Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 220457
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
1157 PM EST Tue Nov 21 2017

.AVIATION...

Late evening satellite observations indicated some breaks developing
in the VFR stratus/stratocu over northern Lower Michigan where also
some streamers of lake effect were reaching down to HTL. Expect a
neutral northwest low level wind pattern to continue producing
breaks in the larger scale VFR cloud coverage during the morning and
reveal bands of MVFR lake effect clouds. The wind direction from
about 310 gives a boost from both Lake Superior and Lake Michigan
and favors the MVFR cloud bands to possibly reach MBS and FNT during
the night. The main question is with coverage and prefer to monitor
trends for a few more hours to see precisely where the larger bands
of lake effect clouds stabilize before adding to the terminal
forecasts. Upstream observations over the Midwest then support
optimistic cloud conditions over Lower Michigan by late morning
through the afternoon. There will remain potential for lake effect
contributions to stratocu coverage which will diminish during the
day as high pressure approaches the region and moves into the Ohio
valley by Wednesday evening.

For DTW... Colder air moving into the region will produce just a few
gusts near 20 knots during the night. The colder air will also be
dry enough for VFR ceiling right around the 5000 ft threshold before
thinning during the morning through afternoon.

//DTW THRESHOLD PROBABILITIES...

* High for ceiling 5000 feet or less tonight through mid morning.
  Low through afternoon.

&&

.PREV DISCUSSION...
Issued at 257 PM EST Tue Nov 21 2017

Discussion...

Cold front will surge through area late this afternoon/early this
evening. Lift from upper trough forcing this front aided to some
degree by right entrance region of H25 jet streak lifting up east
side of the trough will maintain a band of rain showers along and
immediately behind this front. Cold air advection will be strong
enough to allow for some of this precipitation to change to snow,
either mixed with the rain or becoming snow showers outright. With
generally light precipitation rates and boundary layer temperatures
in the mid to upper 30s, do not expect any accumulations before the
precipitation ends abruptly in the 22z-02z time frame from north to
south across the forecast area.

Colder air will settle into the area behind this front, with lows in
the low/mid 20s tonight and highs no better than the middle 30s on
Wednesday as the core of this cold airmass settles over the central
Great Lakes. That said, winds will decrease notably as compared to
the past few days, so the "chill" factor will not be as persistent.

A moderation in temperatures will ensue from Wednesday night into
Thursday night as main upper troughing progresses off to the east.
This process will initially be rather slow as another (weaker)
shortwave pivots into the area and maintains some degree of upper
troughing. This should lead to a progression of temperatures from the
middle 20s once again Wednesday night, rebounding to upper 30s to
around 40 Thursday afternoon, but falling back into the mid/upper 20s
Thursday night.

Precipitation, after early this evening, will be basically nil with
perhaps a small chance of snow showers again for at least portions
of the area late Thursday night as a stronger warm air advection
pattern begins to set up in advance of the next strong shortwave
that will be dropping out of the Gulf/Alaska region mid/late week.

MARINE...

A cold front sweeping across the region will bring gusty northwest
winds across the eastern lakes in it`s wake this evening through
tonight. The switch from southwest flow to northwest flow has
already begun as the front currently resides over central Lake Huron
and Saginaw Bay. The front will pass south of Lake Erie later this
evening with a secondary trough and cold surge lagging a few hours
behind. Cold air funneling into the region with a tight pressure
gradient will lead to a period of northwest gales across northern
Lake Huron through most of the overnight period. Slightly weaker
winds across southern Huron will not necessitate gales, but small
craft advisories are in effect for a portion of the nearshore waters
around the Thumb mainly due to elevated wave heights. Lake-effect
snow showers will be common in the cold air behind the front. Winds
will relax early Wednesday morning as high pressure builds into the
region.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...

MI...NONE.

Lake Huron...Small Craft Advisory until 1 PM EST Wednesday for LHZ441-442.

     Small Craft Advisory until 4 AM EST Wednesday for LHZ421.

Lake St Clair...NONE.

Michigan waters of Lake Erie...NONE.

&&

$$

AVIATION.....BT
DISCUSSION...DG
MARINE.......DRK


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