Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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911
FXUS63 KGRR 282326
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
726 PM EDT THU JUL 28 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EDT Thu Jul 28 2016

A weak system is expected to move across Southern Lower Michigan and
Northern Indiana and Ohio through the weekend. Although this system
is weak, it will keep chances for showers and a few storms in the
forecast through Saturday night. Favored areas for rain through
Saturday night will be along and south of I-96. Clouds and a few
showers will tend to keep temperatures down some with highs reaching
only the 70s to lower 80s.

Conditions should dry out then for the second half of the weekend
and early next week as high pressure builds in behind the weekend
system. Temperatures will gradually warm up next week.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 330 PM EDT Thu Jul 28 2016

Our main focus in the short term is on rain chances through the
period. It looks like a prolonged threat of rain for especially the
srn half of the cwfa with limited thunder chcs. It will not be
raining all of the time, but the chc will be there for the majority
of the period through Sat night.

A few showers/storms are starting to go up along the lakeshore as of
19z this afternoon. These are partially being fueled by the lake
breeze which is starting to come onshore, and also with an upper
wave that is approaching the Quad Cities area. The best threat of
convection for SW Lower will be the wrn half due to the lake breeze
focus. Some of these will try to drift to the east, but will lose
much of their fuel this evening before making it too far east. The
biggest threat with these storms will be locally heavy rain with a
lack of shear and being slow movers.

The wave approaching the area will keep a few showers around through
the night. Thunder chances will remain, but will be rather limited
with diminishing instability after dark.

We will see a somewhat similar set up on Friday through Saturday.
The long wave trough will only slowly crawl to the E/SE with
embedded short waves moving through the trough. The upper waves are
fairly open, but the 850 mb and sfc lows are barely closed off. The
nrn periphery of these features will continue to feed the moisture
in, and work with the upper waves to produce the showers/storms. The
favored area will once again be the srn portion of the area. The
best instability will remain south and deep layer shear will remain
below 20 knots, so severe weather is not likely.

The back end of the upper trough/low level lows will finally rotate
out of the area late Saturday night. Some showers will linger early,
and then move out late.

.LONG TERM...(Sunday through Thursday)
Issued at 330 PM EDT Thu Jul 28 2016

Upper level troughing should be gradually lifting out of the area on
Sunday, with height rises following through midweek. Will go with a
dry fcst Sunday and Monday. However with northwest flow lingering
aloft and the potential for additional weak shortwaves coming
through a few isolated showers/tstms cannot be completely ruled out
on any low level convergence zones during pk heating. The subsidence
and dry air associated with the sfc high should seriously limit that
potential and coverage - so really only a 10 pct chance and hardly
worth mentioning.

Warm advection pattern gradually lifts toward the area from the
southwest by mid week, so shower and tstm potential returns for
Tuesday through Thursday. However the flow is weak and ridging is
shown aloft Tuesday-Wednesday, so coverage those days should be
rather limited. The best risk of storms at this time appears to be
on Thursday when an active frontal boundary and height falls
approach from the northwest.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 723 PM EDT Thu Jul 28 2016

The storms are expected to gradually weaken over the next hour to
two as they track slowly inland. There still could be some local
impacts from this convection.

Will keep the VFR going for tonight...although with the recent
rain a risk for fog development exists. This potential will need
to be monitored through the night.

It does look like a risk for another round of afternoon storms
exists on Friday. I did go with VCTS with this
forecast...generally beginning 19z to 20z.

&&

.MARINE...
Issued at 330 PM EDT Thu Jul 28 2016

We do not expect any marine headlines to be needed right on through
the upcoming weekend and into early next week. There is a bit of
wind today across the nrn marine zones with waves coming up to 2 to
4 feet. We expect that the gradient will weaken tonight and remain
around or below 15 knots through the weekend.


&&

.HYDROLOGY...
Issued at 200 PM EDT Thu Jul 28 2016

Wednesday`s thunderstorms in Central Michigan produced isolated
totals over 2 inches according to radar estimates, which fell in SW
Mecosta County and west-central Clare County. While much of the
water was likely absorbed, some has run off into the rivers of the
Muskegon Basin. Slight rises are noted at Evart and Oak Grove, and
that is all that is anticipated.

Showers and storms this afternoon and evening could produce locally
heavy rainfall totals as well. This time the greatest risk is
farther west and south... focused closer to Lake Michigan and in
areas south of I-96. Weak vertical shear will produce slow-moving
pulse-type storms which will propagate off their own outflow, as is
currently occurring in N Illinois and S Wisconsin. Surface dew
points are still in the mid 60s, and there is greater moisture in
the upper levels versus yesterday. Precipitable water values are
around or over 1.5 inches which is about the 90th percentile for
late July. Brief heavy downpours are expected with today`s storms
but localized areas may see a more persistent duration of rainfall
where updrafts persist. Therefore localized heavy rainfall amounts
will have to be monitored, which may lead to temporary urban and
poor drainage flooding.

&&

.GRR Watches/Warnings/Advisories...
MI...None.
LM...None.
&&

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...Meade
AVIATION...MJS
HYDROLOGY...CAS
MARINE...NJJ



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