Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

Area forecast discussion 
National Weather Service Taunton Massachusetts
746 am EDT Thursday Oct 30 2014

Synopsis...
high pressure will bring dry and seasonable conditions through
the end of the work week. A coastal storm will likely deliver a
glancing blow to the region late Saturday into Sunday...but the
opportunity for a higher impact still exists. Mainly dry weather
follows with a significant warming trend by next Tuesday and
Wednesday.

&&

Near term /until 6 PM this evening/...
745 am update...

Just minor tweaks to the forecast this morning. Patchy fog should
dissipate quicker than Wednesday.

Previous discussion...

For today...expect dry conditions as weak high pressure approaches
from the west during the day as 500 mb short wave crosses the
region...pushing offshore by midday. 850 mb temperatures do fall during the
day...though looks like the core of the cold air remains to the north.
Temperatures will be seasonable for late October...topping off in the
50s. Expect light west-northwest winds with a light pressure gradient across the
region.

&&

Short term /6 PM this evening through 6 PM Friday/...
tonight...
expect the weak high pressure ridge to build east across northern New
England tonight. Light north winds will be in place which will veer to
NE after midnight. May see some more patchy fog develop in the
normally prone valley areas.

Noting low pressure over the Great Lakes tonight as a digging 500 mb
short wave dives southeast. SW flow aloft remains in place...so could
see some middle and high clouds work into western areas after
midnight. With the colder air working in along with a general
light wind in place...expect lows falling back to the 30s for most
areas...ranging to Lower-Middle 40s along the immediate coast. Will
need to monitor for frost/freeze headlines may be necessary for
S/east coastal Massachusetts and Rhode Island.

Friday...
major digging 500 mb long wave trough/cutoff low takes shape across
the Ohio Valley into the central Great Lakes...which sets up an
increasing SW flow aloft along the eastern Seaboard. However...at
the surface...general light flow continues though east-NE winds will
begin to freshen during the afternoon along the S coast. Big
question at this point...where low pressure develops off the middle Atlantic
or southeast U.S. Coast Friday afternoon.

Expect clouds to increase with the increasing low level onshore
flow in place. This will hold temperatures back. Highs will only reach
the upper 40s across the higher terrain of SW New Hampshire/west Massachusetts...ranging to
the Lower-Middle 50s elsewhere.

At this point...not expecting organized precipitation during the day on
Friday as best lift and moisture remains S of the region.
However...could see some ocean induced light sprinkles or even
some coastal drizzle. Did not mention this for now.

&&

Long term /Friday night through Wednesday/...
highlights...

* glancing blow most likely Sat/early Sunday...but greater impact
still possible
* biggest concern is strong winds this weekend especially Cape Cod
* accumulating snow is still possible...but a low probability
* much milder weather returns by next Tuesday and Wednesday

Overview...30/00z guidance had come into better agreement
regarding their handling of a significant coastal storm this
weekend. There are a few ensemble members that suggest a closer
track to southern New England remains possible...but not very
likely. The predominant signal is for a track remaining south and
east of the 40n/70w benchmark. Will favor a consensus blend to
smooth over as many minor differences as possible.

Details...

Saturday and Sunday...
forecast confidence in the details remains moderate for this time
period. The biggest concern remain potential for strong to perhaps
damaging winds...especially across the cape and Nantucket. There
are two main shortwaves involved in this storm/S formation.
Initially...most models form an elongated low pressure system or
even two centers before consolidating into a single primary storm.
Current indications are that this happens too late for a
significant rain/snow event in southern New England.

Precipitation type and timing...a lot of this will depend on how
far west the main precipitation shield reaches. Most of the
frontogenetical forcing is expected to remain offshore...which
would also suggest a rather sharp western edge to the
precipitation shield. Minor wobbles in the track...could have a
significant impact on where this edge to the precipitation
establishes itself.

Initially...all precipitation will be in the form of rain or just
scattered showers Saturday. In fact...most of the precipitation will
be over eastern New England...with just a few showers across western
sections if the current track verifies. If this track shifts west
and we end up getting into heavier precipitation Saturday night and
early Sunday...dynamic cooling could result in some snow across the
higher terrain. Again...based on the currently expected track...accumulating
snow is a rather low probability. Regardless...most precipitation
should have exited our region by middle morning Sunday.

Strong winds...
strong winds are the one thing we are fairly confident that will
develop. Excellent mixing on the backside of this storm should
result in north to northwest wind gusts of 40 to 50 miles per hour developing
late Saturday and especially Sunday as mixing increases. Across
Cape Cod and Nantucket...depending on the track of this storm...we
may see a period of 50 to 60 miles per hour wind gusts. Wind advisories may
be needed for much of the region and perhaps high wind
watches/warnings for the cape and Nantucket. Given many trees
still have at least some leaves on them...the risk for tree damage
and isolated power outages will be enhanced.

Monday through Wednesday...
deep upper trough lifts northeast of the region and we enter an
area of upper level ridging. A significant warming trend expected
with some of the coastal plain possibly seeing highs break 60 by
Tuesday or Wednesday. Mainly dry weather over this time...but a
spot shower or two is possible...especially toward Wednesday.

&&

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

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

Short term /through Friday/...high confidence through
tonight...then moderate confidence Friday.

Today...MVFR-IFR visibilities improve by 13z across CT valley...
otherwise VFR. Scattered-broken clouds 4-5kft from late morning through
this afternoon.

Tonight...VFR. Increasing clouds after midnight. May see local
MVFR-IFR across SW New Hampshire into northwest Massachusetts late. Shallow patchy ground fog
possible at prone terminals.

Friday...mainly VFR. Winds shift to east-NE during day...increasing
along coast to 10-15 knots with some gusts to 20 knots late in day.
May see MVFR ceilings develop along East Coast terminals during the
afternoon. Widely scattered showers along S coast possible late.

Kbos...high confidence in taf.

Kbdl...high confidence in taf.

Outlook...Friday night through Monday...

Friday night...moderate confidence. VFR to start but onshore flow
may result in MVFR ceilings developing. A spot shower or two possible.

Saturday and Sunday...moderate confidence. Still some uncertainty
with the track of a low pressure. Most likely scenario is VFR to
be mixed at times with MVFR late Saturday into Saturday night.
Lower conditions most likely along the coast with rain or
scattered showers.

Low probability for a change to snow at the end. Conditions
improve to VFR by late Sunday...but north to northwest wind gusts
of 30 to 40 knots expected. Strongest winds across Cape Cod and
Nantucket with gusts of 40 to 50 knots possible.

Monday...high confidence. VFR.

&&

Marine...
forecaster confidence levels...

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

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

Today...seas will continue to subside across the outer waters east
and S of Cape Cod this morning. Expecting winds and seas below
small craft criteria.

Tonight...light NE winds and seas up to 3 feet.

Friday...winds become east-NE but will remain below small craft
criteria. Seas slowly increase to 3 feet on southern outer waters.

Outlook...Friday night though Monday...

***storm force wind gusts and 20 foot seas possible late Saturday
into Sunday across the open Atlantic waters east of
massachusetts***

Friday night...high confidence. Increasing NE winds. Gusts up to
30 knots with seas building to around 5 feet on the outer waters.

Saturday and Sunday...moderate confidence. High impact marine
event expected. While uncertainty remains on the exact track and
timing of a coastal low pressure...high confidence gale force
northerly wind gusts across most waters late Saturday into Sunday.
In fact...moderate risk for a period of storm force wind gusts
with 20 foot seas across the open Atlantic waters east of
Massachusetts. Exact wind speeds and wave heights will depend upon
the exact track and intensity of coastal low pressure. A marine
weather statement was issued to address these concerns.

Monday...moderate confidence. Northwest 25-30 knots wind gusts and
seas will likely continue much of the day with good mixing in the
cold air advection pattern.

&&

Tides/coastal flooding...
astronomical high tides are not that impressive late Saturday
into Sunday. Nonetheless...there is at least a low probability for
minor coastal flooding/erosion along the eastern Massachusetts coast as well
as portions of Cape Cod and Nantucket. The concern is for the
early morning high tide Sunday. If we end up realizing 20 foot
seas over the open ocean and northerly wind gusts of 40 to 50
knots...there could be some minor coastal flooding and erosion.
Some of the hot spots would be Salisbury and Plum Island...
Hull...Scituate and perhaps Sandwich Harbor and Nantucket Harbor.
Again...it will depend on exact wind speeds/wave heights out over
the ocean during the early morning Sunday high tide cycle.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
New Hampshire...none.
Rhode Island...none.
Marine...none.

&&

$$
Synopsis...Belk/evt
near term...Belk/evt
short term...evt
long term...Belk
aviation...Belk/evt
marine...Belk/evt
tides/coastal flooding...staff

National Weather Service Glossary of Abbreviations