Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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755
FXUS63 KGRR 212341
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
741 PM EDT Sat Oct 21 2017

LATEST UPDATE...
Update/Aviation

.SYNOPSIS...
Issued at 330 PM EDT Sat Oct 21 2017

Rain will move into Lower Michigan on Sunday afternoon as a cold
front slowly advances east. Low pressure moving north along the
front will bring some heavier rain Monday afternoon and Monday
night before windy and cool weather arrives on Tuesday and
Wednesday.

&&

.UPDATE...
Issued at 736 PM EDT Sat Oct 21 2017

The forecasts were updated to reflect potential for sprinkles
mainly for western parts of the CWA. Holland reported some light
rain. High res guidance shows the potential persisting for a few
hours this eve.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 330 PM EDT Sat Oct 21 2017

Forecast challenge is for Monday and Monday night with potential
heavy rain during that period. Also have to pin down timing for
arrival of showers on Sunday.

For Sunday...arrival of POPs was slowed a bit as dry air holds on
into the afternoon across eastern zones, where max temperatures
were also bumped up a bit. The QPF should be relatively light with
the front until the low moving up along the front arrives on
Monday.

For Monday and Monday night...slug of heavy QPF expected as low
moves north with some embedded thunder possible as total totals
approach 50. Precipitable water is approaching 1.75 inches which
is impressive for late October. Expect an inch or two across
eastern zones with higher amounts possible. Excessive rain of 3 to
5 inches is possible across the SE CWA if warm conveyor belt
feature stalls there for several hours.

.LONG TERM...(Tuesday through Saturday)
Issued at 330 PM EDT Sat Oct 21 2017

A high wind event is still a good possibility on Tuesday as Canadian
and EC solutions continue to show a deep 980 mb sfc low in the
vicinity of nrn Lk Huron. If this scenario verifies, Gale or Storm
force winds and waves in excess of 12 feet could lead to beach
erosion/lakeshore flooding given the above average Lk MI water
levels. Also scattered power outages could occur.

In addition to the winds on Tuesday, guidance suggests the
possibility of another inch or more of rain due to the mid level
deformation zone persisting over the area working in concert with
lake effect/enhancement as subzero H8 temps pour in. Highest
additional amounts expected to be near and west of Highway 131.

The boundary layer will remain too warm to support snow but some wet
flakes cannot be totally ruled out Tuesday night in the higher
elevations up north. Highs Tuesday should occur early then falling
into the 40s. Highs Wednesday will probably stay stuck in the 40s.

System is booted out later Wednesday and warm advection commences
quickly on Thursday as the next upstream trough begins to take shape
and dig into the north central United States. Any lingering showers
Wednesday should diminish/end by evening, with highs back into the
50s to near 60 Thursday.

Strong signals for a significant cold snap and potential first
widespread freeze next weekend or perhaps more toward Halloween.
This would be with the big deep longwave trough which is carved out
over the center of the nation, a typical occurrence a week or so
after a recurving typhoon in the Pacific as we have now. We could
see the season`s first snow showers 7-10 days from now.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 736 PM EDT Sat Oct 21 2017

An increased risk for LLWS overnight as the surface winds weaken
and the winds up around 2k feet stay strong.

Scattered to broken VFR clouds to prevail through the period. A
few sprinkles will be around tonight...then a band of rain will
try to track in from the west Sunday afternoon...but it will
struggle to move in as it encounters the low level dry airmass in
place here in MI.


&&

.MARINE...
Issued at 330 PM EDT Sat Oct 21 2017

South winds will continue to build waves higher than 4 feet north
of Holland through Sunday evening and there are no changes to the
current Small Craft Advisory.


&&

.HYDROLOGY...
Issued at 155 PM EDT Sat Oct 21 2017

Showers will spread into the area from the west Sunday and Sunday
night as a cold front begins to track through the Great Lakes. Rain
may be moderate at times in intensity, but is not expected to lead
to flooding. Total rainfall through 8AM Monday will be up to one-
half inch.

An area of low pressure will lift northward along this frontal
boundary, allowing an area of heavier rainfall to develop late
Monday through Tuesday over the Great Lakes. While confidence in
this scenario is increasing, the precise location of where the
heaviest swath of rain will occur, where amounts could exceed 2
inches, is still uncertain. Latest forecast guidance places a north
to south-orientated band of heavier rain totals anywhere from Lake
Michigan to eastern Ohio. Localized flooding and rises in rivers,
creeks, and stream could occur in this swath. The potential for
heavy rainfall across the western half of Michigan late Monday
through Tuesday will continue to be monitored.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 8 PM EDT Sunday for LMZ846>849.

&&

$$

UPDATE...MJS
SYNOPSIS...Ostuno
SHORT TERM...Ostuno
LONG TERM...Meade
AVIATION...MJS
HYDROLOGY...HLO
MARINE...Ostuno



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