Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 170527
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
127 AM EDT Sat Jun 17 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EDT Fri Jun 16 2017

The region will continue to see showers and thunderstorms, but the
peak time frame will run from late tonight through Sunday morning.
We should finally dry out Sunday afternoon and Sunday night.  Much of
next week appears drier, but a few scattered showers or storms could
occur in the first half of the week.

Temperatures over the weekend will remain warm, from 80 to 85, but
then we should see slightly cooler air move where daytime highs from
Monday through Friday are mainly in the 70s.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 330 PM EDT Fri Jun 16 2017

The active period will continue with more showers and storms
arriving late tonight.  The storminess will linger through Saturday,
before winding down Sunday morning.

We will see a brief lull in the pcpn chances this evening.  But then
as richer moisture moves back into the region late tonight, move
showers and storms will arrive after midnight.  This area of pcpn
will develop near the Twin Cities where the jet dynamics will be the
greatest this evening.  The complex will move into SW MI late, but
begin to out run the dynamics, so no severe weather is expected.
Will carry mainly chc POPs given a weakening trend expected as they
arrive.

The low level jet reaches SW MI on Saturday, nosing into Central
Lower.  So storms will be possible through the day, but after a
morning dissipation, and lull could be seen mid day, then more
storms into the evening and Saturday night.  Severe risk will hinge
on how much we regenerate the instability in the mid day lull.  Its
possible we stay fairly cloudy.  I am not overly impressed by the
severe threat given the set up.  As of now, I think we only may only
have an isolated risk of severe, that moves in Saturday night, at a
min in the instability.

The higher risk will be heavy rain which is always difficult to
determine in convective set ups.  Several areas will see over an
inch of rain, but some locally higher amounts will occur.

Surface low pressure will move to our northwest Sunday morning and
it will drag a cold front through here late Saturday night.  So the
showers and storms will become more scattered into early Sunday
morning, then come mostly come to an end by mid day.

After a string of 80 and 90 degree days, Sunday should see highs of
75 to 80, along with lessening humidity behind the front.

.LONG TERM...(Monday through Friday)
Issued at 330 PM EDT Fri Jun 16 2017

On Monday and Tuesday an upper level trough will be overhead and the
associated cooler temps aloft will support some widely scattered,
diurnally enhanced, showers or tstms. Better probabilities will be
well inland from Lake Michigan due to westerly low level flow,
however on Tuesday a shortwave dropping through will probably result
in a period of higher coverage of precipitation.

If the Tuesday shortwave in the northwest flow aloft arrives at peak
heating, some stronger storms with a hail/wind threat may develop,
especially considering the expected steep lapse rates and 500 mb
temps near -20C.

The best chance of a dry weather day is on Wednesday when sfc
ridging will be impacting the area as the upper trough lifts out. It
may turn stormy again Thursday and Friday though as the warm humid
air returns and fast zonal flow aloft leads to high deep layer shear
values.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 127 AM EDT Sat Jun 17 2017

Quite a complicated forecast through the 06z forecast period, and
likely beyond a bit. Multiple waves of showers/storms will be
possible, with each round dictating where the subsequent rounds
will develop.

The first round of showers/storms looks to come in after 07z to
the lakeshore. The activity across Wisconsin is trending down for
now, but hi-res short term models indicate a spike is likely as
they reach the area. It is looking like a couple of rounds of
showers/storms through about 18-20z for the Nrn terminals. MVFR
conditions under the storms look like a lock, with some localized
IFR expected.

The idea is then that another line of storms will fire on the SErn
periphery of the first couple of rounds where the instability
will build best with little to no rain. This will likely impact
the SE terminals.

Additional showers/storms will become possible toward the end of
the period from S to N. This is the most uncertain, as where the
storms form will be dependent on the previous rounds.

&&

.MARINE...
Issued at 330 PM EDT Fri Jun 16 2017

No headlines expected on the lake through the short term.  We may
see some fog Saturday and Saturday night as higher dew points come
over the cool waters.  Waves will come up a bit Sunday afternoon and
evening behind the cold front, but small craft conditions should not
be met.


&&

.HYDROLOGY...
Issued at 1150 AM EDT Fri Jun 16 2017

A small area of showers and thunderstorms moved through West
Michigan prior to sunrise...producing isolated half inch
accumulations across Ottawa/Kent/Ionia counties. No impacts are
expected on area rivers as a result of this rainfall.

An unsettled weather pattern will continue through Sunday morning...
with multiple episodes of showers and thunderstorms. Precipitable
water values of 1.5 to 2.0 inches are expected through early
Sunday...which would support areas of heavy rainfall.  Model QPF
forecasts differ with the location of the heaviest rainfall...but
locations south and east of Grand Rapids appear to have the
highest likelihood of accumulations of one to two inches by
Sunday morning when the cooler and drier airmass moves into the
region.

Area rivers are running well below bankfull stage. Significant
rises will be possible on area rivers and streams...especially in
the Grand and Kalamazoo river basins...but do not anticipate
rises above bankfull at this time.

&&

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

$$

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



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