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Area forecast discussion 
National Weather Service Taunton Massachusetts
935 PM EST Friday Nov 21 2014

Synopsis...
after a dry but very cold night...temperatures moderate some
Saturday on gusty southwest winds. This will be followed by a
significant warm up Sunday and especially Monday...but with a
period of rain Sunday night and Monday. Quiet for Tuesday but
conditions may change by Wednesday with the threat of a storm
system. Turning colder into the end of the week.

&&

Near term /until 6 am Saturday morning/...
930 PM update...
high pressure in control bringing clear and diminishing wind. Some low
level moisture spilling into the Berkshires may bring a few clouds
to west Massachusetts through 06z then low level drying takes place. Expect a
nice setup for radiational cooling across the interior as winds
continue to decouple resulting in lows into the teens...with
single digits possible across northwest Massachusetts and SW New Hampshire...well below-normal
for this time of year. Mildest readings in the 20s will be in
bos...Outer Cape/islands and areas adjacent to Narragansett Bay.

&&

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

High pressure moves off the middle Atlantic allowing for strong middle
level warm advection to develop. The response will be an increase
in middle/high level cloudiness as the day wears on...but it will
remain dry given the lack of low level moisture.

Despite the warm advection aloft...it will take time for that to be
completely realized at the surface. While it will be milder than
today...high temperatures will still be below normal...mainly in the
upper 30s and lower 40s with some middle to upper 40s on the cape
and islands. However...expecting southwest wind gusts of 20 to 30
miles per hour to develop in the afternoon and perhaps a bit stronger along
the far southeast New England coast. This will still make it feel
rather chilly outside for November standards.

Saturday night...

A moisture starved shortwave will move across the region Sat night.
There still should be enough forcing to bring a brief period of
scattered light precipitation. While it certainly will be too
warm aloft for any snow...the biggest question is will it be cold
enough at the surface for some pockets of spotty light freezing
rain across the interior. Its certainly possible and will need to
be watched...but its not an ideal setup. There is a lot of wind
off the deck and probably enough to prevent most areas from
decoupling. Given were +4c at 850 mb some of this milder air will
be able to mix down. This should limit the overall light icing
threat...but still can not rule out some isolated pockets in the
deeper valley locations. Low temperatures will likely be in the upper 20s
to middle 30s during the evening...but should rise some overnight.

&&

Long term /Sunday through Friday/...
*/ highlights...

- turning warmer and wet Monday
- a possible midweek storm...especially for southeast New England
- looking colder into Thanksgiving

*/ overview and model consensus...

Trending +ao/nao with near-neutral pna suggests a more progressive
pattern and mild. No surprise to see a lack of deep closed-low 500 mb
disturbances...though an active pattern with abundance of Pacific-
origin waves maintaining troughing between sectors of above-average
ocean temperatures over the NE-Pacific and NW-Atlantic.

Some of those waves are well out in the Pacific and have not even
been sampled. The wave associated with the winter-storm potential
for the midweek / Thanksgiving period is just S of the furthest east
aleutain islands of Alaska. Noting this...have highest confidence
through early-next week with the forecast...but low confidence for a
potential midweek storm. Will hit up the details below.

So for Sunday...

Clouds and light showers associated with a weak trough disturbance.
Dissipating beneath a middle-upper level ridge / subsidence. Beneath
the warm-sector and return S-flow round the high pushing off into
the Atlantic...h925 temperatures nearly +10c...may see highs warm
well into the 50s with any sunshine.

As for Sunday night...

Warm-front and accompanying broadscale lift ahead of a deepening low
across the c-Continental U.S. Through the Great Lakes region becomes the focus
for rain across the region. Non-diurnal warming trend overnight. All-
rain event. Main concerns are with both winds and rain.

With winds: strong low-level jet centered around Monday morning with
winds 1-2 kft above ground level model-consensus averaging around 50 miles per hour /45 kts/.
Suggested boundary-layer decoupling beneath much warmer air between
h925-85. But if 2m temperatures are warmer as forecast for Sunday
could be warmer Sunday night aiding in low-level mixing. Also need
to consider any heavy rain which could also aid with dragging faster
momentum to the surface. Overall: main concern across southeast New England
and high terrain above 1 kft. Wind advisories may be necessary. Cips
analog guidance has just above 50-percent for winds > 35 miles per hour.

With rain: broadscale ascent of the warm-conveyer-belt with precipitable waters up
to 1.5-inches and anomalous high-thetae air. Convergence along the
nose of the low-level jet to the parent warm-front. Expect a broad
northwest-southeast band of rain with perhaps an embedded line of heavier rain. It
moves through notably quick. Model-consensus average rain amounts
are around 0.50 - 0.75 inches. Am not expecting any flood issues.

Into Monday...

Rains for the morning...improving afternoon. If we clear as h925
temperatures warm to +14c then we could possibly see highs into the
middle- to upper-60s /+18c/ possibly to near 70. Model-consensus h925
winds average around 45 miles per hour /40 kts/ and with warmer conditions
could see the potential for mixing out to h9 and momentum mix-down.
Will hint at this in the forecast...but moderate confidence.

Monday night through Tuesday night...

Will go with a few lingering showers...but the main pump of moisture
should be well offshore. Otherwise the main cold front attendant to
the deepening low lifting through the Great Lakes region sweeps
across New England. Expecting dry and cooler weather for Tuesday...
perhaps continuing into Tuesday night.

Wednesday and beyond...

Just too early to say. Lots of uncertainty as ensemble members vary
considerably with surface low centers around the ensemble mean which
key upon a low southeast of the 40n / 70w benchmark around Wednesday night.
Have concerns for southeast New England which could see the greatest impact
while noting a ridge of high pressure over S-Canada /with the center
over the c-conus/. The GFS-upgraded /t1534/ is a far outlier and is
not considered with this forecast.

Evaluating synoptics...this does not appear to be a coastal storm
but more of a wave low along the offshore stalled front. As been the
case this year...cold air has been plunging into the central Continental U.S.
But its true bite remains mainly north/west of our region. Do have some
confidence that the wave low will hug closer to the coast. Then it
comes to breaking down timing / associated dynamics / thermal fields
which right now are again too early to diagnose. There has been a
consistent signal. Storm bears watching.

Expecting a return of Arctic air behind whatever midweek system that
may emerge. Day 6-8 cips analogs have high probabilities for below-
normal temperatures for the southeast-Continental U.S. Into the Ohio-River valley
centered around the late-Thanksgiving week period. Ec ensembles at
850 mb have the freezing mark plunging to nearly the Gulf Coast...with
-10c air into New England by next weekend.

&&

Aviation /02z Saturday through Wednesday/...
forecaster confidence levels...

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

Short-term /through Saturday night/...moderate confidence.

0z update...

VFR overnight into Saturday. Lights winds across the interior with
breezy west/northwest flow along the shores will enhance Saturday out of the
SW with likely gusts 20-30 kts by afternoon...possibly up to 35
kts at times /especially over the cape and islands/.

Low-end VFR Saturday night. Brief periods of MVFR possible with
any -shra. Isolated pockets of -fzra possible across the interior.
If any icing it is expected to be very light. Winds remaining an
issue with SW-gusts 20-30 kts...possibly up to 35 kts...mainly
across the coastal plain of east/southeast New England.

Kbos terminal...will hold VFR and keep SW-winds around 240 brisk
throughout beginning Saturday. Perhaps issues on 15/33. Do not
anticipate any -fzra at the terminal. High confidence.

Kbdl terminal...if any threat of -fzra anticipating impacts around
0-6z Sunday /7 PM Saturday to 1 am Sunday/. Moderate confidence.

Outlook...Sunday through Wednesday.

Sunday...moderate confidence.

Initial -shra early Sunday with low-end VFR followed by some brief
improvement. Winds turning S.

Sunday night into Monday...moderate confidence.

Conditions deteriorate MVFR-LIFR Sunday night into Monday morning
with +ra and strong S-winds with gusts around 30 kts possible...
otherwise low level wind shear impacts with 50 knots S-winds 2 kft above ground level. Conditions
improve by midday...but could see continued SW-winds around 25 kts.

Monday night through Tuesday...moderate confidence.

West-flow with mainly VFR.

Wednesday...low confidence.

An offshore storm system could bring significant impacts especially
to the se-terminals.

&&

Marine...
forecaster confidence levels...

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

Short term /tonight through Saturday night/...

7 PM update...

Will allow the small craft advisories to drop on Boston Harbor and
Narragansett Bay...but prevail all other waters towards Saturday
morning as high pressure builds into the region allowing winds to
gradually relax out of the W/NW.

Saturday and Saturday night...moderate to high confidence.

High pressure moves east allowing for a fast-flowing return SW-flow
of air over the waters. Colder air over water waters...expect light snow shower
gusts possibly exceeding gale force late Saturday into Saturday
night.

Gale watch in effect for the threat of gusts over the period of
35 kts. Seas likely building 6 to 9 feet on the outer waters...
especially over the S/se-waters. Will allow the overnight shift to
evaluate as to whether to go with gale warnings or high-end
small-craft advisories.

Outlook...Sunday through Wednesday.

Sunday...moderate confidence.

Conditions improving as SW-winds turn S and relax. Will see wave
action dissipate below Small-Craft Advisory levels.

Sunday night into Monday...moderate confidence.

Conditions deteriorate into Monday morning with rain over the waters
and embedded heavier showers. Visibility impacts possible. Winds
increasing out of the S. Gusts exceeding gale force appear likely.
Waves subsequently increasing to 10 feet on the outer waters.

Monday night through Tuesday...moderate confidence.

Winds turning SW remaining blustery with gusts exceeding 25 kts.
Waves maintained with heights of 8 to 10 feet on the outer waters.

Wednesday...low confidence.

An offshore storm system could bring significant impacts to the
waters yet details uncertain at this time.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
New Hampshire...none.
Rhode Island...none.
Marine...gale watch from Saturday afternoon through late Saturday night
for anz231>235-237-250-254>256.
Small Craft Advisory until 1 am EST Saturday for anz232>235-
237.
Small Craft Advisory until 7 am EST Saturday for anz231-251-
255-256.
Small Craft Advisory until 10 am EST Saturday for anz250-254.

&&

$$
Synopsis...Frank/sipprell
near term...kjc
short term...Frank
long term...sipprell
aviation...Frank/sipprell
marine...Frank/sipprell

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