Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 141843

Area Forecast Discussion
National Weather Service Grand Rapids MI
243 PM EDT Mon Aug 14 2017

Synopsis/Short Term/Long Term/Marine

Issued at 243 PM EDT Mon Aug 14 2017

A few spotty showers and storms will remain possible for areas
mainly east of U.S.-131 this afternoon. These are not expected to be
too strong. Additional showers and storms are expected to move in
late this evening and overnight tonight. The best chance for more
widespread rain will be along and south of I-96. Again, storms are
not expected to become severe. Rain will move out early Tuesday,
with clearing then taking place.

The next chance of rain will then come Wednesday night through
Thursday as the next system moves through the area. Showers will
linger into early Friday before conditions dry out and cool down.


.SHORT TERM...(This evening through Wednesday night)
Issued at 243 PM EDT Mon Aug 14 2017

Our main items of interest include residual storms this afternoon,
rain potential tonight, and then rain trends for Wed/Wed night. Our
main changes in the forecast include higher rain chances tonight
down south, and a delay in rain chances Wed/Wed night.

A few showers and storms have gone up this afternoon as expected
across interior portions of Central Lower. These have fired along a
convergence zone where the lake breeze/shadow from Lake Michigan is
meeting up with the srly flow inland. Storms are pulsing up and
down, likely due to the thin CAPE profile evidenced by fcst
soundings. These will continue to be possible along this convergence
line, and will likely gradually shift east until they diminish
toward sunset.

We have increased the rain chances for areas along and south of I-96
for tonight. Models are in fairly good consensus in bringing a swath
of rain, some decent amounts, late this evening and overnight. This
is the result of a stronger surge of moisture transport via a 30
knot llj, aimed at the srn half of the area. These storms will be
elevated in nature, with thin CAPE profiles once again. Some heavier
downpours will be possible, but we are not expecting much wind or
hail with these. Rain will come to an end early Tuesday, with
clearing taking place as the system moves east of the area.

The next chance of rain then comes very late Wed afternoon, and Wed
night. We will see ridging move by just north of the area from late
Tue into Wed giving us dry weather and seasonable temperatures.
Return flow will start to increase on Wed behind the front, but this
has been trending slower with time. The slower trend is likely as a
result of the system organizing to our west being a bit stronger. We
will have chances Wed night, but the latest trends would even push
the best rain chances to Thu.

.LONG TERM...(Thursday through Monday)
Issued at 243 PM EDT Mon Aug 14 2017

During the extended period...the flow pattern in the middle
atmosphere will transition from a blocking pattern with a low over
Quebec to a more summerlike pattern...with a high over Texas and
most of the significant short wave energy well north into Canada.
This will result in above normal temperatures for West Michigan...
especially next week.

The best chance for precipitation locally will be Thursday into
Thursday night.  Severe potential continues with this system as it
rotates through the region.

High pressure will be in control for most of the weekend...with
another system poised to move into the region later Monday into

Highs will range from mid 70s north to lower 80s south on the mid and upper 70s Friday and Saturday...warming to
lower 80s by Monday.

Lows will range through 60s on Thursday the lower 60s
Friday...and from the middle 50s to near 60 Saturday and Sunday.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 117 PM EDT Mon Aug 14 2017

Visible satellite shows cumulus field continuing to develop this
afternoon. Looking out the window...cumulus have some vertical
extent. Water vapor imagery shows a plume of higher moisture over
northern Illinois heading in our direction. An area of showers had
developed in Central Michigan over the past half hour...moving
northeast. A few returns were also noted along the western shore
of Lake Michigan.

Main issue for the 18Z TAFs is precipitation wording this
afternoon. Agree with widely scattered coverage as depicted by
short range models. Opting for VCTS wording...but reserve the
right to make a last minute adjustment. KGRR and KLAN appear to be
the prime candidates for stronger precipitation wording for this

After a bit of a lull this evening...rain chances increase again
after 06Z stronger wave moves through the region.
Rain should end from west to east between 12Z and 15Z Tuesday.

Model soundings indicate low cloud potential overnight...targeting
areas that receive rain this afternoon. Definitely something to
keep any eye on this afternoon and evening...but not enough
confidence to insert into this set of TAFs.


Issued at 243 PM EDT Mon Aug 14 2017

No marine headlines expected through Wednesday at this time. Winds
should remain fairly limited through most of Wednesday, except for a
brief possible uptick Tue afternoon/evening on the backside of the
system moving through tonight. We expect winds should stay below 20
knots with that increase.


Issued at 1144 AM EDT Mon Aug 14 2017

Isolated to scattered showers may result in a brief dampening of
the ground in localized spots this afternoon. Better chances for
rain will come in overnight tonight and early Tuesday morning.
Measurable rainfall of around one-tenth of an inch may fall. Some
locations could receive a couple of tenths of beneficial rainfall.

A more active pattern is expected to setup for the midweek period
as a result of a strengthening wave that passes over the Great
Lakes Region. A deepening trough may result in showery activity
toward next weekend. It is possible for 5-7 day totals to approach
an inch or more in spots. Given recent dry weather, growing
moisture deficits, and near/below normal river levels, flood
concerns remain low.




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