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Area forecast discussion 
National Weather Service Grand Rapids Michigan
330 am EST Friday Dec 19 2014

Latest update...
synopsis/short term/long term

Synopsis...
issued at 330 am EST Friday Dec 19 2014

After some leftover freezing drizzle and snow flurries move out from
the southeast portion of the area early this morning...we will move
into a fairly quiet weather period then through the first portion of
Monday. Temperatures will also moderate through the weekend.

The weather is expected to become more active next week with a trend
toward colder and snowier conditions....possibly just in time for
Christmas. This colder air will be ushered in by a couple of
stronger storm systems.

&&

Short term...(today through sunday)
issued at 330 am EST Friday Dec 19 2014

The main challenges of the short term portion of the forecast are
dealing with the ongoing headline for freezing drizzle this
morning...and then mainly determining cloud trends through sun.

We will be holding onto the Winter Weather Advisory for now. We
continue to see some light fog being reported at sites in the
advisory...likely indicative of residual freezing drizzle. The
impact is not as great as earlier as Highway speeds are
higher...likely due to treatment of the roads. The trend in the
light echoes on the radar is diminishing as the surface trough continues
to sink south through the area.

The amount of clearing expected to take place is not a totally
certain thing yet for everyone. Model consensus does push the
clearing line just south of the County warning forecast area by later this afternoon. The
higher resolution and typically more pessimistic NAM does hold the
low level cloud cover over the southern portion of the County warning forecast area. We are
running with a forecast where at least some partial clearing takes pace
at all locations.

The clearing looks to hold in through the first portion of the day
on Sat before clouds increase from the SW. We see some middle/high
cloud cover move in well north of the system affecting the southern
portion of the country. Models are lingering a band of low level
moisture over Lake Michigan before pushing it onshore at some point
late Sat into early sun. Precipitation chances look quite low as there is not
really good overlapping of the low level and middle/high level
moisture. Just about all of the forcing is up high...above the
moisture layer.

A bit deeper moisture moves in on sun as the long wave trough moves
out into the plains states. Low level moisture moves north...and
forcing is not really existent so we expect another mainly dry day.

Long term...(sunday night through thursday)
issued at 330 am EST Friday Dec 19 2014

An active weather pattern is expected for Christmas week. Rain is in
store early in the week followed by a transition to snow showers and
windy and cooler conditions on Christmas evening into Christmas.

The evolution of an 500 mb longwave trough and surface low/trough over the
center of the nation early next week induces a southerly flow of
warm moist air into the Great Lakes region. This will lead to rain
showers Monday into Tuesday with highs at or above 40... although a
brief threat of light mixed wintry precipitation may exist at the
onset of the precipitation late Sunday night and early Monday before
sufficient warming takes place.

Forecast confidence remains low for Christmas evening when negative tilt
upper trough pivots northeast through the Great Lakes region. Latest run
of the European model (ecmwf) has a closed upper low within this trough and a deepening
surface low underneath it tracking north through the eastern Great Lakes
region. This suggests the possibility of an impactful event with
some accumulating heavy/wet snow within the trowal and strong winds.

However the European model (ecmwf) solution has not been consistent and the other
scenario shown by the fim is for the deep low to develop over New
England rather than nearby. Regardless of how Christmas evening plays
out... all model solutions indicate cold air advection and cyclonic
flow over Michigan for Christmas day. This supports scattered snow
showers... but the air is not particularly cold and the deeper
moisture lifts out rather quickly so no significant lake effect is
expected at this time.

&&

Aviation...(for the 06z tafs through 06z Friday night)
issued at 1150 PM EST Thursday Dec 18 2014

The freezing drizzle will continue to slowly shift south of
kjxn...kbtl and the kazo region through 08z. Thus impacts are
still expected. Until then some snow could mix in at times.
Generally MVFR weather will prevail to start the period...however
skies will slowly clear from the north later tonight into Friday.
Patchy IFR will still be possible through 08z mainly for kjxn.

Icing will remain a potential issue right into Saturday.



&&

Marine...
issued at 240 PM EST Thursday Dec 18 2014

No concerns at this time. Winds and waves will continue to subside
this evening and stay low into the weekend with high pressure in
control.



&&

Hydrology...
issued at 240 PM EST Thursday Dec 18 2014

No significant Hydro impacts expected for the foreseeable future.

&&

GRR watches/warnings/advisories...
Michigan...Winter Weather Advisory until 8 am EST this morning for
miz065>067-073-074.

Lm...none.
&&

$$

Synopsis...njj
short term...njj
long term...Meade
aviation...mjs
hydrology...ebw
marine...tjt

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