Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Caribou ME
908 am EST Sat Dec 7 2013
high pressure will build east into the area over the weekend with
much colder and drier air. Low pressure from the southwest approaching
late Sunday night and Monday morning will cross the region by late
Near term /through tonight/...
update...only significant changes needed with this update were to
the hrly temperatures to drop them back a few degrees per the last
3 hour trend. Rest of the forecast is looking good at this time.
Dry weather is expected today and tonight as high pressure will
build into the region. The pressure gradient will tighten through
the day as the high approaches, so expect breezy west winds to
develop by early afternoon. Downsloping off the higher terrain
along with drier air associated with the building ridge will allow
skies to clear out across downeast Maine. In turn, temperatures
will reach into the lower and middle 30s. Further north, expect
mostly cloudy skies to develop in response to a weak shortwave
prognosticated to cross southern Quebec. Also can't rule out a flurry or
two. Highs here will be in the lower to middle 20s.
For tonight...the dry weather continues with clouds dissipating as
the aforementioned waves shifts to our east. There will be enough of
a gradient to keep winds from dropping off completely, which will
limit the extent of radiational cooling overnight. However,
temperatures will still be quite chilly, ranging from the single
digits above zero across the north to the middle teens downeast.
Short term /Sunday through Monday night/...
models are in good agreement with the sequence of events through the
short term. Sun will begin dry and cold...with perhaps a thin
broken layer of SC from the St Lawrence in northwest low level winds across the
north half of the forecast area Sun morning into the afternoon. All areas will begin msly
clear sun evening as surface hi pressure begins to crest the region...then hi/middle
cldnss will begin to spread ewrd from approaching surface low pressure from the
Midwest late Sun night as the hi moves east of the region. Clouds will
thicken Monday morning...with snow breaking out from SW to NE from the
late morning through the Erly afternoon hours...with this tmg a blend of
slightly faster 00z GFS and slower European model (ecmwf). Both models indicate
enough low level warm advcn ahead of an occlusion spot low that crosses
the Gulf of Maine Monday evening for snow to mix with rn over interior
downeast areas and mix with and change to rn along coastal areas
during the evening hours...which will somewhat lower the accumulation
potential over this portion of the forecast area. From east central portions of the forecast area nwrd...
precipitation should remain all snow...but even here given the rapid
progression of both the surface low and supporting shortwave aloft...snfl
totals may be limited to 3 to 4 inches at most lctns...as suggested
by the majority of 00z opnl and 21z sref models. Steady snow north and
central and mixed precipitation downeast should wind down to showers late Monday
night and msly end by Tuesday morning.
After chill Erly lows around or just after mdngt sun...temperatures should remain
steady or slowly rise late Sun night then steadily rise Monday reaching
hi temperatures Monday evening before falling late Monday night behind the occlusion.
Long term /Tuesday through Friday/...
Tuesday through Wednesday morning will be colder than Monday and Monday night with
typical cold advcn SC/scattered flurries and snow showers across the northwest half
of the forecast area. But the real cold Arctic air arrives later Wednesday to the
forecast area...becoming firmly entrenched over the region by Thursday morning. With
sub zero lows Thursday morning accompanied by a brisk breeze...we cannot
rule out the first wind chill advection for northern and even perhaps central
portions of the forecast area late Wednesday night into Thursday morning. Based on projected afternoon
925mb temperatures of -19 degree c downeast to -23 degree c northwest...hi temperatures
Thursday with struggle to reach 5 to 10 above north and lower to middle teens
downeast...and this may be optimistic. Aftwrds...tmg differences
exist between the GFS and European model (ecmwf) with regard to a clipper shortwave from
central can which could bring a re-enforcement of high residence
Arctic air for Friday and Sat. Given how cold and dry the air will
be ahead of this shortwave...we kept probability of precipitation in the slight chance category for
now. The European model (ecmwf) in particular is aggressive with bringing this
airmass into the forecast area behind this shortwave...but for now its to Erly to
say what magnitude of Arctic airmass will move across our forecast area behind
this system at this time.
Aviation /14z Saturday through Wednesday/...
near term: other than some brief MVFR ceilings in response to
light snow falling along the coast early this morning, expect VFR
conditions to dominate today and tonight. A 3000-4000 feet cloud
deck is expected to develop at the northern terminals by 16z
today, which could lead to some occasional MVFR ceilings,
especially at kfve.
Short to long term: msly VFR expeceted through Sun night...with brief periods of
MVFR clgs in thin broken SC possible over northern taf sites Sun morning through
afternoon. The next chance of MVFR and IFR clgs/visibilities will be with snfl
associated with the low pressure complex approaching from the Midwest on
Monday. With conditions lowering from SW to NE during the late morning
through middle afternoon hours. Conditions should then remain IFR with
snow northern taf sites and mixed rn/snow downeast sites Monday evening before
improving to VFR downeast sites and MVFR northern taf sites by Tuesday...
which then continues through Wednesday.
near term: a Small Craft Advisory has been issued for the outer
waters from this afternoon through tonight. Cold air advection
will begin in earnest over the waters later today, allowing for
decent mixing over the relatively warm Gulf of Maine. Gusts to 30
knots and waves of 3 to 6 feet are expected. For the inner waters...a
few gusts may approach 25 kt, but this should be the exception as
opposed to the norm. Have therefore not included the inner waters
in the Small Craft Advisory.
Short to long term: it appears that an Small Craft Advisory from the near term will
last a few hours through middle Sun morning across the outer mzs...then
northwest winds should subside by Sun afternoon. Another brief period of marginal
Small Craft Advisory winds and seas is possible Monday afternoon into Monday evening with southeast winds
ahead of the secondary occlusion low approaching the waters from the SW
and again on Tuesday with west-northwest winds behind the low.
Marine...Small Craft Advisory from 3 PM this afternoon to 10 am EST
Sunday for anz050-051.