Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 120511
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1211 AM EST Fri Jan 12 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EST Thu Jan 11 2018

A cold front will bring rain showers this evening that will become
mixed with and then change over to light snow showers. Light snow
and sleet accumulations of an inch or two are expected through
midday Friday with relatively highest accumulations southeast of
Grand Rapids. Temperatures will plummet into the 20s behind the cold
front tonight. The cold air will stick around this weekend through
next week with occasional snow showers.

&&

.UPDATE...
Issued at 1049 PM EST Thu Jan 11 2018

I continued the headlines as they are but I am very concerned that
snowfall amounts will be more like 3 to 6 inches in the I-69 area
by mid afternoon. This is supported by the latest runs of HRRR,
HRRRX, RAP model, SPC SREF plums, NAM12 00z run just to name a
few. The wave looks really good on the water vapor image loops and
that wave is heading north northeast. We have a negative tilt
upper wave over MS and AL this evening and those type systems tend
to track north and west of where the models show them. This system
should be coming into our area just as the deeper cold air
arrives. Thus most of the precipitation should be snow. There will
be strong winds with this system since the cold air is just
starting to come in. Thus if we really get that FGEN band of
heavier snow near I-69 the heavy falling snow and strong winds
will make for dangerous driving conditions. The good news is the
storm moves through quickly and in all areas the snow should be
done by 4 pm or so.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 330 PM EST Thu Jan 11 2018

The cold front will bring rain showers into this evening that will
change over to snow showers overnight as strong caa occurs after
fropa. A very brief period of sleet is also possible. Based on a
consensus of latest higher resolution short range guidance and qpf
we expect snow accumulations of around an inch in our central
fcst area. Snow accumulations of up to around two inches are expected
over our se fcst area by midday Friday with locally higher amounts
to near 3 inches possible near KJXN.

Given plummeting temperatures after fropa and the precipitation
and expectations for snow overnight into Friday morning we
decided to hoist a winter wx advisory for the southern two thirds
of our fcst area where travel conditions will likely become rather
hazardous for the Friday morning commute. Decided against an
advisory for our northern two rows of counties where very little
snow (under an inch) is forecast and based on coord w/DTX and
APX (thanks for extensive coordination on headline decisions
DTX/IWX/APX).

Cold and dry/tranquil wx is fcst for the vast majority of our
fcst area Friday afternoon through Saturday night as high pressure
gradually builds in from the northwest. A few flurries or light
lake effect snow showers will just clip areas right along the Lake
MI shoreline.

.LONG TERM...(Sunday through Thursday)
Issued at 330 PM EST Thu Jan 11 2018

Models are in relative agreement in tracking down a clipper low
starting Sunday Night and lasting through Monday.  Widespread
accumulations look likely with some at least low impacts expected. I
have increased POPs for this event given the better confidence.

A reinforcing shot of arctic air moves in behind this departing
system.  Based on the low level flow...lake effect if any will be
confined to the immediate lakeshore region.  I do feature this
highest POPs there with some potential for accumulations. Well below
normal temperatures will continue.

Mid level ridging arrives for the end of the week.  The Gulf looks
cut off through Friday.  This pattern typically leads to moderating
temperatures and less than normal precipitation.   That could change
next weekend as the Gulf is shown to open up as a Southern Rockies
low kicks out into the Southern Plains.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1211 AM EST Fri Jan 12 2018

IFR and patchy LIFR was over the region as of 05Z. This will
gradually end from west to east through 12Z as brisker winds move
in. A period of snow may impact LAN and JXN and could prolong the
IFR a bit longer into the morning daylight hours. All areas will
improve toward VFR by mid day. The VFR will continue through the
afternoon and evening.

North northwest winds will gust to around 25 knots from roughly
09Z through 23Z.

&&

.MARINE...
Issued at 330 PM EST Thu Jan 11 2018

The small craft advisory was extended through early Saturday
morning.


&&

.HYDROLOGY...
Issued at 330 PM EST Thu Jan 11 2018

Snowmelt is expected into tonight, as warm moist air continues to
invade the region. Most of the snow pack should melt, but not all of
the melt water will make it into the river system before the cold
air moves back in and locks it down later tonight through the
weekend.

There is still 1 to 2 inches of snow, mainly north of Grand Rapids.
No excessive rainfall is expected with the warmup and amounts should
be generally under one half inch through the warm period. This has
resulted in minor river flooding scattered across Southwest Lower
Michigan. Some ponding of water, away from the rivers, will be
possible. The rivers will need to be closely monitored for ice
breakup and potential ice jam flooding.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory from 3 AM early this morning to 6 PM EST
     this evening for MIZ059-066-067-073-074.

     Winter Weather Advisory until 1 PM EST this afternoon for
     MIZ050>052-056>058-064-065-071-072.

LM...Gale Warning until 4 AM EST Saturday for LMZ844>849.

&&

$$

UPDATE...WDM
SYNOPSIS...Laurens
SHORT TERM...Laurens
LONG TERM...MJS
AVIATION...JK
HYDROLOGY...63
MARINE...Laurens



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