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275
FXUS63 KGRR 201742
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
142 PM EDT Tue Jun 20 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 322 AM EDT Tue Jun 20 2017

Very comfortable early summer weather is under way across Lower
Michigan. Highs in the lower 70s are expected with low humidity
followed by lows tonight in the lower 50s. Scattered showers and
thunderstorms are possible again this afternoon.

A fairly wet pattern is unfolding and showers and storms are
expected Wednesday night through Thursday night.

&&

.UPDATE...
Issued at 1118 AM EDT Tue Jun 20 2017

Updated the fcst to bump up pops a bit for this afternoon. Radar
shows a large area of rain showers moving east southeast across
southern WI and out over central Lake MI. This area of showers
will continue to advance ese across our fcst area this afternoon
as suggested by rgnl radar trends and higher res computer model
guidance such as the 3km nam.

&&

.SHORT TERM...(Today through Thursday)
Issued at 322 AM EDT Tue Jun 20 2017

Forecast concerns deal with convective trends through the period.

An upper trough will move across the state today and one final short
wave will rotate through and provide another shot of showers and
thunderstorms, mainly this afternoon and early evening. Pretty
healthy shear values 50-60 kts could certainly provide some
organization, but instability may be a limiting factor, especially
west of US-131. Similar to last night, we should clear out and
temperatures will fall into the lower 50s, perhaps upper 40s over
the far northern cwa.

Much of Wednesday will be dry, but that will likely change Wednesday
night. Models are hinting at an MCS developing over eastern
MN/Western Wisconsin and moving east across the cwa Thursday
morning. A warm front is progd to bisect Wisconsin where a 50kt llj
will intersect it Wednesday night. Add in a short wave moving over
southern Wisconsin and we should see a convective system develop.
Timing into Lower Michigan would be likely after 4 am. Thus much of
Thursday morning could be stormy too, depending on how this unfolds.
Given the various boundaries generated by the MCS, more convection
is expected Thursday afternoon.

After highs in the lower 70s today, temps will steadily rise to the
lower 80s by Thursday.

.LONG TERM...(Thursday night through Monday)
Issued at 322 AM EDT Tue Jun 20 2017

Thursday night could be the most active period during the entire
seven day period ending next Monday. A frontal boundary will be in
the area, with the exact placement quite uncertain due to the
evolution of convection earlier in the day. We do know that there
will be a lot of heat and instability just south of the front. A
wave likely riding along the front will supply the dynamics with a
healthy low level jet forcing the convection.

We should see lingering rain early Friday morning move out by
afternoon for the area. The wave providing the rain chances Thu
night will move ENE out of the area, and nrly flow behind it should
push the front well south of the state. This will bring cooler and
drier air back over the area. We should then stay mainly dry through
Saturday.

The next chance of rain then will come overnight Saturday night
through Sunday. This will be supported by a digging long wave trough
across the Upper Midwest helping to develop a sfc low. This looks to
have a Gulf connection also, so it could be another wet period. The
upper trough will then linger over the area for Mon, bringing the
potential for some showers via the cold pool aloft.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 142 PM EDT Tue Jun 20 2017

Mostly VFR weather is expected over the next 24 hours. The rain
showers currently moving in from the northwest could briefly
produce MVFR conditions through 00Z, but ceilings upstream in WI
have been mostly above 6000 ft and vsbys mostly above 5 miles in
the rain.

The showers will end and cloud cover will decrease from northwest
to southeast after 22-00Z, leaving CLR skies tonight into
Wednesday. Can`t rule out some fog developing late tonight since
sfc winds drop off below 5 kts, but will leave that out for now.
West winds will be gusty to 25 kts through about 21-22Z from GRR
to the south and east.

&&

.MARINE...
Issued at 322 AM EDT Tue Jun 20 2017

Wind and wave are expected to remain below advisory criteria for the
next few days.


&&

.HYDROLOGY...
Issued at 159 PM EDT Mon Jun 19 2017

Two to over three inches of rain fell this past weekend which is
leading to higher river flows. The Flat River near Smyrna may reach
bankfull by midweek, but is the only site expected to do so.
Scattered showers and a few thunderstorms will be possible today and
Tuesday with less than a quarter inch of rain expected on average.
Additional heavier rains will become possible once again Wednesday
night through Friday and should lead to additional rises.

&&

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

$$

UPDATE...Laurens
SYNOPSIS...04
SHORT TERM...04
LONG TERM...NJJ
AVIATION...Meade
HYDROLOGY...63
MARINE...04