Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 230858 CCA

Area Forecast Discussion...CORRECTED
National Weather Service Grand Rapids MI
458 AM EDT Sun Jul 23 2017

Synopsis/Short Term/Long Term/Marine

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 06Z TAFS through 06Z Sunday night)
Issued at 202 AM EDT Sun Jul 23 2017

High confidence for widespread IFR and occasional LIFR conditions
through 12Z, although onset may be slightly delayed farther east
at LAN terminal. We are much less certain after 12Z, but the
general expectation is for a rise to VFR visibilities / MVFR
ceilings with the possibility for thunderstorms moving southeast
into the area before 18Z. After 18Z, VFR should predominate with
scattered thunderstorms in the vicinity. Gusty winds with storms
will be more likely farther east around JXN and LAN terminals.


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.


Issued at 1123 AM EDT Sat Jul 22 2017

We again escaped the heavy to excessive rain that fell in
southern Wisconsin and northern Illinois. While that area floods,
most of our area continues to run drier than normal these past 1
to 2 weeks. With high atmospheric water vapor content, the showers
Saturday morning efficiently put down over a half inch of rain but
only in a few isolated spots. Scattered showers or storms Sunday
will provide only spotty relief to the dry weather. After that, the
next potential for a storm will be Wednesday.




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