Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 181715
AFDDTX

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
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.

&&

.PREV DISCUSSION...
Issued at 310 AM EST Sat Nov 18 2017

DISCUSSION...

Lead shortwave and associated rainfall was pushing east of the
forecast area early this morning.  Attention now turns to the main
wave over the high plains of CO/KS/NB as it moves into the Lakes
region by this evening. Associated with this wave is the deepening
surface low. Models are still struggling with the location, the
strengthening and the timing of this surface low.  Models continue
to be slower with the timing of the deepening of this feature with
the slightly flatter nature of the upper wave. This keeps the surface
low south of the state and moves it from northern IN to central Lake
Erie this afternoon and evening while deepening it into the mid
980s mbs.

The bulk of the forcing with the lead wave has pushed east of the
forecast area. However a ribbon of 700-500 mb FGen across far
southern Lower MI with modest isentropic lift/moisture advection
will keep numerous showers in the forecast for the areas south of M
59 during the morning.  Just a chance of showers north of that
during the morning hours. Between 15z and 18z, very good mid level
Fgen and deformation works back over lower MI and continues through
00z. Also associated with that will be a little couple jet dynamic
from the right entrance region of the jet across the northern lakes
and the left front exit region of the 140kt jet cutting into the
Ohio valley. Precipitable water will be just under an inch for this
event while mid level lapse rates may be just steep enough with the
dynamics to have a rumble of thunder for far southeast Lower MI.
Without a doubt, the best instability and moisture will lie across
northern IN and northern OH near the warm front, but think there
will be enough moisture and forcing between 700 and 300 mbs to bring
widespread half inch rainfall from 18z to 00z for southeast Lower
MI. Will lean toward the cooler end of guidance temps with the
surface low staying south of the state with all the clouds and rain.

NAM is aggressive with the column cooling for the Tri Cities and FNT
areas from 22z to 00z early this evening. Local ensemble output
suggest a non-zero chance of accumulating snow, but more like 20 to
30 percent chance. Will certainly have snow mixing with the rain as
it ends during the evening across much of the forecast area, but
will hold off on any minor accumulations because of how quickly the
forcing pulls out of the region.

As the low deepens winds will increase this evening. Ensemble output
is suggestive of 35 to 40 mph peak wind gusts. This looks good given
not much more than 40 kts in the low level mixed layer.

Expect Sunday to be cloudy with plenty of flurries or even full
fledged snow showers through early afternoon. A good secondary
shortwave passes through over the forecast area and model soundings
indicate good shallow instability up to 8 to 10k feet. That should
be plenty good for scattered snow showers.  Will lean toward a
cooler forecast highs mostly in the mid 30s on Sunday rather than
around 40 degrees of guidance. Hourly model guidance suggest that it
will be a struggle to get up into the mid 30s let alone 40.

After this weekend, weather will be a little quieter as far as
precipitation. Warmer, but seasonable conditions expected on Monday
and Tuesday. A cold front passing through the state on Tuesday will
be accompanied with wind both ahead and behind it. Temperatures will
again fall back to seasonably cool conditions for Wednesday and
Thanksgiving.

MARINE...

Rapidly strengthening low pressure will lift from central Indiana
across Lake Erie this afternoon. As it does so, NNW wind will
strengthen bringing widespread gales to the waters. Portions of the
southern Lake Huron basin may see periods of sustained gales
overnight. Significant wave heights of 12 feet or more will be
common with maximum wave heights potentially eclipsing 20 feet in
the open waters. Gale warnings remain in effect for all marine
zones. After a period of moderate to fresh westerlies Sunday night
through Monday night...potential for SW gales develops early Tuesday
as low pressure 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.

&&

.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.

&&

$$

AVIATION.....DG
DISCUSSION...RBP
MARINE.......JVC
HYDROLOGY....JVC


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