Area Forecast Discussion


776 
FXUS63 KDTX 102330
AFDDTX
Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
630 PM EST Sun Dec 10 2017
.AVIATION...
Ceilings gradually lowering within MVFR over the next several hours, 
as low level moisture temporarily deepens in advance of a weak 
boundary. This will be sufficient to generate a few light snow 
showers/flurries, with some minor visibility restrictions possible 
through midnight. A period of drier northwest flow then emerges 
overnight, favoring a general clearing of low stratus from northwest 
to southeast during the early morning period. Attention then turns 
to advancing low pressure that will bring a period of widespread 
snowfall to the region Monday and Monday night. Initial period of 
lighter intensity snowfall expected to develop during the midday 
period 15z-20z, where conditions largely remain at MVFR restrictions 
outside of the heaviest bursts. Snowfall intensity will increase from
late afternoon into the evening period, with peak intensity and 
accumulation potential centered between 6 pm and midnight. 
For DTW...A few very light snow showers or flurries will accompany 
the existing MVFR stratus across the airspace late this evening. No 
accumulation expected. A period of clear sky across the lowest 5kft 
a possibility during the early morning period, then back to MVFR as 
light snow develops by 15z-16z Monday. Heaviest period of snow 
expected late Monday into Monday evening, peaking 23z-05z. 
Accumulation between 2 and 3 inches expected by early Tuesday 
morning.
//DTW THRESHOLD PROBABILITIES...  
* High confidence for ceilings aob 5000 feet through 06z, then low 
  overnight. High in ceiling dropping below 5000 ft again by 16z 
  Monday in developing light snow. 
* High confidence in precip type being snow this evening and 
  again Monday.
&&
.PREV DISCUSSION...
Issued at 345 PM EST Sun Dec 10 2017 
DISCUSSION...
Several items of interest in the coming week across SE MI. First we 
are monitoring a developing lake effect band coming off central Lake 
Michigan this afternoon. Next up is a clipper that will track 
through the souther Great Lakes Monday afternoon and evening 
bringing the next round of accumulating snowfall. Coldest airmass of 
the season then moves in through mid week dropping lows into the 
single digits and holding highs around 20F. Additional light 
snowfall could come at the end of the week with the next clipper 
followed by a brief warm up next weekend. 
First up is the potential convergent lake band this afternoon. Winds 
have just flipped to the NW at Big Rapids showing the convergence 
seen at the shoreline is now making its way inland but GRR radar is 
less than impressive thus far showing the moisture plume enhancing. 
In addition, hires models less impressed with the setup today as 
they were previously. Lowered pops, qpf, and snowfall north of I69 
this afternoon to mainly flurries or light snow showers with little 
accumulation. The trough dropping into northern lower will reach the 
Saginaw Valley around 00Z, which will then break up the convergent 
feature as it continues southward through the state. 
Models continue to come better in line in regards to the clipper and 
associated snowfall on Monday. In addition to agreements in hires 
models as they now begin to reach out far enough to forecast the 
clipper, there are similarities between medium and long range models 
as well. Bulk of the forecast remains unchanged as we still expect a 
compact clipper to dig southward into the Ohio Valley Monday 
afternoon before getting pulled back NE into a stronger PV anomaly 
on the nose of a 150+ knot jet right on it's heals. The speed of the 
second wave seems to be difference in how the event plays out thus 
far. A faster and stronger wave will phase the two earlier, which 
will start ingesting the smaller clipper faster which pulls the 
fgen/deformation forcing northeastward earlier. A slower or weaker 
solution will allow the clipper to stay more compact and further 
south keeping the main deformation band across the southern part of 
the state. Adjustments have been made for location of highest 
snowfall with qpf/snow amounts not much different. Still looking at 
a wide swath of 1-2 inch snowfall across SE MI with a band of 
heavier snow around 3 inches likely with the deformation band on the 
northeast flank of the low. Currently this band looks to set up 
between M59 and I94. A lead leaf of broad isentropic ascent ahead of 
the broader trough will bring light snow showers to the area 
starting 15-18Z with the heavier band occuring between 21-03Z. 
Remnant light showers will taper off around 12Z Tuesday when drier 
air moves in. 
Northwest flow ramps up behind the departing wave which will usher 
in the coldest airmass of the season thus far with 850mb 
temperatures falling to -20C by Tuesday afternoon and -25C located 
just north of Lake Superior. Tuesday will not be a pleasant day as 
highs reach the low to mid 20s but winds gusting to 20-30 mph will 
result in wind chill values in the single digits most of the day.
Cold arctic airmass remains over the Great Lakes on Wednesday, 
preventing highs in our area from climbing out of the upper teens to 
low 20s with wind chills hovering in the single digits. Surface 
ridging between systems will keep the area quiet and allow for some 
sunshine through the day. Temperatures Thursday begin a slow rebound 
as the coldest air aloft moves off to the east. Models diverge on 
the placement and strength of a potential shortwave/clipper pivoting 
through on Thursday into Friday, but looking at another chance for 
light snowfall across the region.
Above freezing temps to return to Southeast Michigan on Saturday; 
jet energy will help flatten the ridge over the western CONUS and 
allow for the trough over the eastern CONUS to ease up. Warm air 
advection will set up ahead of a developing low in the northern 
plains, with highs reaching a few degrees above normal on Saturday 
and Sunday. The low pressure system is currently progged to move 
over the northern Great Lakes on Sunday with the best of the forcing 
displaced to our north; no significant precipitation amounts are 
expected though some gusty winds will be possible with the 
heightened pressure gradient.
MARINE...
Diminishing winds this evening will transition to light southerly 
for most of Monday. Colder air will spread across the waters Monday 
night with sustained near-gales forecast to gust to strong gales 
early Tuesday morning through Tuesday afternoon. Significant wave 
heights will reach 12 feet during this time with maximum wave 
heights of 20 feet or higher. Gales will diminish late Tuesday.
&&
.DTX WATCHES/WARNINGS/ADVISORIES...
MI...NONE.
Lake Huron...Gale Watch from late Monday night through Tuesday evening for 
     LHZ361>363-421-441>443-462>464.
     Small Craft Advisory until 4 AM EST Monday for LHZ441.
Lake St Clair...NONE.
Michigan waters of Lake Erie...NONE.
&&
$$
AVIATION.....MR
DISCUSSION...DRK/TF
MARINE.......JVC
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at www.weather.gov/detroit.