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Area forecast discussion 
National Weather Service Taunton Massachusetts
628 am EST Thursday Dec 18 2014

scattered rain and snow showers will quickly come to an end by middle
morning. Otherwise...high pressure slowly building across eastern
Canada will result in dry and seasonably chilly temperatures through
Friday. Scattered snow showers will develop Saturday night into
Sunday with a low pressure system moving near the region Tuesday.
An anomalous system will impact the eastern United States
Wednesday into Thursday.


Near term /until 6 PM this evening/...

630 am update...

Good band has set up allowing for localized wet-bulb processes.
This has allowed for Worcester to drop to 32f and with reports of
slick travel in Tolland Colorado CT have issues an Special Weather Statement for slick travel
during the morning commute. Also just received a report of snow
in Providence as well. Since temperatures are marginal am not
anticipating much in the way for accumulation however a quick
coating to an inch of snow is possible in the higher terrain.
Aside from a few minor tweaks the bulk of the forecast remains on
track this morning.

Previous discussion...

Shortwave/cold pool aloft moves across southern New England through
12z...triggering hit and miss rain/snow showers. The best
moisture/forcing will be across our northern/eastern will
have the highest probability of precipitation in those locations. However...enough forcing
is available for a few brief rain/showers across southwest Massachusetts/CT and
Rhode Island.

As for ptype...cold enough for scattered snow showers across the
higher terrain. In the lower elevations and coastal
plain...boundary layer will be mild enough for scattered rain
showers initially. Wet bulb processes may allow for an eventual
mixture or change to flurries/snow showers. Spotty snow
accumulations of a coating to less than 1 inch are possible across
portions of the higher terrain. Most of the scattered precipitation
should exit eastern Massachusetts by 8 or 9 am as shortwave departs.

Otherwise...expect a mixture of clouds and sun later this morning
and into the afternoon. Low pressure over the Canadian Maritimes
and high pressure across the Great Lakes will result in gusty
northwest winds. Wind gusts of 25 to 35 miles per hour are expected to develop
later this morning and into the afternoon. High temperatures will mainly
be in the upper 30s to the middle 40s.


Short term /6 PM this evening through 6 PM Friday/...

Low pressure in the Canadian Maritimes will continue to lift
northeast. This will allow the pressure gradient to weaken a
bit...but not enough for winds to completely decouple even in the
valley locations. Therefore...low temperatures should mainly be in the 20s
to around 30 with partly cloudy skies.


Large high pressure over the Great Lakes should push east into
Quebec. While were not too cold at 850 mb...this high pressure
system should allow some shallow cold air too ooze south...keeping
high temperatures in the 30s for most locations. Should see a mixture of
clouds and sun with less wind than today.


Long term /Friday night through Wednesday/...

* scattered snow/rain showers Sat into Sunday with below average temperatures
* weak wave of low pressure on Tuesday
* anomalous system across the Great Lakes will bring heavy
rain...gusty winds and coastal concerns around Christmas evening


Overall 00z guidance is in agreement synoptically with issues on
timing and smaller scale features. Amplified pattern set to return
to the U.S. As the strong west Pacific jet translates downstream this
weekend into the Pacific northwest. Building heights over southeast Canada should also
help dig the trough into the Ohio Valley midweek and likely close
off as it swings into southern Canada on Christmas day.
Models/ensembles have been fairly consistent in recent runs on this
amplified pattern and the most recent gefs/European model (ecmwf) ensemble guidance
show good correlation to next Thursday.

During this synoptic transition...high pressure and upper level
ridge will be over the northeast Saturday into Sunday. Digging
trough over the central Continental U.S. Will push a shortwave across the southeast
into the mid-Atlantic. Appears that a weak coastal low will develop
moving towards the region Monday into Tuesday. The GFS brings this
low over the benchmark where the ec pushes well eastward thanks to
building high pressure over eastern Canada. This system is weak so
coastal regions have the best shot for precipitation. As this system depart
appears anomalous low over the Great Lakes will develop a secondary
low closer to New England. The GFS is still a tad faster compared to
the ec but overall excellent model agreement 6+ days out.


Saturday into Sunday...high confidence.

High pressure in eastern Canada will build across the region Friday
night into Saturday. However it appears on Friday night into
Saturday northerly flow may allow for some ocean effect clouds/snow
showers to impact the cape. Surface to 850 mb temperature difference is 14c
which is unstable enough for snow showers on Saturday for the cape.
Am not anticipate much in the way of accumulations but a dusting
cannot be ruled out.

Weak wave will move through the flow on Saturday night and with high
pressure shifting eastward expect onshore easterly flow. Guidance
continues to show quantitative precipitation forecast moving onshore and with moisture and the lift
could see snow showers moving inland Saturday night into Sunday.
Biggest question is will the moisture saturate enough to -6c. If not
then the potential for freezing drizzle is possible. For now believe
that there is enough moisture so a quick half inch to an inch is
possible per soundings east of the Worcester Hills.

Monday into Tuesday...moderate confidence.

Weak coastal low pressure system will develop and move somewhere
between the benchmark and well offshore. Believe a solution father
out to sea is possible due to strong high pressure in eastern
Canada. Regardless a round of showers will move across the region
with the coastal areas having the best shot to see precipitation. Thermal
profiles will allow for snow at night and rain during the day.

Temperatures will slowly begin to warm as southerly flow becomes
dominate out ahead of stronger system to the east.

Tuesday high tide will be 11.6 in Boston during the late morning and
with any easterly flow may allow for minor coastal flooding.

Wednesday into Thursday...high confidence in system low confidence
on details.

Strong anomalous system will strengthen over the Great
Lakes...developing a secondary surface low just west of southern New
England. Still a lot of details to work out as this system is still
6 days away...however ensembles show that this system is around 2 to
3 Standard deviations allowing for increasing confidence that a
potent storm will occur. Latest 00z guidance shows that most precipitation
will be liquid with a deep subtropical connection back across
Mexico... precipitable water anomalies forecast to rise to between +1 to +3
/or higher/...and temperatures well above average. In fact we may be
close at breaking record high temperatures if temperatures warm to 60f or above on
Christmas evening. As the system wraps up into Canada...cold air
advection should circulate around and begin a transition from
southwest to northeast in turning p-type to snow.

This system is quite strong so we will need to watch for possible
urban flooding issues as well as wind issues. Guidance right now is
showing a 40 to 50 knots jet at 925 mb which may warrant wind
advisories but this system could strengthen even more so a stronger
jet is possible. Lastly coastal flooding issues will need to be
address as high tide on Wednesday and thus are 11.7 and 11.5 respectively.
Any onshore componet will push the tide above flood so coastal
flooding is possible as well as beach erosion.


Aviation /12z Thursday through Monday/...
forecaster confidence levels...

Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.

4 am update...

Short term /today through Friday/...high confidence.

Today...VFR conditions most of the day. However...brief localized
MVFR conditions possible through 13-14z in scattered rain/snow
showers especially northern and eastern Massachusetts. Brief MVFR ceilings also
will be possible into the afternoon...but expect VFR conditions to
dominate. Northwest wind gusts of 25 knots expected to develop
later this morning into the afternoon.

Tonight and Friday...mainly VFR conditions but brief periods of
marginal MVFR ceilings possible.

Kbos terminal...high confidence. Low risk of brief MVFR conditions
in a few rain/snow showers through 13z.

Kbdl terminal...high confidence.

Outlook...Friday night through Monday...

Friday night into Sunday...high confidence. Mostly VFR with MVFR
conditions any scattered snow/rain showers.

Monday...low confidence. VFR conditions.


forecaster confidence levels...

Low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.

Short term /today through Friday/...moderate to high confidence.

Today...Small Craft Advisory headlines for all waters. High pressure over the Great
Lakes and low pressure over the Canadian Maritimes will result in a
tight pressure gradient. Northwest wind gusts of 25 to 30 knots
expected across all waters. A few gusts near 35 knots are possible
across our southern and eastern outer-waters...but do not think they
will be widespread enough for gale warnings.

Tonight...Small Craft Advisory headlines will continue for most open waters. Winds
will diminish some but still think winds will gust up to 25 knots
for much of the night.

Friday...high pressure building into Quebec will allow the pressure
gradient to weaken. Still expect northwest winds to gust to 20
knots in the cold air advection pattern...but below Small Craft
Advisory thresholds. Lingering small craft seas across the
southeast waters should diminish by late morning.
headlines are anticipated.

Outlook...Friday night into Monday...moderate to high confidence.

Friday night into Sunday...anticipate diminishing winds and seas
subsiding late Thursday night into Saturday leading to below Small Craft
Advisory levels.

Monday...expect NE winds gusting up to 20 knots. Low probability of 25 knots
gusts as well as 5 feet seas.


Box watches/warnings/advisories...
Rhode Island...none.
Marine...Small Craft Advisory until 3 am EST Friday for anz232>235-237.
Small Craft Advisory until 7 PM EST this evening for anz230-
Small Craft Advisory until 6 am EST Friday for anz231-250-251-


near term...Frank/dunten
short term...Frank
long term...dunten

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