Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 202346
AFDGRR

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

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EDT Fri Oct 20 2017

The warm and dry weather will continue into Saturday night before
bigger changes start to show up in the forecast. Another warm day is
expected on Saturday with highs into the 70s. A cold front will
swing through the area Sunday and Sunday night bringing a widespread
rainfall to the area. A change in the pattern is becoming more
likely early next week with a deep fall storm possible bringing high
winds and potentially heavy rain to the area.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 330 PM EDT Fri Oct 20 2017

Main focus in the short term is on the cold front that is forecast
to move through the forecast area Sunday afternoon and Sunday night.
The highest likelihood for rainfall will be during that time frame,
from midday on Sunday through Monday morning. Models are in good
agreement that rainfall totals will on the order of 0.20 to 0.40
with some areas seeing around a half inch.

There should be efficient rain production with surface dew points
rising to around 60 and PWAT values to around 1.50 inches. Deep
moisture is seen in both forecast soundings and plan view progs like
1000-700mb RH. Envision a fairly narrow band of rain, with embedded
heavier showers that will take 6-8 hours to move through any one
location.

Until Sunday we are looking at warm southerly winds continuing with
dry weather forecast. Highs on Saturday will be well above normal
once again up in the lower to middle 70s. The normal high for
Saturday in Grand Rapids is 58.

.LONG TERM...(Monday through Friday)
Issued at 330 PM EDT Fri Oct 20 2017

Confidence is increasing that a major fall storm will impact the
Great Lakes Region early next week, including the threat of
excessive rainfall on Monday and Monday night, followed by strong
winds Tuesday and Tuesday evening. Gale or Storm Warnings on Lake
MI, as well as some beach erosion and scattered power outages,
appear possible. Rather chilly air accompanied by numerous lake
effect/enhanced rain showers will rush in on Tuesday and remain
over the area into Wednesday.

Several runs of the ECMWF have painted a stripe of 2 to 5 inches
of rain across MI but have varied on the placement. While the
GFS still has not come on board with this idea, now the Canadian
model and more EC ensemble members are trending toward the
possibility of excessive rainfall Monday and Monday night. This
strongly FGEN forced precip is within the trowal of the deepening
system lifting north from the gulf coast. EC/Canadian solutions
are bombing this system out as roughly a 980 mb sfc low by the
time it gets into far nrn Lk Huron Tuesday afternoon.

While the cold air lifts out next Thursday, we will have to
monitor the possibility of a more noteworthy cold air outbreak
the weekend of 28 OCT and beyond. A significant/deep longwave
trough may settle into the central U.S. by that time, related to
the recurving typhoon the Pacific.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 747 PM EDT Fri Oct 20 2017

VFR conditions will continue overnight and through Saturday. Winds
will be southerly around 5 to 10 knots tonight and around 10 to 15
knots Saturday with some gusts to 20 knots during the late
morning and afternoon.

&&

.MARINE...
Issued at 330 PM EDT Fri Oct 20 2017

A prolonged period of stronger southerly winds are expected from
the current time through Sunday. We have a Small Craft Advisory in
effect from Grand Haven north up the lakeshore. With this
forecast issuance we are extending the expiration time of the SCA
through 800pm on Sunday. 3 to 6 foot waves look to be common, with
the highest waves occurring up near Big and Little Sable Points
Saturday night and Sunday when the pressure gradient tightens.
Waves up near the points during this time may reach 4 to 7 feet.


&&

.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 Sunday for LMZ847>849.

&&

$$

SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...Meade
AVIATION...Ostuno
HYDROLOGY...HLO
MARINE...Duke



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