Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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979
FXUS63 KDTX 210209
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
909 PM EST Mon Nov 20 2017

.UPDATE...

After a brief drop in sfc winds post sunset, the increasing gradient
has allowed winds to increase. Observations over the last couple of
hours have actually had gusts of 25 to 30 MPH. While ongoing low
level warm air advection may yet limit mixing potential, supporting
some weakening in the sfc winds overnight, current observations
suggest increasing winds a little in the forecast tonight. The
increased gradient has also held temps nearly steady in the lower
40s. Therefore, overnight mins will be nudged upwards a couple
degrees.

&&

.PREV DISCUSSION...
Issued at 603 PM EST Mon Nov 20 2017

AVIATION...

The onset of nighttime cooling in the boundary layer is supporting
decreasing sfc wind speeds. Low level south-southwest flow will
however increase atop this shallow stable layer through the evening.
2k ft level winds are forecast to range from 50 to 60 knots through
the night. This will remain supportive of low level wind shear into
Tues morning, assuming there remains this shallow stable layer near
the surface. A cold front will traverse Se Mi in the 15 to 22Z time
frame on Tues. The front will be marked by a wind shift to the west.
A region of MVFR and low end VFR clouds with a few rain showers
will also accompany the front.

For DTW...With a noted drop in sfc winds at 23Z, the timing of the
low level wind shear will be moved up to 00Z. The onset of daytime
mixing will transition the low level wind shear to mechanical wind
shear mid to late Tues morning, meaning there will be an increase in
the south-southwest sfc wind gusts.

//DTW THRESHOLD PROBABILITIES...

* Medium confidence in cigs aob 5000 feet after 18z Tuesday.

* High confidence in precip type falling as rain tuesday afternoon.

PREV DISCUSSION...
Issued at 237 PM EST Mon Nov 20 2017

Discussion...

Vigorous shortwave disturbance digging through the Canadian Prairie
Provinces is inducing strong cyclogenesis south of Lake Winnipeg.
This system will move east southeast to a position just north of
Lake Superior by Tuesday morning. A strong cold front will sweep
southeast through the northern plains and upper midwest in the wake
of this wave, eventually tracking through southeast Michigan on
Tuesday afternoon.

Relatively mild conditions can be expected within well established
southwest flow in advance of this front with temperatures pretty
close to average for the third week of November (high temperatures
in the mid to upper 40s and low temperatures tonight in the middle
30s. These conditions will hold into the middle of the day Tuesday
before cold air advection steadies temperatures in the early part of
the afternoon and then bring falling temperatures mid/late afternoon
into the evening.

While a large majority of the precipitation with this system will
remain well north over portions of Ontario, models still signal a
pretty decent, albeit brief, shot of rain showers along this front
late Tuesday with some transition to a rain/snow mix or snow into
the early evening before ending. However, surface temperatures will
still be in mid/upper 30s with the last of the band of rain/snow so
no accumulations are anticipated.

High pressure will build into the area in the wake of this front
from Tuesday night into Wednesday, leading to rather calm conditions
after the region experiences southwest winds gusting to 25 to 30 mph
late today and again into Tuesday afternoon. Notably colder readings
can also be expected with high temperatures back into the middle 30s
Wednesday and 20s for low temperatures both Wednesday and Thursday
mornings.

Surface high pressure will remain in control on Thursday before weak
ridging downstream of the next approaching wave moves across the
region on Friday. Low pressure tracking north of the region will
then increase warm advection with 850 mb temps approaching 10 C
allowing highs to make a run for 50 on Friday. The next chance for
widespread rain will arrive Friday night as a cold front extending
south from the low pushes through the region. Upper level troughing
then digs into the Northeast US next weekend setting up a persistent
northwest flow over the Great Lakes with 850 mb temps approaching -
15 C by Sunday. Cloudy, unsettled conditions look to dominate
through the weekend as a series of weak disturbances pivot
southeastward through the region. Saturday will be milder with highs
in the low to mid 40s before a shot of colder air arriving on
Sunday keeps highs in the low to mid 30s.

MARINE...

Southwest winds will continue to ramp up through this evening, and
Gales still appear likely over the open waters of Lake Huron by
Midnight, with 25 to 30 knots along nearshore waters, continuing
into Tuesday before shifting to the northwest late in the day.
Enough cold air advection and mixing expected to sustain Gale force
winds over the north half of Lake Huron during Tuesday evening and
the early morning hours of Wednesday. Scattered snow showers can
also be expected over Lake Huron. High pressure building into the
region will lead to dramatically decreasing winds for Wednesday,
generally in the 10 to 15 knot range out of the west-northwest, with
moderate southwest winds developing on Thursday behind the departing
high.

&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning until 4 AM EST Tuesday for LHZ462.

     Small Craft Advisory until 4 PM EST Tuesday for LHZ442-443.

     Small Craft Advisory until 1 PM EST Wednesday for LHZ441.

     Gale Warning from 10 AM to 10 PM EST Tuesday for LHZ361.

     Gale Warning until 10 AM EST Tuesday for LHZ363-421.

     Gale Warning until 4 AM EST Wednesday for LHZ362.

     Small Craft Advisory until 10 AM EST Tuesday for LHZ422.

Lake St Clair...Small Craft Advisory until 4 PM EST Tuesday for LCZ460.

Michigan waters of Lake Erie...Small Craft Advisory until 4 PM EST Tuesday for LEZ444.

&&

$$

UPDATE.......SC
AVIATION.....SC
DISCUSSION...DG/JD
MARINE.......SF


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