Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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000
FXUS63 KGRR 061751
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1251 PM EST Tue Dec 6 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EST Tue Dec 6 2016

We will be entering a wintry period as we head into Wednesday night,
lasting into at least Friday. Accumulating lake effect snow is
expected towards Lake Michigan. Heavy lake effect snow is possible
especially on Thursday into Thursday night. Highs will be near
normal today before dropping into the 20s for Thursday and Friday.

&&

.SHORT TERM...(Today through Thursday)
Issued at 330 AM EST Tue Dec 6 2016

Lake effect snow looks likely in the latter portions of the short
term, or essentially late Wednesday night and Thursday. Accumulating
snows are expected in west and northwest flow snow belts. All of the
lakeshore counties will see accumulations as well as portions of the
next row of counties inland. The highest totals will likely be found
from the Holland are south down the lakeshore and extending inland
towards Kalamazoo. Also, in the far northwest CWA up towards
Pentwater and Ludington.

Moisture depth Wednesday night into Thursday increases from around
5000ft to 10000ft by Thursday evening. Deep lift is noted as well,
extending into the DGZ. This is especially true on Thursday when we
will be in cyclonic upper flow. Delta Ts will be around 20 degrees C
which is on the higher end of what we see in most lake effect snow
events. Thursday morning the Delta Ts exceed 20 degrees C in fact.

Bottom line it will be turning quite wintry in the lake shore
counties starting Wednesday night and especially on Thursday.
Expecting wind parallel bands that will reduce visibility
significantly. Strong winds on Thursday will likely create white out
conditions at times as the Holland BUFKIT overview is showing 22-28
knots from 3000ft all the way to the surface. Air temps will likely
be in the 20s so deteriorating road conditions will start to come
into play as well. Envision the need for Winter headlines as we get
closer to the event in western portions of our CWA.

Otherwise, some light rain, possibly mixed with some light snow this
morning towards Jackson before quickly turning over to all light
rain. Tonight and Wednesday we will likely see some lake effect
starting up as Delta Ts increase into the teens starting this
evening. Shallow moisture will keep this activity light.

.LONG TERM...(Thursday night through Monday)
Issued at 330 AM EST Tue Dec 6 2016

Seasonably cold weather is anticipated through the long range fcst
period along with several chances for accumulating lake effect and
synoptic snow.

Wnw flow lake effect snow will continue in progress Thursday night
into Friday with deep low level moisture in place through the dgz
and with h8 temps of -12 to -14 C yielding very high delta t/s in
the upper teens to lower 20`s.

At this time the greatest potential for significant les
accumulations appears to come Thursday night while deeper moisture
is still in place along with better omegas through the dgz.
Inversion heights will potentially be favorable and quite high
Thursday night at around 9-11 kft agl before lowering significantly
to around 5-7 kft agl Friday.

Significant les accumulations are likely Thursday night into early
Friday particularly in our favored wnw flow snow belt regions
especially near to west of US-131.

H8 temps will moderate Saturday which will result in and end to the
lake effect snow showers. However 00Z Gfs/ecmwf guidance is in
somewhat better agreement in showing potential for a synoptic snow
event Saturday night and Sunday with several inches of snow
accumulation possible then.

Snow may linger Monday as there is potential for a stronger low to
develop over the southern plains and move northeast into the Ohio
Valley/mid Atlantic regions Sunday night into Monday. The
northwestern periphery of the snow shield with that system may
linger over our fcst area Monday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1245 PM EST Tue Dec 6 2016

MVFR cloud cover will continue across parts of Southwest Lower MI
this afternoon. Some light precipitation will be occuring towards
KJXN and KLAN to start the period as a wave of low pressure pulls
away from that region.

A cold front tracks eastward through the TAF sites 21z to 01z this
evening. A few snow showers may accompany the passage of this
front...especially toward KMKG. A sharp wind shift occurs. Gusty
values arrive in the evening and then persist through Wednesday.

Snow showers will be on the increase Wednesday and it is cold
enough for lake effect snow showers by late morning. I did hold
off on lower visibilities at this time as the set up is much
better later in the day for impacts. We will need to monitor a
weak wave of low pressure that tracks through Nrn Indiana and Ohio
Wednesday morning. If this system tracks further north...it could
spread light snow into southern TAF sites KAZO...KBTL and KJXN.

&&

.MARINE...
Issued at 330 AM EST Tue Dec 6 2016

Will be issuing a Small Craft Advisory from this evening through
Wednesday night. The advisory will need to be extended with time it
appears into Friday as well. Waves should jump this evening in the
wake of the passage of a a cold front. Winds will increase into the
15-30 knot range out on the lake out of the west. In a cold air
advection regime, wave building will be very efficient. Essentially,
the remainder of the work week will be rough out on Lake Michigan.
The largest waves look to be from Thursday into Friday when we may
see waves reaching the 6 to 10 foot range in the nearshore waters.


&&

.HYDROLOGY...
Issued at 1156 AM EST Tue Dec 6 2016

Near and above normal river levels continue to affect southwest
Lower Michigan today. The Looking Glass River at Eagle shows
notable rises, but should remain within banks. Slight rises have
also been noted on the Maple River at Maple Rapids, as expected.

Moist soils will provide opportunity for runoff with additional
precipitation this week. Lake effect snow will distribute most of
the precipitation to lake shore counties this week. The weekend
will feature more of a synoptic setup to provide inland locations
with precipitation. Overall, while high rivers may be a concern,
none of the precipitation is too heavy for any given site or
individual episode. Therefore, river rises are possible, but
flooding is of low concern at this time.

&&

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

&&

$$

SYNOPSIS...Duke
SHORT TERM...Duke
LONG TERM...Laurens
AVIATION...MJS
HYDROLOGY...JAM
MARINE...Duke


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