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Area Forecast Discussion
Issued by NWS Grand Rapids, MI
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FXUS63 KGRR 010332
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1032 PM EST Tue Jan 31 2017

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 300 PM EST Tue Jan 31 2017

Light snow showers and flurries will continue tonight through
Wednesday. A few flurries may linger into Thursday. Tranquil
weather is anticipated Friday and Saturday as a high pressure
ridge builds in.

&&

.UPDATE...
Issued at 1032 PM EST Tue Jan 31 2017

Snow showers have increased in coverage and intensity over the
past hour or two. The snow showers are located ahead of a
shortwave seen in the water vapor imagery diving southeast out of
Wisconsin. Hi res models show streaks of heavier snow tonight
through portions of the forecast area, especially from I-96 off to
the south. We could see localized accumulations of 1-2 inches
across portions of the southern half of the forecast area. Have
likely pops (60-70 pct) area wide overnight.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 300 PM EST Tue Jan 31 2017

Primary short term fcst concerns involve determining probabilities
for light snow showers through Thursday.

Light snow showers and flurries will continue to develop late this
afternoon and evening as another upper level disturbance moves
through. Snow accumulations tonight will be quite light at mainly
under an inch.

However it is noted that some stronger low level (1000-850 mb)
convergence develops this evening and overnight along the I-94
corridor. A 12Z GFS bufkit x-section of omegas w/height shows some
moderate lift (5 microbars/sec) late tonight at KAZO/KBTL.

This is also still in an area of more favorable pva overnight as
well. Therefore we bumped up pops to low likely late this
eve/overnight along the I-94 corridor where around an inch to
perhaps isolated higher amounts to near 2 inches are possible.

Light snow showers and flurries will linger Wednesday as well as
yet another upper level disturbance moves through. However any
snow accumulations would be very light at mostly under an inch
Wednesday through Wednesday night.

A few flurries may linger Thursday but overall short range
guidance trends the past 24 hrs look less favorable for lake
effect snow showers Thursday due mainly to lack of moisture in the
dgz. Therefore we are only expecting a few flurries and those may
stay confined to areas north to nw of KGRR.

.LONG TERM...(Friday through Tuesday)
Issued at 300 PM EST Tue Jan 31 2017

It will surely start the period with colder than normal temperatures
then there will be a moderating trend before some really cold air
comes in just beyond this forecast period.

More significantly there is the threat for a powerful storm in
Tuesday/Wednesday time frame. The models area all over the place
with the track of this system.  There has been a more clear trend on
the ECMWF to take the storm farther west. The 7 pm run on the 30th
had the center of the low near TOL OH at 7 pm Tuesday.  The most
recent run of the ECMWF (31st 7 am) at 7 pm Tue has the 977 mb low
centered over DSM Iowa. That sort of track adjustment puts us deep
into the warm air Tuesday. I could see temperatures getting into the
50s of this track were to play out. This would then be a snow to
freezing rain to rain event for us, with a fair amount of wind too.
Then is arctic air that plunges in behind this system (we can track
that later).

A quick look at the hemispheric scale we see deep upper low /long
wave trough just off the east coast of Russia/China with a ridge
near the dateline and a broad down stream trough over Canada into
the central United States.  A powerful storm comes off shore form
Siberia today and deepens rapidly tracking toward Kamchatka by
Friday. This in turn builds a large closed upper high over Alaska
which then forces the northern stream jet to dig sharply south into
western Canada and even the NW United States by Saturday.

So this storm on Tue/Wed comes from the merging of the northern and
southern stream energy over the western United States. So, since
this system is currently in little pieces over the western Pacific
at this point, we will have to watch to see how this all plays out
over the next few days but Thunderstorms would be more than possible
with this system in Southwest Michigan if the storm does what it is
currently forecast to do.

The bottom line is cold....then milder with some snow over the
weekend...much warmer with rain Tuesday night into Wednesday then
colder with snow after that.

&&

.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 738 PM EST Tue Jan 31 2017

MVFR conditions were in place at most of the TAF sites at 00z. The
thinking is that MVFR conditions will dominate much of the next 24
hours. We are seeing a push of VFR ceilings though from the
southwest which may spread in for a time. Confidence in ceiling
trends are low tonight into tomorrow.

Snow showers are forecast to spread into the I-94 TAF sites
overnight, after 07z or so. 3-5SM visibilities and MVFR ceilings
are expected with the snow showers. On Wednesday, we are
forecasting MVFR ceilings to lift to VFR during the course of the
day. Winds will be westerly the next 24 hours.


&&

.MARINE...
Issued at 300 PM EST Tue Jan 31 2017

A small craft advisory remains in effect through early Thursday
morning. Brisk west northwest winds will continue to cause wave
heights to reach 4 to 8 feet through then.


&&

.HYDROLOGY...
Issued at 133 PM EST Tue Jan 31 2017

River levels continue mostly above normal, including some
minor out-of-bank flooding. Advisories continue for:  the Grand
River At Ionia, the Looking Glass River Near Eagle, and the Maple
River At Maple Rapids. River levels should slowly fall into the
weekend with only light snow possible. Cold temperatures Wednesday
night into the weekend will allow ice to form on area rivers.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 7 AM EST Thursday for LMZ844>849.

&&

$$

UPDATE...Duke
SYNOPSIS...Laurens
SHORT TERM...Laurens
LONG TERM...WDM
AVIATION...Duke
HYDROLOGY...63
MARINE...Laurens
National Weather Service Regional Headquarters
