Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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771
FXUS63 KGRR 181147
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
747 AM EDT Fri May 18 2018

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 328 AM EDT Fri May 18 2018

High pressure over Quebec will provide one more dry day before low
pressure lifting north from the Tennessee Valley spreads showers
into the region tonight and Saturday. Although that system will
exit by Sunday, another slow moving system approaching from the
Central Plains will bring more scattered showers and possible
thunderstorms for early next week.

&&

.SHORT TERM...(Today through Sunday)
Issued at 328 AM EDT Fri May 18 2018

Latest model guidance has trended toward a wetter solution tonight
and Saturday, so have increased pops and qpf. It now appears that
widespread rainfall amounts of one quarter to one half inch are
likely, with locally higher amounts even possible.

Low level cool/dry advection from the east will continue today,
but high cloudiness associated with the next system will continue
to stream in. These clouds should be thin enough to allow for
sunshine the first half of the day, but thicker mid level clouds
are expected to spread in from south to north this afternoon.

Showers may already begin impacting the I-94 corridor by late in
the day, after about 5 pm, as the sharp PWAT gradient arrives from
the south. Values are shown to rise from only 0.50 today, to over
1.5 inches for tonight. The combination of the higher PWAT values
tonight and the negatively tilted upper wave approaching from the
southwest is expected to lead to widespread shower coverage.

The upper system does weaken on Saturday, but is rather slow to
move out, so expect clouds and scattered showers to linger.
Thunder chances look quite low but should any pockets of decent
sfc heating develop there could be a few afternoon storms.

Sunday could end up being a dry day since we will be in between
shortwaves. However confidence is low as to when the next wave
begins to impact the area and will have low chance pops in the
fcst for Sunday.

.LONG TERM...(Sunday night through Thursday)
Issued at 328 AM EDT Fri May 18 2018

The complicated forecast resulting from the uncertainty of the upper
low to our west will continue into the long term. There is good
agreement that once the upper low/wave moves by, we will see drier
and comfortable conditions settle in approaching the holiday weekend
next weekend.

We will have rain chances in the forecast from Sun night through Mon
night, before diminishing on Tue. We are not sure when the best
chance is, as there is quite a bit of disagreement with regards to
when the remnants of the upper wave/low comes through. The change in
the models since yesterday is that the various models bring the
upper low out at different times. The slower versions keep rain
chances into Tue, while the faster models have it gone by Tue.
Unfortunately there is not much to be able to favor one solution
over another.

There is actually better confidence later in the long term that we
will see dry and mild conditions from mid-late week next week. The
confidence comes as all models have an upper low to our NE and an
upper ridge to our west in this time frame. Confluent flow aloft
looks likely, and will limit lift and moisture. A good deal of
sunshine will bring dry and mild conditions mid-late week next
week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 747 AM EDT Fri May 18 2018

VFR conditions today with clouds mainly above 10,000 ft and east
winds gusting to 25 kts. Ceilings lowering later today and tonight
with showers arriving from south to north. Expect MVFR cigs to
develop by midnight and IFR by daybreak.

&&

.MARINE...
Issued at 328 AM EDT Fri May 18 2018

No immediate marine concerns with easterly flow persisting and
best wave action remaining well offshore.

&&

.HYDROLOGY...
Issued at 149 PM EDT Thu May 17 2018

River levels are high across southern Lower Michigan due to the
recent heavy rains. The rivers in central Lower Michigan are near to
a little above normal. A river flood warning continues for the
Portage River near Vicksburg. All other sites have crested below
flood stage. Under three tenths of an inch of rain is expected
Friday night and Saturday with additional rain possible early next
week. This may lead to a slowdown or pause of the river level falls.

&&

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

$$

SYNOPSIS...Meade
SHORT TERM...Meade
LONG TERM...NJJ
AVIATION...Meade
HYDROLOGY...63
MARINE...Meade



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