Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 141243
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
843 AM EDT Fri Jul 14 2017

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 328 AM EDT Fri Jul 14 2017

It will be much cooler today as Canadian polar air moves in behind
the slowly departing storm system. That storm will today be
centered over Lake Huron at sunrise this morning but it will move
east to Lake Ontario by evening. That will allow the Canadian surface
high to move in behind it and bring cooler temperature tonight.
Most area will have lows in the 50s. The next cold front comes
through early Sunday morning. There will likely be a few
thunderstorms ahead of that front. The storms will be scattered so
most locations will likely remain dry even so. Another Canadian
Polar air mass follows for Sunday afternoon and Monday so the
cooler than normal temperatures will continue through the weekend
into early next week.

&&

.UPDATE...
Issued at 843 AM EDT Fri Jul 14 2017

Added a chance of showers with a small area of likely POPs north
of Muskegon as showers are coming on shore there now. These should
move east and dissipate through mid afternoon as drying works in
from the west northwest.

&&

.SHORT TERM...(Today through Sunday)
Issued at 328 AM EDT Fri Jul 14 2017

The biggest issue in the short term is just how much cloud cover
will there be this morning. Other than that it will be much cooler
than it has been over the past four days as our upper level flow
will be from central Canada through the weekend.

There is a large area of low clouds assoicated with the cyclonic
flow of cooler air around the departing storm, currently centered
over Lake Huron. These clouds will overspread the area by sunrise
but will mix out by early afternoon so most areas will be seeing
some sunshine. Skies should be clear o mostly clear and winds will
be light so low will be cooler than they have been the past few
days, mostly in the 50s.

Currently our upper level jet is nearly zonal across the Canadian
board with the United States from the west coat to the east coast.
However, a storm system coming on shore into Southern British
Columbia has a jet streak in front of it and that will help to
build the upstream heights, which in turn will lower the upper
level heights over the Great Lakes and Northeastern United States.
This allows a shortwave over northern Minnesota to dig southeast
and become a closed but progressive system by Saturday morning.
That system is what is bringing the cooler Canadian air to our
area today into Saturday. The next shortwave trailing this one
digs more strongly than todays shortwave does and it actually
pulls the polar jet south of Michigan during the daylight hours of
Sunday.

There is the treat for thunderstorm threat Saturday night into
early Sunday morning. That happens due to that digging upper jet
puts southwest Michigan in the right front left front exit region
of the digging jet core. That also puts western Lower Michigan in
front of the low level jet as it tracks south across Wisconsin
Saturday night into Sunday morning. This also puts southwest
Michigan at the nose of the 1000/850 moisture transport vectors
just ahead of that Canadian Cold front. There is considerable mid
level instability ahead of this front, even at night. So I would
thing there will be thunderstorms around but they will be
scattered since the mean RH is not all that high with this system.

Behind the front on Sunday Canadian poler high pressure moves in
so expect skies to become mostly sunny and it will be cooler than
normal with highs near or just below 80.

.LONG TERM...(Sunday night through Thursday)
Issued at 328 AM EDT Fri Jul 14 2017

The first several periods of the long term look dry thanks to high
pressure that will move from the Upper Mississippi Valley to the
Great Lakes. Chances for showers and storms will increase late
Tuesday night and Wednesday as a cold front moves south. Given that
the ecmwf and gfs are not in synch regarding frontal timing,
confidence is low regarding pcpn timing. The ecmwf brings the front
down to central Lower Wednesday afternoon and then moves it north
again. The gfs pushes the front south into central Indiana and
doesn`t really bring it north until Friday. Meanwhile the ecmwf
moves it north again Thursday and shows pcpn along the front.

We`ve seen several fronts push through this summer with each showing
a bit of a cooling behind the front along with a northeast wind
flow. That history would tend to favor the gfs and so we`ll keep the
low chc pops.

Sunday night and Monday will be the most comfortable time period
with lows Sunday night in the mid to upper 50s and highs Monday in
the upper 70s. Much warmer and more humid conditions are expected
Tuesday and Wednesday with highs in the mid to upper 80s and
dewpoints well into the 60s.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 748 AM EDT Fri Jul 14 2017

Currently most of our TAF sites are solid IFR with ceilings
around 500 feet agl. However, as the morning goes on mixing
should help to break up the clouds. The HRRR and RAP model
forecast for the clouds show most of the area going mostly clear
to partly cloudy by noon. Skies should go clear tonight. There may
be a fog issue after 06z as winds are light and skies should be
clear. I was not to sure about it so I did not put it in our
current tafs but it is more than possible.


&&

.MARINE...
Issued at 328 AM EDT Fri Jul 14 2017

Thanks to the cold air moving into Southwest Michigan today and
Sunday we will come close to needing a small craft advisory but
it seems the winds will not be quiet strong enough so I did not
issue a small craft advisory. Still this will be something to
watch today.


&&

.HYDROLOGY...
Issued at 1054 AM EDT Thu Jul 13 2017

Localized rainfall amounts over 2 inches fell in a stretch from near
Holland, eastward between Lansing and Jackson. Another area of
heavier rain of similar magnitude (or slightly less) fell just
northeast of Ludington.

Almost all of Lower Michigan is seeing streamflows that are above
normal to much above normal. Fortunately, there was fairly limited
spread in aerial coverage with the excessive amounts.

Rivers are likely to rise, but everything is expected to remain
within banks. Quicker responses are more likely on smaller streams
and tributaries given the localized nature of the 1-2+ inch amounts.
In addition, these amounts were received in two waves, allowing some
runoff time after the first round.

Rainfall will be rather limited through Saturday, if anything. The
next chance for rain comes along a cold front on Sunday.

&&

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

$$

UPDATE...Ostuno
SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...04
AVIATION...WDM
HYDROLOGY...JAM
MARINE...WDM



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