Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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151
FXUS63 KGRR 301913
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
312 PM EDT FRI SEP 30 2016

LATEST UPDATE...
Synopsis/Short Term/Marine

.SYNOPSIS...
Issued at 312 PM EDT Fri Sep 30 2016

The area will continue to see occasional showers through Monday of
next week. The showers will be most numerous tonight and Saturday
before they diminish in intensity and frequency through Monday.
There will be a chance of thunderstorms on Saturday, with no severe
weather expected. Temperatures through Monday will generally remain
in the 50s for lows, and 60s for highs.

A break in the cool and dreary weather will come during the middle
portion of next week. Temperatures will warm back into the 70s with
more sunshine. A stronger cold front will then bring rain back into
the area in the Thursday/Friday time frame.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 312 PM EDT Fri Sep 30 2016

We continue to focus on the rain trends for the area through the
weekend with the upper low remaining in control. The wettest periods
of the long term look to come tonight and tomorrow, with a slow
diminishing trend then Sat night through Monday as the upper low
slowly rotates out of the area.

We are expecting a couple of waves of rain showers to move through
through Saturday morning. The first is now approaching the area from
the thumb, Lake Erie, and Ohio. This is expected to move through
this evening and end by midnight. The second is expected to move
into the area before daybreak on Sat. We can not rule out some
locally higher amounts of rain falling. This does not look to occur
quickly however, so the flood threat is limited even with a
saturated ground.

The center of the upper low will move toward the area on Sat. This
will likely mean more scattered showers with some thunder possible,
versus waves of rain that we have seen over the past few days. The
cooler air aloft will help produce a little more instability,
allowing for the threat of thunder. We are not expecting severe
weather with thin CAPE profiles and limited wind/shear under the
low. We can not rule out some cold air funnels around the area on
Sat. The thunder chance will diminish Sat evening, and the showers
should weaken a bit with the loss of diurnal heating.

The better chance for rain on Sunday will be across the east, with
all locations seeing a chance still. The center of the upper low and
cold pool aloft is expected to have shifted east of the area by
then. We will be close enough for a few diurnal showers to pop up
late in the morning and in the afternoon. These should almost
completely diminish for Sun night.

.LONG TERM...(Monday through Friday)
Issued at 202 PM EDT Fri Sep 30 2016

Our next significant weather event will be Wednesday night into
Thursday as the next Pacific system moves across the CONUS. This
looks better today than in previous runs and I could see
thunderstorms on Thursday during the day. Otherwise clearing
slowly on Monday, very nice with sunshine Tue into Wed and
lingering showers Friday as the cold air moves in behind the
system.

We get two systems to impacted by the "Henry rule" yet. The first
one is the one currently over us, it finally gets booted east by
the first upstream Pacific system as it moves into the Rockies.
The creates what almost looks like an omega block over the CONUS
by Tuesday as the Pacific system majorly digs and closes off an
upper low over the central Rockies, building a large upstream
upper high over the Great Lakes. However the next Pacific system
gets to close and Henry Rules that east. The first Pacific system
seems to go nearly negative tilt as it comes into the Great Lakes.
This could bring thunderstorms Thursday. With such a deep trough
we will not see a quick clearly Friday, but cold air, lake
enhanced rain showers.

So, that this means for us in Southwest Michigan is a slow
clearing of the low clouds Monday, then mostly sunny / mostly
clear Tuesday into early evening Wednesday with warming high
temperatures. Highs near 80 are not out of the question (not
actually in the grids yet) Wednesday. Then the system moves
through Thursday with showers and scattered thunderstorms Thursday
but it will still be warmer than normal. The cold air moves back
in Friday with lake enhanced rain showers.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 202 PM EDT Fri Sep 30 2016

Our closed upper low will continue to brings periods of showers to
the area through most of Saturday. With extensive low ceilings I
do not see thunderstorms as threat even through we do get better
mid level instability later today into Saturday. Winds are
expected to slowly decrease into Saturday so that may encourage
lower ceiling and thicker fog Saturday morning that would not be
to quick to lift during the mid to late morning.

&&

.MARINE...
Issued at 312 PM EDT Fri Sep 30 2016

We will be bringing down the small craft advisory just a little
early with the forecast package this afternoon. Waves at the buoys
are all below 4 ft in our nearshore waters, and winds are all below
20 knots.

Our concern then turns to the potential for waterspouts on Saturday.
The upper low lifting north almost overhead will provide more
favorable conditions for waterspouts on Saturday. This threat should
then diminish Sat night as the low begins to finally rotate
slowly away from the area.

&&

.HYDROLOGY...
Issued at 1109 AM EDT Fri Sep 30 2016

The Sycamore Creek is nearing its crest over a foot above
bankfull, and will begin its slow recession which may modulated
by any additional rainfall Friday into Saturday. Other rivers
approaching bankfull the next few days include the Red Cedar above
Williamston, the Looking Glass near Eagle, and the Grand at Ionia.
The current forecasts are dependent on roughly another 0.75 inches
falling in those basins through Saturday morning. Will hold off
on flood advisories for those rivers until confidence is higher.

&&

.GRR Watches/Warnings/Advisories...
MI...None.
LM...None.
&&

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...WDM
AVIATION...WDM
HYDROLOGY...CAS
MARINE...NJJ



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