Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 220545
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
145 AM EDT THU SEP 22 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 326 PM EDT Wed Sep 21 2016

A slow moving front will be over Northern Michigan tonight.  It will
drift south into Southern Lower Michigan by Thursday night and into
Indiana by Friday night.  This front will continue to bring
scattered showers and a few thunderstorm to the region through
Friday night.

We should see a short break in the rain chances for the weekend, but
then more rain should be back in the area by Monday.  This rain
appears to linger into Tuesday night, before we dry out for the
middle part of next week.

Tomorrow will be the last warm day with highs in the upper 70s to
lower 80s.  Then we will see temperatures mainly 70 to 75 Friday and
into the first half of next week.

&&

.UPDATE...
Issued at 916 PM EDT Wed Sep 21 2016

I increased the threat of thunderstorms to likely over our NW CWA
overnight (but changed little else).

As one can see there is a area of thunderstorms from East Central
Wisconsin back northwest into Central Minnesota. At it turns out
that is the leading edge of the 1000/850 mb moisture transport
vector gradient, or on the nose of the low level jet. This area
noses into the Big and Little Sable Point are after midnight. The
most unstable cape shows a max over Lake Michigan... which will
only help the cause of any storms crossing the Lake there. So I do
believe the thunderstorms could make it into Mason...northern
Oceana and Lake Counties toward midnight. This is farther
supported by the SPC 21z SREF which shows a the 3 hour conditional
probability of thunderstorms increasing near zero at 9 pm to
around 30 pct (50 pct by Green Bay) in the midnight to 6 am time
frame. Since the cape is elevated and weak (less then 1000 j/kg)
I do not expect strong storms but some thunderstorms can still be
expected.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 326 PM EDT Wed Sep 21 2016

We will remain unsettled through the short term as a front drifts
south.  Even once the front is south of MI by mid day Friday, we
could still see showers into Friday night.

A bit of a lull in the pcpn will last into this evening.  But more
showers and thunderstorms were developing upstream, over Western and
Central WI.  This appears to be in response to the upper divergence
created by the right entrance region of the upper jet.  This lift
continues to expand over WI this evening and spreads into Northern
and Central Lower toward midnight.  So expect an increase in showers
and storms north of I-96 after about 10 PM.

The front remains fairly stationary until late Thursday afternoon.
The best jet dynamics are progged to gradually weaken through the
morning.  So bottom line, expect the showers and storms will remain
north of I-96 on Thursday and should have a diminishing trend
through the day.

The front sag south through the CWA late Thursday night into Friday
evening.  This should be the period for the highest chances of rain.
Instability looks marginal though, so largely expect showers with a
few embedded thunderstorms.  Jet dynamics no longer look too
favorable, but with moisture pooling along the front and decent low
level convergence we should at least continue to see scattered
showers.  I tweaked POPs upward on Friday.

The models look wetter into Friday night despite the front being
through.  Solid moisture remains behind the front along with some
isentropic lift. It would seem widely scattered showers will remain.
Have increased POPs a bit.

.LONG TERM...(Saturday through Wednesday)
Issued at 326 PM EDT Wed Sep 21 2016

Scattered showers should be ending Saturday morning as mid level
warm air advection weakens and subsidence increases with shortwave
ridging moving in. Fair weather should prevail into Sunday and could
last all the way through early next week if some of the slower
solutions are correct in delaying the height falls associated with a
western CONUS upper trough moving east.

This trough eventually forms a cut off low across the Plains and
there remains a lot of model spread on timing of the low moving into
the Great Lakes. POPs were lowered for Sunday into early Monday
based on a preference for the slower and deeper solutions as there
seems to be a trend in this direction over the past couple days.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 143 AM EDT Thu Sep 22 2016

Patchy dense fog is possible overnight. Visibilities will likely
bounce around quite a bit and may vary from vfr to ifr/lifr. It`s
also possible that MKG could see a shower/tsra after 10z but the
pcpn will more likely remain northwest of the taf sites.

&&

.MARINE...
Issued at 326 PM EDT Wed Sep 21 2016

Rather quiet conditions are expected on the nearshore waters through
the short term.  Of course mariners will have to watch for the risk
of storms mainly north of Muskegon tonight through tomorrow evening.
Then isolated storms will be possible anywhere into late Thursday
night through Friday night.

We will develop a brisk ENE wind flow into late Thursday night that
will last into Friday night.  This offshore flow will result in
building waves, but generally beyond five miles from shore.


&&

.HYDROLOGY...
Issued at 326 PM EDT Wed Sep 21 2016

As much as 1.5 inches of rain fell in several areas north of I-96
Wednesday morning, but river rises are limited. Additional chances
for rainfall will stay mainly north of I-96 the next few days.
Excessive rainfall is not expected through the weekend.

&&

.GRR Watches/Warnings/Advisories...
MI...None.
LM...None.
&&

$$

UPDATE...WDM
SYNOPSIS...JK
SHORT TERM...JK
LONG TERM...Ostuno
AVIATION...04
HYDROLOGY...CAS
MARINE...JK



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