Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 051742
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1242 PM EST Mon Dec 5 2016

LATEST UPDATE...
Aviation

.SYNOPSIS...
Issued at 330 AM EST Mon Dec 5 2016

A period of fairly quiet weather is expected from Today into
Tuesday. High pressure at the surface will be responsible for dry
conditions today. There may even be some sunshine this afternoon.
Dry weather should continue tonight as well with surface high
pressure still influencing our weather. On Tuesday, a weak surface
trough of low pressure will move through the Great Lakes region
bringing some very small chances for light rain or snow, but
significant precipitation is not expected. The main story this week
is that we will turn colder with chances for lake effect snow
increasing from mid week into Friday. Accumulating snows are
expected towards Lake Michigan with highs only reaching the 20s on
Thursday and Friday in all areas.

&&

.SHORT TERM...(Today through Wednesday)
Issued at 330 AM EST Mon Dec 5 2016

Limited concerns for the most part in the short term with clouds and
small chances for precipitation being the focus.

Westerly winds have kicked up this morning which has ended fog that
was beginning to set in after the snow stopped. Low clouds remain
however and extend all the way back into eastern Iowa. We will start
the day cloudy, but there is a chance that we break into some
sunshine this afternoon. The NAM indicates that we erode the clouds
from the south and west this afternoon. Delta T`s are right on the
line over Lake Michigan for cloud production (10C). So, a southwest
flow may continue to try to produce stratocu off the lake, but still
thinking there may be some sun. We should see a slight rebound in
temps today even with the fresh snowpack up to around 40 given a
wind off a warmer lake, some sunshine and warm air advection aloft.

Tonight thinking we should be dry with partly cloudy conditions.
Lows will likely drop off into the 20s given the fresh snowpack.
Increasing winds aloft tonight should keep fog at bay with a melting
snowpack.

Tuesday a surface trough will be swinging through. We will be in
between lows both to our northwest and southeast. Thinking the bulk
of the precipitation from both systems will miss us, but have very
low pops in the forecast to cover things, on the order of 20-30 pct.

Tuesday night into Wednesday colder air begins to filter into the
region with Delta T`s increasing through the teens C. More than
enough instability for lake effect clouds and lake effect snow. The
problem is that moisture is really shallow, below 5000ft. Have some
chances for light snow in the forecast both periods in the western
CWA, 20-30 pct. Given the really shallow moisture not expecting any
impacts from the light lake effect that does develop.

.LONG TERM...(Wednesday night through Sunday)
Issued at 330 AM EST Mon Dec 5 2016

A much colder airmass will continue to advect in Wednesday night
through late in the week with potential for several rounds of
accumulating synoptic and/or lake effect snow. Lake effect snow
showers will ramp up late Wednesday night as h8 temps fall to around
-12 to -14 C by 12Z Thursday. This will yield delta t/s in the upper
teens to lower 20s.

West to nw flow lake effect snow showers will then continue through
late this week with deep low level moisture in place through the dgz
and strong lake induced instability with h8 temps down around -14 to
-16 C that will yield delta t/s into the lower 20s. Snow showers
will likely be enhanced by a trough that will move through Thursday
night or Friday and also when inversion heights reach around 8-10
kft from time to time. However lack of deeper moisture and lower
inversion heights from 5-7 kft agl are inhibiting factors against
more significant lake effect snow accumulation potential.

Nevertheless some lake effect snow accumulations and travel impacts
are likely Wednesday night through late in the week particularly in
our west to nw flow favored snow belt regions near to west of US-
131. High temps Thursday through at least Saturday will only reach
the middle 20`s to lower 30`s with mins down in the teens to lower
20`s. There is also potential for another synoptic low pressure
system to bring more accumulating snowfall for the weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1241 PM EST Mon Dec 5 2016

Broken to overcast stratus with bases around 1500 to 2500 feet
AGL and tops around 3000 feet will be across southern Lower
Michigan this afternoon and evening. The clouds may break up at
times overnight but should thicken on Tuesday morning. Winds will
be southwest 8 to 12 knots today then go southeast at 10 knots or
less on tonight and Tuesday.

&&

.MARINE...
Issued at 330 AM EST Mon Dec 5 2016

Winds have come up as expected behind the surface trough this
morning with all of the lakeshore beach observation sites blowing at
20-30 knots out of the west. Waves have likely jumped into the 4-6
foot range. Therefore, the Small Craft Advisory looks solid.
Extended the end time of the SCA through 100pm to give time for the
wave field to subside a bit more.

Later today and into tonight, southerly flow begins to take hold
with marginal Small Craft Advisory conditions once again, especially
north of Grand Haven. We will need to assess today whether we need
to extend the northern zones into tonight.

Cold air advection wind and waves look likely for Small Craft
Advisory conditions from Tuesday evening to at least into Thursday.


&&

.HYDROLOGY...
Issued at 1219 PM EST Sun Dec 4 2016

The Maple River advisory at Maple Rapids continues with a bit of
question, due to the recent drop in river levels. Trends will need
to be monitored to reconsider this headline this evening. All of
this depends on total precipitation amounts, which are expected to
come in the form of snow today and should not exceed one-quarter
of an inch over south-central Lower Michigan.

Monday should be dry with light precipitation amounts through the
middle of the week. The later half of the week could introduce
another quarter inch or so of precipitation when lake effect snow
kicks in. Much of that should stay confined to locations along
and west of highway 131.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...None.
&&

$$

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


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