Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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171
FXUS63 KGRR 142336
AFDGRR

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

LATEST UPDATE...
Aviation

.SYNOPSIS...
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
Tuesday.

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

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

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 736 PM EDT Mon Aug 14 2017

At this point all TAF sites are VFR and anticipate they will
remain so till around 06z or so. There is a northern stream
shortwave currently moving through WI/MN with showers and some
thunderstorms. This area will move through our TAF sites between
06z and 12z. Looking at an ensemble of most of the high
resolution models it looks like all of our TAF sites will see
showers overnight. It is questionable if there is enough
instability for thunderstorms, so I put VCTS and called that good
for now. There is also a cold front pushing south behind the
surface wave that moves through this area early Tuesday morning.
The combination of the rain and the cold front will more than
likely result in some MVFR or even IFR cigs around sunrise
Tuesday. The push of cooler and dry air is strong enough so that
skies should clear by late morning at all of our TAF sites.

The bottom line is VFR till 06z, MVFR with showers and isolated
thunderstorms from 06z till around 12z, then clearing by 16z.

&&

.MARINE...
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.


&&

.HYDROLOGY...
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.

&&

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

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...MWS
AVIATION...WDM
HYDROLOGY...JAM
MARINE...NJJ



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