Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 161133
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
733 AM EDT Mon Jul 16 2018

LATEST UPDATE...
Update/Aviation

.SYNOPSIS...
Issued at 312 AM EDT Mon Jul 16 2018

A cold front located in Wisconsin will track southeast through
Lower Michigan today. This system will be triggering scattered
showers and thunderstorms as it pushes through. A large area of
high pressure will move in behind this system for Tuesday into
Wednesday.

&&

.UPDATE...
Issued at 727 AM EDT Mon Jul 16 2018

The area of developing shower around Van Buren County were
tracking off to the east. There is a signal in the High Res Models
that suggests they will keep developing as they move into the
Kalamazoo...Hastings and Battle Creek region. I bumped up POPs to
reflect the trends.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 312 AM EDT Mon Jul 16 2018

The main challenge in the short term deals with the timing and
strength of any storms.

Models continue to show the cold front located in Wisconsin early
the morning...tracking southeast through the CWA later this
morning and through the afternoon. The atmosphere out ahead of it
is rather unstable with ML CAPE values of 1000 to 1500 j/kg.
These values will only grow as the front arrives here in MI later
this morning into the afternoon hours. Some high res models have
been generating a few showers/storms early this morning out ahead
of the front here in SW Lower MI. Will feature low POPs to start
the day. Then this afternoon as the instability grows with the
front pushing in...will go with increasing POPs especially the
further east you go through the CWA. Given the stronger forecasted
instability along with a cap in place ahead of the front...it
appears the convection will be strong this afternoon. The
soundings shown an inverted v look down down...so damaging winds
will be the main threat.

.LONG TERM...(Wednesday night through Sunday)
Issued at 312 AM EDT Mon Jul 16 2018

The long term will begin under a dome of high pressure. We`ll see
one more night of cooler weather with lows in the lower to mid 50s
before a change develops for the weekend.

Both the ecmwf and gfs have been showing the development of an upper
trough and corresponding sfc low over the Upper MS river valley for
a few model runs. The 00z is no different and both of the models are
in pretty good agreement regarding the track of the sfc low across
Wisconsin and Michigan Thursday night through Saturday. Confidence
is growing that we`ll see widespread showers and storms during this
time. The upper trough has several short waves moving through it
which will enhance the chances of seeing some beneficial rain.

The system clears out by Sunday leading to dry weather.

&&

.AVIATION...(For the 12Z TAFS through 12Z Tuesday morning)
Issued at 727 AM EDT Mon Jul 16 2018

Showers and some thunderstorms will be tracking through the region
and TAF sites today as the cold front pushes through. Local
impacts are possible. Stronger storms may develop mid afternoon
around KLAN and KJXN...but they will not last long.

The wind shifts behind the front and the airmass dries out. There
could be a secondary frontal passage overnight...so will need to
monitor trends for a period of possible clouds and a local shower
or two. Considerable uncertainty exists on the development of any
showers tonight..and the forecast reflects dry conditions.

&&

.MARINE...
Issued at 312 AM EDT Mon Jul 16 2018

Behind the cold front the winds and waves will be
building...especially Tuesday. Forecasted conditions continue to
look hazardous for swimmers and boaters...Tuesday Afternoon into
Tuesday evening...especially south of Muskegon. There could be
another impactful wave event for this coming weekend.


&&

.HYDROLOGY...
Issued at 157 PM EDT Sun Jul 15 2018

River levels across the area are running near to below normal for
mid-July. Rainfall for the first half of July is running much below
normal at most locations in Lower Michigan.

Shower and thunderstorm activity Sunday afternoon and evening will
be limited, keeping most locations dry. A better coverage of showers
and storms is expected on Monday, especially as you start moving
east of US-131. High water content of the atmosphere will allow any
storm that develops to produce very heavy rain both Sunday and
Monday, with rainfall rates at or exceeding 1-2" per hour. Storm
motion will be slow, allowing heavy rain to last longer over a
single location. This could lead to localized flooding, especially
on roadways or in low-lying areas. Small creeks and streams may rise
rapidly where intense rainfall rates occur, but heavy rain will need
to occur over a fairly wide area to cause even the smaller creeks
and streams to spill out of their banks. Mainstem river flooding
(Grand, Muskegon, Kalamazoo) is not expected.

Dry weather is expected Monday night through Thursday. A wetter
pattern looks to emerge for the end of the week.

&&

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

$$

UPDATE...MJS
SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...04
AVIATION...MJS
HYDROLOGY...HLO
MARINE...MJS


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