Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Taunton Massachusetts
1011 PM EST Sat Nov 28 2015


A much cooler airmass overspreads the region tonight and Sunday as
dry high pressure builds into Quebec. Chilly but dry weather
lingers into Monday as high pressure settles over Maine. The weather
likely turns wet Tuesday into Wednesday as low pressure and a frontal
boundary move across the area. Temperatures will also moderate Tuesday
and Wednesday. Then the trend is drier but cooler late next week.


Near term /until 6 am Sunday morning/...

Tricky overnight forecast. Presently veil of thick low clouds is
pushing S along with some very scattered light rain showers. It
is behind this that north-winds are driving a cooler airmass across
the region that does not appear to be appreciably dry with dew-
points in the 20s. Scattered to broken low clouds linger with some
places clearing out entirely ... beneath a strong dry-inversion
per 0z soundings out of Albany New York and Gray ME.

So the overall question is as to whether low clouds will prevail
and if not and rather it clears out ... anticipating light winds
overall overnight will fog develop instead? Would expect one or
the other.

Decent rains earlier today that exceeded expectations. There is a
lot more moisture in the low-levels that would easily saturate
with the driving cooler airmass S that does not seem so dry. While
guidance does not seem to support either solution of low clouds
nor fog but rather it clears out entirely and we maintain a quiet
night of weather ... am still concerned. Not overly confident as
to which way the forecast will go ... but will need to monitor for
both closely.

So as lows dip downward around the upper-20s to low-30s with areas
across north/NC-mass falling as low as the middle-20s ... and with winds
becoming light ... expect that either see low clouds linger or fog
develops. With any fog it can become locally dense yielding travel
impacts accordingly. Difficult to pinpoint and again not a lot of
confidence with respect to specificity. Anticipating improvement
with sunrise.


Short term /6 am Sunday morning through Sunday night/...


1035 mb high builds from Ontario to Quebec. Middle level flow remains
cyclonic but column is very dry. Therefore other than some cirrus
clouds early and strato-cumulus early over the Outer Cape expecting lots
of sunshine. Although low sun angle and limited blyr mixing due to
subsidence inversion will only yield highs in the 40s...which is
seasonable for this time of year but much cooler than previous days.
Although it will be pleasant given lots of sunshine and light winds.

Sunday night...

Chilly but dry for most of the region as 1034 mb high settles into
northern New England. However this shifts low level winds to the
northeast with modest cold air advection as 850 temperatures drop to -10c by 12z Monday. This
yields a Delta-T of about 20 degree from SST /10c/ up to 850 mb. BUFKIT
soundings indicating mixing is not quite to 850 but to about 900 mb
where temperatures are -7c to -8c. A differential of 17/18c will be
sufficient for the risk of scattered snow showers across Cape
Cod/Nantucket and northward into coastal Plymouth County. Somewhat
confident of at least a few flakes flying given hi res NAM/arw and
nmm offering light quantitative precipitation forecast amounts.


Long term /Monday through Saturday/...


* dry and chilly Monday
* precipitation overspread the region on Tuesday lasting into Wednesday night
* dry and seasonable temperatures likely next Thursday/Friday


12z model guidance as well as their ensembles are in good agreement
for this forecast. Chilly and dry on Monday as Canadian high pressure
builds over the northeast. Approaching low pressure system will move
across the Great Lakes and swing a warm front through the area on
Tuesday followed by a cold front Wednesday. This will bring some
appreciable rain to the region for the mid-week. Behind this system
expect strong high pressure to remain over the eastern Continental U.S.
Through next weekend.


Monday...high confidence.

Chilly airmass over the region as Canadian high pressure builds over
the northeast. A few isolated ocean effect snow flurries or low clouds
will impact the cape/islands and coastal Plymouth early in the
morning. Otherwise anticipate mostly clear skies. 850mb temperatures will
only reach between -8 to -6c during the day which will keep
temperatures well below average. In fact high temperatures will warm into
the upper 30s to low 40s.

Overnight temperatures will be closer to average as warm air advection begins
across the region as a warm front approaches from the southwest.
Overnight low will drop into the low to middle 20s away from the

Tuesday into Wednesday...moderate confidence.

Warm front will begin to approach from the southwest on Tuesday.
This front will warm the middle-levels above 0c...however at the
surface especially with such a cool start on Tuesday surface temperatures will be
below 32f. Most of the guidance keeps precipitation from coming to the
region Tuesday morning...with a better shot during the afternoon
hours. However if the atmosphere decides to moisten up earlier and
precipitation falls in the morning then we could see some freezing
drizzle/rain at the onset of precipitation Tuesday morning. There are also
some indications that the CT valley may experience cold air they may struggle to warm up on Tuesday as well. Still
a lot of details to work out focused on the Tuesday morning/early
afternoon and hopefully guidance will be able to resolve some of the
issues with the next 24 hours.

Heaviest precipitation appears to move across the region Tuesday night into
Wednesday. Nearly occluded system will push the warm front through
by Tuesday night allowing for a warm up in temperatures by Wednesday. However
ahead of the cold front appears a surface low will develop and move
over the area on Wednesday. This low will help increase the heavy
rain potential more so then what guidance is suggesting. Cold front
will pass through the later half on Wednesday allowing for a dry
slot to move through reducing precipitation chances Wednesday night.

Thursday into Friday...high confidence.

Dry weather will prevail for Thursday and especially Friday. Only
issue is cold core low/cyclonic flow will remain over the region on
Thursday morning. This could trigger a few snow showers across the
northwest portion of mass with the higher terrain having the best
shot. As the low moves towards the Maritimes...a secondary cold
front will swing through increasing westerly winds to 20-30 miles per hour.
Winds should begin to decrease after sunset on Thursday.

Both Thursday and Friday temperatures will be seasonable with highs
into the middle to upper 40s each day.


Aviation /03z Sunday through Thursday/...

Forecaster confidence levels...

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

Short term /through Sunday night/ ... high confidence.


Mix MVFR-IFR scattered-broken ceilings with local visibility impacts. Light north-winds
continue. Improving north to S closer to sunrise. Prevailing VFR with
north-winds into Sunday. Yet scattered-broken MVFR to low-end VFR ceilings are
likely to linger over the cape and islands continuing into Sunday
night with the possibility of -shsn.

Kbos terminal ... more confidence towards a mix of MVFR ceilings this
evening lingering into the morning hours. During the day those
ceilings should remain east offshore. North-winds throughout.

Kbdl terminal ... will be watching the evolution of MVFR ceilings
overnight which could lower to IFR. Yet should they clear out
would expect some visibility impacts to the terminal. Threats conclude
with sunrise.

Outlook /Monday through Thursday/...

Monday...high confidence. Mainly VFR. Isolated MVFR/IFR in ocean effect
clouds Monday morning.

Tuesday into Wednesday...moderate confidence. VFR to start with
conditions quickly dropping into approaching rain system. Could see
MVFR/IFR ceilings with visibilities dropping within heavy rain through most of
this period.

Thursday...high confidence. VFR with gusty westerly winds near 20-30



Forecaster confidence levels...

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


NE winds 15 to 20 knots this evening will diminishing a bit and
becoming north toward morning. The combination of modest winds and
leftover east-southeast swells will keep seas at or above 5 feet for much of the ocean
waters. Thus Small Craft Advisory remain posted. Any light rain early this evening
tapers off.


High pressure builds from Ontario to Quebec. Modest north wind 5 to 15 kts.
Seas slowly subside. Dry weather and good visibility too.

Sunday night...

NE winds increase 15 to 20 knots with low risk of a few gusts to 25 knots
possible. Cold air on long NE fetch will result in building seas
along with scattered snow showers.

Outlook /Monday into Thursday/ ...

Monday...high confidence. Gusty easterly winds will start seas out
above 5 feet. However with high pressure building over the water waves
will being to relax and gusts will be below 25 kts. Small Craft Advisory to start but
will be dropping off through the day.

Tuesday into Wednesday...moderate confidence. High pressure over the
waters for much of Tuesday. However approaching warm and cold front
will switch the winds to the south and eventually in a westerly
direction by Wednesday night. Seas will build in response and could see
low visibilities in heavy rain and fog. Small Craft Advisory will be needed.

Thursday...high confidence. Winds will increase out of the west
keeping seas up through Thursday. Wind gusts will breach between 25-
35 kts. Low confidence on gales. Seas will remain up with outer
waters close to 8-10 feet.


Box watches/warnings/advisories...

Rhode Island...none.
Marine...Small Craft Advisory for hazardous seas until 7 am EST Sunday
for anz250.
Small Craft Advisory for hazardous seas until 1 am EST Sunday
for anz251.
Small Craft Advisory for hazardous seas until 10 am EST Sunday
for anz254>256.



near term...sipprell
short term...nocera
long term...dunten

National Weather Service Glossary of Abbreviations