Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 211236

Area Forecast Discussion
National Weather Service Grand Rapids MI
836 AM EDT WED SEP 21 2016

Mesoscale Discussion

Issued at 835 AM EDT Wed Sep 21 2016

Line of storms reaching MKG with observed pea sized hail at 815 AM
EDT. Radar showing winds near 45 knots at 3000 feet AGL offshore
of Grand Haven at 835 AM, so some gusts over 50 mph are possible,
as were observed on the Wisconsin side of Lake Michigan.

With a weakening LLJ the next several hours, we expect the line
of storms to diminish in intensity as they progress though
southwest Lower Michigan. Pea sized hail and gusts over 40 mph
will remain possible across the southwestern forecast area
through 10 AM.


Issued at 330 AM EDT Wed Sep 21 2016

A warm front stretches this morning from the Minnesota/Iowa border
southeast into portions of Central Illinois. The warm front will
lift north today into Southern Lower Michigan which will increase
our chances for some showers and thunderstorms. The front will
remain over portions of Lower Michigan through Friday morning when
it will finally slip back south of the state. Chances for showers
and thunderstorms will exist from Today right into Friday. The
highest chances for precipitation will be across Central Lower
Michigan which will be in closer proximity to the front. It will
remain mild both Today and Thursday before we return closer to
normal temperatures for this time of year into the weekend.


.SHORT TERM...(Today through Friday)
Issued at 330 AM EDT Wed Sep 21 2016

Main forecast concerns revolve around precipitation chances and
areal extent of rain the next few days. A secondary concern is cloud
cover and how it will affect temperatures.

MCS in Wisconsin is working our way this morning although
instability is much less over our area as compared to MN/IA/WI.
Convection allowing models have been consistent in showing the
complex continuing to work our way this morning, slowly diminishing
as it does so. Thinking scattered showers and possibly an isolated
thunderstorm or two may work into the area this morning, but in
general a diminishing trend should be noted.

The warm front will remain across Central and Northern portions of
the state from tonight into Thursday night and will continue to  be
a focus for shower and thunderstorm development. The best
instability is actually this afternoon and then it tapers off each
period as we head into Friday. Thinking the current forecast looks
good with highest chances for rain north across Central Lower
Michigan 50-60 pct, diminishing to isolated or dry across the far

The front will drift south of the area on Friday which should take a
lot if not all of the precipitation with it. Regarding temperatures
thinking we will make another run to highs around 80 today and
likely again on Thursday as well, at least in the south. Warm air
advection may be enough to offset some of the mid and high clouds
that may be around.

.LONG TERM...(Friday night through Tuesday)
Issued at 330 AM EDT Wed Sep 21 2016

Forecast concerns deal with a couple of frontal boundaries that will
be moving across the cwa.

The first boundary is the washed-out cold front that will move north
as a weak warm front Friday night. We may see a shower from that but
chances are fairly low. Saturday looks basically dry with seasonable
temps in the lower 70s. Another cold front will approach Sunday
night and linger through Monday. The gfs pushes the front through
but the ecmwf is slower and may be the better solution given the
digging upper trough noted on both models. We`ll keep chc pops in
the grids through Tuesday to account for the slow moving cold front
and the trailing upper low. Highs in the upper 60s to lower 70s
expected Sun-Tue.


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 759 AM EDT Wed Sep 21 2016

A line of thunderstorms will sweep through the TAF sites this
morning. The line will contain heavy rain that may briefly dip
visibilities into the IFR category and wind gusts potentially into
the 30 to 35 knot range. As the line moves inland towards LAN and
JXN we expect a diminishing trend and the winds to likely gust below
30 knots. Essentially we are looking for some MVFR conditions as
the line moves through (briefly dipping to IFR) then going back to
VFR conditions. VFR weather is forecast for this afternoon and
tonight. Additional showers and storms will likely stay north of
the TAF sites after 18z.


Issued at 330 AM EDT Wed Sep 21 2016

A southerly gradient that will producing winds of 10 to 15 knots
will likely produce waves of 1 to 3 feet on Lake Michigan from Today
into Thursday. The flow becomes off shore Friday into Saturday which
will also keep waves at a minimum in the nearshore. Not expecting
Small Craft conditions through Friday.


Issued at 330 PM EDT Tue Sep 20 2016

Hydro impacts through this weekend will be limited. Rain and
thunderstorm chances will exist Wednesday and Thursday, mainly north
of I-96. A frontal boundary draped across Central Lower Michigan
will be the focus for diurnally-driven shower/storm activity.

Total rainfall amounts will likely exceed half an inch (0.50 inches)
well to the north of I-96, affecting the Upper Muskegon River basin
and Pere Marquette River basin. Mostly within bank river rises
are expected.


.GRR Watches/Warnings/Advisories...


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