Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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238
FXUS63 KGRR 051737
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
1237 PM EST Mon Dec 5 2016

LATEST UPDATE...
Hydro

.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 12Z TAFS through 12Z Tuesday morning)
Issued at 655 AM EST Mon Dec 5 2016

Widespread MVFR ceilings are in place at 12z all across Southwest
Lower Michigan. This will likely remain the case through today. A
couple things to keep an eye on today are the IFR and lower
conditions off to our southwest over Illinois. It is possible
these low ceilings/visibilities will try to push our way through
the course of the day. Current thinking is they will remain off to
our southwest and we will see the MVFR ceilings persist. The other
item of note will be the potential for snow melt fog. At this
point have introduced 6SM vsbys and haze later this afternoon and
evening when the winds slacken off a bit.

Tonight, winds will increase once again aloft into the 20-30
knot range from the southeast between 1000-2000ft. The increase
in wind should tend to blow out the lower ceilings with a trend
toward VFR conditions tonight.


&&

.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 1237 PM EST Mon Dec 5 2016

Liquid equivalent of last night`s snowfall generally ranges from
0.25" over south-central Michigan to 0.50" over southwest
Michigan, where the highest snowfall totals were reported.

The Maple River at Maple Rapids was previously being watched for
rising river levels, but never seemed to follow expected trends,
nor did the site every achieve bankfull. It continued to fall
through this morning and quarter inch amounts are not expected to
bring it anywhere near bankfull. As a result, the advisory has
been dropped. The current downward trend may stall and return to a
slight rise through mid-week. Rises are expected to remain within
banks.

River levels through the area are running near and above normal.
Given the current status, moist soils and active pattern through
the next several days, river activity may need to be monitored.


&&

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

$$

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



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