Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 150000
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
800 PM EDT Sat Apr 14 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EDT Sat Apr 14 2018

A major winter storm will bring mixed precipitation and windy
conditions tonight into Sunday. Many areas will see significant
impacts from icing due to freezing rain and sleet and windy
conditions. Temperatures will remain unseasonably cold through early
next week.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 330 PM EDT Sat Apr 14 2018

At 1845Z KGRR radar trends/sfc obs indicate a mix of freezing
drizzle/light freezing rain and sleet near to north of I-96 with
mainly rain south of I-96. This light precipitation will continue
late this afternoon and early evening and we expect pcpn to
transition to light freezing rain over our southern counties this
evening as sfc temps fall slowly to the freezing mark.

ENE winds will continue to gust to around 30-40 kts late this
afternoon into the evening. Some power outages are likely to
continue to occur late this aftn and early evening especially near
to nw of KGRR where higher res guidance such as the hrrr and 3km
nam show potential for highest gusts with isolated gusts to 45 to
50 kts possible.

Concerns are increasing for significant freezing rain to develop
tonight a little further south into Allegan and Barry counties and
also along the I-94 corridor. A steady period of freezing rain is
expected to develop there late this evening and overnight.

For this reason we decided to upgrade Allegan/Barry counties to a
winter storm warning since it now appears a good portion of those
counties will receive around a quarter to potentially around four
tenths of an inch of ice accumulation overnight.

Impactful freezing rain is also likely to develop along the I-94
corridor late this evening and overnight as suggested by a consensus
of latest higher resolution short range guidance and fcst soundings.
Up to around a quarter of an inch of ice accumulation is possible
especially over northern portions of Calhoun and Jackson counties.
However pcpn there will transition back to liquid form by mid
morning Sunday when sfc temps will moderate back up into the mid
30`s.

Conditions will deteriorate along the I-96 corridor Sunday morning
as precipitation there will transition from sleet to freezing rain
as predominant pcpn type. It may take until around midday for sfc
temps to climb to above freezing there given the continued brisk ne
winds. Further north a mix of sleet and freezing rain will linger
into the early afternoon hours Sunday before the steadier batch of
pcpn moves out as a dry slot works in.

Impacts from this storm system will include numerous to
potentially widespread power outages tonight into Sunday due to
the combination of strong winds freezing rain and sleet. Scattered
power outages have already occurred due primarily to the strong
wind gusts this aftn.

Lighter mixed pcpn will still linger through Sunday night into
Monday but with little if any additional impacts. West winds will
ramp up Monday and the caa will cause any mixed pcpn to change to
some light snow before pcpn finally tapers off.

.LONG TERM...(Tuesday through Saturday)
Issued at 330 PM EDT Sat Apr 14 2018

The slower departure of our current system results in lingering
clouds and a small chance of light rain and snow showers lasting
into at least Tuesday morning. The low level cyclonic flow and cold
advection on the back side of the system actually lingers through
00Z Wednesday, which in prior guidance was a period in which sfc
ridging was supposed to prevail. The ridging and associated clearing
and dry wx is now only a brief period on Tuesday night as the next
system will already be fast approaching from the Plains on
Wednesday.

Once again precipitation type is tricky with the system for
Wednesday into Thursday. Models offer differing solutions on the
track and timing of sfc low and thermal profiles. Consensus solution
at this point is for precip to be a rain/snow mixture to start (if
it arrives in the morning), changing to mostly rain for Wednesday
afternoon, then going back to rain and snow Wednesday night -
possibly even to all snow north of I-96 and lasting into Thursday
morning.

Some wet snow accumulations seem possible north of I-96 in the
cooler nighttime/early morning period of Wed ngt/Thurs, especially
if the ECMWF solution of a potent looking closed mid level
circulation tracking east through srn Lwr MI is correct.

Things turn more tranquil behind the departing Thursday system, with
a moderating trend in temps. Current medium range guidance actually
indicates we could have a very pleasant (and well deserved) spring
weather pattern for next weekend as a surface ridge becomes parked
over the state. This would translate into some sunshine, light winds
and highs up near 60 degrees - which is closer to normal.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 800 PM EDT Sat Apr 14 2018

IFR conditions will become widespread overnight as ceilings
lower blo 1000 feet AGL and freezing rain and sleet redevelops by
06Z. LIFR is possible late tonight into Sunday morning then
conditions should improve to MVFR during the afternoon.

East winds will gust over 30 knots though tonight before
decreasing by Sunday afternoon.

&&

.MARINE...
Issued at 330 PM EDT Sat Apr 14 2018

The gale warning remains in effect through early Sunday evening.

&&

.HYDROLOGY...
Issued at 200 PM EDT Sat Apr 14 2018

As precipitation continues across the region, river levels are
around normal but rising. Precipitation totals will range from over
an inch and a half to around three inches through Sunday night. This
could lead to river flooding, but at this time only the Portage
River near Vicksburg is forecast to go above flood stage. Stay
tuned, as more flood warnings may be on the way if all of the
precipitation is realized.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Storm Warning until noon EDT Sunday for MIZ037>040-
     043>046-050>052-056>059-064>067.

     Winter Weather Advisory until noon EDT Sunday for MIZ071>074.

LM...Gale Warning until 8 PM EDT Sunday for LMZ844>849.

&&

$$

SYNOPSIS...Laurens
SHORT TERM...Laurens
LONG TERM...Meade
AVIATION...Ostuno
HYDROLOGY...63
MARINE...Laurens



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