Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 171929

Area Forecast Discussion
National Weather Service Grand Rapids MI
330 PM EDT WED AUG 17 2016

Synopsis/Short Term/Long Term/Marine

Issued at 330 PM EDT Wed Aug 17 2016

Areas of fog will develop tonight as the atmosphere remains moist.
The warm and humid conditions will continue through Saturday when a
strong cold front comes through.  Prior to the front arriving, the
next chance of showers and storms will move in on Friday and could
linger into Saturday night.  Some of these storm could be strong to
severe, mainly Saturday and Saturday night.

Cooler and less humid air will push into the region for the first
part of next week.  Daytime temperatures should be in the 70s Sunday
through Tuesday, then we may return into the 80s by Wednesday.
Another chance of showers may cross the area Monday night.


.SHORT TERM...(This evening through Friday night)
Issued at 330 PM EDT Wed Aug 17 2016

The cold front continues to march across the CWA this afternoon,
exiting around 00Z.  Somewhat unclear how quickly the low clouds
exit.  If we do clear, it seems like an ideal set up for fog with
minimal winds and high moisture in the boundary layer.  Will have
areas of fog for all areas except I-94.  There are better chances I-
94 will hang on to some clouds, so will just have patchy fog there.
The best chance for dense fog should be across central lower where
clearing is most likely.

The front will sag south, but stall over northern IN as another wave
moves along it.  Much of the CWA will lose the deeper moisture, so
will go with a dry Thursday, but areas along I-94 may see an
isolated shower/thunderstorm where the deeper moisture will yet to
scour out.  This chance of pcpn may linger into the evening too.

Attention then turns to the front and short wave approaching from
the northwest Friday and Friday night.  This will be a slow moving
front that will only gradually increase moisture and lift over SW
MI.  It will move from NW WI Friday morning to the northwest
portion of the GRR CWA by daybreak Saturday.  Will have 30 POPs for
most of the CWA for Friday, rising to 40 POPs Friday night.  The
best jet dynamics remains to our north and west, so not expecting
anything strong or overly concentrated.  Instead expect scattered and
non-severe storms.

.LONG TERM...(Saturday through Wednesday)
Issued at 330 PM EDT Wed Aug 17 2016

An early fall like storm system will move through Southwest Michigan
in the Saturday into Sunday time frame.  This will mean a strong
surge of warm air ahead of the system which will lead to
thunderstorms later in the day Saturday into early Sunday. Much
cooler temperatures will follow for a good part of next week behind
the system.

The models continue to be in very good agreement on taking the
latest system from the Gulf of Alaska forcing it over the mean upper
ridge over the west coast, then it digs strongly into the central
United States this coming weekend. While this is a progressive it is
large enough to impact on southwest Michigan weather for nearly a
week. So we get the warm up in front of it Saturday then a cool
temperatures follow for next week.

There is strong dynamic forcing with this system so we get a decent
low level jet, deep layer shear, significant SB cape ahead of the
system. So strong storms are possible late Saturday ahead of the
cold front.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 141 PM EDT Wed Aug 17 2016

A line of thunderstorms caused by a shortwave moving through the
area will exit the TAF sites by 20z or so then skies should clear
this evening. I expect IFR fog to develop at all taf sites based
on light winds and generally clear skies. The fog should be
shallow and as a result will mix out quickly after sunrise.
Thursday should be mostly sunny.


Issued at 330 PM EDT Wed Aug 17 2016

Rather quiet on the lake, with the next threat coming Friday in the
form of thunderstorms.  WSW winds will be dropping off nicely this
evening, and remaining light through Thursday night.  Southerly
winds will increase Friday, but these shouldn`t last long enough to
build waves any higher than 1-3 feet.


Issued at 330 PM EDT Tue Aug 16 2016

Widespread 1"-5" of rain occurred over the last 24 hours across the
region east of a line from Holland to Clare. This led to numerous
instances of both urban and rural flooding of roads and farmlands as
well as river flooding. River levels will continue to be elevated for
several days on the Kalamazoo River as well as smaller rivers. No
major flooding is expected but some homes, roadways, and farmland
may be subject to water impacts due to the higher river levels.

While widespread heavy rain is not expected this week, there will be
periods of showers and thunderstorms. Basin average precipitation
will not be significant given the more scattered nature of the
rains. Rivers will likely begin falling after crests over the next
few days. Additional precipitation for the weekend will need to be
monitored given very saturated soils that will not be able to
absorb much rain.


.GRR Watches/Warnings/Advisories...


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