Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 230821

Area Forecast Discussion
National Weather Service Grand Rapids MI
421 AM EDT TUE AUG 23 2016


Issued at 329 AM EDT Tue Aug 23 2016

One more sunny day with highs in the lower 80s, then a storm
system from the north Pacific will draw moisture north from the
Gulf of Mexico to bring showers and thunderstorms to the area
from Wednesday into Thursday. Mostly clear skies return for Friday
into Saturday before yet another storm systems bring the threat of
showers and thunderstorms back into the area once again.


.SHORT TERM...(Today through Thursday)
Issued at 329 AM EDT Tue Aug 23 2016

The main issue is timing the convection Wednesday into Thursday.
There is also a question of just how much rain will fall.
Otherwise today should be mostly sunny and pleasantly warm with
highs in the lower 80s.

There are two thing going on that will play into just how much
rain falls and where it falls Wednesday into Thursday. There is a
closed upper low Saskatchewan which is clearly seen in the water
vapor image loops that heads largely east. While that happens the
bermuda high expands west and north to try to push the system
farther northward. Since Southwest Michigan is on the northwest
side of the Bermuda high this puts brings the southern stream jet
core over this area Wednesday night into Thursday. It is the surge
of deep moisture ahead of that southern stream jet core that
brings the showers and thunderstorms to our area tomorrow. What
will be key to all this is that the models tend to open up these
closed upper lows to quickly. If that is true then we would get a
stronger wave on the front Thursday and that would greatly
increase the threat of thunderstorms.

My spin on this is we get to periods of thunderstorms, one with
the surge of deep moisture Wednesday during the day, then again
Thursday as the upper level system puts Southwest Michigan in the
entrance region of the upper level jet.

Since there is nearly 2 inches if precipitable water in the air
over us Wednesday night into Thursday we will have to watch
rainfall amounts given how wet it has been around there. It could
well be the models are way under playing the rainfall from this
next event.

.LONG TERM...(Thursday night through Monday)
Issued at 329 AM EDT Tue Aug 23 2016

The focus of the long term portion of the forecast will be rain
chances for late in the weekend into early next week. Until then, it
looks like quiet weather and seasonable temperatures can be expected
from Thursday night through Saturday.

The rain chances that exist in the short term portion of the
forecast should be pretty much gone by the beginning of the long
term on Thursday night. The main front should be through the area at
that time, sweeping the better moisture south of the state. We will
see upper ridging build in for Friday and Saturday. This combined
with a drier northerly flow becoming southeast will keep pcpn
chances low.

The chances of rain will start to increase Saturday night, but will
remain low as return flow will just start to ramp up at that time.
The best chance for the next bout of rain looks to come late
Saturday night into Sunday. Moisture return should be plentiful at
this time with increasing flow ahead of the next approaching upper

Rain chances will linger into next Monday, but do not look to be as
high as the Sunday time frame. The best moisture will be locked up
south of the state with the initial frontal passage. This front
could linger close enough to the area that a wave could ride along
it and spark a few showers/storms over the area on Monday.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 421 AM EDT Tue Aug 23 2016

No real concerns for aviation interests through 06z Wednesday.
Mainly clear skies can be expected through mid morning at all of
the terminals. Some cumulus development will take place by
afternoon with bases around 4k feet. As the cumulus development
takes place, winds will ramp up, especially toward KMKG. Wind
gusts at KMKG will be up around 20-25 knots, with less wind
further east. Cumulus development and winds will then diminish
toward sunset this evening. Some high clouds based around 20k will


Issued at 329 AM EDT Tue Aug 23 2016

The latest model runs suggest Small Craft Advisory criteria will
be meet today through tomorrow evening in all but the southern two
most Near Shore zones. However, the Port Sheldon buoy is close to
criteria now, so I extended the SCA one more zone group south to
cover that issue. I dropped the southern most zone group since it
seem the winds and waves do not get high enough there. I also
lined up the beach hazard statement with the SCA.


Issued at 300 PM EDT Mon Aug 22 2016

Fair and dry weather will continue through Tuesday evening. A
flood warning remains in effect for the Portage River at Vicksburg
where minor flooding remains possible. However the river level is
forecast to slowly fall to below flood stage by Thursday morning.

The next system will bring potential for around a half an inch to
inch of rainfall Wednesday through Wednesday night. This rainfall
could cause a new rise on the Portage River Thursday into Friday.


.GRR Watches/Warnings/Advisories...
MI...Beach Hazards Statement through late Wednesday night for MIZ037-

LM...Small Craft Advisory until 2 AM EDT Thursday for LMZ845>849.



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