liquid form. Drier air and veering flow to the northwest will end
the rain/drizzle in the morning.

//DTW Threshold Probabilities...

* High in ceilings below 5000 ft through tonight. Medium on Friday.

* High in precipitation type being all rain tonight and Friday
  morning.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Small Craft Advisory until 10 PM EST this evening FOR LHZ441.

     Small Craft Advisory until 4 PM EST this afternoon FOR LHZ421.

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

$$

DISCUSSION...CB
MARINE.......DRK
AVIATION.....DRK


You can obtain your latest National Weather Service forecasts online
at www.weather.gov/detroit.



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