Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 010612
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
112 AM EST Thu Dec 1 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 325 PM EST Wed Nov 30 2016

An upper level trough of low pressure will bring cool and
unsettled weather tonight through late this week with extensive
cloud cover and intermittent rain showers. Some wet snow flakes
will mix in late tonight into Thursday morning as well but
there will be no snow accumulations. High pressure will briefly bring
dry weather for Saturday before another system moves in to bring
potential for mixed rain and snow showers for Sunday.

&&

.UPDATE...
Issued at 1020 PM EST Wed Nov 30 2016

Recent mPING report of a rain/sleet mix around Holland and a few
similar reports were noted earlier around Chicago. This is not
surprising given the convective nature of the precipitation. Based
on radar trends and short range guidance, have raised
precipitation chances to categorical overnight. Expect a
rain/snow mix to develop around or shortly after midnight
generally east of US-131, which is east beyond the influence of
the lake modified plume. Latest RAP guidance suggests that Wet
Bulb Zero (WBZ) height should be dropping below 1500 ft AGL around
this time, which is a good proxy for seeing snow. Dual Pol radar
products already suggest the WBZ is below 2000 ft, so the mix this
should not be too much longer in taking shape. Accumulations
should be negligible due to warm surface temperatures overnight.

&&

.SHORT TERM...(This evening through Friday night)
Issued at 325 PM EST Wed Nov 30 2016

Primary short term fcst challenges involve determining
probabilities for showers and to assess potential for pcpn type
issues mainly for late tonight into Thursday. The upper
level trough will bring cool and unsettled weather tonight
through Thursday.  Showers will develop this evening as deeper
moisture moves in and showers will increase in coverage overnight.

Brisk southwest flow caa tonight will cause pcpn to become mixed
with some wet snow very late tonight through the early to mid morning
hours Thursday as wbz heights and low level critical thickness values
lower and deeper moisture through the dgz moves in. However only a
couple tenths of an inch of snow will fall mainly east of US-131 and
there will be no snow accumulation overnight. Pcpn type will remain
mainly all liquid form west of 131 due to the modifying affect of
Lake MI.

Seasonably cool and unsettled wx will continue through the day
Thursday with scattered light rain showers. Pcpn type Thursday
will be predominantly liquid form although a few wet snow flakes
may mix in mainly early in the day.

Extensive cloud cover and scattered light rain showers will linger
Thursday night through Friday. The relatively best chc for a few
showers will continue to be near to west of US-131. 12z guidance
consensus time height rh/temp progs indicate an unsaturated dgz
Thursday night through Friday so light rain showers/drizzle will
be the predominant pcpn type.

.LONG TERM...(Saturday through Wednesday)
Issued at 325 PM EST Wed Nov 30 2016

Followed the GFS for guidance in the long term as it has had much
better consistency the last few days. The ECMWF has had issues
handling southern stream energy, namely the upper cut off low moving
across northern Mexico. Temperatures through the long term look to
undergo a slow moderating trend through the period and end up a bit
above normal as we head into next week.

The long term period begins on Saturday with some light lake
generated precipitation ongoing. The moisture depth decreases
quickly though, so pcpn shortly after midnight should come to an
end as we move through the day. Expecting a dry Saturday night
with ridging moving through the area.

Sunday a northern stream shortwave will move through the area
bringing some rain and snow to the area. Surface temperatures as
well as 850mb temps would indicate a rain and snow mix with
potentially some light wet snow accumulations possible. Would not
expect more than an inch or so at best.

Ridging takes hold for Sunday night into Monday night with mainly
dry weather expected. The GFS then has a warm air advection event
for Tuesday into Tuesday night when rain will likely be the
predominant precip form.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 112 AM EST Thu Dec 1 2016

A mix of VFR and MVFR ceilings covered the region attm. Expect
this to continue, but gradually becoming more MVFR with time
through the rest of the morning. There could be some patchy IFR
around daybreak, mostly over far Western Lower MI. A few snow
showers will also be scattered about, that may briefly bring
vsbys down to MVFR too.

Little overall change is expected in the ceilings into the
daylight hours, although they should diurnally lift a bit, but
MVFR is largely expected. The snow showers should diminish toward
mid day, although widely scattered showers may linger near the
lakeshore.

Brisk west southwest winds will remain around 10 knots, and
occasionally gust to around 20 knots in the afternoon.

&&

.MARINE...
Issued at 325 PM EST Wed Nov 30 2016

A small craft advisory remains in effect from this evening through
early Friday morning. Southwest winds will ramp up to 15 to 25 kts
tonight and cause wave heights to build to 4 to 7 feet. West winds
of 15 to 25 kts will cause wave heights to remain up at around 4
to 7 feet through Thursday as well.


&&

.HYDROLOGY...
Issued at 200 PM EST Wed Nov 30 2016

Sycamore Creek at Holt has crested a few inches above bankfull and
is now receding. Maple River at Maple Rapids continues its slow
rise toward bankfull. Only light lake enhanced precipitation is
expected this week, but it will not affect river levels. There
will be chances for more substantial precipitation next week.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 4 AM EST Friday for LMZ844>849.

&&

$$

UPDATE...TJT
SYNOPSIS...Laurens
SHORT TERM...Laurens
LONG TERM...Duke
AVIATION...JK
HYDROLOGY...CAS
MARINE...Laurens



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