Area Forecast Discussion
Issued by NWS Grand Rapids, MI

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS63 KGRR 301736
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
136 PM EDT TUE AUG 30 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EDT Tue Aug 30 2016

A slow moving cold front will bring scattered showers and
thunderstorms along with warm and humid conditions today into
tonight.

The front will move south of the area by Wednesday afternoon and
north winds behind it will deliver cooler and less humid air for the
rest of the week.

Currently the majority of the upcoming holiday weekend looks dry
with above normal temperatures. The next chance of storms will
arrive on Labor Day.

&&

.UPDATE...
Issued at 1059 AM EDT Tue Aug 30 2016

No major changes to the forecast this morning. We just freshened
up the forecast a bit to account for current radar trends.

Band of locally heavy rain south of I-94 has weakened a bit and is
propagating south out of the area. A few scattered rain showers
and isolated storms are moving east near I-96. These have been the
result of more rich moist air advecting in from the S/SW. The best
moisture plume is across the far south portion of the CWFA and
south.

We are expecting diurnal shower/storm activity to become more
dominant this afternoon. Breaks in the clouds early should allow
CAPES to increase to over 1000 j/kg this afternoon away from Lake
Michigan. A convergence zone just inland from Lake Michigan will
be a decent focus for scattered convection to pop this afternoon,
in addition to more isolated convection to pop inland.

Deep layer shear remains weak through this afternoon under 20
knots, limiting the severe threat. Heavy downpours will likely be
the biggest threat with slow moving storms expected. Can not rule
out a isolated wind gust around 40 mph or so with a downburst.

&&

.SHORT TERM...(Today through Thursday)
Issued at 330 AM EDT Tue Aug 30 2016

Scattered showers/storms have recently developed over srn Lk MI on
the leading edge higher PWAT/theta-e air. Latest near term HRRR
guidance indicates that this activity will impact areas mainly near
and south of I-96 this morning.

As we head into the afternoon hours and sfc instability builds, look
for scattered diurnal tstms to develop, with highest concentration
of storms inland from lk MI and the lake breeze front - primarily
near and east of Highway 131. The best sfc convergence later today
looks to set up in a band from Kalamazoo to Lansing and this is
where most of the storms should be situated from 4 pm to 8 pm.

The main threat from storms this afternoon and early evening will be
locally heavy rainfall. Juicy air mass will be in place with sfc dew
pts near 70 and PWATs near 2 inches. Fcst soundings reveal deep
skinny cape and high freezing levels, and storms should be very slow
movers. If a localized wet micro-burst occurs it could result in
wind gusts to 50 mph.

Height falls Wednesday/Thursday and evolution of a deep upr trough
over the ern grtlks rgn will shove the sfc cold front to the south
and send a much drier air mass into the state. A shortwave trough
and secondary sfc trough is progged to slide south Wednesday night
into early Thursday and could touch off a period of cloudiness with
some light showers.

.LONG TERM...(Thursday night through Monday)
Issued at 330 AM EDT Tue Aug 30 2016

High pressure will continue to build in and produce fair weather
with seasonable temperatures Thursday night through Saturday. Fair
weather will continue Sunday along with warmer temperatures and
gradually increasing humidity levels as southerly flow waa develops
on the back side of the ridge.

Most of the holiday weekend should be dry but there is a chance for
a shower or thunderstorm beginning on Labor Day as continued
southerly flow results in increasing moisture. However the
relatively better chance for a few showers and thunderstorms should
hold off until next Tuesday or Wednesday as the next system moves in
from the west.

Temperatures will undergo a gradual moderating trend this weekend
into early next week. High temperatures by Sunday and Monday will
average around 5 to 10 degrees above normal.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 128 PM EDT Tue Aug 30 2016

An unstable airmass will be situated over the TAF sites this
afternoon into the early evening hours. As a result...a few
thunderstorms are expected to form. Impacts will be
possible...however confidence of them occurring at any individual
airport is low at this time. Only VCTS has been included in the
forecast. Thus close monitoring of forecasts and conditions will
be needed during this time.

IFR looks likely later tonight and Wed morning as the low level
moisture increases and a slow moving cold front pushes through.
Some instability will be present ahead of this front...but
confidence was not high enough to go with thunderstorms at this
time.





&&

.MARINE...
Issued at 330 AM EDT Tue Aug 30 2016

Period of strong north flow will bring hazardous winds and waves
beginning late Wednesday, continuing into Thursday evening. This
will probably also lead to an upwelling event which could cause our
recent enjoyable stretch of warm lk mi water temps to plunge at the
shore going into the holiday weekend.


&&

.HYDROLOGY...
Issued at 105 PM EDT Tue Aug 30 2016

Scattered slow-moving thunderstorms Tue afternoon are capable of
producing local rainfall amounts over a half inch in a short
amount of time. Deeper atmospheric humidity and correspondingly
higher PW values are in southern Michigan but greater instability
and storm coverage will be in central Michigan Tue afternoon.
Small basins will likely be able to handle any locally heavy
rainfall, but minor ponding of water on roadways is possible.
After the cold front clears on Wed, the next chance for
appreciable rainfall will hold off until next week.

&&

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

$$

UPDATE...NJJ
SYNOPSIS...Meade
SHORT TERM...Meade
LONG TERM...Laurens
AVIATION...MJS
HYDROLOGY...CAS
MARINE...Meade


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.