Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Gray ME
554 PM EST Thursday Dec 19 2013
a cold front will gradually settle south overnight and will stall
over the area on Friday...then push south of the region over the
weekend. Several waves of low pressure will track east along this
boundary Friday through Sunday. High pressure will gradually build
in from the northwest Monday through Wednesday. A cold front will
approach from the northwest Thursday and will cross the region
Near term /through Friday/...
have updated grids based on current conditions. Lowered min temperatures
a few degrees for the overnight hours as temperatures quickly falling
towards their dew points.
Adjusted winds to allow for very gusty winds currently occurring
over the higher terrain. Will probably be lowering scas over the
coastal waters during the next update...as winds have slowly
diminished. Seas will still remain up however for the next hour or two.
a cold front will drop south from Canada overnight as high
pressure builds by to the north and will stall over the area by
Friday morning. This will keep skies mostly cloudy overnight in
northern zones with a chance of a snow shower. Farther south
expect variable middle and high clouds. Lows overnight will be from
the middle to upper teens in the north and lower to middle 20s in the
Short term /Friday night/...
weak low pressure will track east along the stalled frontal
boundary on Friday. This will bring a variety of light precipitation to
the region with light snow or sleet in the north and snow changing
to sleet or freezing rain in the foothills. Temperatures warm into
the middle to upper 30s in the south so the bulk of precipitation in these
areas will likely fall as rain. Expect highs in the middle 20s to
lower 30s north and middle 30s to near 40 in the south.
Expect precipitation to taper off after midnight Friday night as
wave passes. Will see light rain in the south possibly changing to
freezing rain before ending. In the north will see snow...sleet or
freezing rain tapering off late. Will likely need advisories for
winter weather on Friday but will let the midnight shift take a
look at new data and make the decision then.
Long term /Saturday through Thursday/...
a complex weather pattern is setting up Saturday through Sunday with a
significant mixed precipitation even /mainly ice/ setting up for the forecast
area. Previous GFS and NAM models warmed up southern areas significantly
with the fnt pushing into central areas which would produce more rain
than freezing rain while the European model (ecmwf) and CMC models kept the fnt south of the
forecast area providing more freezing rain. The 12z NAM continues to be warm while
the 12z GFS is now turning colder...closer to the European model (ecmwf) and CMC
model solutions. The 12z European model (ecmwf) now supports previous runs of this
model supporting a colder solution that would create freezing rain
all the way to the coast...especially over the middle coast SW towards
pwm. The 12z CMC is cold but not quite as far S initially with the
fnt as the European model (ecmwf).
Still some uncertainty on how this all finally plays out...but
typically it is difficult to push a warm fnt north through the forecast
area especially with a deep snow pack and a building cold Arctic
high north of the forecast area. The Arctic air mass to our north has
minus 30 c and colder at 850 mb at its core...supporting the
strength of the high and its ability to pour cold air southward into
the forecast area. The fnt does push north into the coastal waters due to
little resistance over the water but will likely not reach the
coast. However...models stall it there with weak waves of low
pressure moving along the fnt. The 850 mb flow is from the SW which
parallels the coast and the surface fnt meaning fnt won't be pushed
inland. At most it may affect the islands.
The fnt does try to push into southern New Hampshire as the main surface low
strengthens and moves to the NE well west of the forecast area.
Typically this forces the fnt to move to the north across Vermont and New York as
well as the CT River Valley but struggles over areas further east
due to cold air damming as cold north NE surface winds blow from the high
southward across the forecast area.+-+ If temperatures do manage to climb above
freezing southern and coastal areas it will be later in the day Sunday
after the main prpc has ended and only spotty light prcp lingers. Light
mixed prcp Saturday with steadier prcp and higher quantitative precipitation forecast moving in for
Saturday night and Sunday morning. There is enough cold air over
northern areas to support snow and pl with our most northern areas possibly
seeing significant snow accumulations before changing over to pl and
Models now pushing a dry wedge NE into the forecast area Sunday
afternoon shutting off the more significant quantitative precipitation forecast...though spotty light
prcp likely to continue into Sunday night. The entire system shifts to the
east Monday with improving weather. The sharply colder weather holds off until
Monday night when northwest flow begins to bring in colder Canadian air. The
coldest temperatures arrive Tuesday and Tuesday night as cold high pressure
builds in from the west. The high settles over the region Wednesday
as the cold air mass begins to slowly modify. The high moves off the
coast Thursday allowing a return flow of warmer air on S SW winds
which may produce some light prcp.
It is still too early to pinpoint exactly when prcp will start and
end... how much quantitative precipitation forecast will fall and what the prcp type will be during
the entire event as well as where snow/pl/zr/ra fall. This will be a
prolonged event with mostly light prcp until heavier prcp arrives late
Saturday night and Sunday.
Used a blend of models and MOS guidance along with HPC quantitative precipitation forecast for
periods 4 and 5...then used a super blend of various models and MOS
guidance ... with bias corrected guidance and the previous
forecast for days 4 through 8. Went well below the super blend for
temperatures on Sunday based on model history of being too warm on these
events by trying to push the warm fnt too far north too fast.
Blocking high to the north and very cold air draining southward with
cold air damming keeps cold temperatures at the surface...especially with a
deep snow pack. The CT River Valley most likely area to see warm air
Aviation /00z Friday through Tuesday/...
short term...VFR tonight. MVFR/IFR ceilings developing on Friday
and persisting through Friday night.
Long term /Saturday through Tuesday/...an extended period of low
ceiling/visibility with mixed prcp through Sunday night. The lowest conditions
and highest chance of heavier mixed prcp late Saturday...Saturday night
and through midday Sunday. Improving weather on Monday.
short term...scas remain in effect...but may be dropped with the
Long term /Saturday through Tuesday/...a frontal system will push
slowly south of the forecast area Saturday and Saturday night then
pushing north and stalling over the coastal waters on Sunday as
weak low pressure systems move NE along the fnt. Stronger low
pressure to the west of the region and the fnt finally move out to
sea Sunday night and Monday. Overall this pattern keeps winds
below Small Craft Advisory levels over the waters though seas may build to Small Craft Advisory
levels in part due to swells from increasing SW flow well south of
the fnt over the weekend and continue into Monday. Cold northwest flow
follows for Monday night and Tuesday with Small Craft Advisory conditions likely.
Marine...Small Craft Advisory until 1 am EST Friday for anz150-152-154.