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Area forecast discussion 
National Weather Service Taunton Massachusetts
330 PM EDT Friday Mar 27 2015

a weakening cold front will move across New England this
afternoon...and move farther offshore this evening. A weak low
pressure moving up the coast will bring some light snow to
southern New England tonight and Saturday. High pressure will
push south of New England Sunday. Another batch of precipitation
is possible late Sunday night into Monday ahead of a cold front.


Near term /until 6 am Saturday morning/...
scattered light rainfall continues across portions of southern New
England this afternoon. Temperatures were mainly 40-45 degrees

27/12z guidance suite has come into reasonable agreement with the
overall synoptic pattern tonight. A low pressure passes well
southeast of the 40n/70w benchmark late tonight. Although this low
pressure is expected to pass some 200 miles from Nantucket...we do
still expect an inverted trough to arrive after midnight tonight.

There remains abundant moisture and lift within the dendritic snow
growth we do expect snow to develop. It all then becomes
a matter of boundary layer temperatures...and how quickly they can
can get low enough to support snow all the way to the ground. This
will most likely happen first across the higher terrain of central
and western Massachusetts.

27/12z guidance continues to advertise a banding signature
developing late tonight. However...there are some significant
detail differences yet to be resolved. These differences concern
the location...and duration...of the banding signature. Most of
the guidance...particularly the higher resolution guidance...
favors a position between Worcester County and the western
suburbs of Boston. Some of the guidance...including the latest
runs of the hrrr...bring this band as far west as the CT River
Valley. At this point...thinking the banding most likely stays
east of the CT River Valley...with predominantly north winds
preventing much of a westward push. Will need to monitor this
development over the next 12-18 hours.

Temperatures will be slow to fall with light winds and cloudy
skies. Heavier precipitation will speed up this process later
tonight as wet-bulbing occurs.


Short term /6 am Saturday morning through 6 PM Saturday/...
upper trough over the Great Lakes shifts east during this time.
This brings cold advection aloft...further destabilizing the

Temperatures marginally favor mainly snow...especially away from
the immediate coast. Temperatures will be crucial to snow
accumulation. Could even see a transition to rain with just a
little upward nudge. Model precipitation amounts have increased
with this latest guidance suite. Thinking 1-3 inches of snow is
more than just a possibility. Do not have enough confidence to
issue a Winter Weather Advisory with this package. However...
would not be surprised to see a few locations exceed that
amount...particularly if the band establishes itself across
central Massachusetts...northeast CT and northwest Rhode Island. These are all
locations with higher terrain. Confidence in the storm total snow
accumulations through Saturday is moderate at best.


Long term /Saturday night through Thursday/...

* ocean enhanced snow showers Saturday night
* a weak cold front will move through on Monday bringing scattered showers
* moderating Spring-like temperatures into next week
* Alberta clipper moves through Tuesday night into Wednesday


Unfortunately an active pattern appears to be setting up over
southern New England beginning this weekend into next week. Deep
trough will move over southern New England on Saturday pushing the
Carolina low south of the benchmark and towards the Maritimes. A
quick moving ridge and associated high will follow on Sunday before
northwest flow sets up as ridge build over The Rockies. This will
allow for several waves to push through with the first moving from
the Great Lakes into northern New England dragging a cold front with
it on Monday. Next an Alberta clipper will dive into southern New
England by late Tuesday into Wednesday. Lastly a northern and
southern stream merger appears to approach by late Thursday into

Overall guidance is in good agreement until day 7 where they are
split in timing on the Thursday system as the ec is more progressive
than the amplified GFS. Still mesoscale scale details and thermal
profiles to work out but it does look like there is the potential
for some snow showers into next week.


* Saturday night...moderate confidence.

Temperatures overnight will fall well below normal with lows around the
teens to low 20s with the coolest spots out west as skies will
begin to clear as high pressure begins to build in.

Main focus on Saturday night is the snow potential. NAM/GFS are very
bullish in their quantitative precipitation forecast compared to the conservative ec. Inverted
trough will begin to slide eastward during the evening hours as
surface low moves towards the Maritimes. However secondary shortwave
will continue to trigger lift aloft and with Delta ts near 20 degree
difference expect ocean effect snow showers to develop/enhance
ongoing snow showers. This is also supported by north/northeast
winds and very steep lapse rates. Went with HPC quantitative precipitation forecast to play
conservative but generally could see 1-2 inches additional from what
falls during the day on Saturday. Will need to watch this set-up
closely as we could have a surprise 3 to 4 inch amounts somewhere
along the east mass coastline.

* Sunday...high confidence.

Sunday is a transition day as deep trough begins to pull offshore
and upper level ridge moves into the region. Warm air advection will
begin to push in late in the day allowing for temperatures to eventually
warm into the middle 40s. Expect mostly clear skies in the morning but
they will begin to cloud up during the afternoon as the next system
approaches from the west.

* Monday into Tuesday...moderate confidence.

Next upper level disturbance will impact southern New England late
Sunday into Monday. Still some spread amongst the guidance for
timing with the GFS being 6hrs faster then rest of the guidance.
Therefore trended towards ec/HPC on this portion of the forecast.
Surface low across the Great Lakes will pass just north of
southern New England...dragging associated cold front with it. Temperatures at the onset
look to be cool then warm up during the day on Monday prior to
frontal passage. At the onset of precipitation...expect a few snow
showers...but then transitioning to rain fairly quickly as temperatures
warm up. Moisture is marginal so coverage may be more scattered along the

* Tuesday night into Thursday...low confidence.

Next short wave will quickly dive through the flow from Canada and
move across or just south of southern New England. The ec is more
amplified/stronger with this system cutting off the 850 mb low
compared to the GFS which keeps an open wave. Timing is also an
issue as if it pass overnight then temperatures will be cool enough for
snow showers...vs a daytime passage. Still a good amount of time to
watch this system but depending on the placement of the low...we
could see another 1-2 inches of snow across the area.

Weak ridge will follow behind the system before next low pressure
impact southern New England either Thursday or Friday. Ec is less
amplified and more progressive compared to the GFS. Still plenty of
time to watch this system as well.


Aviation /19z Friday through Wednesday/...
forecaster confidence levels...

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

Short term...tonight and Friday...

Tonight and Saturday...moderate confidence.

Another area of showers moves in with MVFR ceilings and MVFR/IFR
visibilities. Temperatures cool enough during the night to change any
rain to snow across the interior. Most of the IFR visibilities should be
concentrated over eastern Massachusetts...and possibly Rhode Island. This continues
into Saturday morning. Temperatures Saturday should warm into the
30s which should change the snow to rain in places across the
coastal plain...while the interior remains snow.

Kbos taf...moderate confidence in taf.

Kbdl taf...moderate confidence in taf.

Outlook...Saturday night through Tuesday...high confidence.

Saturday night into Sunday...VFR conditions likely. Scattered MVFR along
and southeast of I-95 due to ocean effect snow showers. Visibilities may be
reduce if heavy band of snow sets-up.

Monday...VFR dropping to possible MVFR in scattered rain showers as weak
cold front moves through.



forecaster confidence levels...

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

Short term...tonight and Saturday...moderate confidence.

North winds pick up as colder air moves south and a disturbance
passes well offshore. Expecting winds gusting to 25 knots on the
eastern outer waters with seas lingering at 5-7 feet. There is
potential for winds gusting to 25 knots on Cape Cod Bay and
Nantucket Sound as well.

Small craft advisories continue for the outer Massachusetts and Rhode Island coastal

Outlook...Saturday night through Tuesday...

Moderate confidence into Tuesday.

Saturday night...surface low will pass well south and east of the
benchmark. However this will increase winds up to 25-30 kts and
build seas through the night. Small Craft Advisory will be needed.

Sunday through Monday...high pressure quickly builds in on Sunday
allow for winds and seas briefly subside. By Sunday night...winds
back to SW and with approaching cold front on Monday will see seas
increase in response. This will allow for Small Craft Advisory to continue through
the period.

Tuesday...weak lull in between systems however winds will be gusty on
the backside of the front reaching near 30kts. This will keep seas
up above Small Craft Advisory.


Box watches/warnings/advisories...
Rhode Island...none.
Marine...Small Craft Advisory until 6 PM EDT Saturday for anz235-237-


near term...Belk
short term...Belk
long term...dunten

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