Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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297
FXUS63 KGRR 231746
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
146 PM EDT Sun Jul 23 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EDT Sun Jul 23 2017

Low pressure passing through the state today will bring scattered
showers and thunderstorms. High pressure will provide a stretch
of dry and less humid weather Monday and Tuesday before the next
front brings more scattered showers and storms later Wednesday
into early Thursday.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 330 AM EDT Sun Jul 23 2017

Combination of H5 upr low/shortwave and sfc cold front dropping
southeast through the Great Lakes Region will lead to scattered
convection today. Cape/shear profiles suggest the possibility of a
few strong to perhaps severe storms by afternoon, with SB capes
near 1500 J/KG and 0-6 KM shear around 35 knots.

However the latest RAP soundings have a rather dry look and it
will be somewhat of a race against time of building up enough
surface based instability before the west/northwest low level flow
off Lake Michigan develops and strengthens. Models do seem to be
a bit slower/less aggressive in this regard which suggests the
possibility of a longer window of time with decent sfc convergence
before the lake shadow spreads inland.

In general, the developing west/northwest flow off Lake MI should
tend to focus most convection east of Highway 131 by 18Z, and
east of U.S. 127 by 21Z. Mostly sunny skies should be sweeping
eastward off the lake as well this afternoon.

One other thing to watch for later today is the potential of a
stronger convective cluster that may impact the Chicago area which
could clip far srn Lake Michigan/Van Buren county.

Otherwise some other things of note in the short term include
areas of dense fog early this morning which will lift by mid
morning, and a potential for considerable clouds on Monday. The
presence of a thermal trough aloft and low level cyclonic flow
will probably result in considerable diurnal cloudiness, particularly
inland from Lake MI.

.LONG TERM...(Tuesday night through Saturday)
Issued at 330 AM EDT Sun Jul 23 2017

Main concern is thunderstorm potential late Wednesday into early
Thursday. Latest medium range guidance suggests a line of convection
will enter the area around or shortly after dark Wednesday night. As
noted already, there is sufficient forcing and instability for the
mention of thunderstorms. Storm intensity could depend chiefly on
when they occur relative to peak afternoon heating. Regardless, they
should progress rapidly through the area with little flood concerns
anticipated at this time.

After precipitation exits Thursday, dry conditions and seasonable
temperatures are expected to persist into Saturday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 142 PM EDT Sun Jul 23 2017

The atmosphere has destabilized through the day. A cold front will
push through the region this afternoon. The most favorable setup
for thunderstorms is inland...closer to the KLAN...KBTL and KJXN
TAF sites. I have included vcts for these site for a few hours
this afternoon.

A risk for low clouds and fog to redevelop exists tonight. The low
level humidity values will be relatively high to start the
evening. Then as we cool down...the fog and low clouds will likely
develop. The TAF sites will feature MVFR or lower conditions later
tonight.

&&

.MARINE...
Issued at 330 AM EDT Sun Jul 23 2017

Areas of dense fog over Lake Michigan this morning are expected
to mix out this afternoon with arrival of drier air/westerly
flow. Scattered storms will pose a threat to mariners, mainly
this morning. Rough conditions with waves up to 4 feet and north
winds to 20 knots will develop on Lake Michigan late tonight and
continue into Monday. Will have to monitor for the possibility of
Small Craft Advisory/Beach Hazard, but currently it`s borderline.


&&

.HYDROLOGY...
Issued at 111 PM EDT Sun Jul 23 2017

No flooding concerns for the next 7 days. A frontal passage
Wednesday night into Thursday may bring thunderstorms but this is
not the setup that favors high basin average rainfall amounts.
Therefore, the rivers should behave for the foreseeable future,
especially with a cooler and drier pattern likely to follow for
late in the week and weekend.

&&

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

$$

SYNOPSIS...Meade
SHORT TERM...Meade
LONG TERM...TJT
AVIATION...MJS
HYDROLOGY...Hoving
MARINE...Meade



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