Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 300504
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
104 AM EDT TUE AUG 30 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 313 PM EDT Mon Aug 29 2016

Clouds will be on the increase later tonight, with showers and a few
storms becoming possible on Tuesday. These showers and storms will
be out ahead of and along a frontal system that will slowly drop
through the area. The showers and storms will gradually end across
the area late Tuesday night and on Wednesday.

Much cooler air will then filter in across the area for the end of
the week behind the front. Temperatures will then gradually warm
through the upcoming holiday weekend. The holiday weekend should
also remain mainly dry.

&&

.SHORT TERM...(This evening through Wednesday night)
Issued at 313 PM EDT Mon Aug 29 2016

Our main focus for the short term is on the convective potential for
Tuesday through Wednesday.

Stratus up toward the Clare/Mt. Pleasant area has been pesky this
afternoon and is taken a bit longer to mix out than earlier thought.
The rest of the CWFA has seen sct-bkn cumulus development with the
moist air mass in place. Fcst soundings show quite a cap in place
from just below 850 mb to almost 700 mb that is keeping any
showers/storms from forming this afternoon. We should tend to clear
up this evening as the diurnal cumulus clouds dissipate, before
clouds move back in later tonight with the approach of the front.

Most of the convective potential on Tue looks to be diurnal
showers/storms that form in the afternoon and early evening. Models
show that the cap will be much weaker on Tue, with over 1000 j/kg of
CAPE expected. We do not expect much organization to the storms as
deep layer shear is at or below 20 knots during the daytime. This
would support pulse type storms. Locally heavy downpours will be
possible with PWATS between 1.5 and 1.75 inches combining with slow
moving storms.

Additional storms will remain possible Tuesday night, even as the
diurnal component wanes. Models are showing that we could hold on to
a bit of MUCAPE overnight with moisture pooling immediately ahead of
the front. This is usually a good sign that convection will remain
possible overnight, even with the loss of the diurnal component. Sfc-
6km shear does go up a bit Tue night to around 25 knots or so, still
remaining marginal. However the storms will likely not be sfc based.

The trend remains for some showers/storms to hold on for at least a
portion of Wed, especially along and south of I-96. Instability
should remain limited with little to no heating taking place there.
The threat should then end Wed afternoon as the front slips south
ofthe area.

Quite a bit of drying takes place then. We can not rule out a shower
coming in Wed night with the short wave diving southeast into the
area. The limited moisture will keep us from adding in pcpn chcs for
now.

.LONG TERM...(Thursday through Monday)
Issued at 313 PM EDT Mon Aug 29 2016

Sfc ridging and rising heights will bring fair weather and warming
temperatures Thursday through Saturday. The sfc high moves east by
Saturday with some moisture return Saturday night.

Showers should hold off until at least Sunday when deeper moisture
and warm air advection increases and may actually not occur until
late Monday as suggested by 12Z model guidance, which does not show
any precip Sunday or Sunday night in the WAA regime. We will keep
showers and thunderstorms for those periods for now as models
sometimes under estimate QPF associated with WAA/isentropic ascent.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 100 AM EDT Tue Aug 30 2016

Vfr conditions will continue for most of the overnight period
before deteriorating to mvfr and possibly ifr around or shortly
prior to daybreak Tuesday due to patchy fog. Fog will linger
through mid morning before dissipating when conditions will
improve to vfr.

Scattered showers and thunderstorms will develop Tuesday
afternoon. Prevailing conditions will remain vfr Tuesday afternoon
but could briefly dip to mvfr/ifr in heaviest showers and storms.
Scattered showers will linger Tuesday evening along and ahead of
the cold front that will be moving through overnight.

&&

.MARINE...
Issued at 313 PM EDT Mon Aug 29 2016

We are looking at relatively quiet conditions through at least early
Wednesday. Winds should be at or under 15 knots until then. Winds
will pick up a bit late Wednesday behind the front, and could
remainup a bit on Thu when the much cooler air comes in over the
warmer Lake Michigan waters. We could be looking at some possible
headlines at that time.


&&

.HYDROLOGY...
Issued at 1100 AM EDT Mon Aug 29 2016

The Portage River at Vicksburg has fallen below flood stage and is
slowly receding, so the Flood Warning has been canceled. Showers
and thunderstorms Tuesday into Wednesday are expected to provide
basin-average rainfall amounts between a tenth and quarter inch.
Dry weather the rest of the week signals a low flood potential.

&&

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

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...Ostuno
AVIATION...Laurens
HYDROLOGY...CAS
MARINE...NJJ



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