Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 210536
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
136 AM EDT Wed Jun 21 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 325 PM EDT Tue Jun 20 2017

Showers will gradually end late this afternoon and evening with
fair weather to follow for Wednesday. Showers and thunderstorms
are anticipated late Wednesday night into Thursday morning and
then again for late Thursday night. A cooler airmass will move in
behind the cold front for this weekend into early next week.

&&

.UPDATE...
Issued at 809 PM EDT Tue Jun 20 2017

The showers were pulling away from the CWA early this evening with
clearing skies behind. The combination of light winds and mainly
clear skies will lead to good radiational cooling. With recent
rain and somewhat elevated crossover temperatures...it looks like
we will see some fog developing. This has been added to the
forecast for tonight...after midnight.

The higher waves have pushed off to the southwest and values are
generally between 1 to 2 feet. With the pressure gradient
continuing to weaken tonight the waves should continue to
diminish.

&&

.SHORT TERM...(This evening through Thursday night)
Issued at 325 PM EDT Tue Jun 20 2017

Primary short term fcst concerns involve determining convective
potential late Wednesday night and again for late Thursday night.

A band of showers will continue to move ese across the rest of our
fcst area late this afternoon. An isolated thunderstorm is also
possible but convective potential is quite low due to weak
instability. Showers will taper off early this evening with fair
wx late tonight through Wednesday evening as a high pressure ridge
builds in.

An mcs will develop over northern WI Wednesday evening due to
forcing from a warm front and vigorous llj. This mcs will move
into our fcst area during the early morning hours Thursday. The
relatively best chc for convection will be over our northern fcst
area near to mainly north of I-96 as suggested by 12Z ecmwf
guidance.

We expect the MCS to be in a weakening/decaying stage by mid
morning Thursday with weakening lingering convection followed by
some lingering showers.

The best chance for more widespread convection across our fcst
area will come late Thursday night as a cold front moves through.
Forcing for convective initiation will come from the front and a
strong llj with ample low level moisture in place out ahead of the
front. Deep layer shear will be strong reaching 40-55 kts.
Therefore some strong to severe storms are expected Thursday
night. Vigorous 1000-850 mb moisture transport and precipitable
water values in the 1.75 to 2 inch range suggest that some heavy
rainfall is likely.

.LONG TERM...(Friday through Tuesday)
Issued at 325 PM EDT Tue Jun 20 2017

The long term period looks fairly quiet with below normal
temperatures.

The active sfc cold front is progged to move south of Michigan by
Friday afternoon, taking the showers and thunderstorms with it.
Cooler and drier air will be filtering in behind the front, with dry
weather likely Friday afternoon and night. Saturday will probably be
dry as well but there is a shortwave in the northwest flow aloft
progged, so a few isolated showers or storms can`t be ruled out
especially east of hwy 131 and the lake shadow.

The pattern Sunday through Tuesday looks quite similar to the
pattern we are currently in, with H5 troughing and cool air aloft.
This pattern supports the possibility of isolated to scattered
showers and possibly a storm each day, otherwise predominately dry
with pleasantly cool temperatures and low humidities for the end of
June.

At this time, the remains of Tropical Storm Cindy is progged to stay
well south of MI with the latest NHC fcst showing a 7 am Saturday
position over Kentucky. The Great Lakes Region should stay under the
influence of the nrn stream, steering the tropical system/remaining
moisture more east than north after Friday.

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 135 AM EDT Wed Jun 21 2017

Fog is our initial concern for the first few hours of the
forecast. There is a good chance for fog tonight with the rain
that fell this afternoon/evening and with winds becoming light. We
have gone with IFR conditions everywhere. The I-94 terminals are
expected to be worst as the rain lingered longer and there was
less drying before sunset.

Fog will dissipate quickly with the early sunrise for the
solstice. We will then see some diurnal cumulus develop toward
afternoon away from Lake Michigan. This should all be VFR so
limited impacts expected. Winds will likely stay under 10 knots
with a light gradient remaining in place.

Some mid clouds will stream in late in the period, ahead of
showers/storms that are expected to develop over WI. These storms
will likely hold off moving in until after this forecast period.

&&

.MARINE...
Issued at 325 PM EDT Tue Jun 20 2017

Wave heights will subside to around a foot or less tonight as
winds subside. Wave heights will remain below 2 feet Wednesday
through Wednesday evening with high pressure in control.
Thunderstorms will pose a hazard to mariners late Wednesday night
into early Thursday and again Thursday night.


&&

.HYDROLOGY...
Issued at 203 PM EDT Tue Jun 20 2017

Rivers levels are around to a little above normal for this time of
year. The Flat River near Smyrna may reach bankfull over night, but
is the only site expected to do so. Scattered showers and a few
thunderstorms will be possible today with less than a tenth inch
of rain expected on average. Additional heavier rains will be
possible Wednesday night through Friday and should lead to
additional rises on area river systems.

&&

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

$$

UPDATE...MJS
SYNOPSIS...Laurens
SHORT TERM...Laurens
LONG TERM...Meade
AVIATION...NJJ
HYDROLOGY...63
MARINE...Laurens



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