Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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000
FXUS63 KDTX 182031
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
331 PM EST Sat Nov 18 2017

.DISCUSSION...

Categorical rainfall has been spreading across all of southeast
Michigan this afternoon. The center of the surface low is now
located on the central IN/OH border. A cold front also continues its
progression southeastward through central Michigan keeping widespread
rainfall likely through this evening. The current track of the
surface remains further south across northwestern Ohio and through
central Lake Erie. This will focus the highest rainfall totals across
the further southeast counties. It has also kept the more unstable
warm sector south of the MI/OH border. However, some lightning and
rumbles of thunder earlier this afternoon were observed in far
southern portions of the state given mid level lapse rates of around
6 C/km. Do not expect much thunder the rest of the day.

The biggest challenge for this forecast will be this evening with
the timing of the surface low deepening and the arrival of the cold
air resulting in potential snowfall accumulation in the Flint to
Tri-Cities areas. Latest guidance has a stronger push of colder air
in the evening coinciding with precipitation within the area of
strong deformation. Add in the diurnal cooling component and the
column will cool enough to transition from all rain to a rain/snow
mix or mostly snow between 22Z to 00Z. Confidence is increasing for
areas to see some minor accumulations in portions of the northwestern
CWA around the Tri-Cities and Flint area. Enough forcing exists
after the lower levels cool to produce some higher snowfall rates
through the evening. The winds will also pick up substantially
heading into the evening and overnight period. The surface low will
begin to deepen as it reaches the eastern Great Lakes. This will
result in cold and brisk northwest winds as the surface pressure
gradient increases this evening and lasting through tomorrow morning.
Wind gusts up to 35-40 mph still look possible late this evening and
overnight as winds of around 40 knots should be able to mix down.

The bulk of the forcing and precipitation with the system will exit
east of Michigan by 05Z to 06Z leaving Michigan under good northwest
flow. Plenty of clouds are in store tomorrow with the lakes providing
some added moisture. An embedded shortwave within this northwest
flow will progress southeastward across Michigan should provide lift
in conjunction with some lower level instability should support snow
showers tomorrow morning through the early afternoon. Do not expect
much accumulation from this round of light snow showers. High
temperatures will dip below normal topping out in the mid 30s as 850
mb temperatures of -10 C move in by Sunday afternoon.

More dry and quiet weather expected by Monday as height rises drift
through the Great Lakes. Cold temperatures in the mid 20s are
forecast for Monday morning with the deeper cold air still in place.
Winds will shift to the southwest by Monday afternoon ahead of the
next low pressure system to affect the region. This will allow a
brief period warm air advection to bring temperatures back up to the
low to mid 40s, which is more towards normal for this time of year.

Low pressure tracking eastward through Ontario will pull a cold
front through the region on Tuesday. Ahead of the front gusty
southwest winds will develop as highs rise into the upper 40s across
far southeast Michigan. A few showers will be possible with the
frontal passage before colder air quickly filters into the region by
Tuesday night. A calm, dry stretch of weather is then expected
through the rest of the workweek as high pressure remains in place
across the region. Temperatures will remain slightly below average
with highs in the mid to upper 30s/lows in the mid to upper 20s for
the Thanksgiving holiday before moderating slightly by late next
week.

&&

.MARINE...

Gale Warnings remain in effect for all marine areas this evening
into Sunday.

Rapidly strengthening low pressure will lift across Lake Erie this
evening on its way east of the Great Lakes by Sunday morning. Winds
will increase substantially during the rest of the day. Northwest
gales are expected to develop near the low from western Lake Erie
into southern Lake Huron early this evening. As winds peak during
the late night hours, gales will expand into northern Lake Huron
with gusts increasing to 40 knots, and perhaps 45 knots at times,
over southern parts of the lake. These wind conditions will produce
waves in the 12 to 16 foot range.

Gales will persist into Sunday, but gradually diminish during the
afternoon and evening. A period of moderate to fresh westerlies will
follow the gales from Sunday night into Monday night. Southwest
gales will then be possible early Tuesday as the next low pressure
system tracks across northern Ontario.

&&

.HYDROLOGY...

Light rain will remain mainly focused south of the M59 corridor for
the next several hours. Rain coverage to the west will fill in
throughout the morning as it tracks closer to the area. By this
afternoon, all of SE Michigan will see moderate rain. Additional
rainfall totals will range from around 0.5" in the Saginaw Valley
area to an inch near the Ohio border. The heaviest rain will be
focused in the 1pm to 7pm time frame. Minor urban flooding remains a
possibility.

&&

.PREV DISCUSSION...
Issued at 1215 PM EST Sat Nov 18 2017

AVIATION...

Rain with IFR/LIFR ceilings will be common into early this evening
as deepening low pressure passes to the south. There is a definite
trend today with rain mixing with and/or changing to snow. This is
especially true KMBS/KFNT (to some extend KPTK), but I-94 corridor
is not out of the question either. With temperatures in the middle
30s (at the coldest), this will not cause much issues. Northwesterly
winds will, however, become quite gusty as this colder air rushes
into area behind the exiting low pressure. Expect a period of gusts
to 30 knots or a bit more (peaking in/around midnight as best surge
of colder air arrives). Thereafter, grungy northwest flow pattern
sets up with cigs in the 2500-3500 foot range north to south late
tonight into Sunday.

For DTW...Rain will continue with IFR/LIFR cigs. There is a small
chance snow will mix with the rain in the 00z-03z time frame before
ending, but will leave as all liquid for now given boundary layer
conditions attm. It will be hard to cool this column with downslope
northwest flow off Irish Hills this evening. Wind gusts will be an
issue though with gusts to 30-33 knots most likely (peaking several
hours around midnight).

//DTW THRESHOLD PROBABILITIES...

* High for cigs aob 5kft.

* Medium for cigs at 200ft this afternoon.

* Low for snow mixing in with rain 00z-03z.

* Moderate for exceeding crosswind threshold from 340 to 310 degrees
  00z-06z.


&&

.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Warning until 7 PM EST Sunday for LHZ361>363-462>464.

     Gale Warning from 7 PM this evening to 10 AM EST Sunday for LHZ421-
     441>443.

     Gale Warning from 7 PM this evening to 7 AM EST Sunday for LHZ422.

Lake St Clair...Gale Warning from 7 PM this evening to 10 AM EST Sunday for LCZ460.

Michigan waters of Lake Erie...Gale Warning from 7 PM this evening to 10 AM EST Sunday for LEZ444.

&&

$$

DISCUSSION...AA/JD
MARINE.......DG
HYDROLOGY....DG
AVIATION.....DG


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at www.weather.gov/detroit.



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