Area Forecast Discussion
Issued by NWS Grand Rapids, MI

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FXUS63 KGRR 130241
AFDGRR

Area Forecast Discussion
National Weather Service Grand Rapids MI
941 PM EST Fri Jan 12 2018

LATEST UPDATE...
Update

.SYNOPSIS...
Issued at 324 PM EST Fri Jan 12 2018

Snow that spread across West Michigan earlier today has moved east.
Additional snow showers are expected through the weekend, mostly
near the lake shore due to a trough moving through and then another
low Monday. Saturday will be the coldest day of the next week with
highs in the teens. Then, 20s are expected most of next week.

&&

.UPDATE...
Issued at 941 PM EST Fri Jan 12 2018

The on-going forecast is tracking nicely tonight. The lake effect
snow bands have moved inland over Big and Little Sable points this
evening and as winds become more northerly from being north
northeast the snow bands will continue to slowly move into to
Muskegon by sunrise. I do not expect much in the way of
accumulation. Inland the dense mid/high clouds will move out of
the area between midnight and 3 am, this will allow temperatures
to fall to near zero over our NE CWA.

&&

.SHORT TERM...(This evening through Sunday night)
Issued at 324 PM EST Fri Jan 12 2018

Forecast concerns deal with pcpn trends through the period.

As mentioned above, the snow has largely diminished as the pcpn
shield moves east out of the state. In its wake though, north winds
have produced light lake effect snow showers. However, given 15 dBz
echos or less, not much more than flurries have occurred. The
exception is near the Points where visibilities have fallen to 2-4sm
in light snow.

North winds in the boundary layer will continue to keep shsn near
the lake shore. By Saturday, they will begin to get a westerly
component to them and also get an assist via another upper trough
that will move across the Great Lakes. High pressure at the sfc
though will limit moisture content.

The better chance of snow will come Sunday afternoon and Sunday
night as another clipper moves through. Several inches of snow seem
possible along the lake shore and a headline may be needed.

.LONG TERM...(Monday through Friday)
Issued at 324 PM EST Fri Jan 12 2018

Models are in relative agreement and continue to show a mid level
wave digging down from the Canadian Prairies into the Great Lakes
Region Monday.  This system evolves into a closed low that slowly
drifts through the area through Tuesday. Typically these kinds of
systems lead to widespread impacts.  How much of an impacts is
somewhat uncertain...but the synoptic aspect of the low will support
accumulating snow for the region.  The atmospheric will be plenty
cold enough to keep the precipitation as all snow.  One uncertainty
will be the potential for a mid level dry slot to work in...which is
shown by the GFS at 00z Tue across the Kalamazoo to Jackson region.
It is hard to say this far out whether this will happen.  For now
will feature  high POPs and the potential for accumulations right
through Mon night.

As the system pulls away later Tuesday the lake enhanced band could
continue to impact the lakeshore region well into Tuesday night.

Overall the models show mid level height rises Thursday into Friday.
This will support a moderating trend to the temperatures.  If the
trends continue we may see well above normal temperatures by
Saturday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 627 PM EST Fri Jan 12 2018

VFR conditons prevail at all of GRR TAF sites this evening and it
should stay so till late Saturday morning. The storm that brought
the snow this morning has departed and the snow has ended at all
locations expect LAN but it will end there soon.

Due to north winds, not crossing Lake Michigan, there are no low
clouds expected to move into the TAF sites through 06z or so.
Early Saturday morning some clouds from Lake Superior and northern
Lake Michigan will finally reach the TAF sites but I believe this
will bring only VFR ceiling. As winds turn more northwest instead
of north, during the day time hours of Saturday, ceiling will
start lowering and MKG will start having flurries by 12z. By 16z
to 18z snow should increase enough for MVFR cigs/vsby at MKG. All
sites near and west of US-131 should have mvfr cigs by 18z
Saturday due to Lake Michigan moisture getting into the clouds by
then.


&&

.MARINE...
Issued at 324 PM EST Fri Jan 12 2018

We canceled the gale warning and issued a small craft advisory. The
SCA will be in effect through 6 pm Saturday.


&&

.HYDROLOGY...
Issued at 324 PM EST Fri Jan 12 2018

The water from the snow melt of late has made it into the rivers
across the area and some minor river flooding is ongoing. The colder
temperatures that have moved back into the region will cause ice to
reform and solidify into next week. Therefore, additional flooding
is not expected and river ice will likely be locked down by the end
of the weekend. Will need to monitor rivers for potential ice jam
flooding.

&&

.GRR WATCHES/WARNINGS/ADVISORIES...
MI...None.
LM...Small Craft Advisory until 6 PM EST Saturday for LMZ844>849.

&&

$$

UPDATE...WDM
SYNOPSIS...04
SHORT TERM...04
LONG TERM...MJS
AVIATION...WDM
HYDROLOGY...63
MARINE...04



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