Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 150728
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
328 AM EDT Sun Oct 15 2017

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

.SYNOPSIS...
Issued at 318 AM EDT Sun Oct 15 2017

A deepening low pressure system will track through Lower Michigan
today. The heavy rain that fell on Saturday and through early this
morning will pull away from the region leaving behind flooding for
parts of far Southwest Lower Michigan. Strong wind gusts will
accompany this storm and power outages are possible today. An area
of high pressure builds eastward in the the Central Appalachians
on Monday and Tuesday resulting in mainly dry weather for here in
Michigan.

&&

.SHORT TERM...(Today through Tuesday)
Issued at 318 AM EDT Sun Oct 15 2017

Will cancel the flood watch slightly early. The axis of heaviest
rain was pushing away from the region. Still very heavy rain fell
and many counties are under flood warnings or advisories through
the day today.

Will maintain the wind advisory. There is somewhat less confidence
on how widespread the event will be. However with strong low level
winds winds and cold air advection we could see some gusts over 40
mph...especially on the lakeshore. The HRRR was showing gusts over
40 mph at some point for much of the region today.

Impact potential looks limited after today.


.LONG TERM...(Tuesday night through Saturday)
Issued at 318 AM EDT Sun Oct 15 2017

A consensus of latest 00z medium range guidance continues to
indicate that fair wx will continue mid to late week into next
weekend. In addition temperatures will undergo a gradual moderating
trend mid to late week as sw flow warm air advection remains very
persistent through then into next weekend.

High temperatures will reach well into the 60`s to lower 70`s for
mid to late week with the mildest wx anticipated for Thursday
through Saturday as an upper level ridge amplifies over our region
and h8 temps moderate. This will be around 10 to 15 degrees above
normal for this time of year.

We concur with the previous shift that 00z numerical guidance maxes
are a little conservative late in the week. Given the evolution of
the sfc/upper level pattern and anticipated h8 temps by then and
continued sw flow high temps may reach well into the 70`s by
Thursday through Saturday.

Latest medium range guidance consensus still suggests that the next
chance for any pcpn will hold off until Sunday as a weak cold front
moves in from the west.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 116 AM EDT Sun Oct 15 2017

The last wave of showers and storms will passing through the CWA
over the next couple of hours. The TAF sites should see the last
of the rain by 09Z. Thereafter the region should be largely VFR
with some patchy MVFR ceilings at times.

The story into the early morning through the afternoon will be the
wind. SW winds will gust to around 30 knots early on, but it will
gradually swing to the W by mid/late morning, then finally NW
toward evening. The winds will drop off toward evening.


&&

.MARINE...
Issued at 318 AM EDT Sun Oct 15 2017

Still looking at the likelihood of gale force winds for the
nearshore waters. Already saw some gale gusts north of Muskegon.
With a tight pressure gradient and cold air advection on the
backside of the departing storm especially this afternoon...gales
are expected.

&&

.HYDROLOGY...
Issued at 1217 PM EDT Sat Oct 14 2017

Multiple waves of convection, some of it training, are expected to
provide the entire area with a soaking rainfall by Sunday morning.
PW values will be at or above 1.5 inches for the entire day, which
are about as high as they can get this time of year (based on DTX
sounding climatology). With elevated instability being maintained
through a thick layer of this deep atmospheric moisture, rain
production will be efficient in convection.

Mesoscale models have been consistent with providing 1 to 3 inches
of rain to the area, but have reasonable disagreement on where the
axis of heaviest rain will fall. There could be two heavy rain
swaths that end up falling, as convection this morning and afternoon
will focus south of I-96, then convection will tend to blossom north
of I-96 later this evening and tonight. Several runs of the HRRRX
have shown the potential for isolated 4 to 6 inch totals. Already
southern Van Buren and Kalamazoo counties are approaching 2.0
inches in the past 6 hours.

A flood watch has been issued through late Saturday night. River
flood advisories or warnings may be needed if heavy rain falls in
flood-prone drainage basins. With basin-average totals between 2 to
3 inches plugged into river models in the lower Kalamazoo and upper
Grand basins, several river points climb above bankfull (the usual
suspects: Holt, Eagle, Maple Rapids, Ionia, Hastings).

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Wind Advisory until 8 PM EDT this evening for MIZ037>040-043>046-
     050>052-056>059-064>067-071>074.

LM...Gale Warning until 8 PM EDT this evening for LMZ844>849.

&&

$$

SYNOPSIS...MJS
SHORT TERM...MJS
LONG TERM...Laurens
AVIATION...JK
HYDROLOGY...CAS
MARINE...MJS



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