Scientific Forecaster Discussion
fxus61 kgyx 130851
Area forecast discussion
National Weather Service Gray ME
351 am EST Fri Dec 13 2019
high pressure moves east tonight with a warming southerly wind
developing today. Low pressure tracking up the East Coast will
spread rain across the region tonight and Saturday, although
this could begin as some light icing especially in interior
areas. Low pressure moves off to the northeast Saturday night
with a cold front ushering colder air back into the area from
the west. Some showers could linger into early Sunday with the
temperature falling into Monday. The next low pressure system
will bring snow on Tuesday.
Near term /until 6 PM this evening/...
high pressure will gradually release its hold over the area
today as strong low pressure approaches from the SW and
negatively-tilted upper level troughing will push the system up
the East Coast. Today we will see increasing moisture ahead of
the system. It will take some time for top-down saturation to
occur as evident from last night's kgyx sounding and with
current dew points in the single digits to teens across the
area. By this afternoon we may see some drizzle beginning to
fall. Although temperatures will increase to the mid to upper
30s in most spots, mountains valleys may still be below freezing
initially, with spotty freezing drizzle developing. This should
be brief before temperatures increase enough to change p-type
over to rain. Therefore have not issued a Winter Weather
Advisory at this time, but it will be something to keep an eye
Short term /6 PM this evening through Saturday night/...
temperatures will continue to increase in a non-nocturnal curve
overnight as warm air advection increases. Warm moist air will
continue to pump from the Gulf of Maine, with a coastal front
setting up just inland. The rain/snow line retreats northward as
warmer temperatures creep northward into the 40s north to near
50 along and south of the coastal front. By the early morning
hours Saturday, we will be seeing moderate to heavy rainfall,
with pwats a good 3 Standard deviations above normal. This
coupled with an anomalously strong low level jet will ensure heavy
rainfall rates at times. Looking at the ensemble river
forecasts, southern New Hampshire as well as coastal (and just inland) ME
are likely to see some sharp rises on area rivers with possible
flooding. Have issued a Flood Watch for these areas beginning
overnight tonight through Saturday. Quantitative precipitation forecast of 1-2" with locally
higher amounts are expected across the entire area. Snowfall
amounts will be negligible except for the very highest peaks.
There will be a break Saturday night in the precipitation as the
warm front lifts northeast. Before daybreak Sunday morning
however, the upper level system will be rotating through the
region, producing some lighter additional precipitation. This
should be snow in the mountains, with rain elsewhere.
Long term /Sunday through Thursday/...
two periods of elevated impact in the extended forecast.
The first will be in the wake of intense low pressure moving
into Quebec early sun. The period of strongest pressure rises
will be moving thru the forecast area around daybreak sun. This
alone would be enough for ME to favor some gusty winds...but we
will also see a cold front crossing the region with cold air advection adding
to the efficiency of low level mixing. It is possible we have
two stronger bursts of gusts...one with the isallobaric
component and the other with the strongest cold air advection.
Regardless...forecast soundings certainly support gusts in the
the 35 to 40 mph range out of the west during the day. Overall the
only precip accompanying the wind will be upslope snow
showers...but given the steepening low level lapse rates these
should not concentrate upwind of the terrain but propagate over
it and keep any accumulation light.
After a brief surface ridge builds into the area late Sun night
thru Mon the next system of concern approaches form the SW.
Along the trailing cold front the next shortwave trof will induce a
weak wave to form and ride newd along the boundary. As opposed
to the last system that tried this...mid level flow is forecast
to back to a more sly direction as the wave passes S of the
forecast area. This will promote stronger isentropic ascent
locally. While a period of snow looks likely...there are still
some red flags that give ME pause on a more widespread
advisory-type snowfall. One is that models forecast saturation
of the snow growth zone to be rather brief...with the layer
drying out quickly Mon night. This could lead to a longer period
of poor snow growth and/or freezing drizzle. Another is that the
SW/v trof is still over the central Pacific...and not likely to
be well sampled by the raob network until Sat night at the
earliest. That being said...current forecasts from deterministic
and ensemble guidance are supportive of at least a several hour
window of strong frontogenesis favoring a laterally translating
band of snow. Any accumulations would be roughly uniform across
the area...and given the concerns mentioned above would not go
any higher than 2 to 3 inches at the moment. This may bleed over
into the Tue morning commute for some parts of the forecast
area...and so impacts may be somewhat elevated due to that.
Aviation /08z Friday through Tuesday/...
short term...VFR conditions will hold through this afternoon as
high pressure moves to the east. Conditions approach MVFR by
this afternoon as clouds increase and lower. -Fzdz may fall at
khie and kleb initially this afternoon, with all taf sites
changing to rain as the evening GOES on. Rain or even +ra is
possible, especially along the coast. Expect LIFR at most sites
by 00-02z Saturday.
Long term...conditions will be quickly improving to VFR across
most terminals Sun morning...as wly downsloping flow develops.
The exception will be hie...where upslope cigs will likely
remain around MVFR. I cannot rule out some local IFR in that
area in shsn. Surface gusts to 25 or 30 kts possible in the cold air advection
flow behind the cold front sun. Winds diminish and widespread
VFR returns Sun night into Mon. A weak wave will pass S of the
forecast area Mon night...spreading -sn thru much of nrn New
England. Widespread IFR or lower conditions are probable thru
short term...a gale watch has been issued for Saturday for both
the bays and outer waters as a strong low pressure system moves
through. This may need to be extended into Saturday night, but
at this time it looks like borderline Small Craft Advisory/gale conditions, so
have opted to just take the gales out through Saturday.
Long term...after the cold front sweeps across the waters strong
wind gusts are expected to pick back up this time from the west.
Another period of gales is looking more likely sun. The period
of strongest winds will run roughly thru the daytime
hours...with winds and seas gradually diminishing Sun night into
Mon as high pressure builds towards the area. A weak wave will
form along the trailing front and bring widespread precip to
the waters...but the greatest impact will mainly be reduced
visibility in snowfall. The reinforcing cold front will not
cross the waters until Wed...when another period of Small Craft Advisory
conditions is expected.
most rivers have long since peaked after our recent rainfall
event, although river levels remain high. Most of the snow south
of the mountains has been eradicated except for some areas of
southern New Hampshire. We expect a period of rain beginning
tonight and lasting through Saturday. A general 1 to 2 inches of
rain is expected, with locally higher amounts.
Areas most likely to see rises closer to flood stage would be
in southern and possibly central New Hampshire where some
snow remains. A Flood Watch has been issued for these areas
extending into the coastal plain of Maine towards the mid
we are entering a period of higher astronomical tides, and this
will coincide with the next storm system moving through the area
tonight into Saturday. The highest tides are on Saturday and
Sunday afternoons, each at 10.6 feet in Portland. The tide on
Saturday will have the greatest potential for an added storm
surge as onshore flow may increase water levels by about a foot.
Waves on top of this could cause splash over and beach erosion
in vulnerable areas. By Sunday winds will be offshore and expect
the surge to no longer be a factor.
ME...Flood Watch from late tonight through Saturday evening for
New Hampshire...Flood Watch from late tonight through Saturday evening for
Marine...gale watch from Saturday morning through Saturday evening for