Scientific Forecaster Discussion
fxus61 kcar 251918
Area forecast discussion
National Weather Service Caribou ME
issued by National Weather Service Gray ME
318 PM EDT Thu may 25 2017
a strengthening area of low pressure will move into the Gulf of
Maine on Friday...bringing widespread rainfall to the region. Drier
and milder conditions will move into the region for Saturday and
Sunday as a weak area of high pressure builds overhead. The weather
looks to turn unsettled again beginning on Memorial Day and
continuing through much of the week as a large area of low pressure
remains anchored over eastern Canada...bringing numerous rounds of
showers the northeastern United States.
Near term /until 6 am Friday morning/...
high impact weather potential: some splash over possible at the
time of high tide tonight.
Current pattern: deep southerly moisture plume up the eastern
Seaboard is evident in water vapor imagery early this afternoon as
impressive trough over the eastern United States develops a negative
tilt with primary low over Ohio gradually yielding to secondary
development over the Delmarva that will strengthen as it moves
northeast into the Gulf of Maine by 12z Friday.
Through this evening: top down saturation continues...with
thickening/lowering mid and upper cloud cover. Upstream
observations have shown that the leading edge of the precipitation
shield has had some trouble reaching the ground with cold air
damming pressure pattern in place and a somewhat dry llevel easterly
flow. Have seen krkd report a few sprinkles last hour. However...
as the warm front at 800 mb lifts north and southerly flow spreads
north behind it...expect shower activity to continue to reach
further north...with our first sprinkles/light showers arriving
along the coast towards 5-6pm. Temperatures will begin falling
back through the 50s. Easterly winds will continue to strengthen
as the gradient increases as low pressure approaches from the
south and west.
Tonight: scattered showers should continue to spread north in
conjunction with the warm front at 800 mb this evening...but heavier
precipitation will wait for well after midnight as core of mid
level vorticity rotates north with surface low responding by
deepening as it moves north and east into the Gulf of Maine.
This mid level forcing will have modest 1.25" precipitable waters to work with
along with a coupled jet and good convergence along the low/mid
level warm front. This should help form a blossoming area of
heavier rainfall south of our region by midnight...which will
rotate north...arriving towards daybreak. Temperatures will
only fall to around 50 given the increasing cloud cover.
Short term /6 am Friday morning through Friday night/...
high impact weather potential: not expected at this time.
Mid level low catches up with surface low during the day Friday with
the latter feature thus slowing as it arrives in the Gulf of Maine
before beginning to slowly fill and head to near Halifax by 00z
Saturday. The 12-18z period looks best in terms of dynamic forcing
for ascent...and expect a heavy rain shield to spread north during
the morning hours...covering the entire forecast area by about noon
before weakening during the afternoon as the low becomes vertically
stacked and slowly pushes east. Remaining shower activity will
come to an end from west to east Friday night with low clouds
lingering as moist cyclonic flow continues.
Winds will remain from the east and northeast 10-15mph during
the day /stronger at the coast/...with the strongest winds
along the coast coming early in the day.
Temperatures: a chilly day for sure with highs stuck in the 50s
given cool easterly flow. Showers and low clouds will not allow
for much cooling Friday night with temperatures only retreating
about five degrees...back into the 40s.
Qpf: ensemble signal supports 0.5 to one inch which is well
agreed upon in the guidance consensus but represents a slight
downward trend from recent guidance support.
Long term /Saturday through Thursday/...
high impact weather potential: no signals for significant weather
impacts at this time. Some potential for thunder in the
Pattern: a look at water vapor imagery over the northern hemisphere
shows a pretty active pattern with longwave trough over the eastern
United States...with another trough digging south in to the northern
plains east of The Rockies on the eastern flank of longwave ridging
over the eastern Pacific. This amplified pattern will temporarily
relax as the eastern trough lifts north and east of our area by
Saturday. Beyond this...however...there will be a re-amplification
of the pattern across the eastern Pacific and western North America
with an impressive ridge building along the US West Coast by Sunday.
This will help drive the aforementioned northern plains trough south
and east...with it broadening and becoming a near stationary
longwave trough over eastern North America for much of/if not all of
Pattern implications: relatively quiet for Saturday/Sunday (and
perhaps into monday) with brief shortwave ridging expected. Beyond
this...the gradually nearing longwave trough portends showery
weather...with temperatures near or above normal given our location
east of the trough axis.
Saturday through sunday: shortwave ridge axis moves into the region
on Saturday and remains overhead Sunday with a return to
drier/milder conditions expected. Weak warm advection continues
through the period...with t8s around +5c Saturday increasing to +8c
Sunday...this suggests mid/upper 60s Saturday with upper 60s to
near 70 on Sunday...well captured by the model consensus.
Monday: with upstream shortwave broadening and nearing from the
west...there is decent model consensus in an area of low pressure
north of the Great Lakes pushing another occluded front into the
region from the west. At the same time...there has been some
indication from the GFS of a cold front trying to sneak it/S way
south into the area from Canada. Thus...high chance pops are
warranted...with temperatures a bit lower than those over the
weekend /highs likely nearer to 60/ with the increasing cloud
cover and precipitation chances.
Tuesday through thursday: vertically stacked surface low will set
up shop south of James Bay by Tuesday...only very slowly moving east
while waves of mid level energy rotate around the mid level low.
These waves arrive about once every 24 hours...but given their fast
movement and small scale...are hard to time at this range. Suffice
it to say that each afternoon will likely see some showers...and
can/T rule out thunder given proximity of the mid level low...with
MUCAPE progs showing non-negligible values especially for Wednesday
and Thursday. With continued clouds and showers...temperatures look
to be no warmer than seasonal norms...despite our area being east of
the mean trough location.
Aviation /19z Thursday through Tuesday/...
near term: clouds will thicken and lower tonight ahead of low
pressure moving northeast into the Gulf of Maine. VFR all sites
attm will lower to MVFR/IFR towards daybreak from bgr south.
Easterly winds strengthen to 12g22kts overnight.
Short term: rain continues to spread north with IFR/LIFR
restrictions in moderate to potentially heavy rain from car/pqi
south...with precipitation reaching fve around 15z on Friday.
Rain continues through Friday evening before tapering to showers
Friday evening with IFR/MVFR restrictions gradually improving
to VFR Saturday morning and continuing through Sunday. Another
frontal system arrives from the west on Monday with MVFR
near term: scas continue through tonight as easterly flow
strengthens ahead of strengthening low pressure system. Wind
gusts will near gale force in the 3-9utc timeframe...and will
have to keep an eye on this...but at the current time do not
expect sufficient gale gusts to warrant an upgrade of the
Short term: winds turn north and gradually weaken late Friday
through Friday night with scas possibly continuing through
high astronomical tides will occur from tonight through
Memorial Day weekend. Current predictions have water levels
getting up to right around hat levels at Bar Harbor and Eastport
gauges. New total water level guidance keeps most areas below
minor flooding levels, but could have some minor splash over
Marine...Small Craft Advisory until 8 PM EDT Friday for anz050>052.