Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 140534
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
134 AM EDT Sat Apr 14 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EDT Fri Apr 13 2018

A major storm system will bring a wintry mix of precipitation and
windy conditions this weekend. Many areas will likely see
significant impacts from icing due to freezing rain and sleet in
conjunction with windy conditions and falling temperatures.
Impacts from significant snow are also expected a little further
north across central lower Michigan.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 330 PM EDT Fri Apr 13 2018

A major storm will impact the Great Lakes region Saturday into
Sunday and bring a mix of rain... freezing rain... sleet and
windy conditions.

Overall short range computer model guidance trends including many
of the higher resolution models and latest href show greater
potential for more sleet rather than freezing rain Saturday into
Sunday. This notion is also supported by a polling of numerous
fcst model soundings from across much of our area.

Freezing rain is still expected and significant ice accumulations
from freezing rain on the order of a quarter to a half an inch are
possible across portions of our fcst area. We still cannot rule
out isolated higher amounts to around three quarters of an inch
where predominant pcpn type is in the form of fzra.

However given short range computer model guidance trends that
show greater potential for more sleet rather than freezing rain we
decided to upgrade all of the counties that were in a winter
storm watch to a winter storm warning (rather than an ice storm
warning given greater potential for sleet and somewhat shorter
duration of fzra). With the colder air making it further south we
decided to issue a winter storm warning for Eaton and Ingham
counties as well.

Also give latest computer model guidance trends we increased the
amount of snowfall forecast somewhat for our far northern fcst
area where around two to four inches of snow is anticipated.

Numerous power outages are likely to occur due to the combination
of freezing rain/sleet/windy conditions and falling temperatures
tomorrow and tomorrow night. Some lighter mixed precipitation
will still linger into Sunday night but the most impactful part of
the storm will come from early tomorrow morning through around
midday Sunday.

.LONG TERM...(Monday through Friday)
Issued at 330 PM EDT Fri Apr 13 2018

Temperatures will continue to average below normal most of next
week. Main chances of precip are on Monday and Wednesday.

Guidance has slowed down the departure of the big system a bit as
the closed upper low comes overhead by 12Z Monday. Consequences of
this may be to delay the arrival and strength of the cold advection
on the back side of the system. Also the deeper moisture associated
with the deformation zone may not fully curl in from the west until
Monday afternoon. If we get any sunshine at all on Monday morning in
a mid level dry slot, we could get some rather impressive convective
snow showers developing under the upper low by afternoon.

Pesky system finally does eventually get totally booted out by 12Z
Tuesday as the next upstream system moves into the plains.  That
system arrives in Michigan for Wednesday with primarily rain showers
although possibly changing to snow showers Wednesday night before
exiting. Things appear to turn more tranquil for the end of next
week as sfc ridging takes control, but still on the chilly side.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 134 AM EDT Sat Apr 14 2018

Rain showers are ramping up this morning, especially to our SW as
of 0530z with some thunder down there. That rain will move in over
the next couple of hours. Instability parameters would keep
thunder mainly SW of the area this morning. Low cigs around 700 ft
are in place at most locations. These cigs will likely not change
much during the day.

Showers will gradually change over to freezing rain and sleet from
NE to SW late this morning and this afternoon as colder air oozes
in from the NE. We think temps will hit freezing around 16-17z at
KMKG and KGRR, and then change over toward 00z at the I-94
terminals. Thunder becomes more likely mid-late afternoon and will
last through the end of the fcst period.

Winds will become gusty this morning, with gusts up around 35
knots or so likely. These winds will likely persist through the
end of the fcst period.

&&

.MARINE...
Issued at 330 PM EDT Fri Apr 13 2018

The gale warning remains in effect from 8 pm this evening through
8 pm Sunday evening.


&&

.HYDROLOGY...
Issued at 330 PM EDT Fri Apr 13 2018

Region still on track for widespread precipitation event over the
next 72 hours.  Models continue to show one to two inches in general
with isolated higher amounts.  While confidence is on the expected
amounts is high...the type of precipitation is uncertain and will
impact the speed at which area rivers are affected.  Recent model
trends have been to push the colder air farther to the south...
which could produce significant delays in runoff.

Current river forecasts have locations rising to between bankfull
and flood stage.  While this seems reasonable at this time...expect
later forecasts to hone in on a solution as the precipitation type
question is answered.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Storm Warning from noon today to noon EDT Sunday for
     MIZ056>059-066-067.

     Winter Storm Warning from 5 AM early this morning to noon EDT
     Sunday for MIZ037>040-043>046-050>052.

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

&&

$$

SYNOPSIS...Laurens
SHORT TERM...Laurens
LONG TERM...Meade
AVIATION...NJJ
HYDROLOGY...MWS
MARINE...Laurens



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