Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 120730
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
330 AM EDT Sat Aug 12 2017

LATEST UPDATE...
Synopsis/Short Term/Long Term/Marine

.SYNOPSIS...
Issued at 330 AM EDT Sat Aug 12 2017

An isolated shower or two are expected today as a cool airmass flows
over the warmer Great Lakes. Most areas will remain dry however.
High pressure will build in for Sunday and Monday with partly cloudy
skies expected. Highs today will top out in the 70s, returning to
around 80 degrees for Sunday and Monday. The next good chance for
rain doesn`t come until mid week Wednesday or Wednesday night at the
earliest.

&&

.SHORT TERM...(Today through Monday)
Issued at 330 AM EDT Sat Aug 12 2017

Main concern in the short term pertains to shower chances today.
Upper troughing and cyclonic flow remains in place today with a
shortwave pivoting through the area this morning into the early
afternoon. In addition, delta T`s over Lake Michigan are on the
order of 13C (+21C lake temps and +9C air at 850mb), which is just
enough to touch off lake effect rain showers. For these reasons will
maintain a 20 pct chance for light rain showers through much of the
day. Both the NAMnest and HRRRx show isolated showers right through
the day given the lake instability and instability via August
sunshine into a cool airmass aloft.

After today, concerns are limited as high pressure will be in place
the remainder of the time. Envision potentially more in the way of
clouds currently in the forecast with mid and high clouds streaming
in from the plains Sunday into Monday. A warm front will be located
to our southwest on Monday and debris clouds from upstream
convection is likely. The models are indicating a decent looking
shortwave moving our direction as well during this time frame adding
credence to an increase in cloud cover.

.LONG TERM...(Monday night through Friday)
Issued at 330 AM EDT Sat Aug 12 2017

A high pressure ridge will bring fair wx with seasonable temps
Monday night through Tuesday night. Fair wx will continue into early
Wednesday and it will become warmer as a southerly flow waa pattern
develops. High temps by Wednesday will reach the lower to middle 80s.

Showers will develop late Wednesday or Wednesday night as the
continued southerly flow waa results in increasing moisture out
ahead of the next cold front. This front will bring potential for
showers and thunderstorms through Thursday. Temperatures will return
to near normal for this time of year late next week behind that
system.

&&

.AVIATION...(For the 06Z TAFS through 06Z Saturday night)
Issued at 1156 PM EDT Fri Aug 11 2017

Vfr conditions will continue for most of the overnight period
before slowly deteriorating to mvfr at some of the terminals as
some low clouds move in during the early morning hours Saturday.
However the mvfr conditions will not last very long and conditions
will improve back to vfr at all the terminals by mid to late
Saturday morning.

We will go with a dry forecast for Saturday as scattered diurnally
driven showers in the afternoon should stay east of all the
terminals.
Conditions will remain vfr through Saturday evening as skies become
mostly clear. Wind direction will remain out of the northwest
through the next 24 hours.

&&

.MARINE...
Issued at 330 AM EDT Sat Aug 12 2017

Winds look a bit more marginal today for our wave event as compared
to 24 hours ago. Much more wind above 20 knots was noted in BUFKIT
profiles with last nights runs and now the wind is near or below 20
knots. That said, this is a cold air advection north flow event and
they always seem to over perform. The waves will emanate from the
better gradient across the northern reaches of the lake, with the
waves propagating south with time. Will maintain both the Small
Craft Advisory and Beach Hazards Statement. High pressure will bring
more quiescent conditions late tonight into early next week.

&&

.HYDROLOGY...
Issued at 303 PM EDT Fri Aug 11 2017

River levels are around normal for the time of year. This is much
below bankfull. Had some locally heavy rain over the last 24 hours,
but little impact on the rivers. A low chance of showers next
Tuesday and Thursday is not expected to produce much rain.
Therefore, no river impacts are expected through next weekend.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement through late tonight for MIZ056-064-071.

     Beach Hazards Statement through this evening for MIZ037-043-050.

LM...Small Craft Advisory until 8 PM EDT this evening for LMZ847>849.

     Small Craft Advisory until 2 AM EDT Sunday for LMZ844>846.

&&

$$

SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...Laurens
AVIATION...Laurens
HYDROLOGY...63
MARINE...Duke



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