Area Forecast Discussion
Issued by NWS Portland, ME

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FXUS61 KGYX 152326

Area Forecast Discussion
National Weather Service Gray ME
726 PM EDT Thu Mar 15 2018

A broad area of low pressure will spin over the Canadian
maritimes tonight and Friday, with snow showers continuing in
portions of the mountains. Temperatures will be a little cooler
than normal with abundant cloud cover. The next trough will
drop down out of the Canadian Arctic and arrive in New England
on Saturday with colder conditions expected for the weekend.


Have made only minor adjustments to the forecast for tonight.
Drier air is moving in from the northwest overnight, which
should help to shut down the upslope snows which have only been
sparsely reported in recent hours, thus have lowered PoP as the
night goes on. No other significant changes were made.

Some ridging aloft allowed for partial clearing today, however
some CU did fill in during the daytime as the atmosphere
remains rather unstable. Most of the cloudiness and moisture
will remain over the upslope regions of the mountains as a WNW
flow continue to produce snow showers. This will be mainly
terrain driven precipitation with the valley floors remaining
relatively dry. A couple inches of snow is possible across the
higher peaks.

There will be a well mixed atmosphere overnight with cold air
advection occurring. H8 readings fall to the -9C to -14C
readings by morning. Overnight lows will mainly run in a
relatively small range from the mid teens in the north to the
mid 20s in the south.


Plenty of clouds will remain over upslope areas with some snow
shower activity continuing. More sun is expected in the south.
It will be chilly and breezy with temperatures continuing to be
below normal for this time of the year.

Another reinforcing shot of cold air arrives Friday evening with
the passage of an upper level trough and a surface cold front.
Cold air advection will be maxed out during the overnight hours.
H8 temperatures drop down to -16C to -22C from south to north by
Saturday morning. With gusty winds it will feel even colder than
the projected single numbers for lows in the north to mainly in the
teens in the south.

Will need to watch for a couple snow showers or even possibly a
snow squall with this shot of cold air during the night
potentially making it down into southern areas. The atmosphere
will remain unstable with a large upper low overhead.


Most people like snow for the holidays...and the extended
forecast is looking increasingly likely that holiday may be
Easter. The next 7 days should ensure the majority of the
current snow pack remains at the end of next week.

For starters upper low rotating around NErn Canada will propel a
chunk of very cold air across the region this weekend. H8 temps
around -20 C...around 2 standard deviations below normal...will
set the stage for afternoon temps struggling to break the
freezing mark. The angle of delivery...from the awfully
favorable for minimal moderation of this air mass. In fact on
Sat...I have temps remaining in the 20s for much of the area
as the core of the coldest air is overhead. As the trof axis
passes some snow shower activity is also possible...though
significant accumulation is not expected.

Only slight moderation is expected into early next
cold...Canadian high pressure edges towards the area. We will
remain in the cyclonic flow upstream of the upper low...and that
will allow fresh supply of cold air. Sun and Mon both look to be
at least 10 degrees cooler than normal.

Then the focus turns to model guidance still
remains in broad agreement in a higher than normal chance for
precip. Again I am not willing to delve too much into deterministic and ensemble guidance is now trending
towards a more convoluted evolution involving one baroclinic
zones and two low pressures back to back. Ensemble guidance is
showing significant spread among the individual members...and so
this is a low confidence forecast. In fact the ECMWF EPS has a
mean surface low off the East Coast for over 48 hours...due to
multiple S/WV trofs triggering cyclogenesis events in that
window. It is safe to say there will be a storm system to track
in the mid to late week time frame...but my feeling is that
models will eventually focus on one S/WV. For that reason PoP
has it is potentially spread out over more days
due to uncertainty. As things stand now though there is high
pressure in a good location to hold cold air...and more than
enough forcing aloft for a coastal storm. This one will have to
be watched closely.


Short Term...Mainly VFR conditions in the short term portion of
the forecast (through Friday night). There will likely be
periods of MVFR conditions in low ceiling or any snow showers
at HIE with low clouds at times at LEB and AUG.

Long Term...Widespread VFR conditions are expected this weekend
into early next week. Gusty WNW flow will continue Sat...with
surface gusts to near 20 kts. High pressure will gradually nose
in thru early next week...continuing VFR conditions thru Tue.


Short Term...Have extended the SCAs tonight through Friday
night for the outer waters and just for Friday and Friday night
for the bays. Winds may approach gale force in a few spots
Friday night, however confidence is not high enough at this time
for gale watches or warnings.

Long Term...SCA conditions will continue for the coastal waters
Sat. As deeper mixing occurs during the day a few gusts near
gale force are possible well outside the bays. Will likely see a
brief lull in SCA conditions Sun into Mon as high pressure noses
into the area. By midweek NE flow will be increasing...and
SCAs...possibly gale force winds...are likely.


MARINE...Small Craft Advisory from 6 AM Friday to 6 AM EDT Saturday for
     Small Craft Advisory until 6 AM EDT Saturday for ANZ150-152-



LONG TERM...Legro is the U.S. government's official web portal to all federal, state and local government web resources and services.