Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 130520
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1220 AM EST Tue Feb 13 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 242 PM EST Mon Feb 12 2018

A Canadian Polar high pressure system will cross Lower Michigan
tonight brining lows near zero but with mostly clear skies.
Tuesday will warmer afternoon temperatures as the surface high
moves east of the area. The next storm system will track just
south of Michigan Thursday. That will bring scattered rain showers
to the area Wednesday night into Thursday. The southerly flow
ahead of that system will bring our temperatures into the 40s by
Wednesday afternoon. Another Canadian cold front will head our way
behind that system so we should see some light rain showers
change to light snow showers later Thursday into Friday. Colder
temperatures with partly cloudy skies are expected on Saturday.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 242 PM EST Mon Feb 12 2018

One last very cold night before a warm up sets in Tuesday. Quiet
weather is expected through most of Valentines Day. There is a
chance of showers (drizzle) later in the day Wednesday into
Wednesday night.

Thanks to a reorientation of the polar jet stream this week, warmer
weather and melting snow will be this weeks dominant weather
theme over Southwest Michigan. Tonight the surface high (Canadian
Polar) crosses the state. That will bring clear skies and light
winds. With all that snow on the ground, this will be a good setup
for low temperatures near to just above zero near and south of
Grand Rapids but near to below zero north and east of Grand
Rapids.

A southern stream wave will track south of Michigan midweek. The
combination of the departing Canadian Polar high pressure system
and the income southern stream storm will result in a warming
trend into Valentines Day. Since the jet streak associated with
the southern stream storm will actually be south of Michigan we
will not get into the deep moisture with this system so we will
not see any rain from this system. Some drizzle is possible toward
Wednesday evening.

.LONG TERM...(Thursday through Monday)
Issued at 242 PM EST Mon Feb 12 2018

Starting Monday but extending well beyond Monday we may have a
very wet period. The ECMWF storm total rainfall ending Thu Feb 22
at 7 am has 5" in Berrien County with 2 to 4" of rain between
Interstate 94 and Interstate 96. As I have been writing about the
past few days, the polar jet reorientation will result in a
western CONUS trough and eastern CONUS ridge. That will put
southwest Michigan dead center in the storm track. We will see
several waves of low pressure track along a stationary front over
southern Michigan starting Monday and continuing into the middle
of that week. Given the snow on the ground, and the water in our
snow pack (between one and two inches) and that our rivers are
running high already with some ice jams, adding that sort of
rainfall will more than likely result in some serious hydrological
issues. We will have to monitor this closely over the next week to
see how this plays out.

Between Thursday and Monday we do get another polar high to come
into Southwest Michigan. This will push the warm air south once
again and the cold air should get deep enough for some weak lake
effect snow showers Friday. However a strongly digging Pacific
system will help to curve out a deep western CONUS trough by late
in the weekend. That will boot out the cold air once again and
bring deep Gulf moisture north toward Michigan by Monday. We could
see a snow and freezing rain event at the start Sunday night or
Monday but this looks to be mostly just a rain event for our
area.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1220 AM EST Tue Feb 13 2018

VFR conditions will prevail through the next 24 hours. Southerly
winds will increase to around 10 knots along the lakeshore by mid
day and continue into the evening. Elsewhere it will remain
lighter.

&&

.HYDROLOGY...
Issued at 150 PM EST Mon Feb 12 2018

A warmup will be underway as the week progresses, with highs
reaching the 40s by Wednesday. Up to a quarter inch of rain is
possible Thursday into Thursday night. These events should cause
river ice to partially melt and shift toward the end of the week,
and could lead to ice jam formation as temperatures fall back
below freezing toward the weekend.

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



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