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813
FXUS63 KGRR 260549
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
149 AM EDT MON SEP 26 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 324 PM EDT Sun Sep 25 2016

A strong cold front will move across the state tonight and set the
stage for much cooler weather for this week. Showers and storms are
possible tonight through Wednesday. Highs will remain mostly in the
lower to mid 60s through Wednesday before climbing to around 70 for
the rest of the week.

&&

.UPDATE...
Issued at 856 PM EDT Sun Sep 25 2016

Based on a generic lack of instability (see SPC SREF) I had
decided to (after consulting with others in the office) to
expunge most of the mention of thunderstorms from the zones
tonight. I did leave it along the lake shore for a few hours since
there is still some instability over Lake Michigan but none of
the models take any of that inland significantly.

Also there will be two periods of showers. The first is coming
through now and the second will be well after midnight. That
second one is associated with the jet entrance region getting
close enough to allow lift over our during that time.

&&

.SHORT TERM...(This evening through Tuesday night)
Issued at 324 PM EDT Sun Sep 25 2016

For several days the models have had a decent handle on the cold
front that will move through the cwa tonight. Latest sfc analysis
shows the cold front extending from near DLH south to near the Quad
Cities. A couple of broken lines of showers and storms accompany
this front and we`ll see them move over the cwa tonight.
Precipitable water values increase to nearly 2 inches this evening
so a few of the stronger storms may produce heavy rainfall.

Much cooler air will flow over the lakes tonight through Tuesday.
The core of the cold air aloft moves over the lake Tuesday night and
we could see a few storms develop as lapse rates steepen quite a
bit. Lake effect showers will be possible through the short term as
h8 temps fall to around 2c and water temps are in the lower 20s c.

.LONG TERM...(Wednesday through Sunday)
Issued at 324 PM EDT Sun Sep 25 2016

Models remain in decent agreement in showing the mid level low
dropping southward through the CWA on Wednesday morning.  Given that
the airmass will be cold enough for lake enhanced moisture feeding
into the system...showers will continue to be around the region. The
low convergence is the greatest over southwest parts of the CWA
which is where I will keep the POPs the highest.  Well below normal
temperatures are expected with a cold core system overhead.

The potential for showers is expected to diminish Wednesday night
through Thursday as the flow becomes offshore and heights rise. Will
keep temperatures fairly close to normal values.

Bigger differences in the models show up for Friday into Sunday. The
GFS keeps the mid level low far enough east of the CWA to support a
dry forecast.  The new High Res Euro lifts the mid level low
northward back into the CWA...which would be very unusual.  I
somewhat favor the GFS...but will hold onto the low risk for a few
showers in that period.

&&

.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 149 AM EDT Mon Sep 26 2016

Cold front has moved through the lakeshore, and is now headingfor
the inland areas. Scattered showers have popped up and will
continue to do do ahead of, and behind the front. Cigs are
expected to drop into the MVFR category behind the front with the
showers. Some pockets of IFR will be possible to the SE. Winds
will switch from SE to W/NW and become gusty to over 20 knots.

The MVFR cigs will last for a few hours before a bit of drier air
works into the area. This will diminish the clouds some, and all
areas should go VFR. Winds will ramp up more by afternoon. We are
looking at potential gusts of around 30 knots. The clouds will
remain VFR and sct through the evening. Winds will come down
toward sunset, but still may occasionally gust toward 20 knots.

&&

.MARINE...
Issued at 324 PM EDT Sun Sep 25 2016

A strong cold front will move across the lake tonight. The colder
air coupled with stronger winds will create hazardous conditions for
small craft tonight through Tuesday and a small craft advisory was
issued.


&&

.HYDROLOGY...
Issued at 102 PM EDT Sun Sep 25 2016

River levels are around normal for this time of year. Showers and
thunderstorms are expected tonight and lake effect rain showers are
possible Monday into Wednesday. Through Wednesday, over an inch of
rain is possible to the north and west of Grand Rapids with less
than a half inch to the south and east. Rivers and streams should
remain below bankfull through the week.

&&

.GRR Watches/Warnings/Advisories...
MI...None.
LM...Small Craft Advisory until 9 PM EDT Tuesday for LMZ844>849.

&&

$$

UPDATE...WDM
SYNOPSIS...04
SHORT TERM...04
LONG TERM...MJS
AVIATION...NJJ
HYDROLOGY...63
MARINE...04