Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 221534
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1134 AM EDT MON AUG 22 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 328 AM EDT Mon Aug 22 2016

A large high pressure system will provide Southwest Michigan two
days with abundant sunshine, pleasant temperatures and lower
humidities. A storm system from the North Pacific will merge with
a subtropical system to bring the risk of abundant rainfall again
Wednesday afternoon into early Thursday. Cooler temperatures will
return for late in the week into the weekend before another warm
up starts.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 328 AM EDT Mon Aug 22 2016

Looks like we are once again facing an event with abundant
moisture and good shortwave energy on Wednesday. This could mean
heavy rainfall once again for our area. Otherwise high pressure
crossing the area in coincidence with an upper ridge will provide
dry weather today into Wednesday morning.

As for our system on Wednesday, turns out it has a good
subtropical moisture feed ahead of it, similar to the last event.
Looking at the water vapor image loops one can plainly see both
systems. The one coming onto the west coast looks rater impressive
at the current time (it has a closed upper low associated with
it). Meanwhile the southern system can be seen over Utah, New
Mexico, Arizona and colorado. That southern system kicks out as
the northern stream Pacific system continues to dig. Helping this
is the bermuda high building significantly during this time
frame. The result of all this is subtropical moisture is in place
when the northern stream frontal system comes through. This is
typically a wet scenario for Southwest Michigan and I see this
being another wet event.

Due to the phasing the northern and southern stream jets we get a
good low level response which means we get a decent low level jet
Wednesday afternoon to help the cause for convection. Having 850
LI values near -3c and having the GFS sounding capes reach around
2,500 j/kg (surface based) helps the cause too. So the bottom line
is I increased pops to likely for Wednesday afternoon.

.LONG TERM...(Wednesday night through Sunday)
Issued at 328 AM EDT Mon Aug 22 2016

The main concern during the long term period will be chances for
thunderstorms Wednesday night. Short and medium range models have
been honing in on a cold front that will move across the Mississippi
Valley toward Michigan mid week. It looks like though, the
convection will be along a prefrontal trough. The trailing cold
front won`t be quite as strong as the one that just moved through.
However, models do show a 40-50 kt llj preceding it. However, by
Wednesday night, the llj is already moving east of the cwa and we
will tend to decrease the energy available for convection. The main
short wave will also be east of the cwa by 00z Thursday. So while
there may be lingering pcpn along the trough, chances for pcpn will
be decreasing as the evening wears on.

The actual cold front and wind shift to the west will occur Thursday
morning, if model timing holds true. By that time, though, moisture
will be east of the cwa and we`ll likely be dry. The end of the week
and weekend look dry too as high pressure moves in from the west.

Highs will be 75-80 through the period.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1132 AM EDT Mon Aug 22 2016

Vfr conditions will continue through Tuesday afternoon. A bkn fair
wx cu deck of clouds will continue to develop through the
afternoon and persist into the early evening before quickly
dissipating. Skies will be mostly clear overnight. Fair wx cumulus
will redevelop late Tuesday morning.

&&

.MARINE...
Issued at 328 AM EDT Mon Aug 22 2016

Likely we will need to re-issue out Small Craft Advisory by
Tuesday morning as waves increase to 3 to 5 feet over the northern
sections by mid morning Tuesday.


&&

.HYDROLOGY...
Issued at 322 PM EDT Sun Aug 21 2016

Strong thunderstorms produced swaths of heavy rainfall that totaled
up to 1 to 2 inches on Saturday. The Vicksburg area in southern
Kalamazoo County received around 1 inch of rainfall, which has
resulted in additional rises on the Portage River near Vicksburg.
A Flood Warning remains in effect for the Portage River near
Vicksburg through Wednesday morning.

Only light scattered showers are expected this afternoon and
evening. Dry weather with plenty of sunshine is expected Monday and
Tuesday. The next best chance for appreciable rainfall will be late
Wednesday into Thursday.

&&

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

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...99
AVIATION...Laurens
HYDROLOGY...EBW
MARINE...WDM


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