Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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369
FXUS63 KGRR 171129
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
629 AM EST Tue Jan 17 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 140 AM EST Tue Jan 17 2017

A storm system moving through the Great Lakes will bring rain and
freezing rain to the area into mid morning. As the system moves
out of the area later today some showers are possible. High
pressure will bring dry conditions with slow clearing Wednesday
into Wednesday night. Dry weather with warmer than normal
temperatures are expected into Friday.

&&

.SHORT TERM...(Today through Thursday)
Issued at 330 AM EST Tue Jan 17 2017

The primary issue is of course the threat for freezing rain. Then
the secondary threat is thunderstorms this morning as the surface
low crosses the area.

The area of below freezing temperatures had rapidly decreased over
the past few hours and our meso-net obs show only area east and
north of Big Rapids being at or below freezing. County dispatch
indicated only back roads were really icy in most of the headline
counties. So I ended the headlines in all areas where temperatures
were already above freezing. The rest of the area will see
temperatures rise above freezing by mid morning.

The surface low as just south of the Chicago area at 3 am this
morning and will track nearly eastward along I-94 this morning.
reaching the Detroit area by noon. There is an area of
thunderstorms just north of center of the surface low under and
area of enhanced colder cloud tops. Model sounding show some weak
but workable instability (200 to 400 j/kg of most unstable cape)
in that area. The 09z RAP model and the SPC 3 hour calibrated
thunderstorm forecast all show this area of thunderstorms crossing
the I-94 to I-96 area this morning. So I updated the grids to
include the treat of thunderstorms.

As for the rain, once the surface low is east of the area the rain
should end and I expect scattered showers into this evening.
High pressure should follow Wednesday bringing a slow decrease in
the clouds.


.LONG TERM...(Thursday night through Monday)
Issued at 330 AM EST Tue Jan 17 2017

A rather unusual long term period for this time of year...where
normally we see some of the coldest air of the season.  This period
features no snow and no surge of cold air from Thursday night
through Monday. Not January-like at all.

H8 temps hold around +5C throughout the extended period allowing
daytime temperatures to get into the 40s each day. A fairly cloudy
period will also keep overnight lows mild, mainly in the 30 to 35
degree range.

A weak surface low is progged to move across the Southern Great
Lakes and could spread some light rain into Southerly Lower MI
Friday into Friday night.  Then much of the weekend appears dry. A
higher chance of rain should develop into Sunday afternoon/evening
as a southern stream stacked low moves across the OH Valley.  This
could become a fairly steady rain maker due to it`s slow movement,
with the rain continuing into Monday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 629 AM EST Tue Jan 17 2017

Once the area of showers and isolated thunderstorms gets through
our TAF sites (by 15z) the rain should end. The low clouds however
will resist through the night. Areas of drizzle and light rain
are expected this afternoon through tonight.

&&

.HYDROLOGY...
Issued at 122 PM EST Sat Jan 14 2017

Rivers are running above normal across the area due to rain, melted
snow and ice jams. The Grand River at Robinson Township has an
active warning for minor flooding. Multiple sites also have active
advisories. A period of colder than normal temperatures through the
weekend may allow river ice to thicken. Next week looks warmer than
normal with highs possibly reaching the 50s. This could melt the
river ice and allow the rivers to flush out.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Winter Weather Advisory until 9 AM EST this morning for
     MIZ038>040-045-046-052.

LM...None.
&&

$$

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



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