Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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292
FXUS63 KGRR 240556
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
156 AM EDT SUN JUL 24 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EDT Sat Jul 23 2016

Very warm and humid weather will continue tonight into Sunday.
Scattered showers and thunderstorms will develop Sunday and Sunday
night in the humid and moderately unstable airmass ahead of an
approaching cold front. Fair weather will return Monday through
Wednesday but it will remain very warm early to mid next week.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 330 PM EDT Sat Jul 23 2016

Primary short term fcst concerns involve determining convective
potential very late tonight through Sunday night.

A large area of showers and thunderstorms is noted well off to our
west from south central WI nw to eastern MN this afternoon. This
activity will stay west of our fcst area through the evening.
However we expect a larger and better organized MCS to develop
this evening across MN and WI on the nose of a 40-50 kt llj.

The relatively best chance for severe weather will be across WI
this evening. However the slowly weakening MCS will likely move
ese across Lake Michigan during the early morning hours Sunday and
should continue to diminish as it`s remnants move into our fcst
area Sunday morning.

We will maintain chc pops for redevelopment of scattered
convection later Sunday through Sunday night. However convective
potential tomorrow afternoon is largely contingent on evolution of
the MCS overnight.

There is potential for our area to have rather extensive cloud
cover around and scattered showers and a few storms Sunday morning
that would tend to limit instability. The severe weather threat
tomorrow looks quite marginal given weak to moderate instability
and potential for the airmass to be worked over by the morning
clouds and showers. Guidance trends suggest there will be weaker
lift with the approaching system and stronger upper dynamics pass
by well to our north across the upper midwest and the upper
peninsula.

There is still a chance for scattered convection Sunday evening
into Sunday night along and just ahead of the cold front. A high
pressure ridge will build in behind the front on Monday to produce
fair weather.

.LONG TERM...(Tuesday through Saturday)
Issued at 330 PM EDT Sat Jul 23 2016

Long term starts off Tuesday with quiet weather due to surface high
pressure and zonal flow aloft. A shortwave aloft will move through
the Great Lakes during the Wednesday night and Thursday time frame
which is when we have the highest chances for showers/storms in the
long term (40pct). At the surface a low is forecast to move through
the Great Lakes associated with the lead shortwave. The surface low
and trough aloft both deepen some as we head into the weekend. The
low depth and track is a bit uncertain though with GFS being a bit
further north. Forecast confidence out in the Fri/Sat time frame is
low. We currently have very low chances for light showers in the
forecast for Fri/Sat, but that could pivot either way as we watch
model trends. High temperatures through the period will start out
slightly above normal mid week, likely cooling a bit into next
weekend with the troughing.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 156 AM EDT Sun Jul 24 2016

VFR conditions are expected most of the time through this TAF
period, but occasional MVFR or even brief IFR will be possible in
an environment supportive of isolated to scattered thunderstorm
development. An area of stratiform rain was moving across Southern
Lower Michigan this morning, with clusters of thunderstorms across
far SW Lower MI and NW Indiana. Light rain is expected to impact
most sites over the next few hours. JXN will be the driest early
this morning.

Scattered thunderstorms have developed over Wisconsin, and that
activity is expected to drift east-southeast over Lower Michigan
after 08-09z. Additional thunderstorm development will be possible
as well. These storms could certainly result in occasional MVFR
vsbys. Aside from multiple storm chances today, winds will
increase out of the southwest after 14z. Gusts should be in the
20-25 kt range this afternoon.

&&

.MARINE...
Issued at 330 PM EDT Sat Jul 23 2016

Minimal wave heights of 2 feet or less are anticipated through
tonight. Southwest winds Sunday will increase to 15 to 20 kts and
result in wave heights building to 1 to 3 feet... perhaps as high
as around 4 feet at times up near Big and Little Sable points.

Scattered thunderstorms will pose a hazard to mariners very late
tonight through Sunday evening with higher waves in and near
storms. Patchy fog may also pose a hazard to mariners tonight
through Sunday.


&&

.HYDROLOGY...
Issued at 1256 PM EDT Sat Jul 23 2016

No river flooding is expected through next week. Up to three
quarters of an inch of precipitation is possible tonight into
Sunday night. A small chance of rain is also in the forecast
Wednesday through Friday. River levels are at or below normal for
this time of year, so this rain should not bring any rivers near
flood. Strong thunderstorms could produce localized rainfall
totals over 1 inch and lead to localized ponding of water.
Rainfall totals will probably vary substantially over short
distances.

&&

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

$$

SYNOPSIS...Laurens
SHORT TERM...Laurens
LONG TERM...Duke
AVIATION...EBW
HYDROLOGY...63
MARINE...Laurens



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