Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 231532
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1132 AM EDT Tue May 23 2017

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 330 AM EDT Tue May 23 2017

A weak system, centered over western Wisconsin early this morning
will slowly move east southeast across central Lower Michigan
during the day time hours of today. That will bring periods of
showers and an isolated thunderstorm (not severe). Meanwhile an
new and much stronger system develops over northern Kentucky this
evening. That system will have Gulf moisture with it as it moves
nearly due north into Southern Lower Michigan Wednesday evening.
That will bring rain, heavy at times to areas near and south of
I-96 late Wednesday afternoon into Wednesday night. Meanwhile a
coastal storm will develop near New Jersey Thursday afternoon and
that system will take over as the dominant circulation over the
Northeastern United States. This will mean showers will linger
from the initial surface low into Thursday afternoon. There will
likely be a quiet period from Friday into Saturday but another
frontal system may bring showers back to the area Sunday. Memorial
day may see lingering showers.

&&

.UPDATE...
Issued at 1132 AM EDT Tue May 23 2017

Have maintained a mostly cloudy forecast this afternoon, as a fair
amount of clouds are already in place and more should develop. The
cumulus scheme shows that breaks should try to fill in this
afternoon in an unstable environment.

SPC mesoanalysis page shows CAPE values on the order of 100-200
J/KG at the present time, a fairly meager amount. 3kmNAM and RAP13
guidance shows instability building into the 500-1000 J/KG range
this afternoon. The instability develops with some heating of the
boundary layer in breaks in the overcast as well as via mid level
cooling.

The upper trough is located upstream from northern Wisconsin to
southern Minnesota at 15z. The trough pivots our direction this
afternoon just a bit which will add some synoptic scale lift.
There is an 850mb low level jet aiding much of the current
precipitation but it is forecast to weaken through the afternoon.
Expecting areas of rain and rain showers with a few thunderstorms
developing this afternoon. Have 60-80 pct chances for showers
and a thunderstorms this afternoon.

&&

.SHORT TERM...(Today through Thursday)
Issued at 330 AM EDT Tue May 23 2017

There are two systems to watch in the short term the system from
Wisconsin that moves through our area today with showers and
isolated thunderstorms, then a more significant rain producing
system for late Wednesday into Thursday.

For today we have that system rotating around the departing system
who`s center at midnight was over western Wisconsin. That system
will track into central Lower Michigan this afternoon. That puts
most of Southwest Michigan in the inflow area of the moisture
transport at low to mid levels. There is already a low level jet
(20 to 30 knots) from BEH to FNT this morning and that in
combination with the approaching system will result in showers
and isolated thunderstorms. There is some weak instability but
with so much cloud cover I do not expect the instability to be
strong enough to do more than result in a few isolated storms.

The system on Wednesday into Thursday is looking better and better
(which means more likely to impact SW MI). The ECMWF surface low
track which 48 hours ago had it over CLE at 8 pm Wed, and 24 hours
ago had it over TOL, now has it west of CMH Ohio at that time.
Clearly the trend is your friend so this would put Southwest
Michigan in the trowal Wed night with this system. This brings the
precipitable water to over an inch over most of the area by
Wednesday evening. That is nearly double normal I would expect
between .5 and 1.5 inches of rain over most of our CWA from this
system. WPC has a max of around 1.9 inches near FNT from the
storm. We do not get into the warm air with this system to the
severe storm treat is near zero. It will be a rain event more than
anything else.

.LONG TERM...(Thursday night through Monday)
Issued at 330 AM EDT Tue May 23 2017

Most of the showers will be over by Thursday night as the stacked
low moves into PA and continues to drift east.  I did add more
clouds to Thursday night with the typical lingering low level
moisture behind an upper low and little mixing.  We`ll bank on
clearing into Friday for now as a weak upper ridge moves into the
Western Great Lakes.

It appears we`ll have a drier start to the holiday weekend then
originally thought.  The upper ridge only moves into the Eastern
Great Lakes by Saturday night which should result in a dry Saturday.
 However, as the ridge slips away, a cold front should be moving
across WI Saturday, and into Lower MI Saturday night into Sunday
when it appears we`ll see scattered showers and storms.  As
mentioned yesterday, we will have to continue monitor trends of
this upper ridge.  As of now it appears to have moved the rain back
to Saturday night/Sunday.  If this slower trend continues, more of
the first half of the holiday weekend could remain dry.

It appears the deeper we get into the holiday weekend however, the
better chance of pcpn.  The models are suggesting a slow moving
front, that in turns becomes another developing upper low.  The
models show this upper low develops near the MN arrowhead, probably
plaguing our Memorial Day.

Temperature-wise, we will remain cool until the mid week upper low
departs.  But by Friday night/Saturday we will be in solid warm
advection, with temps returning to near or even slightly above
normal.  The near normal temps should continue into Sunday, but then
expect a cool down into Sunday night/Monday when the next upper low
forms.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 748 AM EDT Tue May 23 2017

It would seem to this forecaster that VFR conditions should
largely prevail through at least midnight at most of the TAF
sites. MKG will be on the edge of the lower clouds today so they
will be in and out of it for while this morning but mostly VFR
this afternoon. There will be showers around but for the most part
they should be to light to impact vsbys/ceilings. After midnight
enough moisture may come in at low levels to bring ceilings to
mvfr.


&&

.MARINE...
Issued at 330 AM EDT Tue May 23 2017

I see no significant issues in terms of headlines with this
forecast as the track of the storm does not seem to bring strong
winds into our near shore.


&&

.HYDROLOGY...
Issued at 125 PM EDT Mon May 22 2017

River systems in Southern Lower Michigan are running above normal,
while river levels in Central Lower Michigan are around normal.
Tonight through Thursday, unsettled weather will bring up to an inch
of rain. This should keep levels elevated, but not expecting
flooding to result. The following forecast is based on observed and
forecast 24 hour precipitation.

&&

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

$$

UPDATE...Duke
SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...JK
AVIATION...WDM
HYDROLOGY...63
MARINE...WDM


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