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Area forecast discussion 
National Weather Service Grand Rapids Michigan
639 am EST sun Dec 28 2014

Latest update...
aviation

Synopsis...
issued at 329 am EST sun Dec 28 2014

Much colder air arrives this week as an Arctic front sinks south
through the area tonight. Snow will be possible at times tonight
through most of the coming week. More significant chances for
accumulations will be Monday night as well as Tuesday night and
Wednesday. Highs may struggle to reach 20 degrees on Wednesday.

&&

Short term...(today through tuesday)
issued at 329 am EST sun Dec 28 2014

Ongoing light snow showers are expected to wind down by 7 am...but
will hold on to a slight chance in the northwest through the
morning.

Fairly quiet weather is expected today with highs in the low to
middle 30s. Surface ridging will build in from the west...and
pressure rises are expected out ahead of an Arctic front sinking
south from Canada. Some sun is expected in the afternoon.

Surface winds will veer more northerly after 00z this evening as the
Arctic front moves through followed by stronger cold air advection.
Lake effect snow showers will be possible tonight through the rest
of the short term. There is some enhanced potential for accumulating
snow right along the Lakeshore with northerly flow on Monday night.
A piece of shortwave energy currently over the Pacific northwest rounds the
trough and ejects eastward toward the Great Lakes on Monday.
Moisture remains shallow...but this shortwave along with much colder
air at 850 could be enough for some more significant accumulations.

While the polar jet stays south of US...the 1059 mb surface high
over western Canada at 18z Monday tracks to the northern rockies by
18z Tuesday...allowing the Arctic air to stream in.

Lows tonight will drop into the teens and lower 20s and highs on
Monday will likely not reach freezing. Then colder with single
digits and teens Monday night and highs in the low to middle 20s for
Tuesday.

Long term...(tuesday night through saturday)
issued at 329 am EST sun Dec 28 2014

The main challenge in the long term deals with the potential for
snow and possible impacts.

Trends continue to support an increase in the snow for this forecast
period. West to northwest flow Tuesday night into
Wednesday...favorable instability and a moist dgz support some
accumulations. Inversion heights remain low which will act to limit
total accumulations I did raise probability of precipitation to account for the possibility
of accumulations. The flow strengthens as we go into Wednesday
night...which could force smaller bands tracking further inland. We
will need to monitor this event for possible headlines given the
risk for accumulations...gusty winds and Arctic air around. I will
mention possible impacts in the hazardous weather outlook.

Models are coming into better agreement on a deepening low to track
northeast through the Great Lakes region Friday night into
Saturday. The exact track and strength will determine how much if
any impacts for the area. Enough confidence exists to bump up probability of precipitation
and mention possible impacts in the hazardous weather outlook.

&&

Aviation...(for the 12z tafs through 12z Monday morning)
issued at 633 am EST sun Dec 28 2014

MVFR clouds to start should scatter out this morning as drier air
works its way in from the west. Satellite imagery shows the
clearing skies crossing Lake Michigan at this time. Kldm has gone
scattered within the past hour.

Another cold front will track down from the north tonight. This
will cause the clouds to return...with MVFR ceilings possible for
some of the sites. In addition there could be some snow...but at
this point it should remain light...with limited impacts forecasted.

&&

Marine...
issued at 329 am EST sun Dec 28 2014

Continued the Small Craft Advisory through 11 am today. Waves are
expected to subside to 2 to 4 feet later today as winds are
diminishing. West winds 10 to 15 knots expected today.



&&

Hydrology...
issued at 329 am EST sun Dec 28 2014

No significant precipitation is expected today or tonight.
However...more significant snowfall accumulations are possible
Monday night right along the Lakeshore. A more significant Hydro
impact this week will be colder temperatures. With temperatures
below 20 degrees at times this week...ice will begin forming on rivers.

&&

GRR watches/warnings/advisories...
Michigan...none.
Lm...Small Craft Advisory until 11 am EST this morning for lmz844>849.

&&

$$

Synopsis...ebw
short term...ebw
long term...mjs
aviation...mjs
hydrology...ebw
marine...ebw

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