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Area forecast discussion 
National Weather Service Taunton Massachusetts
754 am EDT Wednesday Aug 27 2014

Synopsis...
high pressure offshore will draw warm air across New England
today. A cold front will then sweep through during the late
afternoon and early night. Dry and cooler conditions return
Thursday and Friday behind the front. Hurricane Cristobal will
pass well offshore late tonight into Thursday morning...but will
bring rough surf and rip currents to south facing beaches. A front
may stall across New England...bringing unsettled conditions
Sunday into early next week.

&&

Near term /until 6 PM this evening/...
730 am update...
other than a few patches of dense fog...skies were mainly clear
with some high cirrus starting to move into central and northern
areas at 11z. Temperatures bottomed out mainly in the 60s with a few
spots dropping down to the upper 50s including kowd...ktan...kore
and keen.

Forecast is on track this morning other than temps/dewpts. Brought
those elements current and incorporated into near term trends.

Previous discussion...
cold front approaches from the St Lawrence Valley with a band of
thicker clouds. Meanwhile sun this morning and midday will
generate sufficient mixing to reach 850 mb...where temperatures are
16-17c. If we attain full mixing then maximum temperatures should reach near
90. Increasing sky cover as the front approaches may limit maximum
temperatures a few degrees below this.

Main question will be the potential for convection and its
severity. Instability fields from the European model (ecmwf) are somewhat supportive
of convection with totals in the middle 40s and cape 500-700
j/kg...while the GFS has similar middle 40s totals but is more gung-
Ho with cape 1500-2000 j/kg. Even with the milder European model (ecmwf)
values...general thunder is reasonable. We will continue to
advertise chance probability of precipitation for showers/tstms.

Severe storms are less likely. Most of the favorable dynamics will
be north and west through the afternoon/evening. Winds at 850 mb
will be mostly below 20 knots while 500 mb winds of 35 knots or
higher are at best reaching our extreme northwest areas around
00z...near sunset. Precipitation water values increase during the
afternoon with GFS and NAM showing 1.75 to 2.0 inches. Even if we
stay nearer to 1.5 inches...this will be around 1.5-1.9 Standard
deviations above normal. Putting it together...can/T rule out
isolated severe wind gusts but better chance of a few locally
heavy downpours.

Other concern will be increasing swell from Hurricane Cristobal.
Five foot swell doesn/T arrive in the southern waters until after
00z. While conditions may deteriorate a little during the
day...expect the significant changes to hold off until after
sunset.

&&

Short term /6 PM this evening through 6 PM Thursday/...
tonight...
consensus of the model solutions brings the cold front to the
coastal plain around sunset and offshore early tonight. Expect
lingering shower/thunderstorm through 10 PM in Rhode Island and eastern mass...and
through midnight cape and islands. Winds turn northwest behind the
cold front and draw cooler drier air down from Canada. This will
mean clearing skies and dew points in the 50s and lower 60s.
Swell from Hurricane Cristobal continues to increase...with 5 foot
swell moving into our southern waters early tonight. We have
issued a high surf advisory starting tonight.

Thursday...
upper shortwave moves across New England with brief cooling aloft.
Moisture fields show lingering 80 percent relative humidity values between 800 and
900 mb. This suggests diurnal cumulus will form during the day.
Mixing will reach to 850 mb where temperatures of 10-12c would support
maximum surface temperatures in the upper 70s and low 80s. Winds aloft within the
mixed layer are forecast at 20 knots...which may get mixed to the
surface in gusts.

High surf will continue through the day as Cristobal passes well
offshore. The high surface advisory will continue through the day.

&&

Long term /Thursday night through Tuesday/...
highlights...

* cool and dry weather under high pressure Friday
* warm and humid conditions into the weekend
* scattered showers/thunderstorms Sunday into early next week

Overview and model preferences...
medium range models and their ensembles all continue to signal a
low amplitude upper level pattern across the northern tier
states... which generally means a fast moving pattern in place.
Noting a decent short wave developing across the Great Lakes late
this week...then pushing along in the general west-northwest upper flow
toward New England. A front also tries to shift S...but becomes
parallel to this upper flow...so may see unsettled conditions move
in for Sunday and Labor Day. Noting increasing variance amongst
the op model runs early next week in trying to clear the short
wave...with possibly another weaker one moving in.

Leaned toward a blend of available models for the early portion of
the forecast...which showed good continuity and run to run
consistency over the last several model runs...then trended toward
the GFS/ec ensembles beginning Sunday through Tuesday.

Details...

Thursday night through Friday night...
expect dry and cool conditions as large high pressure builds out of
the Great Lakes...shifting east in the broad upper level westerly
wind flow. Will mainly clear skies Thursday night and winds becoming
light/variable mainly after midnight...temperatures will tumble...with
readings away from the immediate coast and urban centers dropping
to the middle 40s to around 50. Some diurnal clouds will develop
during Friday...but it will remain cool with highs mainly in the
Lower-Middle 70s. Northwest winds may gust up to around 20 knots during the
afternoon.

Conditions will remain dry Friday night...but the high will crest
across the region overnight. Expect some middle and high level clouds
working in with lows in the 50s.

Saturday...
transition day as 500 mb short wave moves out of the Great Lakes.
Temperatures will rebound as west-SW winds kick in...bringing in the milder
conditions with increasing humidity especially late in the day
into Sat night. A front will begin to slowly shift S out of Quebec
and S Ontario...so may start to see some showers move into western
areas Sat night. Carried only low chance probability of precipitation at this point. Highs
will be in the 70s...up to around 80 in the CT and Merrimack
valleys.

Sunday through Monday...
with the high anchored off the middle Atlantic and southeast U.S. Coast...along
with general west wind flow aloft...the front that tries to push S
will get hung up in this upper flow. The short wave will move
along the front...so will see scattered showers push across Sunday into
the Holiday...with best shot Sunday night and Monday morning. Dewpoints
also increase. Precipitable waters will also increase...on order of 1.7 to 1.8
inches /about +2 South Dakota for late August/. Some marginal instability
also works in...so can not rule out some thunderstorms. May also
see a few producing locally heavy rainfall.

Temperatures will rise to the upper 70s to middle 80s...mildest on
Sunday...with dewpoints rising to the middle 60s both days.

Tuesday...
some question as to timing of exit of precipitation...and whether
another short wave develops and pushes toward the region. For
now...expect mainly dry but warm conditions...but not a lot of
confidence for this portion of the forecast.

&&

Aviation /12z Wednesday through Sunday/...
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.

Today...mostly VFR. Scattered showers/thunderstorms should develop this
afternoon...initially inland from around mht to baf and bdl but
the potential spreads east to bos-pvd later in the day. Brief
MVFR/IFR under the core of any showers/storms...also brief heavy
rain and maybe a strong wind gust. Low confidence on timing.

Tonight...mostly VFR. Any lingering showers/thunderstorms in eastern
mass/Rhode Island will move offshore or dissipate during the first part of
the night. Winds then become northwest overnight as the cold front
moves offshore.

Thursday...VFR. Northwest winds may gust to 20 knots with
scattered to broken sky cover around 5000 feet from midday to
evening.

Kbos terminal...moderate confidence in taf. SW-winds prevailing.
Scattered rain showers/thunderstorms and rain possible around 21z...low confidence on direct hit
for terminal so no mention at this time.

Kbdl terminal...moderate confidence in taf. SW-winds prevailing.
Scattered rain showers/thunderstorms and rain possible around 19z...low confidence on direct hit
for terminal so no mention at this time.

Outlook...Thursday night through Sunday...

Thursday night into Friday...high confidence.
VFR with sky clear Thursday night into Friday. Light winds. Patchy fog
after 06z Friday with local MVFR to IFR conditions possible in
normally prone areas. Sea breezes Friday.

Saturday into Sunday...moderate confidence.
VFR. Increasing S-SW winds. Better chances for rain showers/thunderstorms and rain Sunday
across the interior.

&&

Marine...
forecaster confidence levels...

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

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

Today...high pressure over the waters will shift farther offshore.
Expect light winds/patchy fog first thing this morning...otherwise
good visibility with southwest winds 10-15 knots. An approaching cold
front may bring scattered showers/thunderstorms toward evening.

Tonight...increasing south swell from Hurricane Cristobal. The
southern waters will experience a 5 foot swell in the early night
and 6 to 8 foot swell by morning.

Thursday...south swell continues through the day with 6 to 9 foot
seas...mainly swell...on the southern waters. Northwest wind will
be gusty near shore with maximum gusts around 20 knots.

Outlook...Thursday night through Sunday...

Thursday night...high confidence.
Expect S swell from Hurricane Cristobal to continue through the
night...though may start to subside late. Seas up to 7-9 feet on the
outer waters. North-northwest wind gusts up to 20 knots on the eastern outer
waters.

Friday...high confidence.
North winds gusting to 20 knots early...then will veer to east-NE and
diminish during the day. Seas may linger at around 5 feet on the
outer waters during the day before subsiding.

Saturday and Sunday...moderate confidence.
Winds become S-SW during Sat and continue through sun. Gusts
should remain below small craft criteria...but seas may build up
to around 5 feet on the southern outer waters.

&&

Box watches/warnings/advisories...
CT...air quality alert from 1 PM this afternoon to 9 PM EDT this
evening for ctz002>004.
Massachusetts...high surf advisory from 8 PM this evening to 8 PM EDT Thursday
for maz020-022>024.
New Hampshire...none.
Rhode Island...high surf advisory from 8 PM this evening to 8 PM EDT Thursday
for riz006>008.
Air quality alert from 11 am this morning to 11 PM EDT this
evening for riz001>005.
Marine...Small Craft Advisory for hazardous seas from 5 PM this
afternoon to 8 PM EDT Thursday for anz235-237-254>256.

&&

$$
Synopsis...wtb/evt
near term...wtb/evt
short term...wtb
long term...evt
aviation...wtb/evt
marine...wtb/evt

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