Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Caribou ME
557 PM EST Sat Nov 22 2014
strong high pressure will build south of the area tonight and
move east on Sunday. Meanwhile...an weak upper level disturbance
will move across far northern Maine through this evening. Strong
low pressure from the Great Lakes will approach later Sunday and
then move northwest of the region on Monday.
Near term /through Sunday/...
6 PM update...patchy light snow over the north is diminishing.
Made some minor modifications to sky cover and dew points.
Otherwise, no major changes this hour.
The challenge this term will be temperatures and potential for freezing
drizzle. The latest radar mosaic loop showed some light returns
across the northern tier and over the downeast region. The returns
across the north more indicative of snow/light snow as evidence
from the obs(kfve) and webcams. Still expecting an inch or so of
new snow mainly across the Allagash and St. John valley. Further
south toward downeast, most of the returns mostly virga west/possibly
some flurries or sprinkles. The laps soundings support this west/dry
air above below 700mbs. Decided to carry 50-60% across the far
north through the remainder of the afternoon and then wind things
down by the evening as the best forcing moves east.
Now, for the central and downeast areas, there is a weak impulse
in the upper levels moving out of southern Quebec that is picked
up well by the NAM and moves across west-central areas tonight.
NAM soundings show some moisture through 500mbs west/temperatures cooling in
the blyr(aob 32f) and a warm ribbon(abov 0c) from 925-850mbs. Low level
convergence west/the weak impulse could be enough to kick off some
light precipitation. Attm, decided to carry the mention for some patchy
freezing drizzle along west/rain and snow showers through midnight.
The best chance for the freezing drizzle will be away from the
immediate coast. Due to the brief period of freezing drizzle, not
expecting any icing and therefore, decided to leave out a winter
weather headline. The evening crew can assess this further this
Moderating temperatures for Sunday west/middle to upper 30s north and low to middle
40s downeast to the coast west/west-southwest winds. Need to keep any eye on
the forecast this package as moisture could keep be trapped west/a warm
layer aloft and drier air. This is picked up well once again by
the NAM and even the GFS. This would lead to more clouds as well
as some drizzle. The best potential for this would be across the
north and west. Temperatures at the surface look as though they
will be warm enough for liquid precipitation. The caveat to this will be
across far northwest Maine in the early morning hours west/some light
freezing/frozen precipitation possible(fzdz/--sn). Attm, left the mention
of freezing precipitation as the llvls dry out for a time before
moistening up by the afternoon.
Short term /Sunday night through Tuesday/...
intense low pressure will move northeast from the Great Lakes
Sunday night into Quebec province by Monday night. Expect strong
warm advection resulting in precipitation across the area during
the day Monday. Some mixed precipitation expected at the beginning
of this event however with strong southerly jet...expect warming
to progress quickly aloft and mix rapidly down to surface without
deep snow cover....so do not expect long period of mixed
precipitation. A strong cold front passage expected Tuesday behind
the low but coldest air should hold off until passage of 500
trough late in day. Will use model consensus approach and blend
the NAM...GFS and European model (ecmwf) for probability of precipitation... sky and quantitative precipitation forecast. For winds will
use the nam12 to better handle boundary layer. Temperature and dew
point grids from raw blend with rapid air mass change expected
this forecast period.
Long term /Tuesday night through Saturday/...
weak high pressure will pass to the south early Wednesday. Low
presssure will then develop along the middle-Atlantic coast late
Wednesday afternoon the move northeast to near southern Nova
Scotia Thursday morning. Operational GFS puts this low center near
Cape Sable island around 1200 z Thursday. European model (ecmwf) is much further
west with this system. GFS ensemble perturbations are divided as
some members take low on a track close to Cape Sable while others
favor a more westerly track. Overal a trend favoring a more
westerly track appears to be taking shape but still not enough
confidence to draw specific conclusions. Will use the super blend
to populate grids.
Aviation /00z Sunday through Thursday/...
near term: VFR for most of the terminals west/the exception of kfve &
kcar as -sn and clouds will bring periods of MVFR/IFR into early
evening. VFR for Sunday but this could change across the northern
terminals by middle afternoon as MVFR and possible IFR for ceilings after
Short to long term: expect IFR conditions Monday improving to VFR
conditions Tuesday and Wednesday. IFR conditions are expected
near term: a Gale Warning remains for the outer zones west/a Small
Craft Advisory for the intra coastal zones. Winds are picking up
as evidence from the buoys hitting 25-30 kts. Seas have come up
as well to 6-7 feet. Expecting winds to hit 30-35 kts this evening
and then fall back as the low level jet exits the region tonight. Seas
will climb to 9 feet over the outer waters seas lower near shore.
Winds will drop off to 20-25 kts west/seas subsiding after midnight.
Looking for conditions to drop off on Sunday below headline
Short to long term: for Monday and Tuesday will use the nam12 for
sustained winds. Expect gale conditions for period Monday
afternoon then another period of gales Monday night with cold
advection destablizing boundary layer behind low. For waves:
expect southerly fetch to develop from Gulf of Maine southward
early Monday and persist until broken up by wind shift Monday
evening. Wind wave build to maximum of 14 feet/10 seconds by early
Monday evening then transitioning to swell Wednesday and
subsiding. Wind/waves could build again ahead of approaching low
late Wednesday into Thursday.
Marine...Small Craft Advisory until 4 am EST Sunday for anz052.
Gale Warning until 4 am EST Sunday for anz050-051.