Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 182334
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
634 PM EST Sat Nov 18 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 302 PM EST Sat Nov 18 2017

Precipitation associated with a strong storm system moving through
the region will end from west to east this evening. Windy
conditions will persist tonight and into Sunday as cold air spills
into the region. Lake effect snow will be possible late tonight
into early Sunday afternoon along and west of US-131...with little
if any accumulation expected. Clipper type storm systems will move
through the region Tuesday and again Thursday...producing light
precipitation.

&&

.UPDATE...
Issued at 606 PM EST Sat Nov 18 2017

Most of the eastern counties have swapped over to snow...from
Jackson to Mt Pleasant. Thus the forecast was updated to reflect
mainly snow there. Temperatures are a little warm for
impacts...but perhaps up to an inch of slushy accums are possible
on colder surfaces.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 302 PM EST Sat Nov 18 2017

Main area of precipitation associated with surface system
passing to our south will end from west to east early this evening.
Surface observing stations indicated a wintry mix across portions
of West Central Michigan...and expect this to continue along the
trailing edge of the precipitation shield as it departs the area.

Expecting a lull in the precipitation later this evening...with
lake effect showers developing prior to sunrise and continuing
through mid day Sunday. Highest chances will be along and west of
US-131...which is depicted well in the current forecast. Not
expecting significant accumulations or impacts from this snow
event. Thanks to IWX/LOT/APX for coordination on this aspect of
the forecast.

Strong winds will develop this evening and continue through Sunday
afternoon. Coastal areas could briefly flirt with advisory
criteria winds...but do not anticipate a headline for winds at
this time.

Quiet weather is expected Sunday night through Monday night. A
southerly wind will develop and strengthen Monday ahead of the
next storm system to affect the region. Below normal temperatures
on Sunday will be short lived... with near normal temperatures
resuming Sunday night into Monday.

.LONG TERM...(Tuesday through Saturday)
Issued at 302 PM EST Sat Nov 18 2017

No big storms in the extended but a series of fast moving clippers
will track north of Michigan. Typical of such a fast flow regime,
there are some model timing differences.

The first clipper brings a sharp trailing cold front through on
Tuesday afternoon. Bumped up or added POPs Tuesday afternoon through
Wednesday and trended temperatures a bit colder during this period.
Strong cold advection follows behind the front with 850 mb temps
falling to minus 10C to 12C Tuesday night. Model soundings show
inversion heights around 5 to 6 kft AGL through Wednesday with
northwest flow, and warm advection is already by Wednesday afternoon
which would limit lake effect snow showers.

The next clipper swings a cold front through on Thursday afternoon
and is followed closely by a stronger storm for the weekend. There
are some model differences in timing and location of where the warm
advection precipitation will develop on Friday. No changes were made
to the blended forecast, given the uncertainty.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 630 PM EST Sat Nov 18 2017

The main band of precipitation will shift east of the TAF sites by
02z. A period of snow will occur for the eastern sites...KLAN and
KJXN...with IFR or lower likely. Then primarily MVFR to occur
through tonight as a drier and colder airmass moves in. Gusts
could be an issue tonight with values over 25 knots likely...and
possibly over 30 knots for southern TAF sites KAZO...KBTL and
KJXN. Close call for KMKG for stronger wind gusts as well.

Current indications are that a trend to VFR will occur on Sunday
as the drier air is shown to move in.

&&

.MARINE...
Issued at 302 PM EST Sat Nov 18 2017

Gale warning in effect through Sunday morning looks good and no
changes are needed. Winds will decrease later Sunday and Sunday
night but the pressure gradient increases again on Monday ahead of
the next storm system.  Additional headlines will be required
later Monday into Wednesday.


&&

.HYDROLOGY...
Issued at 1200 PM EST Sat Nov 18 2017

Observed rainfall amounts are on pace to be in fairly good
agreement with forecasts. As a result, several rivers are
expected to rise over the weekend. Most sites will remain within
banks, while those exceeding banks are within the Grand and
Kalamazoo basins. This is where most of the rain has fallen and is
also where the second wave of precipitation is expected to be
greatest. The only site projected to get close to flood stage is
Holt on the Sycamore Creek.

The positive news is that while minor flooding can be expected
immediately along streams and rivers, any larger impacts should be
mitigated by quieter conditions in the upcoming week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Gale Warning until 7 AM EST Sunday for LMZ844>849.

&&

$$

UPDATE...MJS
SYNOPSIS...MWS
SHORT TERM...MWS
LONG TERM...Ostuno
AVIATION...MJS
HYDROLOGY...JAM
MARINE...MWS



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