Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 150516
AFDGRR

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

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 327 PM EDT Sat Oct 14 2017

A strong fall storm system will affect the area through Sunday. This
storm will bring a good deal of rain to the whole area through
tonight. Some of this rain will be accompanied by embedded storms,
some of which could become locally strong to severe. Winds and
localized flooding will be the main threats. Strong winds will
develop late tonight and last through much of Sunday as colder air
flows into the area.

Once lingering showers end on Sunday night, much of the upcoming
week looks dry and increasingly warmer. Monday will still be a bit
cool after some possible frost across Central Lower Sunday night.
Highs could reach up into the 70s by the end of the week.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 327 PM EDT Sat Oct 14 2017

No major changes for the forecast this afternoon as the table has
been well set for all of the weather expected through Sunday. The
flood watch still looks well justified, as does the wind advisory
for late tonight and on Sunday.

We are thinking that we have three organized waves of showers/storms
that will work through the area between now and Sunday morning when
the front moves through. The first is coming into the CWFA right
now, the next one is south of the Quad Cities, and the third and
strongest one is over NW MO and SW IA.

The first two are expected to bring mainly heavy rainfall to the
area with only some embedded storms. We are watching the track of
these, as heavy rain has already fallen from Van Buren county to
Calhoun county. If these areas see additional heavier rain, we may
have to upgrade to a flood warning there. We will be watching any
other areas for possible advisories/warnings if too much training
over one area occurs.

The third wave continues to be our main concern for tonight. This
looks to arrive mid-late evening, and last into the early morning
hours on Sunday. This wave is the one that is being fueled by the
RRQ of the strengthening upper jet to our NW, and the resulting 60+
knot low level jet zipping up through here. Instability is limited
in our area to as much as 400-500 j/kg of MU Cape. The concern is
that with the strong wind fields, any downdraft reaching the sfc
could bring down the 50-60 knots winds only 1500-3000 ft up.

Then once the convection moves out, the concern focuses to the
frontal passage, and the strong synoptic winds that will ensue.
Models are fairly similar in showing the ability to mix 45 knots
down from late tonight and lasting through much of Sunday. There
will be a few showers on Sunday with the wind. The showers could be
enhanced a bit along the lakeshore with land/lake delta t/s in the
mid to upper teens C. The showers will then end late Sunday night as
ridging builds in. Inland areas could see some patchy frost up in
the normally colder locations toward Mt. Pleasant and Clare.

After Sunday night, the weather quiets down. We will remain rather
cool on Mon in comparison to the recent weeks with highs only in the
50s.

.LONG TERM...(Tuesday through Saturday)
Issued at 327 PM EDT Sat Oct 14 2017

A steady warmup is on tap for the middle and latter portion of next
week as upper level heights build and H850 warm air advection
settles in. We`re looking at the warmest days likely being toward
the end of the week and weekend as H500 heights surge back into the
580s dm. H850 flow will advect temps in the 14C to 16C range, or
possibly higher, if the Ohio Valley ridge develops as advertised.

This equates to a few things for our region. First, if this pattern
materializes, high temperatures late in the week and weekend may
overachieve given the anomalous pattern and the challenges that
numerical models can have resolving the degree of warmth. For now,
we have low 70s featured from Thursday through Saturday. Actual
highs may be several degrees warmer. With average highs around 60
degrees this time of year, we are expecting temperatures to be 10 to
15 degrees above normal by late next week. Secondly, we will likely
be precipitation free through Saturday with a good amount of
sunshine for the region. It should be a quiet stretch.

&&

.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 327 PM EDT Sat Oct 14 2017

No changes needed to the marine headlines with this forecast
package. The latest data continues to support solid gales for the
waters this evening ahead of the front, through Sunday with the
strong cold air advection. The chance for Storm Force winds is not
zero, but looks way too low for now to consider an upgrade at this
time.


&&

.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...Flood Watch until 4 AM EDT early this morning for MIZ043>046-
     050>052-056>059-064>067-071>073.

     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...NJJ
SHORT TERM...NJJ
LONG TERM...Hoving
AVIATION...JK
HYDROLOGY...CAS
MARINE...NJJ



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