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Area forecast discussion 
National Weather Service Taunton Massachusetts
722 PM EDT Wednesday Aug 27 2014

Synopsis...

Showers and thunderstorms ahead of a cold front will continue to
sweep across southern New England overnight. Drier and less humid
air overspreads the region Thursday and Friday yielding mild days
and cool nights. Hurricane Cristobal will pass well offshore late
tonight into Thursday bringing dangerous surf and rip currents to
south facing ocean beaches of Rhode Island and Massachusetts. Pleasant weather lingers
into Saturday...then a front will sweep across New England late
Sunday into Monday bringing unsettled conditions.

&&

Near term /through Thursday/...

730 PM update...

Line of showers / thunderstorms diminishing as it progresses southeast
encountering a less unstable airmass. Within an environment of
less favorable shear...main threats with any storms will be heavy
rain /pwats around 1.50-1.75 inches/ and gusty winds subsequent as
noted by the previous forecaster by inverted-v soundings. Feel
such threats will only last into the early evening. Thereafter a
line of showers is expected to be maintained by the middle-level
trough and attendant synoptic scale forcing of available moisture
convergent along and ahead of the parent frontal boundary.

Feel the latest hrrr / rap forecast solutions have the best
handle on the present situation. Have modeled forecast trends
accordingly. Likely low clouds and fog ahead of the front will
impact southeast Massachusetts that include Cape Cod and the islands into the
morning hours. Lows around the low-60s with the warm spots southeast
and coolest areas northwest.

&&

Short term /Thursday night through 6 PM Thursday/...

Thursday...

Post frontal airmass overspreads the region as cold front departs
the South Coast during the early morning. Middle level flow remains
cyclonic as mean trough axis aloft remains over New England.
However strong drying through the column with negative k-indices
overspreading the region along with dew points tumbling into the 50s
and possibly the u40s. However given the cool temperatures aloft and
cyclonic flow should see scattered-broken cumulus/scu during the peak heating
hours of the afternoon.

Nevertheless a spectular day with low humidity...a refreshing northwest
breeze of 10 to 20 miles per hour and temperatures noticeably cooler with highs 75
to 80.

High surf....

Hurricane Cristobal passes well offshore but wna and the hurricane
version of the wna yields 5-10 feet swells entering the near shore
waters and up to 12 feet well south of mvy and ack. Our in house
surf calculation suggest breakers of 6-12 feet at south facing ocean
beaches tomorrow. Thus very dangerous surf and rip currents.
Obviously will continue the high surface advisory which may have
to be extended into Friday as the wave models typically erode swell
energy too quickly. Surf and rip currents will not be as dangerous
along the eastern Massachusetts coast as the swell energy will be parallel to
this coastline.

Thursday night...

Core of cool airmass moves over the region with 850 mb and 925 mb
temperatures about +1 South Dakota cooler than normal. North-NE winds will preclude
eastern Massachusetts from cooling off too /l60s/ much given ocean wind
trajectory. However interior valleys that decouple could see mins
in the mu40s with 50s elsewhere.

&&

Long term /Thursday night through Wednesday/...

*/ highlights...

- seasonable and dry weather for Friday...enjoy it!
- Hot and humid conditions through the weekend
- thunderstorms possible across north/west New England Sunday
- wet weather anticipated Sunday night into Monday night
- could remain warmer than average into next week

*/ overview and model preference...

Better agreement among ensemble members would suggest a zonal flow
regime with some weak ridging as both the nao/pna remain negative to
near-neutral. Expecting an above average temperature pattern as the
ecens/gefs/naefs/CPC would suggest into early September...anomalous
on the order of +2-3 Standard deviations. With anticipated warmer
conditions subsequent of ridging...expecting prolonged S-flow to
advect muggy conditions north. Looking to be a warm and humid timeframe.

For the forecast period over the next week beginning Friday...expect
the west-Atlantic ridge to be the dominant influence over the regions
weather. Favor the European model (ecmwf) with the confluent flow setup and attendant
surface frontal position between the NE-Canada trough and west-Atlantic
ridge remaining north of the region parent with better jet-dynamics and
sheared middle-level energy. Only as a c-Continental U.S. Disturbance invokes a
weak-wave low along the front will wet-weather shift into our area
around Monday based on a consensus of model data.

Despite model variance...a broad signal is discernible of a brief
period of dry weather after passage of the weak-wave
low...followed by a sharp cold front and perhaps the return of
more seasonable conditions. Low confidence at this time as
ensemble means would suggest the propensity for zonal-flow with
weak ridging. Favor the deterministic European model (ecmwf) with possible
outcomes.

Highlights/confidence are broken down in the daily discussion below.

*/ Day-to-day details...

Friday...

High pressure. Light/variable winds. Sea-breezes along the coasts.
Seasonable and mostly clear conditions...slightly cooler along the
shores...with highs around the mid-70s. Middle- to high-level clouds
possible ahead of an encroaching warm-front from the SW. Along with
winds turning S overnight as high pressure shifts east...expect milder
conditions with lows around the mid-50s.

Saturday...

Surface warm front lifting NE across New England late...joining with
a trailing cold front from a low disturbance over NE-Canada. As the
ridge subsequently enhances ahead of the frontal disturbance and a
weaker disturbance over the c-conus...believe wet-weather activity
will be pushed well north of the region by the influence of the ridge.
Thus will go with a dry-weather forecast.

Expect prevailing S-flow to begin ushering warmer / humid conditions
across the region. Will see highs warm into the low-80s as a well-
mixed boundary layer allows for scattered cumulus along with the mix-
down of breezy S/SW flow. Feel this will restrict sea-breezes...so
expect interior winds to push the warm / humid conditions all the
way to the E-shores.

Mild and dry overnight. With a lingering dry-subsidence inversion...
higher dewpoint air advecting north could lend to low clouds / fog along
the S-shore. Expecting lows around the low- to mid-60s.

Sunday...

Warm-front well-defined to the north. Push of 850 mb +16-18c air across the
region. Expect S New England to be within the warm-sector of a hot
and humid airmass. Collocated within a well-mixed boundary layer...
breezy S/SW-flow during the day should allow for interior winds once
again to restrict sea-breezes and push forecast high temperatures
around the upper-80s to the E-shores.

Heights fall as the c-Continental U.S. Disturbance shifts east within the quasi-
zonal flow regime. Showers / thunderstorms are certainly plausible north
and west within modest instability and shear...closer to regions of
favorable dynamics / ascent as well as the convergent nose of higher
Theta-E air ahead of the front. Likely the majority of activity is
across the east Great Lakes into NY/PA...but its possible that activity
develops into north/west New England late. This would possibly be the case
as the convective temperature is met such that any inversion would
erode and both surface-based instability and effective shear could
be utilized. Can not rule out strong storms...especially across short wave
facing slopes of high terrain over northwest CT / west Massachusetts / S New Hampshire as orographic
processes aid in lifting the warm / juicy airmass aloft. But it is
possible that the ridge wins out. Still a forecast way out in time
and as we have seen just in the past several model runs there has
been a fair amount of variability. Have moderate confidence with
this forecast timeframe.

Ridge and subsidence inversion lingers for the S/east so will keep with
a dry-forecast for those areas.

Sunday night through Monday night...

Weak-wave low along the front through the quasi-zonal flow pushes east
and across the region. Though appearing as a nocturnal passage...the
collocation of deep-layer moisture...minor instability and shear...
and forcing along the frontal boundary will likely yield widespread
showers with the possibility of heavy rain and thunderstorms. Though
it appears the better forcing dynamics shift N/E...shunted by the
ridging pattern and Bermuda high remaining dominant.

Low confidence forecast as the consensus of model solutions contains
a fair amount of variability. Will prevail with slightly above-
average conditions.

Tuesday Onward...

A lull in activity is possible behind the weak-wave disturbance. A
sharper cold front into midweek followed by high pressure. Not all
entirely convinced on such outcomes based on ensemble trends. Would
anticipate ridging to remain dominant with temperatures being above-
average for the timeframe.

&&

Aviation /00z Thursday through Monday/...

Forecaster confidence levels...

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

Short-term /today through Thursday/...moderate confidence.

Thunderstorms and rain concluding towards 2z evolving into a rain showers-line progressing
southeast towards ack by morning. VFR rearward of the line under northwest
winds...with possible IFR-LIFR ceilings / visibilities along and ahead under
S/SW flow...especially for S-coastal terminals.

VFR into Thursday with gusty northwest winds up to 20 kts. Scattered-broken ceilings
around 5 kft during the day...clearing overnight with winds
weakening towards Friday morning.

Kbos terminal...high confidence in taf. Will hold VFR with rain showers
until 1z. Thereafter...winds reverting northwest as ceilings lift.

Kbdl terminal...high confidence in taf. Rain showers should move out. Northwest
winds and VFR prevail. Ceilings lifting.

Outlook...Friday through Monday...

Friday...high confidence.

VFR. Light winds. Sea-breezes along the shores. Sky clear.

Saturday into Sunday...moderate confidence.

VFR. Breezy S/SW winds. Scattered ceilings 4-6 kft Saturday. MVFR-IFR ceilings /
visibilities possible along the S-coast Saturday night. Rain showers/thunderstorms and rain possible
for north/west New England late Sunday.

Sunday night into Monday...low confidence.

Mix of low-end VFR to MVFR. Widespread rain showers across the terminals.
Possible thunderstorms and rain. Continued S/SW winds.

&&

Marine...

Forecaster confidence levels...

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

Short-term /tonight through Thursday/...high confidence.

Tonight...

South swells from Cristobal continue to increase. A few showers
possible this evening and overnight. South-southwest winds become northwest toward
sunrise as cold front approaches from the west.

Thursday...

Swells peak at 5 to 11 feet tomorrow across the South Coast waters.
Adding to the rough seas will be a developing northwest wind wave behind
the frontal passage. Otherwise dry weather with good visibility. However
a few showers may linger early in the morning across the south
coastal waters.

Thursday night...

Northwest winds become north-NE late. Good visibility and dry weather.

Outlook...Friday through Monday...

Friday...high confidence.

High pressure in control. Light winds. Diminishing seas with only
the S/southeast outer waters experiencing wave heights in excess of 5-feet
by morning. Good boating weather.

Saturday into Sunday...moderate confidence.

Increasing S-winds. Prolonged S-fetch lending to wave heights in
excess of 5-feet across the S/southeast waters. Fog possible during the
overnight hours...especially along the S-coast.

Monday...moderate confidence.

Continued S-winds. Wet-weather moving across the waters. Fog may
remain an issue over the waters...especially during overnight
periods.

&&

Box watches/warnings/advisories...
CT...air quality alert until 9 PM EDT this evening for ctz002>004.
Massachusetts...high surf advisory until 8 PM EDT Thursday for maz020-022>024.
New Hampshire...none.
Rhode Island...high surf advisory until 8 PM EDT Thursday for riz006>008.
Air quality alert until 11 PM EDT this evening for riz001>005.
Marine...Small Craft Advisory for hazardous seas until 6 am EDT Friday
for anz235-237-254>256.

&&

$$
Synopsis...nocera/sipprell
near term...nocera/sipprell
short term...nocera
long term...sipprell
aviation...nocera/sipprell
marine...nocera/sipprell

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