Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 281751

Area Forecast Discussion
National Weather Service Grand Rapids MI
151 PM EDT WED SEP 28 2016

Long Term/Aviation

Issued at 330 AM EDT Wed Sep 28 2016

An expansive area of low pressure moving south through the Great
Lakes Region this morning will stall south of Michigan Thursday and
Friday then lift back north through the state over the weekend.
While it won`t be raining all the time, clouds and scattered
showers associated with this low will impact the area for the next
several days.


Issued at 1032 AM EDT Wed Sep 28 2016

The on going forecast looks good. The rotation around the upper
low is apparent as the radar echos are now moving toward the west.
The next area of rain and showers is over the Detroit area and
will be also moving westward this afternoon so expect an increase
in rainfall across most of Southwest Michigan by early this
afternoon. With all the clouds temperatures will not rise a lot
today so highs in the mid 60s still seems good.


.SHORT TERM...(Today through Friday)
Issued at 330 AM EDT Wed Sep 28 2016

Shortwave currently over srn Lk MI, rotating through the base of the
upper trough, will bring a bring a brief increase in showers and
isolated tstms to areas west of Hwy 131 early this morning. However
as the upper low settles south into Indiana, that shortwave heads
back to the west toward WI, which should lead to a decrease/lull in
showers for a time during the mid to late morning. Also the low
level flow goes offshore so any lake component will shift away from
the coast and toward the Milwaukee/Chicago areas.

Primary feature of interest later today is another shortwave
pivoting around the south side of the upper low which takes aim on
southeast and south central lower Michigan this afternoon. Guidance
is similar in showing numerous showers/isolated tstms developing
south and east of GRR as a trowal-like feature curls in from the
southeast and wraps around the north side of the low.

Highest pops tonight and Thursday will continue to be south of I-96,
particularly along I-94, within persistent trowal/deformation zone
on the north side of the upper low. Meanwhile, as the upr low
reaches it`s southern-most position, the potential exists for some
sunshine on Thursday northwest of GRR per RH progs. Downsloping low
level northeast flow with sun could lead to high temps in the lower
70s for the Muskegon/Ludington areas.

Thursday night/Friday sees clouds/pops lift back north/northwest
through the area as the upr low bounces back northward again. A
heavy rain threat may eventually develop as easterly flow around
north side of the low pulls in Atlantic moisture, with PWATs near
1.5 possible within the trowal area by Friday.

.LONG TERM...(Saturday through Wednesday)
Issued at 150 PM EDT Wed Sep 28 2016

The main issue today is when does the upper low move away far
enough to end the periods of rainfall. There is a decent amount of
model agreement on Sunday night being that time period when the
rain should finally end. There is an issue of heavy rainfall into
at least Saturday from the wrap around on the north side of the
system, feeding moisture from the Atlantic back into Michigan.
That will have to be watched but where the heaviest rain will be
is hard to say this far out in time.

Once that system gets out of the way we should see upper ridging
bring a dry period Monday into Wednesday. Then the next Pacific
system will bring the threat of rain back to the area later Wed
into at least Friday.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 150 PM EDT Wed Sep 28 2016

Really this is a complex forecast as we have to time in periods
of rain from shortwaves rotating around the upper low. VFR
conditions should largely remain at MKG as most of the rain
should be south of there and even if it does rain there later this
afternoon it should not be enough to cause deteriorating
conditions, VFR should continue. The I-94 TAF sites should see
the most persistent rain later this afternoon into Thursday. I
would expect IFR cigs/vsbys by Thursday morning for those TAF
sites. GRR and LAN are on the north edge and are the most
questionable. There is an area of rain rotating westward from the
Detroit area now and that should reach the GRR/LAN TAF sites by
21z or so. It should move out of there through by 00z or so and I
would expect it to be dry there most of the night before more rain
moves in by midday Thursday with at least MVFR there.


Issued at 330 AM EDT Wed Sep 28 2016

Will be cancelling the small craft advisory early as winds and waves
have subsided below criteria. However will keep a mention of
waterspouts over the lake through the day. Strengthening northeast
flow could necessitate new small craft advisories for the
southernmost zones later tonight into Thursday.


Issued at 140 PM EDT Tue Sep 27 2016

River levels are around normal for this time of year. Lake enhanced
rain showers are possible through Wednesday. Rain showers continue
to be possible into Sunday. Rainfall totals into the weekend will
range from a half inch up to an inch and a half. Rivers and streams
should remain below bankfull through the weekend.


.GRR Watches/Warnings/Advisories...


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