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000
FXUS63 KGRR 240517
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
117 AM EDT Wed May 24 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EDT Tue May 23 2017

Rain showers and a few thunderstorms will continue into the evening
hours before tapering off to some light showers overnight. A low
pressure system will strengthen over the Ohio Valley tonight and
slowly lift north into the Great Lakes region Wednesday and
Wednesday night. Periods of showers and thunderstorms will accompany
the low from Wednesday into Thursday. Locally heavy rain is possible
from Wednesday night into Thursday across Southern Lower Michigan.
Rain chances will persist into the Holiday weekend with showery
conditions at times and near normal temperatures.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 330 PM EDT Tue May 23 2017

Upper trough to the west this evening continues to funnel moisture
northward into the Great Lakes region. The upper trough slowly moves
east through the area over the next couple of days. So, chances for
showers and some thunderstorms will continue in the forecast.
Thunderstorm chances return again on Wednesday as CAPE values
increase to around 1000 J/KG again. Not expecting enough instability
for severe weather on Wednesday given the clouds and precipitation,
but we do have 30-40 knots of deep layer shear so there may be some
storm organization.

The best chances for rain look to come Wednesday night into Thursday
as a trowel sets up across Southern Lower Michigan. Models are still
indicating some one inch total rainfall amounts in and near Southern
Lower Michigan. We will slowly dry out from Thursday into Thursday
night as ridging begins to slide in from the west.

Bottom line, fairly wet and slightly cooler than normal.

.LONG TERM...(Friday through Tuesday)
Issued at 330 PM EDT Tue May 23 2017

Confidence is fairly high that Friday will be a dry day due to
shortwave ridging behind the departing upper low, although cloud
cover is more uncertain. Low clouds on the back side of the old
upper low should depart/dissipate in the morning, but may be quickly
replaced with mid/high clouds streaming in from the west in the
afternoon.

ECMWF and Canadian solutions now show southern Lower Michigan being
impacted by a sfc low tracking south of MI on Friday night and
Saturday morning. Will need to include some chance pops for this
feature near and south of I-96 however it should be moving fast
enough to provide at least a partly sunny afternoon on Saturday with
highs in the mid to upper 70s.

Could see a round of storms roll through on Saturday night into
Sunday morning as the next digging upper trough upstream approaches
from the west. It will cool off a bit behind the related sfc
trough/cold front, but it may also dry out and be a decent day with
stable westerly low level in it`s wake.

General cold advection and upper troughing pattern develops as we
head into Memorial Day. This should lead to cooler than normal temps
again along with a risk of showers.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 117 AM EDT Wed May 24 2017

VFR conditions prevailed over the region as 0530Z. This is
expected to continue overnight. However more showers and isolated
thunderstorms are expected to move into the area toward daybreak,
bringing some MVFR. The I-96 TAF sites may see the MVFR linger
much of the day, while the I-94 TAFs see VFR with periods of MVFR.

Expect that the MVFR will become more widespread into the evening,
with some IFR developing after nightfall.

&&

.MARINE...
Issued at 330 PM EDT Tue May 23 2017

A strengthening low to our south tonight and Wednesday will increase
northerly winds on Lake Michigan. At this point thinking the higher
winds and waves will remain off shore of our nearshore waters. So,
not expecting to need Small Craft Advisory at this point. The
strongest winds look to be in the Wednesday night and Thursday time
frame where open water winds may reach the 15 to 30 knot range.
Thinking the nearshore waters will again remain just below advisory
criteria with north winds of 10 to 20 knots and waves of 2 to 4 feet
at times.


&&

.HYDROLOGY...
Issued at 330 PM EDT Tue May 23 2017

While many rivers across West Michigan continue to run at above
normal levels...a falling trend should continue through Wednesday.
Areas of light rain will persist through Wednesday morning but
should not impact river stages.  The rainfall event from Wednesday
afternoon through Thursday...however...is more likely to produce
significant runoff...which could produce a new round of rises on
area rivers. Latest guidance suggests that the heaviest rainfall
will occur over the upper portions of the Grand and Kalamazoo river
basins.

&&

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

$$

SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...Meade
AVIATION...JK
HYDROLOGY...MWS
MARINE...Duke