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Area forecast discussion 
National Weather Service Taunton Massachusetts
352 am EDT Thursday Sep 3 2015

Synopsis...
a cold front will sweep across New England today and will be
accompanied by scattered afternoon/evening showers and
thunderstorms. Canadian high pressure builds over New England Friday
and into the Labor Day weekend. The high moves just offshore early
next week yielding mainly dry but warmer than normal temperatures.

&&

Near term /until 6 PM this evening/...
leftover upper level cirrus debris from early convection continues to
spill across the northern tier of southern New England this morning.
Otherwise...clear skies and calm conditions prevail. These clouds
may limit somewhat the risk for early morning fog in spite of the
dewpoints in the low-middle 60s. However...some areas already reporting
modest fog in the valleys of western CT/MA.

Backdoor cold front will be sliding into the region through the
day today...stalling as it meets the more robust incoming sea
breeze front from the S. Bulk of the instability is
elevated...within a corridor of 6.0-7.0c/km lapse rates...which
will shift southeast...then offshore in the evening. Expect convection to
start across the higher terrain in Vermont/New Hampshire thanks to elevated heat
source better realizing the available instability. Then it will be
a race against time as this convection shifts S and interacts with
the various fronts /cold and sea breeze/ across southern New England.
Agree with previous forecaster that the most likely corridor to
maintain some of this convection will be around the I-495 corridor
and into Rhode Island...where the fronts are likely to meet. Plenty of
instability aloft with ml convective available potential energy exceeding 1000j/kg...but with the
core of best lapse rates shifting offshore through the
evening...it may struggle. Therefore...feel that capping both
T-storm and shower activity at scattered still remains the best
forecast. Precipitable waters near 2 Standard deviations above normal...but given the
scattered nature it/S possible several locations still remain dry.

Should any storms hold through the evening...the upper level
instability will be the only thing to maintain updrafts as shear
is very weak. Therefore...still not mentioning any enhanced
wording with this update as heavy rain...gusty winds and/or hail
would be a very isolated event.

Heat continues especially inland...onshore flow will limit highs
further east. Highs range from the 90s west...to low 80s near shore.

&&

Short term /6 PM this evening through 6 PM Friday/...
tonight...
with backdoor front slowing and gradually diminishing as it moves
offshore...lingering risk of isolated -shra will give way to drier
conditions late with loss of diurnal support. Little change in
airmass overnight so with dewpoints in the 60s some fog still possible
over interior Massachusetts/CT especially where/if rain falls. Eastern Massachusetts/Rhode Island will
be under the influence of increasing pressure gradient and breezy
conditions during the am hours. Lots of cloud cover...so mins
remain in the 60s in spite of cooler airmass spilling over from
the NE.

Friday...
breezy and cooler thanks to a combination of onshore flow and 850 mb
temperatures dipping to around +12c by the afternoon hours. The high
pressure building over will lead to strong enough subsidence to limit
bl depth. Therefore...unlikely mixing to 850 mb...limiting highs
mainly in the low 70s to low 80s inland. Low 70s will be near
shore...thanks to SST/S near these values. The NE winds will
diminish during the afternoon even as skies gradually clear.

&&

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

* warmer than normal temperatures most of this period
* mainly dry weather prevails

Synoptic overview...

Gefs and ecens ensembles in good agreement that subtropical ridge
from Texas to the northeast states will dominate our weather much of
this period. Its not until the middle of next week that the northern
stream jet begins to descend southward and erode the northern
periphery of this ridge. Thus other than temperatures briefly at or
cooler than normal Friday night into Sat morning...the remainder of
this forecast period will be warmer than normal. In fact the Euro
ensembles suggesting 850 temperatures warming to +18c across southern New England by Monday and
Tue! Gefs and deterministic guidance just slightly less at
+16c/+17c. This would support highs approaching 90 away from the
South Coast. Regarding precipitation...subtropical ridge will provide dry
weather most of this period with the next chance of convection the
middle of next week as northern stream jet energy begins to break
down the northern periphery of the ridge. Potential wildcard next
week regarding the amplitude of the northern stream jet across the
Continental U.S. May be linked to Tropical Storm Ignacio...as it heads
northeast toward Gulf of Alaska early next week and becomes absorbed
and potentially energizes the northern stream.

Daily details...

Friday night/Saturday...

Anomalous 1025 mb anticyclone/surface high advects into southern New England. This
modified Continental polar airmass will combine with clear skies and
light winds to yield cool temperatures Friday night/Sat am. Some of the
guidance suggesting the typically cooler locations could see temperatures
dip into the u40s! This deep layer ridge /h5 heights of 591 dm and
1024 mb surface hi/ over the area will provide dry weather with temperatures
rebounding into the u70s and l80s Sat afternoon after a cool start to the
day. Comfortable humidity with dew points in the 50s.

Sunday and Monday...

Deep layer ridge remains over the area so dry weather prevails.
Ridge axis is across the region Sunday and then slides just off the
South Coast Monday. This will result in a gradual warming trend sun and
Monday however humidity looks to remain tolerable with dew points only
climbing into the u50s and l60s.

Tuesday and Wednesday...

Subtropical ridge lingers along the eastern Seaboard. Ensembles and
deterministic guidance suggest a weak front approaches Tuesday but may
just washout as ridge wins out. A more significant front may arrive
middle to late next week. Thus warm and humid weather likely to linger
into Tuesday and possibly Wednesday.

&&

Aviation /07z Thursday through Monday/...
forecaster confidence levels...

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

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

Through 12z...
areas of fog at typically prone airports mainly between 08z and
11z this morning...MVFR/IFR conditions in this fog. VFR elsewhere.

Today...
mainly VFR. Late afternoon/evening widely scattered -shra/thunderstorms
possible...with localized lower categories. Winds shift from the
SW to east-NE through the day.

Tonight and Friday...
mainly VFR after any showers and late night fog tonight burn off.
Breezy early Friday.

Kbos terminal...high confidence in taf. Sea-breeze for the middle
morning period.

Kbdl terminal...high confidence in taf.

Outlook /Friday night through Monday/...high confidence.

VFR through the period. Areas of early morning IFR ceilings/visibilities
possible in fog Saturday and Sunday. Light flow over the weekend
with sea breezes possible Saturday. Increasing west-southwest flow
Sunday-Monday.

&&

Marine...
forecaster confidence levels...

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

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

Today...
high pressure will move east of the waters as a cold front backdoors from
the Gulf of Maine. Mainly quiet boating weather prevails...but an
isolated shower or T-storm late today may lead to localized rough
conditions.

Tonight into early Friday...
north-NE winds will gradually increase through the overnight hours.
Gusts may approach 25-30 knots at times early am into about middle day.
Seas increase as well...reaching near 5 feet first on the east
waters...then the outer southern waters by middle day. Therefore...small
craft advisories have been hoisted for this risk.

Late Friday...
conditions will gradually recede but some small craft advisories
Massachusetts linger as seas take a bit longer to diminish.

Outlook /Friday night through Monday/...high confidence.

Friday night through Monday...tranquil boating weather this period as
1025 mb high pressure builds over the waters. Wind and seas Friday
night diminish over the weekend to light/variable Saturday and
southwest Sunday-Monday.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory from 8 am to 8 PM EDT Friday for
anz231>235-237-254>256.
Small Craft Advisory from 5 am to noon EDT Friday for anz230.
Small Craft Advisory from 5 am to 2 PM EDT Friday for anz236.
Small Craft Advisory from 5 am to 6 PM EDT Friday for anz250-
251.

&&

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

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