Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 201747
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
147 PM EDT Fri Oct 20 2017

LATEST UPDATE...
Aviation/Hydro

.SYNOPSIS...
Issued at 312 AM EDT Fri Oct 20 2017

Dry conditions are expected into Saturday night. High temperatures
will be 10 to 15 degrees above normal Friday and Saturday with highs
in the lower to mid 70s. Sunday into next week will be unsettled
with frequent rain showers. Much of next week will also be
considerably cooler with highs in the 50s.

&&

.SHORT TERM...(Today through Saturday night)
Issued at 312 AM EDT Fri Oct 20 2017

No impact weather expected. Only change of note was to bump up
Friday and Saturday high temperatures to the mid 70s for much of the
area. This is a bit greater than model guidance and was done in
coordination with the Detroit and Gaylord offices.

Rainshowers are expected to have spread eastward into our waters and
western zones by early Sunday morning. Timing with this has been
quite consistent with successive model runs. Therefore, confidence
with timing the onset of this precipitation is currently good.

.LONG TERM...(Sunday through Thursday)
Issued at 312 AM EDT Fri Oct 20 2017

Confidence is high that we`ll see rain Sunday as a cold front moves
across the state. The gfs and ecmwf haven`t changed much in their
solutions. The gfs is still a bit quicker and the ecmwf continues to
develop a wave on the front over the souther U.S. before moving it
north along the frontal boundary. The change from yesterday is that
the bulk of the rain from this wave is now depicted over
southeast Lower MI. Thus the chances for significant
rainfall...over an inch...is lower than yesterday. Still think we
could see a third of an inch or so from this system Sunday.

Chances for thunderstorms aren`t zero Sunday, but aren`t high
either. LI`s fall to around 1c as the front passes through. There
may be a better chance at seeing convection along the lake shore
Tuesday when LI`s fall to around -2c. Lapse rates will steepen quite
a bit (~8c/km) when the colder air aloft moves over the warm lake
water. Opted to include a isolated mention of storms Tuesday
afternoon along the lake shore.

An impressive upper low will develop over the Great Lakes Mon-Wed
resulting in more showers and much cooler temperatures. This cool
down has also been well advertised by the models for several days
and highs in the 50s are expected Tue-Thu. We`re likely to see
temperatures fall into the 30s Tue night and Wed night.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 147 PM EDT Fri Oct 20 2017

VFR conditions will continue through Saturday. Southerly sfc
winds will be 10-20 kts during the day and 5-10 kts at night.

&&

.MARINE...
Issued at 312 AM EDT Fri Oct 20 2017

We have made some adjustments to the Small Craft Advisory. First,
it`s been expanded southward to Grand Haven based on WW3 guidance.
Second, we have made the beginning time earlier based on WW3
guidance and also on the Ludington buoy, which already has reported
4 foot waves north of Pentwater.

&&

.HYDROLOGY...
Issued at 147 PM EDT Fri Oct 20 2017

Dry weather will persist through Saturday. A cold front passing
through the region will then provide a high coverage of showers
Sunday and Sunday night. Rainfall amounts will generally run about
0.50 inches, but locally heavier pockets of rain will exist. These
pockets could bring rain amounts in excess of one inch. These
heavier amounts could cause rivers, creeks, and streams to rise,
especially in the Kalamazoo River basin where water levels are still
high following heavy rain last weekend.

The frontal boundary may then stall over either Michigan or the
Eastern Great Lakes Monday into Tuesday, and become a focus for
additional rainfall. This rainfall could potentially become heavy
(over an inch of rain) and could lead to additional rises in rivers,
creeks, and streams. Changes to the rainfall forecast Monday into
Tuesday are possible.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 8 PM EDT Saturday for LMZ847>849.

&&

$$

SYNOPSIS...TJT
SHORT TERM...TJT
LONG TERM...04
AVIATION...Meade
HYDROLOGY...HLO
MARINE...TJT



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