Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 031205
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
705 AM EST Sat Dec 3 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EST Sat Dec 3 2016

Quiet weather is expected both today and tonight as high pressure
moves into and through the area. There may be a few sprinkles or
flurries today but otherwise an uneventful day weather wise. A
surface trough of low pressure will slide through the Great Lakes
from the plains Sunday afternoon and evening. Light snow is expected
to break out Sunday morning and persist into Sunday evening.
Accumulating snow is expected with 1 to 2 inches of snow possible
inland and 2 to 3 inches in the lakeshore counties. Dry weather
returns for Monday. Colder air and lake effect snow is expected
mid to late in the upcoming work week.

&&

.SHORT TERM...(Today through Monday)
Issued at 330 AM EST Sat Dec 3 2016

Main focus is on the light snow event which should begin mid morning
on Sunday and persist into Sunday evening. Outside of that event the
short term looks to be fairly uneventful.

The precipitation with the Sunday event looks to be mainly if not
all snow. Will have straight snow in the forecast as wet bulb zero
heights look to be favorable for all snow, at 1500ft or lower all
day. Surface temps may rise into the mid 30s through the course of
the morning, but once the precipitation starts we should cool back
into the lower 30s. 850mb temperatures follow a similar trend,
cooling into the -3C to -5C range through the heart of the event.
The bulk of the precipitation should come down during the afternoon
hours.

Models are consistent in showing precip totals between 0.15 and 0.35
which should correlate to 1 to 3 inches of snow. Expecting an inch
or so inland towards Lansing and Jackson. Around 2 inches in the
Highway 131 corridor and possibly around 3 inches toward Lake
Michigan. There should be some lake enhancement as Delta T`s will be
around 13C and southwest winds of 10-15 knots in the cloud layer.
Overall, not expecting significant impacts as temperatures will be
near or slightly above freezing through the event.

Snow will be aided by a potent looking 500mb shortwave and deep
moisture. A 6 to 12 hour period of decent lift should accompany the
shortwave passage, with the lift extending into the DGZ.

Otherwise, there may be a little bit of flurries/sprinkles today and
we are already seeing some of this in Grand Rapids this morning.
There may also be some drizzle/freezing drizzle on the back end of
the Sunday system on Sunday night as the DGZ becomes unsaturated.

.LONG TERM...(Monday night through Friday)
Issued at 330 AM EST Sat Dec 3 2016

A much colder airmass will move in mid to late week along with
potential for accumulating lake effect snow. Dry weather is forecast
for Monday night. A low pressure system will move northeast across
the Ohio Valley region Tuesday.

Most of the precipitation in association with that system will stay
southeast of our fcst area. However the northwestern periphery of
the pcpn shield of this system will likely affect our southeast
forecast area Tuesday morning and afternoon. Thermal profiles and
low level critical thickness tools suggest that rain showers will
the predominant pcpn type.

00Z GFS guidance remains consistent with it`s previous runs in
showing that much colder air will move in around 18-24 hours faster
then the ECMWF. 00Z GFS guidance suggests h8 temps will already fall
to -10 to -11 C by Wednesday evening and to -15 to -16 C by 12Z
Thursday. The ECMWF does not project h8 temps to fall to -15 C until
Thursday evening.

This is significant because it has implications on how quickly the
lake effect snow will develop mid to late week and consequently when
and how quickly travel conditions will become hazardous. At this
time we prefer the GFS guidance given much better run to run
consistency recently as opposed to other medium range guidance
solutions.

As such we expect lake effect snow to ramp up Wednesday night and
continue through Thursday and Friday in our favored WNW flow lake
effect snow belt regions particularly near to west of US-131. High
temperatures by Thursday and Friday will only reach the middle 20`s
to lower 30`s.

&&

.AVIATION...(For the 12Z TAFS through 12Z Sunday morning)
Issued at 701 AM EST Sat Dec 3 2016

Widespread MVFR ceilings are in place at 12z, with a bit of
flurries and drizzle occurring as well. The flurries and drizzle
will likely come to an end as we move through the day, but the
MVFR ceilings will persist.

The MVFR conditions will last through today if not all of
tonight. Some model guidance is trying to scatter us out tonight
with VFR conditions developing. This time of year it is a much
better bet that the ceilings will persist and that is what we
forecast in the 12z set of TAFs.

Bottom line, MVFR ceilings the next 24 hours. Winds will be west
at 6 to 10 mph today, becoming light and variable overnight.

&&

.MARINE...
Issued at 330 AM EST Sat Dec 3 2016

Winds and waves should remain below Small Craft Advisory criteria
through Sunday as a light wind regime will be in place. Winds of 10
knots or less are expected from midday today through Sunday evening.
High pressure moving through the area is responsible for the lighter
winds which should keep the lake fairly flat. A southwesterly wind
develops Sunday night which may increase towards 20 knots over the
water. It is possible we may approach wind/wave criteria for an
advisory Sunday night.

&&

.HYDROLOGY...
Issued at 314 PM EST Fri Dec 2 2016

The Maple River continues its slow climb toward bankfull, and may
reach that stage by early next week. A tenth to quarter inch of
liquid equivalent precip, in the form of snow for much of the area,
is expected late Sunday. Additional chances for precipitation will
arrive the latter part of next week, most likely in the form of lake
effect snow. This moisture should have little impact on rivers in
the short term.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...Laurens
AVIATION...Duke
HYDROLOGY...CAS
MARINE...Duke


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