Scientific Forecaster Discussion
fxus61 kcar 302040
Area forecast discussion
National Weather Service Caribou ME
440 PM EDT sun Apr 30 2017
high pressure will move east tonight. Low pressure approaching
from the west will lift a warm front across the region later
Monday and Monday night. An occluded front will cross the
Near term /through Monday/...
the dry Canadian high pressure will move east tonight and a very
rich flow of upper level moisture will ride over an upper ridge
across Quebec and into Maine tonight. Pops will ratchet upward
towards 100 percent for most of the area by late tonight. This
moisture will be in advance of a surface warm front which will
inch northward towards the forecast area Monday, but will make
minimal progress as cold air damming sets up and a blocking
upper ridge amplifies to the east. The damming will keep
monday's high temperatures in the upper 30s to lower 40s on the
1st day of may. Worse than the cold temperatures is the Prospect
of morning snow and sleet in northern zones. Although some of
the critical thicknesses being quite high, the air aloft is
quite cold and dry as the precipitation rolls in tonight. The
issue will be eliminating boundary layer warmth through
evaporative and dynamic cooling to allow snow to reach the
ground. The cooling can be facilitated by heavier precip...which
is possible given some instability aloft. Some of the latest
guidance is showing a nice intersection of strong Omega in the
dendritic growth zone by late tonight into early Monday morning.
Forecast soundings are showing this mostly north of a line from
Greenville to Houlton. As always for late season snow,
elevation will play a vital role for any noteworthy
accumulations. Towards Greenville and the mountainous terrain of
southern Piscataquis, there's more warm air above h850, but a
deep layer of cold air from h925 to h850. The result is that
southern Piscataquis will have sleet rather than snow.
Short term /Monday night through Wednesday/...
an occluded front will approach the region Monday night. An area
of rain, heaviest across northern areas, will cross the forecast
area in advance of the occlusion. The rain will then begin to
taper to showers late. The occluded front crosses the region
Tuesday with showers. A cold front then approaches Tuesday
night along with an upper trof. Skies will remain mostly cloudy
with a chance of showers across northern areas Tuesday night,
with decreasing clouds downeast. The cold front and upper trof
then cross the region Wednesday with mostly cloudy skies along
with a chance of showers north, with partly cloudy skies and a
slight chance of showers downeast. Temperatures will be at near
normal, to slightly above normal, levels Tuesday/Wednesday.
Long term /Wednesday night through Sunday/...
could still have a shower across mostly northern areas
Wednesday evening. Otherwise, high pressure builds across the
region Wednesday night through Thursday with generally partly
cloudy skies north and partly cloudy/mostly clear skies
downeast. High pressure will begin to move east of the region
Thursday night with increasing clouds. Surface/upper level low
pressure is expected to move north across New England later
Friday through the weekend. However...the exact track and timing
of the lows is uncertain. Rain chances will increase later
Friday into Friday night. Unsettled conditions with occasional
rain or showers is then expected through the weekend. However,
rain totals and the persistence of rain will be dependent on the
eventual track and timing of the surface/upper lows. Near
normal level temperatures are expected Thursday then again
Saturday/Sunday. Slightly below normal level temperatures are
Aviation /20z Sunday through Friday/...
near term: it will be VFR with excellent vis and cigs above
fl050 until later tonight. Conditions will deteriorate late
tonight to IFR from gnr to hul northward due to cigs, snow and
sleet. South of that line, low cigs and drizzle will generate
IFR conditions. In the afternoon, any snow and sleet will be
gone, but the low cigs and drizzle will remain an issue for all
sites and IFR conditions continue.
Short term: IFR/LIFR conditions are expected across the region
Monday night through early Tuesday, with MVFR/IFR conditions
later Tuesday. Occasional MVFR conditions are expected across
mostly the north and mountains Tuesday night into Wednesday with
generally VFR conditions downeast. VFR conditions are expected
across the entire region Thursday. Conditions will then lower
to IFR/LIFR levels later Friday.
near term: no headlines are expected through Monday. Winds will
pick up later in the day, but with the expected stability of the
warmer air moving over the cold waters, have adjusted model
guidance downward. Fog will be an issue later in the day with
the humid air arriving from the south.
Short term: winds/seas will build to Small Craft Advisory levels
later Monday night. Small Craft Advisory conditions are then
expected Tuesday through Wednesday. Visibilities will be
reduced in rain and patchy fog Monday night, with showers and
patchy fog Tuesday.