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000
FXUS63 KGRR 231924
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
324 PM EDT Wed Aug 23 2017

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

.SYNOPSIS...
Issued at 324 PM EDT Wed Aug 23 2017

A more early fall like weather pattern into the weekend as
Canadian Polar Air remains over the area through Sunday.
The coolest temperatures will be tomorrow and Friday then there
will be a slow warm up. It would not be out of the question to
have a little patchy frost near Route 10, east of Reed City
tomorrow morning and Friday morning.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 324 PM EDT Wed Aug 23 2017

The cold air has arrived in Southwest Michigan and will remain
over this area through most of the weekend. There is an issue with
lake effect rain showers and it is not out of the question that we
could see patchy frost in the normally colder locations near Route
10, east of Reed City.

We have a few cold air instability rain showers over our eastern
and central CWA this afternoon but those should be gone with
sunset. The coldest air we will see from this event is behind the
next shortwave, which can be seen on the latest water vapor image
loops north of International Falls MN. This shortwave dives
southeast enough so that the polar jet axis will actually be south
of the State of Michigan during the day time hours of Thursday.
This brings 850 temperatures down to 4c as far south as Big Sable
Point tomorrow morning. This is cold enough of lake enhanced rain
showers but due to the north wind, this will not really impact
much of our CWA as it turns out. Thanks to the shortwave there
will be a fair amount of clouds around Thursday so I do not think
highs will get out of the 60s in most areas.

Thanks to surface high pressure over the area I expect winds to be
light tonight and that will allow temperatures to fall below mos
forecast values. It just may get cold enough in isolated locations
to get some patchy frost but since current dew points are well
above freezing, it would seem unlikely this would be widespread
issue so I did not put that in our grids.

The polar jet goes back north and east of this area by Friday
morning. More often than not that morning turns out to be the
coldest in this sort of weather pattern. Once again frost is not
out of the question and I would not be surprised to see locations
like Leota to get near freezing.

Bottom line is early fall like weather through Friday night.

.LONG TERM...(Saturday through Wednesday)
Issued at 324 PM EDT Wed Aug 23 2017

This forecast is slightly wetter than the previous one and features
at least some chances for rain showers Monday through Wednesday. The
greatest chances for rain in the general area look to be Monday with
thunderstorms also possible in the afternoon. Overall, forecast
certainty is very low due to poor predictability with placing the
key ingredient involved with producing rain.

This key ingredient is an upper trough originating from southwestern
Canada that digs and then cuts off over the vicinity of Illinois by
late Monday. Medium range deterministic models like the
GFS/ECMWF/CMC are in fairly good agreement with this evolution but
afterwards start to diverge. This is not surprising for a cutoff low
in general - and this one is extra tricky in terms of placement due
to very split flow aloft associated with upper ridging over Ontario
to the northeast. A large number of ECE and GEFS member solutions
remain dry during this time and the overall wide range of solutions
emphasizes the poor predictability.

As such, this forecast is highly subject to change. But for now
seasonably cool and unsettled seems like the best bet for the first
part of the coming work week.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 146 PM EDT Wed Aug 23 2017

No IFR conditions expected through the period. Scattered clouds
just under 3000 ft AGL may briefly spread into broken ceilings,
particularly at the KAZO, KBTL and KGRR terminals. Certainty and
possible durations for any ceilings are both very limited and
therefore not mentioned in TAFs. Cloud layers will climb above
3000 feet by around 20Z and dissipate around 00Z with diminishing
sunlight.


&&

.MARINE...
Issued at 324 PM EDT Wed Aug 23 2017

Winds and waves continue to diminish/subside. The Holland buoy had
wave heights as high as 7 feet during the mid morning hours but
the waves are now down to 3 1/2 feet. The Ludington Buoy has
fallen from 5 3/4 feet this morning to around 3 feet now. So, I
will leave the marine headlines as is. The southern sections will
have the higher winds and waves the longest, all should be done by
midnight. With high pressure over the area Thursday into Friday,
we should not have any issues with high winds and waves.


&&

.HYDROLOGY...
Issued at 1213 PM EDT Wed Aug 23 2017

Area rivers are around normal levels for the time of the year and
well below bankfull. The rivers have already recovered from the
recent rainfall. No significant precipitation is expected through
the weekend, so no river issues are expected.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Beach Hazards Statement until 11 PM EDT this evening for MIZ064-
     071.

     Beach Hazards Statement until 6 PM EDT this evening for MIZ037-
     043-050-056.

LM...Small Craft Advisory until 6 PM EDT this evening for LMZ846>849.

     Small Craft Advisory until 11 PM EDT this evening for LMZ844-845.

&&

$$

SYNOPSIS...WDM
SHORT TERM...WDM
LONG TERM...TJT
AVIATION...TJT
HYDROLOGY...63
MARINE...WDM