Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 162254
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
654 PM EDT Sat Sep 16 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EDT Sat Sep 16 2017

After a quiet night, we will see scattered scattered showers and a
few thunderstorms arrive on Sunday.  The showers should linger into
the evening, especially southeast of Grand Rapids.  Another chance
of widely scattered showers may move in by late Monday night into
Tuesday.  Our dry area may see yet another chance of rain by
Thursday night and Friday.  Temperatures are expected to stay warm
through the week, with daily high temperatures a few degrees either
side of 80.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 330 PM EDT Sat Sep 16 2017

A chance of rain for the parched region moves in for Sunday and may
linger into Sunday night for some areas.  Another possibility of
showers may arrive Monday night.

The upper ridge that has been over the Great Lakes for the latter
half this week will slowly drift east.  This will bring move zonal
flow, which will bring a cold front through CWA Sunday.  Decent
moisture pooling either side of the front, so expect a period where
we will see scattered showers along with a few thunderstorms.

Added a 20 POP over the far NW CWA tonight, where some of the WI
showers may clip this area before 12Z.  Otherwise the showers and a
few storms will increase from the NW through Sunday.  With slightly
quicker frontal arrival I increased POPs in the morning in the NW,
and included POPs for the south into the afternoon.  It seems like
the deepest moisture moves to the north of I-96 where POPs will be a
bit higher, but still in the chance category due to the scattered
nature of the expected showers.  The front slows down over the SE
CWA where the scattered showers and storms should linger into the
evening.

The front slips south of the CWA by Monday.  The models handle the
moisture depth in an over running pattern differently.  Tend to
believe and drier pattern and removed any POPs for Monday.  The
moisture does try to deepen overnight, but even this appears
questionable.  Will leave low POPs mainly over the SW CWA for a few
showers.  There is no instability in this time frame, so only some
light shower potential.

.LONG TERM...(Tuesday through Saturday)
Issued at 330 PM EDT Sat Sep 16 2017

An approaching upper trough will bring a chance for rain showers
Tuesday. Not much precipitation is expected due to the weakness of
the system and little if any return flow of moisture ahead of it. As
noted previously, abnormally dry conditions are likely to continue
along with above normal temperatures.

There is a suggestion of a second chance of rain Wednesday, but this
is not high probability and predictability in general from Wednesday
on really begins to fall off the shelf. This is due to very weak and
split upper flow between a weak upper trough in the vicinity and a
broad upper ridge to the north over Ontario. Morning precipitation
is not out of the question because this type of pattern occasionally
allows the development of a weak low level jet as a forcing
mechanism. However the more likely outcome, especially from Thursday
on, is continued dry conditions.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 651 PM EDT Sat Sep 16 2017

VFR weather is predicted for the forecast period...although we
will need to monitor some potential local impacts. To start a
small risk for fog exists late tonight/early Sunday am. At this
time the risk looks limited because there will be some wind
around. Then Sunday afternoon the atmosphere becomes
unstable...especially inland. With a possible lake breeze
forming...a few inland TAF sites could see a nearby thunderstorm.
VCTS was added to the forecast.

&&

.MARINE...
Issued at 330 PM EDT Sat Sep 16 2017

South flow will cause choppy conditions again Sunday for areas north
of Grand Haven.  Expect a few three foot waves, but no headline is
expected.  After Sunday afternoon conditions improve as winds lessen
and become more easterly.


&&

.HYDROLOGY...
Issued at 1142 AM EDT Sat Sep 16 2017

Dry weather continues with no concerns for area rivers.

A cold front will bring chances for showers and a few
thunderstorms Sunday afternoon/evening. Widespread precipitation
is not likely, as the front continues to weaken and the best
support for rainfall is well off to the north. Another weak system
brings additional chances for light precipitation Monday night.

Overall rainfall amounts through the week are forecast at one-half
an inch or less.

&&

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

$$

SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...TJT
AVIATION...MJS
HYDROLOGY...JAM
MARINE...JK



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