Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 221653
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1153 AM EST Mon Jan 22 2018

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 304 AM EST Mon Jan 22 2018

A storm system will track through the region today and into
tonight...bringing rain and even a few thunderstorms to the area.
As the storm pulls away on Tuesday...any remaining rain will
change to snow...especially in the afternoon. An area of high
pressure will move in for the middle part of the week leading to
mostly dry weather.

&&

.UPDATE...
Issued at 1153 AM EST Mon Jan 22 2018

A few spots have already reached over an inch of rain. GRR has had
0.81 since midnight. The good news is that the heaviest rains are
exiting as the dry slot moves in. Most areas will only see an
additional quarter inch of rain through this afternoon and
evening. River forecasts are being sent as I type this.

I bumped up max temps a bit based on current trends (51 at LWA at
1135 AM). Maxes around 50 should reach to areas south of I-96, and
40s elsewhere.

Cannot totally rule out the chance of additional thunder, but I
have removed it for the rest of the day. A narrow band of
thunderstorms could develop over NW IL where some heating occurs
within the dry slot. But this will be surface based, and struggle
to cross Lake Michigan into early this evening.


UPDATE Issued at 539 AM EST Mon Jan 22 2018

The dense fog had diminished considerably as the heavier showers
moved in. The forecast has been updated to remove the dense fog
advisory.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 304 AM EST Mon Jan 22 2018

Models are in reasonable agreement in showing a deepening area of
low pressure tracking northeastward through the Great Lakes Region
Today and into Tonight. This system will be rather dynamic with a
favorable coupled upper level jet. The combination of strong lift
and a very moist airmass with pwat values well over 200 percent
above normal will support widespread rain...especially this
morning. There could even be a few thunderstorms as elevated
instability will advect in from the southwest this morning and is
then forecasted to persist for the afternoon. Will maintain the
high pops and show a northeastward progression of the thunderstorm
risk today. Will keep the dense fog advisory going til 7 am...and
may need to extend it depending on how the showers moving in
impacts the thicker fog.

A mid level dry slot moves in from the southwest this afternoon
and evening. Will lower the pops into the evening as a result.
There is still some uncertainty as to how quickly we transition
over to snow and how much precipitation will be around. The latest
trend supports a slower transition. Will trend the forecast this
way. There is still a risk for snow related impacts on
Tuesday...with the High Res Euro trying to lower surface
temperatures below freezing in the afternoon.

.LONG TERM...(Wednesday night through Sunday)
Issued at 304 AM EST Mon Jan 22 2018

There may be a few snow showers along the lake shore at the start of
the long term, but they won`t last long. H8 temps are marginal at
best and will begin to warm Wednesday night. A upper ridge will
quickly build into the Great Lakes and we`ll see a couple of dry
days.

A cold front will move across the state Friday night. Dynamics with
this front are fairly weak as the supporting sfc low is well north
in Ontario and the trailing upper trough if mostly diffuse. Moisture
pooling along the front may lead to some rain showers Friday night
and Saturday and a few rain showers associated with the upper trough
Saturday night into Sunday will mix with and then turn to light snow
showers as colder air flows in behind the departing cold front. This
system doesn`t look like a big pcpn producer.

Friday and Saturday will be the warmest days when temperatures climb
into the 40s. Otherwise, highs will be in the mid 30s.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 644 AM EST Mon Jan 22 2018

A powerful storm is forecasted to push through the TAF sites
today with impacts expected. Widespread IFR and lower conditions
around the region to start the period. There were even a few
thunderstorms to the southwest of KMKG moving northeast. These low
conditions are expected to persist for much of the morning along
with a risk for thunderstorms...but as we go through the
afternoon...the clouds may start to break up from the
southwest...especially from mid afternoon on. However...the
atmosphere remains unstable...thus toward evening...storms my
start to develop upstream and overhead. Aviators will need to
monitor trends through the day.

Moisture wrapping around the departing storm later tonight could
support a return of the low conditions.


&&

.HYDROLOGY...
Issued at 214 PM EST Sun Jan 21 2018

A complete melting of the natural snowpack is expected by Monday
in the Grand, Kalamazoo, and Muskegon river basins. This will
release a quarter to perhaps half inch of water. Rain totals on
Monday will mostly range between 0.6 and 1.2 inches (ECMWF and
ensemble have been consistently lower than GFS and ensemble).
Depth of frozen soil varies but overall expect the ground to
remain frozen enough to allow efficient runoff.

A number of river forecast points will likely rise above bankfull
in the upcoming week. There is a chance of minor flood stage being
reached at a few sites (of earliest concern are Holt and Eagle),
particularly if higher rainfall totals verify. A breakup of river
ice is expected, and any ice jams that form can cause
unpredictable fluctuations in water levels. Road closures are
possible in low spots near river banks. Water could also approach
buildings in flood prone areas.

&&

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

$$

UPDATE...JK
SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...04
AVIATION...MJS
HYDROLOGY...CAS


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