Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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760
FXUS63 KGRR 182252
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
652 PM EDT Fri Aug 18 2017

LATEST UPDATE...
Marine

.SYNOPSIS...
Issued at 328 PM EDT Fri Aug 18 2017

Skies will remain mostly cloudy tonight into Saturday.  Scattered
showers and perhaps a clap of thunder will move in mainly after
midnight, then end Saturday morning.  Clearing skies can be expected
into Saturday afternoon, which will lead to a quiet Saturday night
through Sunday night time frame.

Another period of showers and storms will be possible Monday and
Tuesday, before drying out again for the remainder of the work week.
Temperatures will remain near or a bit above normal through Tuesday,
with daytime highs mainly 80 to 85.  Then we should cool into the
70s for Wednesday through Friday.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 328 PM EDT Fri Aug 18 2017

A deepening short wave will cross SW MI late tonight into early
Saturday.  A few showers and storms will be scattered about with
this feature, then the rest of the short term will be dry.

The short wave has showers and a few storms with it over MN/IA/MO
this afternoon.  These will move east and arrive into SW MI after
03Z.  The highest concentration of pcpn should be over the far
southern CWA toward I-94, but I have introduced low POPs over the
Northern CWA due to the large north/south sprawl of pcpn that the
wave has with it as of this afternoon.

The wave will be over the CWA at 12Z Sat, so expect the scattered
showers to linger into Saturday, especially south and east of GRR.
However as the wave heads east we will see clearing skies from west
to east toward the noon hour.  All areas should become mostly sunny
through the afternoon, making for a nice ending to the day, with
highs in the upper 70s to around 80.

High pressure builds in behind the system for Saturday night and
Sunday.  Sunday will be a touch warmer, in the low and mid 80s, with
plenty of sunshine.  Clouds will increase from the NW Sunday night
as a cold front is expected to reach Central WI by daybreak Monday.
Pcpn is expected to hold off until at least Monday as this should be
a slow moving front.

.LONG TERM...(Monday through Friday)
Issued at 328 PM EDT Fri Aug 18 2017

Two issues to focus on in the extended, first is the cloud forecast
for the partial solar eclipse that will be visible across west
Michigan Monday afternoon and then the potential for severe
thunderstorms on Tuesday.

For Monday, the sfc high is retreating and a broad area of warm
advection is setting up with showers and thunderstorms forecast to
form Sunday night across Wisconsin in area of mid level isentropic
ascent north of a warm front extending from Nebraska to southern
Wisconsin. These storms should dissipate as they move east Monday
morning with the weakening of the low level jet, but additional
storms are expected to fire up by the late morning across Wisconsin
and move east, reaching western zones during the afternoon.

At this point, model forecast soundings show the potential for a
layer of mid to high clouds during the afternoon that could at least
partially obscure the eclipse across western Lower Michigan. This
will in large part depend not only on the timing for the daytime
convection, but the amount of debris clouds remaining from the
previous night`s storms. Overall it appears the better viewing
conditions will be further east across Lower Michigan as the clouds
are moving in from the west.

One thing worth mentioning here is that even thick cirrostratus
clouds wouldn`t necessarily ruin the show as the partially eclipsed
sun may still be visible, but if combined with even a thin deck of
mid level clouds such as a layer of altocumulus could obscure it.

For Tuesday, flat upper ridging begins to get replaced by an
amplifying trough and impressive height falls for this time of year
occur late Tuesday into Wednesday. This is attended by strong speed
shear and if there is enough instability Tuesday afternoon and
evening, a line of strong to severe storms could form along or out
ahead of the cold front.

Cooler and dry weather follows for the rest of the week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 152 PM EDT Fri Aug 18 2017

West winds will gust over 20 knots at times this afternoon then
decrease to less than 10 knots this evening. There will be areas
of ceilings with bases around 3280 feet this afternoon then VFR is
expected this evening.

Low stratus with ceilings around 1500 feet are possible early
Saturday morning along with visbys in the 3 to 5 mile range but
conditions should improve to VFR by 18Z Saturday.


&&

.MARINE...
Issued at 652 PM EDT Fri Aug 18 2017

Canceled the marine headlines as conditions were improving early
this evening. This diminishing trend will continue through
tonight.

&&

.HYDROLOGY...
Issued at 329 PM EDT Thu Aug 17 2017

Rivers continue running well within their banks and that is the
expectation this weekend as well. The flows at most sites are near
to below normal. Rises on at least the small rivers and streams look
possible for the middle of next week based on medium range guidance
QPF. An inch or more of rainfall is certainly a possibility Monday
night into Tuesday night.

&&

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

$$

SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...Ostuno
AVIATION...Ostuno
HYDROLOGY...Hoving
MARINE...JK



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