Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 151930
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
330 PM EDT Sat Jul 15 2017

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

.SYNOPSIS...
Issued at 330 PM EDT Sat Jul 15 2017

A cold front will move through the region late tonight into Sunday
and will bring a period of showers and storms.  Most of the
precipitation will occur tonight, but areas southeast of a Alma to
Kalamazoo line could still see showers and storms into Sunday.  All
the rain will be out of the area by Sunday evening.  The weather
into Monday and Monday night will be quiet.  The next chance of rain
should hold off until Thursday and Thursday night, with another
chance by Saturday.

Daily highs will be 75 to 80 Sunday and Monday, then we will warm
into the mid and upper 80s for the rest of the week, with a slight
cool down by Saturday.

&&

.SHORT TERM...(This evening through Monday night)
Issued at 330 PM EDT Sat Jul 15 2017

Pcpn chances look rather good overnight, with more showers and
storms expected to develop along the front.  The front slows down as
it crosses the CWA, so lingering showers and storms will be possible
into Sunday over the SE CWA.  Thereafter, we will see pleasant
weather to start the work week.

Tonight`s front was moving across the U.P. this afternoon.  It will
reach Central Lower by 06Z. But as the upper wave moves in, we
develop a surface low along the front toward morning, as the front
moves to I-96 by 12Z Sun.  It`ll take until 18-00Z tomorrow for the
front to completely clear the CWA.

A fork in the upper jet (one over Superior, and a second over
Eastern IA) will result in divergence over Southern WI and West
Central Lower MI toward 06Z tonight.  This in large part is why I
expect an expansion of showers and storms overnight along the front.
This upper divergence travels southeast through the CWA between 06Z
and 18Z Sunday.  There will also be a very weak low level jet (only
about 25 knots) moving from Southern WI to Southern Lower MI in the
same time frame.  The instability seems marginal for severe storms,
but I can not completely rule them out overnight.  With the storms
mainly elevated, large hail will be the main threat.

The instability becomes more surface based on Sunday over the SE CWA
and a severe threat could redevelop.  Hail and high winds will be
the threat then.  If this occurs the threat would mainly be late
morning into mid afternoon when the upper jet is still in good
position.

High pressure fills in behind the departing front for Sunday night
through Monday night.  It will be comfortable with night time lows
of 55 to 60, and a high on Monday in the mid and upper 70s.

.LONG TERM...(Tuesday through Saturday)
Issued at 330 PM EDT Sat Jul 15 2017

The Great Lakes region will continue to be in a fast west-northwest
flow regime between a sprawling subtropical high to our south and
upper troughing over central and eastern Canada. A series of
shortwave troughs will move through bringing chances for precip
during the period.

The first one comes through Tuesday night but is damping out and not
much is expected from it with a weakening cold front possibly
touching off scattered showers and thunderstorms mostly across the
northern zones.

Wednesday night into Thursday a stronger front moves in with
instability and shear sufficient for some strong storms during the
afternoon and evening. Still a long way off but severe weather
potential has to be monitored.

Sfc high builds in for Friday but moves east with return flow and
warm advection pattern developing for Saturday, with chances for
showers and thunderstorms returning for the afternoon.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 137 PM EDT Sat Jul 15 2017

VFR conditions will continue through this evening. A few
thunderstorms are possible after midnight across western Lower
Michigan. Low clouds will move in Sunday morning with MVFR and IFR
conditions developing after 12Z.

Winds will be from the west to southwest less than 10 knots
through Sunday.

&&

.MARINE...
Issued at 330 PM EDT Sat Jul 15 2017

Issued marine headlines late this morning, starting on Sunday. Brisk
northerly flow and cold advection behind the front will kick the
waves to as high as six feet.  Conditions will improve by late
Sunday night.

&&

.HYDROLOGY...
Issued at 330 PM EDT Sat Jul 15 2017

Streamflow on a few rivers has returned to normal levels, while the
majority continue to run above normal. Almost all rivers in the
forecast area are falling or beginning to fall.

Little has changed in the forecast with scattered storms possible
tonight into Sunday. This will result in rainfall amounts generally
less than one-quarter of an inch. There is the possibility that a
storm or two could be strong. In the event a strong storm does
develop, localized amounts may be higher.

In the bigger picture, precipitation amounts over the next week do
not look all that concerning. No flooding is expected at this time.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement from Sunday afternoon through late
     Sunday night for MIZ050-056-064-071.

     Beach Hazards Statement from Sunday morning through late Sunday
     night for MIZ037-043.

LM...Small Craft Advisory from 8 AM Sunday to 4 AM EDT Monday for
     LMZ848-849.

     Small Craft Advisory from 1 PM Sunday to 4 AM EDT Monday for
     LMZ844>847.

&&

$$

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



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