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000
FXUS63 KGRR 241745
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
145 PM EDT Sat Jun 24 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EDT Sat Jun 24 2017

A cool airmass will gradually continue to filter into the Great
Lakes region over the next few days. Highs today will reach the
lower 70s, be near 70 on Sunday and top out in the middle to upper
60s on Monday. Normal highs are in the lower 80s this time of year
so we are well below normal. Partly to occasionally mostly cloudy
skies can be expected the next few days with isolated showers. Each
afternoon a thunderstorm will be possible as well.

&&

.SHORT TERM...(Today through Monday)
Issued at 330 AM EDT Sat Jun 24 2017

This time of year 850mb temps at times surge past +20C, but not in
the short term. 850mb temps are in the lower teens C this morning
and will continue to slide throughout the period. It may be out of
season, but the talk of delta T`s over Lake Michigan is on the
docket. The lake is around +17C right now, so lake clouds are
possible as temps drop to +7C, with lake generated precipitation
possible at +4C. We fall below +7C this evening and to around +4C on
Monday.

So, lake generated clouds are possible tonight through Monday, with
rain showers off the lake possible on Monday. The area will be in a
fall-like northwest flow with periodic shortwaves. Three distinct
shortwaves look to affect the area. One today, another tonight and
yet another on Monday.

We have isolated to scattered showers in the short term (20-40 pct
chances for precip). During the afternoon hours, diurnal instability
is forecast to build into the 600-1200 j/kg range which is plenty
for an isolated storm. Thunder wording is therefore confined to the
afternoon hours. Not expecting significant precipitation this
weekend, but Monday has the potential to end up being a bit more on
the rainy side as the lake component kicks in with delta T`s around
13C. Given that level of instability and the upper trough in place,
waterspouts are not out of the question on Monday with any of the
deeper showers/storms that develop.

.LONG TERM...(Monday night through Friday)
Issued at 330 AM EDT Sat Jun 24 2017

Surface high pressure will move by to the South of Michigan Tuesday
into Wednesday and should result in dry weather for the area. A Low
pressure system is then expected to pass to the Northwest of Lower
Michigan and drape a front across the region. Waves of low pressure
will then train from southwest to northeast along the front. If
these waves move across Lower Michigan, we could see areal and river
flooding by the end of the week.

Temperatures will be warming through the long term. They will be
below normal into mid week and near to a little above normal by
Friday. Normal highs are around 80 degrees and normal lows are in
the upper 50s.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 145 PM EDT Sat Jun 24 2017

Mostly VFR conditions through Sunday morning except for some
ceilings in the 1800 to 2500 foot range at times this afternoon
and late Sunday morning. Showers and thunderstorms this afternoon
are expected to stay north of GRR and LAN and east of JXN but
could come close so we will be watching radar trends through 00Z.

Winds will be west 10 to 15 knots and gust over 20 knots at times
this afternoon and again by 18Z Sunday.

&&

.MARINE...
Issued at 330 AM EDT Sat Jun 24 2017

Have maintained the Small Craft Advisory and Beach Hazards Statement
for the southern three nearshore zones/counties. Essentially they
are in effect from Grand Haven southward through Sunday evening.

The winds and waves are fairly borderline for this event however
with westerly winds of 15 to 22 knots much of the time. The waves
today are forecast to build to near 4 feet, but it is not a slam
dunk. Given water temps are still in the 60s and there will be
clouds and a few showers, this is not a high impact event.

On Sunday, winds look just a bit weaker, although we will be cold
air advecting, which always seems to overperform. So, letting the
headlines ride for Sunday as well. 4 to 5 footers look possible on
Sunday. Sunday will be even cooler, so again impact is not high.

A similar setup appears likely for Monday, so the marine headlines
for boaters and swimmers may need to be extended.


&&

.HYDROLOGY...
Issued at 1231 PM EDT Sat Jun 24 2017

The Chippewa River at Mount Pleasant crested at 14.77 feet Friday
night, about 10 inches below the record flooding of 15.58 feet in
September 1986. All river forecast points in our area have crested
as the water is being routed down through the Muskegon and Saginaw
river systems. Scattered showers Saturday through Monday should
have little effect on the rivers. Heavy rain potential may return
during the latter part of the upcoming week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through Sunday evening for MIZ056-064-
     071.

LM...Small Craft Advisory until 8 PM EDT Sunday for LMZ844>846.

&&

$$

SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...63
AVIATION...Ostuno
HYDROLOGY...CAS
MARINE...Duke