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619
FXUS63 KGRR 230529
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
129 AM EDT Tue May 23 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 328 PM EDT Mon May 22 2017

An upper low over the Great Lakes will keep the chance of rain in
the forecast for the next few days. Wednesday night into Thursday
looks like the highest chance of rain and that`s mainly south of I-
96. Temperatures will be near to slightly below normal this week.
Warmer weather is expected for the Memorial Day weekend.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 328 PM EDT Mon May 22 2017

Forecast concerns deal with pcpn trends through the period. Regional
radar shows a decaying area of showers extending from southeast
Wisconsin through northern Missouri. This area of light rain was
moving east but struggling as it encountered drier air. We kept a
low chance of rain in the grids tonight, but we`re not expecting
much.

A sfc low will move toward Lake Michigan Tuesday as the upper trough
edges closer to Michigan. This will increase chances for rain
Tuesday afternoon . Li`s fall below 0c Tuesday and models show 500-
1k j/kg MUCAPE so we added a slight chance for thunder too.

A deeper low is progd to move north toward the state Wednesday. This
is when we`ll see the highest chance for showers/storms. The LLJ
increases during the day, but pwats remain fairly low. Thus heavy
rain isn`t expected.

.LONG TERM...(Thursday through Monday)
Issued at 328 PM EDT Mon May 22 2017

Still some scattered showers expected on Thursday, especially east
of highway 131, with upper low lingering over the eastern Great
Lakes Region. Would not even rule out a few isolated showers on
friday but ridging is shown to be moving in, so probably a
predominately dry day.

At this time, Saturday looks to be the best day of the holiday
weekend. Sfc ridging should lead to light winds, and H8 temps near
12C suggest highs in the mid to upper 70s. Currently the guidance is
keeping the warm frontal related convection south of the state on
Saturday.

Precipitation potential appears to increase on Saturday night and
Sunday due to the approach of the next H5 trough/upper low from
the west/Northwest. ECMWF/GFS differ on handling of this feature
over the second half of the holiday weekend, with the ECMWF more
progressive, so confidence is low regarding precipitation
potential and coverage, and if/how much it cools off heading into
Memorial Day.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 129 AM EDT Tue May 23 2017

VFR conditions prevail across the region early this morning. But
there will be scattered showers about the region for the next 24
hours, and this will probably bring in some MVFR, especially
toward I-96. With the showers becoming more commonplace, expect
some MVFR development for the I-96 TAF sites toward daybreak.
With a SSW wind coming off of Lake Michigan, MKG may even see some
IFR. These sites may see a period of VFR in the afternoon, but
overall the MVFR should prevail much of the daylight hours.
Meanwhile, it appears the I-94 TAF sites largely remain VFR. As
the system slides east and we see winds swing around to the ENE,
the I-96 TAF sites should improve to VFR by mid evening.

Within the scattered shower pattern there will also be widely
scattered thunderstorms mainly after 14Z. These should dissipate
into the mid evening hours.

&&

.MARINE...
Issued at 328 PM EDT Mon May 22 2017

We cancelled the small craft advisory a few hours early. Web cams
reveal little in the way of white caps and buoys are generally aob 3
ft. This suggest that mixing is struggling over the water.


&&

.HYDROLOGY...
Issued at 125 PM EDT Mon May 22 2017

River systems in Southern Lower Michigan are running above normal,
while river levels in Central Lower Michigan are around normal.
Tonight through Thursday, unsettled weather will bring up to an inch
of rain. This should keep levels elevated, but not expecting
flooding to result. The following forecast is based on observed and
forecast 24 hour precipitation.

&&

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

$$

SYNOPSIS...04
SHORT TERM...04
LONG TERM...Meade
AVIATION...JK
HYDROLOGY...63
MARINE...04