Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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963
FXUS63 KGRR 020538
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1238 AM EST Fri Dec 2 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 PM EST Thu Dec 1 2016

Showery weather will remain possible across the area into Saturday.
The best concentration will be found across extreme SW Lower
Michigan. These showers will tend to mix with, or change over to
some snow at night. Rain will then mix in during the afternoon.
Snow accumulations are generally expected to be a dusting or less.

A system will move toward the area on Sunday. This looks to bring
some light snow to the area, with a chance of some rain mixing in.

&&

.SHORT TERM...(This evening through Saturday night)
Issued at 330 PM EST Thu Dec 1 2016

Our main focus of the forecast in the short term is on pcpn trends,
including p-type and probabilities.

Showers are ongoing this afternoon, with the best concentration
being found between I-96 and I-94 where the best convergence is
found downwind of Lake Michigan. Delta t/s are running around 14-15C
which is only helping the shower activity in conjunction with the
cyclonic flow aloft and a short wave coming in from WI. Pcpn type is
mainly rain this afternoon across the entire area with sfc temps in
the lower 40s and wet bulb zero heights up around 2kft.

Showers will persist tonight, but should become less intense and mix
with, or change over to some snow showers overnight. The upper jet
will lift to the NE, allowing the cyclonic flow aloft to move north
of the CWFA. Moisture profiles will become more shallow as a result.
The slight cooling overnight and lowering wet bulb zero hts will
allow for the snow to reappear. Accumulations more than a dusting
anywhere is unlikely at this time.

Cooler air will continue to filter in over the area through Sat with
the low level W/NW flow holding in. This colder air will continue to
keep a chance of showers possible. Again, limited inversion
hts/moisture depth and the nrn branch of the upper jet north of the
area, nothing significant looks likely. Ridging at the sfc will
build in Sat night, and should cut off the pcpn chcs entirely for a
short period.

.LONG TERM...(Sunday through Thursday)
Issued at 330 PM EST Thu Dec 1 2016

First item of note in the long term is an upper shortwave trough
forecast to move through the region Sunday and Sunday evening.
Surface and 850mb temperatures are near critical values for both
rain and snow and have both precip types in the forecast Sunday and
Sunday evening.

As we head into Tuesday, upper energy swinging north out of the
southern stream will push a surface low through the eastern Great
Lakes. A surge of warm air will be associated with this system with
mainly rain expected Tuesday into Tuesday night.

The southern stream upper energy phases somewhat with a northern
stream developing trough, which in turn deepens it. A very mid
winter look to the 500mb pattern takes shape then from Wednesday
into Thursday.

We look to plunge fully into winter mid next week with any rain
showers changing rapidly over to snow showers. Lake effect snow
should be in full swing on Wednesday it appears and surely for
Wednesday night into Thursday. Delta T`s off the latest GFS would be
on the order of 25 degrees C or so by next Wednesday evening, which
is extreme. The plunge of -16C air or so has been in the models for
a couple runs so confidence is increasing. The ECMWF was delayed
today, so will be watching it as it comes in late this afternoon to
see if the GFS and ECMWF are on the same page with the cold air.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 1238 AM EST Fri Dec 2 2016

A mix of VFR and MVFR conditons will continue for much of the next
24 hours, however a more widespread MVFR is expected toward sunset
Friday.

Lake effect rain and snow showers will also continue. Localized
IFR may occur between 10-16Z. This will be the period when the
coldest air moves over the lake and should increase the pcpn
coverage and intensity. Then the afternoon will feature the mix of
VFR and MVFR again. The showers will diminish to only isolated by
late afternoon.

We will finally see the winds drop off around sunset. Due to the
less mixing we should see MVFR ceilings fill in across the area
and continue through 06Z.

&&

.MARINE...
Issued at 330 PM EST Thu Dec 1 2016

We are expanding the Small Craft Advisory through Friday afternoon
with the afternoon forecast package. Winds will be gradually taper
off after this evening, but waves look to hold around 4 ft into Fri
afternoon. We should see conditions then remain below Advisory
criteria through early next week with relatively limited winds
expected.


&&

.HYDROLOGY...
Issued at 330 PM EST Thu Dec 1 2016

Periodic light lake enhanced precipitation is expected into the
weekend, which will not have much affect on river levels. Maple
Rapids continues its slow climb toward bankfull while Sycamore Creek
has fallen below bankfull. A couple chances for more substantial
precipitation are possible next week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 7 PM EST this evening for LMZ844>849.

&&

$$

SYNOPSIS...NJJ
SHORT TERM...NJJ
LONG TERM...Duke
AVIATION...JK
HYDROLOGY...CAS
MARINE...NJJ



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