Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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897
FXUS63 KGRR 161743
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1243 PM EST Mon Jan 16 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 306 AM EST Mon Jan 16 2017

A low pressure system will track from Texas today through Michigan
on Tuesday. This system will result in a wintry mix of
precipitation for the region that changes to rain as some warmer
air tries to move in. An area of high pressure then moves in for
Wednesday.

&&

.UPDATE...
Issued at 1019 AM EST Mon Jan 16 2017

UPDATE Issued at 813 AM EST Mon Jan 16 2017

The forecast was updated to reflect a high probability of
precipitation this morning given the reports from the ASOS
observations. AMDAR sounding from GRR this am does show a rather
deep warm layer...so less of a risk for snow as well.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 306 AM EST Mon Jan 16 2017

Challenging forecast today and tonight as far as timing and type
of precipitation. The main culprits is the dry airmass that is in
place and surface temperatures that will hover around freezing
for a period this afternoon and tonight as steadier and heavier
precipitation moves in.

We will issue winter weather advisories for much of the region.
The band of precipitation upstream across IL and NRN IN is mostly
aloft at this time. This is forecasted to move into southwest
lower MI this morning and early afternoon. Tough call as to how
soon and what type the onset will be. However the main type across
southern parts looks to be ZR or R depending on the surface
temperature...while further north a mix looks likely. Icing seems
to be the main risk given the warm layer that moves in today.
The window for ZR looks shorter for the southernmost counties so
we did not include them in the headline. This is is from South
Haven to Jackson. It is possible that if they do not warm up above
freezing as quickly as forecasted...the may need to be
incorporated into the headline. Up to a quarter inch of ice looks
possible further north. Fortunately the wind does not look that
strong at this time...mostly under 15 knots. A small risk exists
for even heavier amounts of ice if surface temps end up rising
above freezing slower than expected. So close monitoring is
needed for today and tonight.

.LONG TERM...(Wednesday night through Sunday)
Issued at 306 AM EST Mon Jan 16 2017

A mild period is expected for the end of the week and into early
next week.  H8 temps hold from +4C to +7C throughout the long term.
This should keep temps well above normal for this time of year,
with daytime highs mainly 45 to 50.

The overall pattern that should bring this persistent warm air into
the Great Lakes is a rather stagnate one.  Upper troughing remains
fairly stationary over the center of the nation, leading to deep
southerly flow over the Eastern U.S.  A couple of weakening waves
spin off of this trough and head toward us, but they run into an
upper ridge and weaken further.  A few rain showers may occur
Friday, then another higher chance into Sunday.  Otherwise the
January warmth will come with relatively dry conditions.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1243 PM EST Mon Jan 16 2017

Our two main issues with the 18z fcsts are determining the timing
of the transition from freezing rain to rain, and then the
increase of IFR and lower conditions into the area.

As of 1730z, temperatures have pretty much come up above freezing
at the I-94 corridor terminals. This means that pcpn at these
sites should remain just rain from this point onward. The I-96
corridor terminals are all still freezing rain, and we expect
temperatures to warm above freezing by 19-20z. This will change
any fzra over to rain.

It appears now that based on the position of the IFR and lower
conditions just south of the area, that this will lag the change
over to rain by a couple of hours or so. We expect conditions to
drop from 20-22z into the IFR category, and then dropping further
after that. LIFR looks likely most of the time frame then, with
VLIFR very possible. In fact, data suggests that once the more
widespread rain moves out around daybreak Tue morning, conditions
may drop a bit more after that.

&&

.MARINE...
Issued at 306 AM EST Mon Jan 16 2017

Despite a low pressure system moving in...the wind values are
forecasted to remain relatively low with an offshore component. As
a result...not headlines are planned with this issuance.


&&

.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...Freezing Rain Advisory until 2 AM EST Tuesday for MIZ050-056>059-
     064>067.

     Winter Weather Advisory until 9 AM EST Tuesday for MIZ037>040-
     043>046-051-052.

LM...None.
&&

$$

UPDATE...04
SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...JK
AVIATION...NJJ
HYDROLOGY...63
MARINE...MJS



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