Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 131813

Area Forecast Discussion
National Weather Service Grand Rapids MI
213 PM EDT Fri Oct 13 2017


Issued at 318 AM EDT Fri Oct 13 2017

Drizzle will end this morning and fair weather is expected
until this evening when showers will move into western Lower
Michigan. Thunderstorms with heavy rain can be expected for
Saturday and Saturday night as low pressure tracks across Lower
Michigan. Windy and cooler weather will arrive on Sunday.


Issued at 1059 AM EDT Fri Oct 13 2017

We have made some small tweaks to the forecast for today,
including going more optimistic with some sunshine for this
afternoon, which will result in some warmer temperatures.

The low clouds are being pushed and mixed out this morning as the
SSW flow aloft ahead of the strengthening system to our west moves
in. A short wave sfc ridge is building overhead which is helping
the clearing out this morning. We expect that much of the
afternoon will remain this way. This will allow for temps to
approach or exceed 70 degrees at many locations.

There is a chance very late in the period that a few showers may
sneak in over the far NW portion of the CWFA. This will be with
the cold front that is leaning in from the NW, and with the
moisture transport that will ramping up late.


.SHORT TERM...(Today through Sunday)
Issued at 318 AM EDT Fri Oct 13 2017

Forecast issues in the near term center around rain amounts and
thunder chances with the low tracking through Lower Michigan over
the weekend.

Drizzle and light showers will be lifting north today along with
area of warm advection/isentropic ascent, but lull in the wet
weather is brief as baroclinic zone sets up across the region
tonight and sfc low moves along it on Saturday, deepening on
Saturday night and pulling a cold front through on Sunday.

The best chance for convection and heavy rain will be on Saturday
afternoon and evening across the central and northern zones. There
will be some elevated instability, with total totals near 50. If
there is enough sfc heating on Saturday, thunderstorms could
become strong to severe as forecast profiles show 35 to 40 knots
of shear.

Storm total QPF is in the 1 to 2 inch range there and there could
be much higher amounts in areas where thunderstorms form as it
appears there will be favorable conditions for storms to train or
backbuild. The heavier rain moves east with the cold front Sunday
morning with breezy and much cooler weather behind the front for
Sunday afternoon.

.LONG TERM...(Sunday night through Thursday)
Issued at 318 AM EDT Fri Oct 13 2017

Once the system is through we will see sharply colder air dipping
into the region Sunday night and lingering through Monday night as
the upper flow becomes northwesterly.  The models continue to trend
colder with this air as H8 temps are now shown to drop to around -2C
Sunday night.  Many overnight lows Sunday night into Monday morning
will reach the 30s.  However there does appear to be a fair amount
of clouds and wind where frost should not form.  Monday`s highs will
only be in the mid and upper 50s.

The center of high pressure should drift to our south, with a warmer
return flow developing by Tuesday.  Highs should largely be in the
60s during the Tuesday through Thursday period.

The only chance of rain in the extended period should come Wednesday
night or into early Thursday.  A weakening cold front will be coming
into the surface and upper ridge, so some light pcpn will be
possible then.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 213 PM EDT Fri Oct 13 2017

MVFR to VFR is expected through this evening, then cigs/vis will
fall to IFR between 04Z (at MKG) and 12Z (at JXN). Periods of LIFR
may occur around MKG and GRR in the early morning hours. Southwest
winds will relax this evening but will generally be light
east/southeast tonight into tomorrow morning. Rain showers,
perhaps moderate intensity at times, can be expected tonight into
tomorrow. TS may have be included after 06Z in future TAFs.


Issued at 318 AM EDT Fri Oct 13 2017

Winds and waves will be on the increase over the weekend and a
Gale Warning may be needed for Saturday night and Sunday.


Issued at 1235 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 early Saturday night. 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.

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 fallen leaves that might clog
smaller drainage systems.

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 at this point, but this is highly contingent on 48
hour QPF, which is subject to change as we get closer to the


LM...Gale Watch from Saturday evening through Sunday evening for



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