Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

fxus61 kgyx 100315 
afdgyx

Area forecast discussion
National Weather Service Gray ME
1015 PM EST Mon Dec 9 2019

Synopsis...
rain expected to continue overnight along with very mild
temperatures for this time of year. Readings overnight will be
25 to 30 degrees above normal. Rain winds down around sunrise
but showery weather will continue through the day Tuesday.
Temperatures will remain in the 40s and 50s early Tuesday before
a cold front crosses the area and brings US back to near or
below normal. Some light snow will skirt the coast Tuesday
night, but most likely remains offshore enough to bring only
around an inch to coastal areas. An active weather pattern
looks to continue for late week into the weekend.

&&

Near term /until 6 am Tuesday morning/...
1010 PM...forecast thinking overnight still in good shape, and
other than those stubborn spots that always take longest to mix
and scour out the cold air / kizg and k1p1 are good examples/,
most places have warmed to 40 or above. /Klci went from 37 to
49 in one hour/. There's still a few hours of steady rain left
to g, but should be more intermittent, especially in the south
during the pre-dawn.

650 PM...the arrival of the low level jet has allowed better
mixing near the sfc and allowed temps to rise and fog to thin
out, thus the dense fog adv was allowed to expire. Overall, no
real changes to overnight forecast, ans temps will likely stay
fairly steady around 50 in the coastal areas, and will gradually
rise overnight in inland areas, with most places making to the
mid-upper 40s. After another round of steady rain this evening,
will see precip become more showery after midnight and toward
morning.



Previously...otherwise periods of rain will continue tonight in
several waves. This first is moving newd out of the forecast
area now...with another one or two expected tonight with
moderate rain. Still expecting around 0.5 to 1 inch
quantitative precipitation forecast...locally higher amounts midcoast and upslope areas of the
whites...and around an inch snow melt. This will lead to sharp
rises on area rivers and streams...but water levels were not
particularly high to begin with and forecasts generally fall
short of action stage at most locations. See the Hydro section
for more information.

As for winds tonight...still not seeing a big potential for
widespread strong gusts...even for midcoast. The advisory
remains in place mainly for coastal areas where the surface warm
front will be well onshore. Best window for winds will be from
around 8 PM until 2 or 3 am.

Will also see very warm temps overnight for this time of year.
Lows will be 25 to 30 degree above normal...with possible record
warm low temps set across much of the area.

&&

Short term /6 am Tuesday morning through Tuesday night/...
will keep showery wx going mainly in the higher terrain
Tue...but with dry slot overhead any precip will be lighter and
scattered in nature. Will see early mixing get many coastal
areas to rise a few degrees into the low to mid 50s before the
cold front arrives. Interior zones will likely stay steady in
the morning before falling. Stayed mainly with a heavy blend of
raw 2 M temps overnight with cold air advection keeping the boundary layer
mixed.

The other question is snowfall Tue night. A shortwave trof will
approach and a weak wave will be induced on the low level
baroclinic zone. It will be pretty far offshore and with dry air
moving in plus downsloping northwest flow we have a bit working against
US. I am leaning on the drier side of guidance...but keeping at
least a chance to high chance pop for coastal zones and far srn
New Hampshire. Could see around an inch or two accumulation if things
break right. I adjusted pop so as to sharpen the transition from
likely pop offshore to chance pop over land.

&&

Long term /Wednesday through Monday/...
looking at the week ahead we'll spend much of it in a now quite
familiar long wave pattern. A ridge of high pressure continues
to remain build up the West Coast into the Alaska/Yukon border.
This has set it up for the cold polar air to drop southwards
across Hudson Bay and into the Great Lakes. In northern New
England we continue to sit on the edge of this upper level cold
pool, with short waves pushing US onto the colder side and then
moving US back onto the temperature gradient/storm track on the
warmer side. These minor changes in the upper level flow are
what will guide our sensible weather for the next week.

Wednesday a front will be lingering just offshore with some light
snow extending nward into the cold air. Expect a sharp cut off on
the backside for the precipitation shield as the colder drier air
moves into the region. With this in mind have decreased the quantitative precipitation forecast
amounts and the consensus placement appears to be leaning
offshore with just some light snow along the coast.

Colder air filters into the region from Wednesday night into
Thursday. We'll see decreasing temperatures throughout this time
period. As high pressure builds in expect Thursday night to be the
coldest night as high pressure crests over Maine. For both
Wednesday and Thursday nights have leaned on the MOS guidance for
temperatures. On Thursday this puts the mountain valleys below
zero.

Heading into the weekend another low begins to develop over the
southeast US. This low will move northwards along the 500 trough
into the northeast. Lots of spread amongst the low placement
with this system. Several of the deterministic models would keep
US on a west track bringing US into the warm sector and all
rain. However a look at the ensemble spread would hint at two
other possibilities to consider. First that the surface low
could move further east - paralleling the Maine coast- which
would bring US closer into a snow/sleet mix scenario. To add to
the mixed precipitation potential the departing cold high
pressure may aid in setting up surface temperatures to remain
colder - at least through the first part of the system. This
too would lead to a sleet/freezing rain mix. While all of these
options are on The Table, the confidence is low enough that have
stuck with a rain or snow wording for this forecast cycle.

&&

Aviation /03z Tuesday through Saturday/...
short term /through Tuesday/...widespread LIFR in low cigs and
areas of fog. Visible is improving as the surface warm front moves
into the area...but cigs remain low. That will be the rule thru
the overnight for the majority of the area. One pocket of VFR or
MVFR will be hie...where downsloping winds will keep cigs
higher. Eventually as flow turns more wly...hie will see MVFR
cigs become more common. May see some minor improvement by
morning across srn New Hampshire terminals. Low level wind shear continues thru the night
and will gradually diminish as low level jet moves newd before dawn. Expect
that until cold front sweeps thru the afternoon that MVFR cigs
remain entrenched. Very low confidence on -sn Tue night...so I
expect VFR or MVFR to prevail along the coast and srn New Hampshire.

Long term...a front draped off shore on Wednesday will keep some
high to mid level clouds into the coast, with MVFR shsn possible
for rkd, pwm and psm. High pressure builds in for Wednesday
night into Thursday with VFR and cold temperatures holding fast
in the valleys. Another low will move up the coast on Friday
into Saturday with widespread IFR in rain or snow expected.

&&

Marine...
short term /through Tuesday/...no change to marine headlines.
Strengthening low level jet is expected tonight and widespread gales are
likely with some areas of low end storms north of Cape Elizabeth. It
should be a relatively short window of strongest winds...with
the low level jet lifting north of the waters by sunrise. The trend will be
down after that point...with Small Craft Advisory conditions lingering thru at
least Tue night.

Long term...
a front will sit over the coastal waters on Wednesday with
showers moving through the region. Northwesterly flow will take
hold on the cold side of the front. High pressure builds in for
Thursday with calming winds and seas. The next system will move
through for the start of the weekend.

&&

Hydrology...
warm temperatures combined with rain will result in runoff and
modest rises on area rivers. Total quantitative precipitation forecast of 0.5-1.25" will fall across
the area with the highest amounts in the south along the coast.
Nohrsc analysis shows the highest snow water equivalent of 2-3
inches across southern New Hampshire. While temperatures in the
50s will likely result in substantial snow melt, the snowpack
started the day with density running near 20% so a fair portion
of the initial warming will go towards compacting the existing
snow. Bottom line is while snow loss is expected, it is unlikely
the entire snowpack will go over to runoff which will spare most
location from flooding. The most likely areas for flooding
include southern New Hampshire with the Warner river at
Davisville and the Suncook at North Chichester expected to near
action stage. Across the northern mountains, the snow density is
lower, as are the quantitative precipitation forecast amounts and the combination will likely
result in most of the rain being absorbed into the snowpack with
low chance of any of the rivers meeting action stage.

&&

Gyx watches/warnings/advisories...
ME...Wind Advisory until 4 am EST Tuesday for mez022-027-028.
New Hampshire...none.
Marine...Gale Warning until 4 am EST Tuesday for anz153-154.
Storm Warning until 4 am EST Tuesday for anz150>152.

&&

$$
Synopsis...
near term...cempa/legro
short term...legro

National Weather Service Glossary of Abbreviations