Scientific Forecaster Discussion
fxus61 kcar 180923
Area forecast discussion
National Weather Service Caribou ME
423 am EST Mon Dec 18 2017
a weak area of low pressure will approach from the west today
and then move east tonight. Another low pressure system will
pass to the north of the region Tuesday through Tuesday night
followed by the approach of Canadian high pressure for Wednesday
Near term /through tonight/...
cold high pressure at the surface will continue to move east
through early today. As it does so, overunning snow is expected
to develop across central and down east areas by early
afternoon, in advance of a weak short wave approaching from the
Great Lakes region. There will be a sharp cut off to the
northern edge of the snow shield, with the steadiest snow
confined to a line south of a Greenville-Millinocket-Danforth.
Very little in the way of snow is expected to the north of this
line, with far northern Aroostook County not expected to see
any in the way of any measurable snow, under mainly cloudy
skies. Elsewhere, as far as snow totals go, looks like generally
about one inch of snow can be expected from the Central
Highlands through the upper Penobscot valley. Across down east
areas, including the greater Bangor region, we are generally
expecting two to three inches, thus will not be issuing any
advisories. That being said, commuters should expect the
potential for some snow covered roads by the afternoon drive
time across down east areas, including the greater Bangor
region. Afternoon high temperatures will be a few degrees warmer
than the last few days. Highs across northern areas will range
from the low to mid teens and upper teens to mid 20s across
central and down east areas.
Snow is expected the continue into early this evening across
down east areas before tapering off to snow showers by midnight,
as the short wave moves east into the Canadian Maritimes.
Otherwise, it will remain mainly cloudy overnight. Couldn't rule
out the possibility of patchy freezing drizzle very late
tonight with abundant low level moisture expected and some
drying aloft, although not confident enough to mention quite
yet. Tonight will be much milder than previous nights with
abundant cloud cover expected and light southerly flow.
Therefore, expecting lows to range from the low to mid teens
north and upper teens to mid 20s along the coast.
Short term /Tuesday through Wednesday night/...
immediately on the heels of Mon/Mon ngt's S/WV, will be a more
nrn S/WV and associated sfc low movg E from NE ont and cntrl qb
provs for Tue aftn into Tue ngt, with the main impact from this
system with ovrrng snfl xpctd across the north as the sfc low
tracks ewrd just north of the St John Vly. Snfl amts by Erly Wed
morn will range from 2 to 3 inches across the far north with
progressively lesser amts swrd to the coast. In fact, milder
marine air brought into the rgn from a S wind with this system
could result in a mix of lgt sn/rn ovr downeast and perhaps even
cntrl ptns of the forecast area Tue aftn and Erly eve.
After the passage of this S/WV, other S/wvs crossing the forecast area from
cntrl can and qb will bring intermittent sn shwrs msly to
nrn/wrn ptns of the forecast area very late Tue ngt thru Wed alg with a
return to brisk northwest winds and much colder conditions as a new
batch of Arctic air moves into the rgn. Sct sn squalls/St
Lawrence streamer sn bands cannot be ruled out Wed across the north
to as late as Wed eve across the far north. Any remaining sn shwrs
across the north should end late Wed ngt as the subsidence invsn Alf
lowers below 850mb, but brisk northwest winds will continue.
Long term /Thursday through Sunday/...
Thu will cont fair and brisk and cold with winds diminishing
Thu ngt as the sfc ridge axis crests the rgn by Erly Fri morn.
Some potential radiational cooling is xpctd Thu ngt with ovrngt
lows sig below zero with the only lmtg factor some hi cldnss.
Cldnss then thickens and lowers durg the day Fri as a sig regime
chgng S/WV Alf and associated sfc low from the Midwest and
great lks begins to apch our rgn. Sn from this system will break
out across the rgn by late day Fri, but at this point, all
model guidance has now shifted the track of the sfc low well northwest
of our forecast area. Subsequently, the potential of chgovr to rn has now
encompassed all of the rgn beginning ovr downeast areas by late
Fri ngt aft an inch or two of snfl and reaching the the St John
Vly tentatively by midday Fri aft 2 to 4 inches of snfl. We
indicate a sn, sleet, and rn transition for this fcst update,
but could easily see a sleet/fzra transition potentially
requiring a wntr wx adv for our rgn, but a little Erly to
advertise fzra in our fcst grids attm.
Following a pd of all rn Sat aftn, a cold front followed by a
sharp dry slot Alf will end ovrrng precip for the rgn by Sat
eve, perhaps followed by isold-sct sn shwrs Sat ngt with a
returns to fair wx and seasonably cold temps on sun.
Aviation /09z Monday through Friday/...
near term: there will be a wide variation in aviation weather
conditions from north to south across the forecast area. Across
the far north, kfve/kcar/kpqi/ expect generally VFR today.
Further south, especially kbgr/kbhb/, VFR conditions this
morning will give way to IFR in developing snow from mid morning
and continuing into tonight. Expect the potential for MVFR
ceilings to develop across the far north late tonight.
Short to long term: VFR all taf sites until late Tue morn then
clgs/vsbys lowering to IFR/LIFR Tue aftn in sn across nrn taf
sites and MVFR for lgtr sn and mixed precip downeast sites.
Nrn taf sites remain MVFR clgs in bkn-ovc SC and ocnl sn shwrs
Tue ngt into Wed while downeast sites improve to low VFR. All
sites should be VFR Wed ngt, xcpt kfve which may hold MVFR into
Wed eve, with all sites contg VFR Thu thru Fri.
near term: winds/seas will remain below headline levels through
tonight. Visibility will be reduced to 1 to 3 nm at times today
through tonight in snow this afternoon and in snow and rain
Short to long term: initially no hdlns Tue morn, then winds with
seas potentially ramping up to gale force msly in gusts by Tue
ngt and cont so at least thru Wed morn, which tm pds we advertise
a gale watch for all of our waters. Winds and seas then remain
at or below Small Craft Advisory range Wed aftn thru Thu. Used a blend of ww3 and
nwps guidance for fcst WV hts.
Marine...gale watch from Tuesday evening through Wednesday morning for