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Area forecast discussion 
National Weather Service Taunton Massachusetts
237 PM EDT Thursday Sep 18 2014

Synopsis...
a weak cold front will cross the area today...but moisture is
limited so it will come through dry. Cold high pressure builds
into New England tonight and Friday...possibly bringing a touch of
frost to the interior. The high will move offshore through the
weekend resulting in a warmup. A cold front moves through on
Monday...followed by cooler weather Tuesday and Wednesday.

&&

Near term /until 6 PM this evening/...
210 PM update...
dry cold front continues move S out of north New England at midday...
crossing into north Massachusetts at 18z. Noting a few showers developing across
the middle Hudson Valley from near kalb to kgfl which are tending to
dry out as they shift east toward the western Vermont/Massachusetts border over the
last couple of hours as seen on latest NE regional mosaic radar
Loop. A blend of diurnal and frontal clouds have moved in and
developed across central and northern areas through midday.
Looking at visible satellite trends...appears the southern extent
of the frontal clouds are tending to break apart as they shift S
while the diurnal clouds have taken over. More clouds will work S
behind the front. These are expected to push into S New Hampshire/north Massachusetts late
this afternoon/this evening.

Temperatures have risen to the middle 60s well inland to Lower-Middle 70s
across S Rhode Island/southeast Massachusetts as with light northwest winds...which are tending to
shift to a light sea breeze along the East Coast generally from
Boston southward.

Have updated grids to reflect current trends and incorporated into
the remainder of the near term forecast.

&&

Short term /6 PM this evening through 6 PM Friday/...
clearing will take place this evening from north to S as Canadian high
pressure builds across New England and subsidence increases behind
departing upper trough. This will set stage for a cold night as
lows drop back into 30s and 40s...with touch of frost possible
across parts of northwest Massachusetts and SW New Hampshire. Per collaboration with
neighboring offices there are a few concerns which may limit
widespread frost...including how fast clearing occurs and do winds
drop off enough to allow frost formation. Given these concerns we
will hold off on issuing advisories and allow day shift to get a
better look.

High pressure remains in control Friday. Onshore flow combined with
cooler airmass in place should keep afternoon highs in 50s along
immediate coast and higher terrain to middle 60s elsewhere.

&&

Long term /Friday night through Wednesday/...
overview and model preferences...
long range is likely to be defined by upper level longwave trough and
associated cutoff low pressure extending out over Hudson Bay and
baffin island. Initially...this trough is shunted to the north of New
England...as middle level ridge moves to the east...yielding zonal flow.
This is the weekend timeframe...and the rising heights and modest
SW low level flow will lead to moderate warming through Sat and sun.
However...strong cold shortwave associated with cp airmass near
Alaska...will once again dig and deepen the trough across the east
early middle next week...leading to another round of cooler temperatures
across the region. For the most part...these synoptic scale
features are reasonably well agreed upon...and the 18.00z GFS is
now more in line with European model (ecmwf) timing of the cold front associated
with the early week wave. Therefore...feel a blend of
deterministic guidance is a good starting point.

Details...

Friday night through sun...

High pressure will hold fast across the region...yielding an inverted
ridge as the center shifts offshore thanks to confluent zonal flow
aloft. Friday night...weak pressure gradient and near sky clear skies may lead
to enough radiational cooling in northwest Massachusetts and SW New Hampshire valleys for frost
development. Something to watch over the next 24-36 hours. For the
rest of the weekend...modest return flow and warm advection lead
to increasing 850 mb temperatures from +11c Sat to +14c sun.
Therefore...highs range in the low-middle 70s Sat...then middle 70s to
around 80 on sun. Precipitable water values look too low at this point to
support the light quantitative precipitation forecast GFS continues to show each afternoon...and
with subsidence in place beneath the inverted ridge...will opt to
maintain a dry forecast through most of the day sun.

Sun night into Monday...

Cold front is expected to cross the region as low pressure moves
through southern on and qc. Modest precipitable water values around 1.5 in...right
equatorward region of upper level jet streak and modest low level
f-general all support the possibility of showers across the region as
this front moves through. Models starting to line up on
timing...moving it through generally during the am hours Monday. This
timing will limit convective potential and soundings look
relatively stable...even k values remain mostly below 30.
Therefore...suspect mainly just widespread -shra activity to move
through during the morning hours with gradual improvement late day
Monday. This timing will also keep coastal low pressure offshore...so quantitative precipitation forecast
values should generally remain below a half inch given current
thinking.

Tuesday into Thursday...

This cold front will allow moderately cool airmass to begin to
build in early next week. In fact...guidance suggests that by
Tuesday...546dm thickness values may approach the northwest corner of the
forecast area along with 850 mb temperatures around +2c. Therefore...under
the cool northwest flow and cold advection...highs Tuesday may struggle to
break out of the 60s...with some 50s possible. Gradual moderation
is expected into Wednesday and Thursday...but with temperatures still leaning
slightly below normal. The high may not crest across the region
until Wednesday...only moving slightly east by Thursday...so suspect mainly dry
conditions prevail.

&&

Aviation /18z Thursday through Tuesday/...
forecaster confidence levels...

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

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

Through 00z...VFR. Will see scattered-broken clouds at 4500-6000 feet through
00z mainly from the Mass Pike northward...though will push S
toward sunset /around 23z/ as the weak cold front moves across.
Local sea breezes along the East Coast will become NE by 22z-23z. May
see brief local sprinkles as front passes mainly across the
interior. Not expecting wet runways.

Tonight...VFR. Clearing skies from north-S as front pushes offshore.
North-NE winds may gust to 20-25 knots along East Coast from Boston S to
Cape Cod and the islands overnight.

Friday-Friday night...VFR. NE winds gusting to 20 knots early Friday
across Cape Cod and the islands then diminishing. East winds 10 knots
or less late Friday...shifting to S-southeast Friday night.

Kbos terminal...high confidence in taf. Sea breeze through 22z-23z.

Kbdl terminal...high confidence in taf.

Outlook...Saturday through Monday...

Saturday and Sunday...high confidence.
Mainly VFR through the period although some ground fog is possible
Sat morning and Sun morning at typically prone airports. Winds
mainly S-SW...with gusts around 20 knots possible sun.

Sun night into Monday...moderate confidence.
Cold front crosses the region during the morning hours Monday.
Showers and possibly MVFR/IFR conditions may move through with
this front. Otherwise...improving back to VFR by late day Monday.

&&

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.

Through 00z...weak cold front crosses the waters this afternoon.
Expect northwest winds will shift to N-NE. Long ground swells of 3 to 4
feet continue from distant Hurricane Edouard. May see brief swells
to 5 feet on the outer waters S and east of Cape Cod and Nantucket
which should slowly subside.

Tonight...will see pressure surge working down from the north across
the waters behind the cold front. Expect wind gusts up to around
25 knots...highest across the eastern waters. Small craft remains in
effect for all waters except Boston Harbor...Narragansett Bay and
Block Island Sound.

Friday...winds and seas diminish as high pressure becomes
centered over Gulf of Maine...but will maintain Small Craft Advisory for outer
waters where seas will take time to drop below 5 feet.

Outlook...Saturday through Monday...moderate confidence.

Saturday-Sunday...winds swing around to southwest with daytime
gusts around 20 knots...possibly near 25 knots Sunday. Seas will
remain 2-4 feet. A cold front approaches late Sunday with a chance
of showers Sunday night.

Monday... a cold front crosses the waters early in the day. West
winds behind the front will remain less than 20 knots. Seas will
build to 5-7 feet on the outer and exposed waters...as a south swell
increases to 3-5 feet. Small craft advisories may be needed.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
New Hampshire...none.
Rhode Island...none.
Marine...Small Craft Advisory from midnight tonight to 6 am EDT Friday
for anz231>235-251-256.
Small Craft Advisory from midnight tonight to 6 PM EDT Friday
for anz250-254-255.

&&

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

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