Scientific Forecaster Discussion
fxus61 kcar 292219
Area forecast discussion
National Weather Service Caribou ME
619 PM EDT Wed Mar 29 2017
high pressure will build down from eastern Canada tonight and
Thursday and crest over the area Thursday night...then move
east Friday. Low pressure will track off the mid-Atlantic coast
Friday night and pass south of the Gulf of Maine on Saturday.
Near term /through Thursday/...
605 PM update: we delayed the dissipation of sn shwrs and cldnss
ovr spcly nrn and cntrl ptns of the region until later this eve
based on latest radar ref and Sat imagery trends. Otherwise,
latest obsvd sfc temps and dwpts were used to make minor chgs
to fcst hrly temps/dwpts into the ovrngt hrs, with no chgs in
fcst ovrngt low temps this update.
Orgnl disc: any lingering snow showers across the area early
this evening will dissipate as an upper level shortwave trough
slides east into the Maritimes. High pressure will gradually
build down from eastern Canada tonight and Thursday. This will
bring gradually clearing skies. Thursday will then be mostly
sunny with afternoon temps just a couple degrees short of late
March normals for the season. The gradient behind departing low
pressure will bring a gusty northwesterly breeze on Thursday.
Winds will diminish a bit late in the day as the gradient eases.
Short term /Thursday night through Saturday/...
a surface ridge of high pressure moving over the region, with an
upper ridge moving in from the west, will act to bring mostly
clear skies and calm winds to the County Warning Area Thu night into Fri. Clouds
will increase from west to east Fri aftn and eve as the next
system approaches. This system manifests itself at the upper
levels as a cut-off eating into and flattening out the ridge,
with sfc low moving from the Ohio Valley across the mid-Atlantic
and then south of Long Island between Fri am and Sat am. Sig
disagreement between NAM/European model (ecmwf) and GFS/CMC on the layout of the
precip shield and pops. The former shows an upr trof north of
the cut-off, inducing more robust pops to extend north of the
sfc low thanks to a stronger mid-lvl - 700mb - trof north of the
sfc low. The latter pairing both show the sfc low going further
south, and don't show a significant 500mb or 700mb trof north
of the sfc low, keeping precip contained around the sfc feature
and largely out of our County Warning Area. The pops and quantitative precipitation forecast were made to show a
general lean toward the NAM/European model (ecmwf) solution, but don't jump
fully in with that pair in terms of the rather high pops and
quantitative precipitation forecast. Pops were generally capped at high-end likely, with storm
total quantitative precipitation forecast generally 0.25-0.50 inches for central and downeast
areas. Temps expected to complicate snow totals, with many areas
switching to rain, at least for a time, during the day Sat.
Between the temps and track disagreement, definitely plenty of a
chance for someone to get fooled on this system.
Long term /Saturday night through Wednesday/...
continuing with a lean toward the European model (ecmwf) from the short term,
current forecast thinking is that any lingering precip departs
quickly Sat night. The GFS, with delayed passage of an upr trof,
would keep some light snow shwrs across the County Warning Area into the day
Sunday. Sun night into Tue am look to be clear with sfc and upr
ridging. Model disagreement returns mid-week with the reverse
of the weekend scenario - the GFS takes a forecasted low further
north, while the European model (ecmwf) keeps it to the south. For now, kept pops
pretty low given the disagreement.
Aviation /22z Wednesday through Monday/...
near term: MVFR conditions should improve to VFR downeast this
evening then VFR across the north late tonight. VFR conditions
are expected across the area on Thursday.
Short term: VFR conditions expected Thu night through Fri. Mid-
lvl clouds move in Fri eve, with MVFR and IFR cigs and vsbys
sweeping in from west to east with arrival of snow Fri night.
Kpqi to kfve may have a chance to keep higher vsbys and possibly
higher cigs depending on the track of the low pressure. Patchy
MVFR and IFR cigs could linger Sat night with any lingering snow
shwrs, but clearing to VFR for all places expected sun into Mon.
near term: a Small Craft Advisory will be up tonight through Thursday for gusty
northwest winds gusting up to 30 kt across the offshore waters
and 25 kt over the intracoastal waters as high pressure builds
down from the north.
Short term: seas are expected to remain below Small Craft Advisory levels through
the short term. Wind gusts will be borderline for offshore zones
at the start of the period, but then decrease by Fri am. Wind
directions and speeds Fri night into Sat will be highly
dependent on the track of the low pressure system.
Marine...Small Craft Advisory until 8 PM EDT Thursday for anz050>052.