Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 230544
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
144 AM EDT Mon Oct 23 2017

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 310 PM EDT Sun Oct 22 2017

A slow moving cold front will cause showers to continue to develop
tonight. A strengthening area of low pressure will move north
along the boundary and cause rain to become heavy at times Monday
afternoon through Monday night. It will become windy and cooler
Tuesday with showers through the day.

&&

.UPDATE...
Issued at 807 PM EDT Sun Oct 22 2017

The evening update is a little early to handle the expiration of
the small craft advisory. Waves are still up to around 4 feet in a
few places but have been trending downward. The latest observation
from the buoy off of Ludington shows the waves have dropped 2 feet
there in the past hour and are now down to 3 feet. So...the
advisory was allow to expire.

I did bump up POPs tonight...especially NW zones. Radar does show
widespread showers over Lake MI with a large area developing
upstream over srn IL. Thus as the front slips southeast and stalls
out over the region...the rain in IL should move in later tonight.

&&

.SHORT TERM...(This evening through Tuesday night)
Issued at 310 PM EDT Sun Oct 22 2017

Main short term fcst concerns involve determining potential for
heavy rain Monday through Monday night into Tuesday.

The slow moving cold front moving in from the west will cause
showers to continue to develop from west to east across our fcst
area late this afternoon through tonight. This notion is supported
by rgnl radar trends, sref pops and a consensus of latest higher
resolution guidance such as the 3km nam.

A strengthening area of low pressure will move north and bring
portions of our area heavy rain Monday afternoon through Monday
night. We continue to prefer the 12Z ecmwf and ecmwf trends for
several runs now that have been consistent in showing that a
southern stream disturbance currently over the panhandle of Texas
will strengthen as it moves east.

It will then eventually get pulled north by the upper low/amplifying
upper trough over our region tomorrow. This leads to development
of a stronger sfc low and potential for heavy rain near to east
of US-131 tomorrow afternoon through tomorrow night where very
strong mid level pva will develop.

The area near to mainly east of a line from Mt. Pleasant to
Kalamazoo is most favored for highest rainfall totals of around
1.5-3 inches Monday through Monday night into Tuesday. Highest
end totals within that range will most likely occur over our
eastern fcst area around KLAN and KJXN as suggested by the 12Z
ecmwf.

Given the strength of moisture transport there Monday afternoon
and evening I would not be surprised to see locally higher totals
of around 4-5 inches for this event in our eastern fcst area. Our
going flood watch headline will remain unchanged. We considered
dropping Osceola and Mecosta counties from the watch but felt it`s
a close enough call to keep those counties in it at this time.

It will be windy and cooler Tuesday with numerous showers with the
upper low and trof axis overhead. Showers will linger Tuesday
night.

.LONG TERM...(Wednesday through Sunday)
Issued at 310 PM EDT Sun Oct 22 2017

he wet and unsettled weather will continue through the long term
along with below normal temperatures.

A moderately strong short wave is progd to dig the back side of the
upper long wave trough Wednesday. This will result in scattered
showers. Thursday should be dry as short wave ridging moves over the
state. Then, another trough moves south from Canada Friday through
the weekend. Scattered to numerous showers, especially along the
lake shore will prevail through Sunday.

Wednesday is probably going to be the coldest day with highs in the
upper 40s. Thursday could end up being warmer than the mid 50s highs
we have in the grids if the GFS verifies. It shows h8 temps near 10c
Thursday afternoon under the ridge. By Friday night, the system will
occlude as cold air wraps around the low and we`ll see cold
advection from the southwest from late Friday through Sunday. Both
Saturday and Sunday should be below normal temperature wise with
highs in the lower 50s.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 144 AM EDT Mon Oct 23 2017

A wet period with significant aviation impacts due to IFR/LIFR
conditions can be expected over much of the next 24 hours. IFR has
already arrived at KMKG and KGRR with rain showers with the
passage of the front. This will continue for the next couple of
hours, and will then start to creep to the SE. It will take a
while before IFR finally gets to KJXN, like toward 19z or so.
Cigs will remain rather stable once the IFR settles. Vsbys will
vary a bit depending on the intensity of the showers that move
through. The bottom line though is that conditions will be
IFR/LIFR.

We will see conditions improve slightly with regard to cigs late
in the period as the low moves far enough north to take the lowest
conditions with it. We are looking MVFR moving in toward the end
of the period. Winds will also come up as the low starts to move
away. We will start to see gusts in the 20-25 knot range also
later in the period.

&&

.MARINE...
Issued at 310 PM EDT Sun Oct 22 2017

The small craft advisory continues in effect through 8 pm this
evening from Holland northward. Wind speeds and wave heights will
subside overnight into Monday before ramping back up significantly
Monday night and especially on Tuesday when gales are likely to
develop.


&&

.HYDROLOGY...
Issued at 310 PM EDT Sun Oct 22 2017

Showers will spread into the area from the west through this
evening, with coverage of rain filling in overnight. This looks to
bring about a half-inch of rain to west Michigan by about 8AM Monday
morning. Rain may be moderate in intensity at times, but is not
expected to cause flooding overnight.

There should be a brief decrease in shower activity Monday morning
before another round of rain develops over Lower Michigan Monday
afternoon and lasts into Tuesday. Most locations look to receive at
least an additional inch of rainfall, but a north-to-south
orientated swath of heavier rain, with amounts of possibly 3 to 5
inches, is expected over the Lower Peninsula. At this time, it looks
like this heavier swath of rain will be located somewhere between
U.S. 131 and the Detroit-area. A Flood Watch therefore remains in
effect for counties generally east of U.S. 131. Localized flooding,
ponding on roadways, and rises in rivers, creeks, and streams could
occur within the area of heaviest rain. Confidence in the location
of the heaviest rain is not high, and refinements to the forecast
are still possible.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Flood Watch from this afternoon through Tuesday morning for
     MIZ039-040-045-046-051-052-057>059-065>067-072>074.

LM...None.
&&

$$

UPDATE...MJS
SYNOPSIS...Laurens
SHORT TERM...Laurens
LONG TERM...04
AVIATION...NJJ
HYDROLOGY...HLO
MARINE...Laurens



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