Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 011826
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
226 PM EDT SAT OCT 1 2016

LATEST UPDATE...
Long Term

.SYNOPSIS...
Issued at 311 AM EDT Sat Oct 1 2016

Low pressure will slowly spin across Lower Michigan bringing
occasional rain showers through the weekend. Fair weather will
arrive early next week as the low finally moves away.

&&

.UPDATE...
Issued at 945 AM EDT Sat Oct 1 2016

I updated the zones/grids to put significantly more detail in
where and when it would be raining. The HRRR and RAP model
continue, run after run to show the band of showers moving
westward across our now western CWA. That will move off shore by
noon. The area of broken clouds over northern Indiana will rotate
northward into our southern CWA (as the entire system continues to
drift northward) bringing more instability to area near and south
of I-96 by early afternoon. As a result I put isolated
thunderstorms back in the forecast for late morning into early
evening. Since a little sunshine would result in the instability
being surface based, cold air funnels are not out of the question
with these storms. I do not see another concentrate band of
showers crossing our CWA this afternoon or this evening but
scattered showers and isolated thunderstorms should be expected.

&&

.SHORT TERM...(Today through Monday)
Issued at 311 AM EDT Sat Oct 1 2016

Current radar loop looks remarkably similar to the past two
nights, with rain showers still streaming in from the southeast
into the SE forecast area as the upper cutoff low spins across
the Ohio Valley. It is slowly moving back north into Lower
Michigan before finally getting kicked east as longwave trough
moves into the western CONUS early next week.

Expect rain showers to continue into tonight and Sunday before
tapering off Sunday night as the occluded low moves out of the
forecast area. Marginally steep lapse rates this afternoon makes
diurnal enhancement of thunderstorms possible. We are seeing
cellular convection forming on radar south of the Ohio and Indiana
border already and expect this to move north today.

.LONG TERM...(Tuesday through Saturday)
Issued at 226 PM EDT Sat Oct 1 2016

The main issue for this forecast is the precipitation event for
Wednesday night into Friday as the next system from the Pacific
shears east into the Great Lakes. Seems likely we will have
showers and thunderstorms Thursday as the front comes through.
Showers will more than likely be just light rain showers Friday as
they will be lingering showers behind the cold front.

With the upper low out of the picture we have a short lived closed
upper level high over the Great Lakes Tuesday into Wednesday. This
should bring considerable sunshine and warming afternoon temperatures.
I still believe highs may be pushing 80 degrees over parts of
Southwest Lower Michigan Wednesday.

Both the ECMWF and GFS both continue to show a closed upper low
developing over Rockies by Monday that is sheared northeast due to
the next upstream Pacific system. This will bring the next system
through here Thursday. There is decent jet dynamics and moisture
with this system to I do believe showers and thunderstorms should
be expected as it moves through.

Bottom line is warm and dry Tuesday and Wednesday, warm and wet
Thursday then cooler and wet Friday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 154 PM EDT Sat Oct 1 2016

The area of clearing of the low ceiling continues to progress
northward this afternoon as forecast and as forecast convection is
developing where there is some sunshine. the showers are moving
northwest. I expect all locations to become VFR this afternoon.
The storms will be around but not concentrated enough to put in
the TAF explicitly so I put VCTS. If a storm gets close enough to
a TAF site I will update the forecast to reflect the storm moving
through that TAF site.

tonight winds area light and there should be enough breaks in the
clouds to allow fog to develop so I gave nearly all TAF sites ifr
conditions tonight. This may be slow to clear Sunday as winds
remain on the light side. Afternoon showers will be possible on
Sunday.


&&

.MARINE...
Issued at 945 AM EDT Sat Oct 1 2016

I have added water spouts back into our near shore forecast since
with the upper low drifting northward the instability will do the
same. Given the water is warmer than the air and the low to mid
level winds have decreased below 20 knots below 500 mb, any
convective elements developing or moving over the Near Shore could
result in water spouts development. Due to the northeast winds
and water spouts that do develop would move away from shore.


&&

.HYDROLOGY...
Issued at 1109 AM EDT Fri Sep 30 2016

The Sycamore Creek is nearing its crest over a foot above
bankfull, and will begin its slow recession which may modulated
by any additional rainfall Friday into Saturday. Other rivers
approaching bankfull the next few days include the Red Cedar above
Williamston, the Looking Glass near Eagle, and the Grand at Ionia.
The current forecasts are dependent on roughly another 0.75 inches
falling in those basins through Saturday morning. Will hold off
on flood advisories for those rivers until confidence is higher.

&&

.GRR Watches/Warnings/Advisories...
MI...None.
LM...None.
&&

$$

UPDATE...WDM
SYNOPSIS...Ostuno
SHORT TERM...Ostuno
LONG TERM...WDM
AVIATION...WDM
HYDROLOGY...CAS
MARINE...WDM


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