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029
FXUS63 KGRR 232327
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
727 PM EDT Fri Jun 23 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EDT Fri Jun 23 2017

Colder than normal temperatures can be expected this weekend
through early next week, with widely scattered showers and
thunderstorms. Rainfall will not be excessive.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 330 PM EDT Fri Jun 23 2017

Trough aloft and series of vorticity maxima/shortwaves sliding
through the northwest flow will bring periods of cloudiness and
scattered showers over the weekend.

Best coverage of convection, and the best time for a few tstms,
should generally be in the afternoon and evening hours when the
diurnal contribution/instability is highest. Also,the lake shadow
should tend to focus things inland from lake Michigan.

Lowering freezing heights through the weekend may eventually lead to
a chance of some small hail in some of the low topped convection,
which would be more possible on Sunday than on Saturday.

Scattered/intermittent nature of the convection of the weekend
should lead to total QPFs of generally no more than a quarter
inch, with highest amounts north of I-96.

.LONG TERM...(Monday through Friday)
Issued at 330 PM EDT Fri Jun 23 2017

Monday will see cooler than normal weather with diurnal enhancement
of showers and a few thunderstorms as upper level troughing brings
steep lapse rates. No severe weather is expected although the
storms could bring small hail during the afternoon as freezing
levels are unusually low.

The trough axis moves east by Tuesday with shortwave ridging
returning Wednesday along with warming temperatures. We will also
see moisture return in southwest flow with chances for rain by
Wednesday afternoon. Surface low center tracks north of Lower
Michigan on Thursday and showers and thunderstorms along and ahead
of trailing cold front will persist into Friday as the front sags
south of Lower Michigan and stalls across the Ohio Valley.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 727 PM EDT Fri Jun 23 2017

Expect VFR conditions to prevail through Saturday night. That
said, there are several short waves rotating around the upper low
that will move across SW Lower Michigan both tonight and Saturday.
For tonight skies will be nearly clear for most areas but for GRR
and MKG there may be mid clouds through most of the night (shown
by the HRRR and NAM PCT CLOUD forecast). Winds will become lighter
overnight so it would not be impossible for a little fog toward
morning but I feel there will be enough mixing to mitigate that.
Also during the day time hours of Saturday the air will be
unstable but with west winds only the TAF sites near I-69 have a
significant threat for convention. I limited the VCTS to those
locations. Even then if anything does develop it will be brief.

&&

.MARINE...
Issued at 330 PM EDT Fri Jun 23 2017

Wave heights will probably flirt with small craft advisory
criteria much of the weekend, especially on Sunday, and we may
need to issue some headlines eventually. Typically in a cold air
advection pattern this time of year, the waves tend to over
perform and current water temps around 70 will lead to well mixed
conditions similar to what we normally see in the later
summer/early fall.


&&

.HYDROLOGY...
Issued at 257 PM EDT Fri Jun 23 2017

Major flooding is expected along the Chippewa River in Isabella
County and sharp rises are also occurring along the Muskegon basin
and will continue the next couple days as the crest moves down
the river. From 3 to 5 inches of rain fell last night combined
with earlier heavy rains.

The good news is that no heavy rain is expected through the
middle of next week which will allow those areas that are flooding
to recover. The next chance for significant rain will be Thursday
of next week.

&&

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

$$

SYNOPSIS...Meade
SHORT TERM...Meade
LONG TERM...Ostuno
AVIATION...WDM
HYDROLOGY...Ostuno
MARINE...Meade