Area Forecast Discussion
Issued by NWS Detroit/Pontiac, MI

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FXUS63 KDTX 062050

Area Forecast Discussion
National Weather Service Detroit/Pontiac MI
Issued by National Weather Service GRAND RAPIDS MI
351 PM EST Wed Dec 6 2017


Water vapor imagery shows a couple features of note rotating around
the broader upper low centered just south of Hudson Bay. The first
is a small PV max zipping across southern Lower MI at this time with
trailing subsidence. Beneath this subsidence we see lake effect
clouds over northern and central Lower MI spreading southeast into
the forecast area.

An even stronger PV max has entered IA as part of a broader area of
enhanced PV rotating around the low. As this feature approaches Lake
Michigan, the boundary layer and convective instability will both
grow, as seen with increasingly negative theta-e lapse rate
forecasts. A gradient in this instability develops and stretches
eastward roughly along the I-94 corridor Thursday morning into
afternoon, suggesting low level fgen is in play with drier and
colder air wrapping around the lake. Convection allowing models have
been consistent in depicting organized banding of the snow as is
already depicted farther north at this time with the Gaylord radar.

Although accumulations over southeast Lower MI will be curtailed by
the long distance from Lake MI, we are looking at a potentially
impactful setup Thursday morning into the afternoon with rapid
localized changes in travel conditions around I-94/I-96/I-69 related
to visibility and icing. Additionally, this will be the first event
of its kind in quite a while.

The next uptick in snow is expected Friday night into Saturday as a
compact PV max drops south along Lake MI before rotating across the
Ohio Valley. This will continue to be a familiar refrain through the
week as the mean upper low moves little through the period and a
succession of PV maxima rotate through.



Southern Lake Huron buoy observations indicates wind gusts are
dropping to 35 knots in spite of favorable channeling scenario along
Saginaw Bay with southwesterly flow. We have therefore cancelled the
Gale Warning.



Southwest flow with gusts in the 25-30 knot range are expected with
gusts ending shortly after 00Z. High confidence for VFR through 00Z
with increasing chances for MVFR ceilings through 06Z. Confidence is
moderate to high that ceilings will remain above 2000 ft agl /fuel
alternate threshold/. Scattered light snow showers or flurries will
also be possible during late evening and overnight while lake effect
is better organized farther west, closer to the Lake Michigan

For DTW... Wind gusts 25-30 knots will maintain a SSW direction
favorable for traffic flow today. Clouds near the Ohio border
featuring cigs near 5000 ft AGL will push southeast during the early
afternoon. Ceiling will be VFR but less than 5000 ft during this
time, along with some virga on radar, before the pattern exits
eastward by mid afternoon. MVFR ceiling with flurries or light snow
showers will be possible tonight, after midnight. No accumulation is


* High for ceiling 5000 ft or less late into early afternoon, low
  through early evening, and then high again tonight mainly after


Lake Huron...Small Craft Advisory until 5 PM EST Thursday for LHZ361.




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