Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 130718
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
318 AM EDT Fri Oct 13 2017

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

.SYNOPSIS...
Issued at 318 AM EDT Fri Oct 13 2017

Drizzle will end this morning and fair weather is expected
until Saturday afternoon when showers and thunderstorms will
be around as low pressure tracks across Lower Michigan. Windy
and cooler weather will arrive on Sunday.

&&

.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 06Z TAFS through 06Z Friday night)
Issued at 1244 AM EDT Fri Oct 13 2017

Conditions continue to range from VFR to IFR across the region,
making for a difficult forecast. In general expect much of the
overnight to remain MVFR, but occasional periods of IFR will be
mixed in. So overall little change until late morning when more
wind/mixing it expected and the lower ceilings and vsbys will
lift/improve.

A VFR period is expect from late morning through the afternoon.
Then the I-96 TAF sites should trend back to MVFR into the
evening, while the VFR should be maintained closer to I-94. Some
showers should move into the I-96 TAFs toward the end of this
forecast period, 06Z.

As mentioned above, the winds will increase by late morning and
continue through the afternoon, with SSW wind around 10 knots.
This will lessen again toward evening.

&&

.MARINE...
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.

&&

.HYDROLOGY...
Issued at 1236 PM EDT Thu Oct 12 2017

We are monitoring the potential for heavier rains and possible
flooding for this weekend. A frontal system settling over the area
beginning Friday night and lasting into Sunday will bring multiple
periods of rain.

Precipitable water values will be about as high as possible by
mid-October standards with values over 1.5 inches expected. This
will bring the potential to see locally heavier downpours, and
some narrow bands of heavier accumulations through the period.
The axis of the heaviest rain for now looks to occur generally
north of a line from South Haven to Saginaw Bay. This is still
subject to change depending on where exactly the front sets up.
Right now, heaviest amounts looks to be over 2 inches, with some
areas possibly seeing locally up to 4 inches.

Thankfully this is displaced a little north from the heavier
rains earlier this week. We still could be looking at some minor
flooding.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

SYNOPSIS...Ostuno
SHORT TERM...Ostuno
LONG TERM...JK
AVIATION...JK
HYDROLOGY...NJJ
MARINE...Ostuno



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