Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 140729
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
329 AM EDT Sat Oct 14 2017

LATEST UPDATE...
Synopsis/Short Term/Long Term/Marine

.SYNOPSIS...
Issued at 315 AM EDT Sat Oct 14 2017

A storm system will track northeastward through the region today
through Sunday. This system will bring several rounds of showers
and thunderstorms with heavy rain at times. Flooding will be
possible. In addition some of the storms could be severe. Strong
wind gusts are expected on Sunday as the storm pulls away.

&&

.SHORT TERM...(Today through Monday)
Issued at 315 AM EDT Sat Oct 14 2017

Decided to go with a flood watch. Trends in the high res models
seem to support stalling the frontal boundary in my CWA with the
northward movement of the front less certain to occur. This is
because the mid to upper level winds remain fairly parallel to the
front. PWAT values are very unusual for this time of the year up
around 1.75 inches. Low lcls and thin deep cape support efficient
rainfall. Aloft diffluence is noted across the boundary into
tonight...enhancing the lift. With the boundary not moving
much...training is likely to occur. Concern for more than 4 inches
exists. Leaves may clog drains as well creating enhanced urban
issues.

Slight risk for severe weather into tonight. Impressive low level
wind fields are forecasted to develop...thus damaging winds seem
to be the main risk. Isolated Tor possible...but not much CAPE
down low.

Gusts over 40 mph look likely for Sunday. Will need to monitor the
wind advisory potential.  Will mention this in the HWO.



.LONG TERM...(Monday night through Friday)
Issued at 315 AM EDT Sat Oct 14 2017

Any lingering light pcpn Monday should end by Monday evening and
winds will become southwesterly by then. Min temps Monday night will
range from the upper 30`s over our far ne fcst area to the middle
40`s south. Frost is not anticipated given these temps and sw winds.

Fair wx will continue for mid to late week as a sfc high pressure
ridge takes hold of our wx pattern. Very persistent sw flow waa will
continue through the rest of the week and allow temps to undergo a
slow gradual moderating trend. Temperatures will average around 5 to
10 degrees above normal for this time of year from Tuesday through
Friday and high temperatures could reach the lower 70`s by late
week.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1130 PM EDT Fri Oct 13 2017

Conditions will gradually deteriorate from primarily VFR to MVFR
and then IFR overnight into Saturday morning from north to south
as low clouds and rain develop. On Saturday conditions will likely
remain IFR at our northern terminals (KMKG and KGRR) while
further south and east we expect conditions to be quite variable
from VFR to MVFR through the morning and afternoon with some IFR
at times with heaviest showers.

Thunderstorms will develop mid to late Saturday afternoon and
continue through Saturday evening and result in LIFR conditions at
times in heaviest rain and thunderstorms. Prevailing conditions
most of the time will be a mix of MVFR and IFR Saturday evening.
Stronger storms will also bring potential for gusty winds.


&&

.MARINE...
Issued at 315 AM EDT Sat Oct 14 2017

Will keep the gale watch going. Tight pressure gradient develops
ahead of and behind the deepening low that tracks through the CWA.
Not sure how strong the winds will be in the warm air
advection...but 925 mb winds top 40 knots by 06z.This will likely
need to be upgraded later this am.

&&

.HYDROLOGY...
Issued at 326 PM EDT Fri Oct 13 2017

We continue to expect a large area of 1 to 2 inch rainfall across
much of the forecast area with the most intense rainfall occurring
Saturday evening. There is potential for significantly greater
amounts in excess of 3 inches in spots, which could produce moderate
localized flooding. There is some disagreement about exactly where
the heaviest rain will fall.

Some of the larger scale forecast models place a broad swath of 2+
inch accumulation totals from Muskegon to Mount Pleasant, which
would mostly affect the Muskegon and Chippewa river basins. Some of
the finer scale convection allowing models place the greatest
precipitation farther south towards the I-94 corridor.

Ensemble river forecasts suggest that even with the greater rainfall
amounts, there remains a limited chance for achieving flood stage in
mainstem rivers in the affected basins. River advisories seem much
more probable.

The overall environment highly favors training or back building
convection which could produce rainfall rates of 1-2 inches per hour
and totals well over 3 inches in spots. Smaller streams, basins, and
urbanized areas could see significant flooding if overlapped by
these local areas of enhanced rainfall. Another factor that may
exacerbate nuisance flooding is the falling leaves that might clog
smaller drainage systems.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Flood Watch from 8 AM EDT this morning through late tonight for
     MIZ043>046-050>052-056>059-064>067-071>073.

LM...Gale Watch from this evening through Sunday evening for
     LMZ844>849.

&&

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...Laurens
AVIATION...Laurens
HYDROLOGY...TJT
MARINE...MJS



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