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Area forecast discussion 
National Weather Service Gray ME
735 PM EST Thursday Dec 18 2014

Synopsis...
weak high pressure will start to build in this evening. Some
ocean effect snow may be possible Sunday into Monday due to onshore
flow. A weak low will likely strengthen and pass to our west
Tuesday and may spread light precipitation into New England. An stronger
area of low pressure will most likely develop off to our west on
Wednesday and possibly bring heavy rain and strong winds Wednesday
and into Christmas morning.

&&
00z update...
not much happening around the forecast area this evening. Have
updated temperatures and sky condition to reflect persistent cloud cover
and resulting warmer than expect temperatures. Have also adjusted probability of precipitation in
the mountains downward but still carrying low chance probability of precipitation for any
lingering flurries. Expect low level moisture to continue
diminishing in southern and coastal zones through midnight. No
other changes planned at this time.

Previous discussion...
near term /until 6 am Friday morning/...
blocked upslope signal is pretty strong currently...with khie
dropping below 2sm visibility. This is usually a pretty good indicator
of heavier snowfall heading into northern Coos County. Suspect a similar
story eastward into the western ME mountains with Froude numbers forecast to
continue falling through the evening...will keep pop confined to the
northwest side of the mountain tops. Snowfall grids look in good shape...with
additional light accumulations possible. However since event has
transitioned to mostly the higher terrain in localized favored
areas...winter weather advisories will be cancelled.

Cloud cover should hang tough tonight...and gradient will remain
up just enough to keep a light breeze going. As such I have
blended in mesoscale model 2 M temperature guidance...as we shouldn/T
really see much if any radiational cooling.

&&

Short term /6 am Friday morning through Friday night/...
upslope shsn gradually taper off as lift over the terrain
decreases due to the approaching ridge. As ridge moves in aloft a
bit of middle level moisture looks like it may get trapped and sink
southward across the County warning forecast area during the day. The latest NAM...GFS...and CMC
do indicate at least partial cloud cover...so have blended these
models into the latest sky grids. Otherwise the sensible weather should
be quiet Friday.

&&

Long term /Saturday through Thursday/...
surface high pressure builds north of the region during the day
on Saturday and then slides off to the east on Sunday. This will
set up return flow for Monday and Tuesday. This may produce some
ocean effect snow showers but amounts should be very limited.

Closed upper level low pressure system over the western Great
Lakes will begin to impact New England weather as early as Tuesday
night. Weak disturbance gets ejected from the base of the trough
on Tuesday night and Wednesday morning. The surface reflection of
this may only be a trough but diffluent flow aloft will provide
enough instability for some fairly widespread rain. The larger
event gets going later in the day as a secondary surface low
begins to develop. Models are differing a bit with the details as
the GFS keeps the surface low further east and the Euro takes it
west of US over Vermont. Given the westward extent of the upper
level low...the expectation is that the Euro has a better handle
on the surface low. The current track would take it west of US and
keep all of northern New England in the warm sector of the storm.
The system looks like it could generate a large amount of
precipitation...with most of it in the form of rain for Thursday.
As the storm winds up it will likely produce some strong winds as
well.

&&

Aviation /01z Friday through Tuesday/...
short term...areas of MVFR ceilings will continue into the
overnight...gradually lifting and scattering out to VFR. The
exception will be northwest facing higher terrain...where upslope flow
will keep MVFR ceilings locked in place into Friday. In addition...scattered
IFR conditions are possible in vicinity of khie where shsn will continue in
the upslope flow regime. These shsn taper off early Friday...and VFR
conditions prevail at all terminals for the remainder of the
period.

Long term...primarily VFR conditions over the region. Onshore flow
late Sunday into Tuesday could produce some IFR ceilings and reduced
visibility in ocean effect snow showers.

&&

Marine...
short term...Small Craft Advisory conditions will continue into Friday morning. Wind
gusts near 25 kts and seas around 5 feet on the outer waters will
gradually subside early Friday.

Long term...will likely need flags over the waters Tuesday night
and then through Thursday.

&&

Gyx watches/warnings/advisories...
ME...none.
New Hampshire...none.
Marine...Small Craft Advisory until 4 am EST Friday for anz150>154.

&&

$$

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