Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 131718
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1218 PM EST Tue Feb 13 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 308 AM EST Tue Feb 13 2018

High pressure will bring fair weather today and into Wednesday.
Low pressure will track south of Lower Michigan on Thursday with
rain changing to snow by Friday.

&&

.SHORT TERM...(Today through Thursday)
Issued at 308 AM EST Tue Feb 13 2018

Only forecast issue in the near term is for precip type late
Thursday across the northern forecast area as colder air filters
back in. Model soundings continue to show the moisture is shallow
on Wednesday with the DGZ unsaturated and even drizzle appears to
be a long shot...so no POPs in the forecast until Wednesday night.

Model consensus is that the northern and southern streams remain
separate through Thursday with Lower Michigan on the northern
periphery of the precip shield of a sfc low tracking across the
Ohio Valley. Bulk of the precip looks to remain south of the
Michigan border and light rain showers across the forecast area,
with a change to snow beginning in the afternoon across the
higher elevations of the northern tier.

.LONG TERM...(Thursday night through Monday)
Issued at 308 AM EST Tue Feb 13 2018

A cold front will push through Thursday night.  There will be a
strong surge of cold air behind this system.  So rain will switch
over to snow overnight.  This will be followed by a brief period of
lake effect snow mainly Friday morning.  It will wind down mid day
Friday as a surface high builds in.  This brief period of snow may
put down an inch or less of accumulation mainly along the lakeshore
counties.

It will stay cold Friday into Saturday, but then we will see another
warming trend starting Saturday night and continuing into early next
week as we get on the backside of the surface high.  There could be
some very light snow Saturday on the leading edge of the warm
advection.

The models are not in good agreement with the timing of next system
that arrives Sunday into Monday.  The operational GFS is quicker
than it`s ensembles, and the ECMWF is leaning toward a slower
solution too.  So I also leaned toward the slower solution which
will allow for temps to remain warmer longer, and give the region a
chance of rain initially, starting Sunday afternoon/evening.

Difficult forecast by late Sunday night into Monday given the models
differences and attempting to forecast pcpn type.  The front may
slow even further Monday as low pressure moves along the front.  For
now will expect the rain changing to snow across Central Lower late
Sunday night and continuing into Monday.  However if the front does
stall, areas along and south of I-96 may stay all rain into Monday.
We have time to iron this out with future model runs and as we
monitor timing trends.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1218 PM EST Tue Feb 13 2018

The area of mid and high clouds will depart by late this afternoon
leaving mostly clear to clear skies through the night. However a
strong southwest flow develops just above the surface so I have
added LLWS to all of our TAFs overnight.

The glitch for tomorrow is if and went the low clouds (IFR
ceiling) move in. Most of the models show enough low level
moisture returning Wednesday so as to allow for a cloud deck with
bases near or below 1000 ft moving in from the south during the
afternoon or early evening. This will have to be watched as it
may come in as early as 12z at the I-94 taf sites.

&&

.HYDROLOGY...
Issued at 1101 AM EST Tue Feb 13 2018

A warm up this week and up to a quarter inch of rain Thursday should
result in melting snow and ice, and rising river levels. This could
also result in shifting ice and additional ice jam formation.

A flood advisory remains in effect for the Looking Glass River near
Eagle due to elevated levels of water/ice from an ice jam. River
levels in the vicinity of ice jams will continue to fluctuate by
several feet until the ice breaks free.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

SYNOPSIS...Ostuno
SHORT TERM...Ostuno
LONG TERM...JK
AVIATION...WDM
HYDROLOGY...63



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