Small Craft Advisory 94, NWS Grand Rapids, MI

Area Forecast Discussion
National Weather Service Grand Rapids MI
334 PM EST Tue Dec 20 2016

LATEST UPDATE...
Synopsis/Short Term/Long Term/Hydro/Marine

.SYNOPSIS...
Issued at 334 PM EST Tue Dec 20 2016

A bit of light snow will spread across central Lower Michigan
Wednesday afternoon, followed by dry condition on Thursday. The
extended forecast includes gradually moderating temperatures,
melting snowfall and possibly even rainfall late in the holiday
weekend.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 334 PM EST Tue Dec 20 2016

Immediate concerns deal with ongoing winter weather headlines due
to gusty winds, blowing snow and reduced visibilities. Gusts along
the lakeshore have approached 50 mph during the early afternoon,
while a number of inland locations have recorded gusts generally
ranging 30-40 mph. Bufkit overviews show a core of 60+ mph low
level winds at 850mb, pressing eastward through the area during
the late morning and early afternoon. Low level winds are expected
to gradually wane through the evening, in addition to losing any
diurnal mixing. This will allow us to consider dropping headlines
sometime late this evening and conditions improve. Until then, be
aware that periodic gusts to around 40 mph may continue to result
in limited visibilities late this afternoon and evening,
especially in open areas.

Our next system is a clipper system that arrived over the British
Columbia coastline this morning. It will quickly rocket eastward
into the Great Lakes Region by Wednesday afternoon. We keep good
distance between us and the surface low, as it track through the
U.P. In addition, plenty of dry air remains entrenched in the
mid- levels. Much of the precipitation comes ahead of the system,
as winds switch out of the south and provide an isentropic
environment. Accumulations are expected to remain around an inch
or less, mainly running from Lutington to Harrison. Snowfall
amounts rapidly diminish southward toward I-96.

The clipper quickly moves east by Thursday. Aside from a few
lingering snow showers Thursday morning, dry conditions extend
through the day Thursday.

.LONG TERM...(Friday through Tuesday)
Issued at 334 PM EST Tue Dec 20 2016

Main weather focus of the long term remains on the strong low
pressure system moving through the upper midwest on Christmas Day
and the day after. The operational runs of the GFS and ECMWF are in
line with there ensembles in showing a low that will track well off
to the west of Lower Michigan. What this means for our area is a
surge of warm air that will come with rain. There appears to be a 24
to 36 hour period where we are clearly in the warm sector. Midday
Sunday (Christmas Day) through midday on Monday is the time frame
when we will be in the warmer air. This period will likely feature
periods of rain, advection fog and melting snow. Have temperatures
surging into the 40s at this point, but could see the need to
possibly touch the 50s. Do not have thunder in the forecast yet, but
given the strength of the front and dew points at 850mb's nosing
toward +10C its not out of the question.

Otherwise, fairly quiet until we get to the Christmas system.
Temperatures will be slightly above normal with a zonal flow aloft
keeping the colder air pushed to the north. Colder air is forecast
to wrap in behind the Monday cold frontal passage, but its
intrusion into our area looks brief.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 116 PM EST Tue Dec 20 2016

Mainly VFR weather is expected the next 24 hours. The only
exception will be some restrictions to visibility this afternoon
due to blowing snow. The blowing snow will likely reduce
visibilities no lower than 2SM in most cases. The blowing snow
should end after 21z to 22z.

Winds will be strongest this afternoon through about 21z or 22z,
with winds dropping after sunset to 12 knots or less.

Clouds in the 8000ft-14000ft layer will advect in after midnight
and into Wednesday morning.

&&

.MARINE...
Issued at 334 PM EST Tue Dec 20 2016

Gusts above 34 knots are expected drop off later this afternoon
and evening with sustained winds gradually dropping off late
tonight. A bit of a lull exists early Wednesday morning before
winds ramp back up into the 20-25 knot range Wednesday afternoon.
While we drop below gale conditions tonight, a small craft
advisory may need to be considered to cover Wednesday into
Thursday. Waves decrease tonight to around 2-4 feet, before
increasing back into the 3-6 feet range Wednesday afternoon.

&&

.HYDROLOGY...
Issued at 230 PM EST Tue Dec 20 2016

Ice expansion will likely halt across area rivers since mean daily
temperatures will not exceed 20 degrees through the weekend. Warming
temperatures should slowly melt some of the ice cover but temps in
the 30s this week likely won't be high enough to completely break up
and release the ice. A quick warmup into the 40s and potentially
higher by Sunday or Monday could accelerate the melting process
and/or begin breaking up some ice. That would be the main period of
concern for ice jam development since ice would be more likely to
move at that point.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 7 PM EST this evening for MIZ037-
     038-043-044-050-056-057-064-071.

LM...Gale Warning until 7 PM EST this evening for LMZ844>849.

&&

SYNOPSIS...JAM
SHORT TERM...JAM
LONG TERM...Duke
AVIATION...Duke
HYDROLOGY...Hoving
MARINE...JAM

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