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Area forecast discussion 
National Weather Service Taunton Massachusetts
722 am EDT Tuesday Jun 2 2015

Synopsis...
stalled front south of New England will keep unseasonably cool
and wet conditions in place through today. High pressure returns
with drier weather Wednesday and Thursday. Showers are possible
Friday into Saturday...as another cold front moves through then
high pressure follows for Sunday.

&&

Near term /until 6 PM this evening/...
7 am update...
rainfall rates have actually diminished in the last few hours or
so. Mainly from widespread 0.2-0.3inch/hour rates to more of
0.1-0.2 inch per hour rates. This is likely to due a slight
slackening of the middle level baroclinicity as the low level jet works upon it.
Suspect this trend to continue over much of the inland locations.
The caveat will be south coastal locations...which have a better
shot at more convective activity with the increasing daylight and
proximity to the stalled frontal boundary offshore.
Therefore...although confidence is waining. Not enough confidence
to drop current Flash Flood Watch until the morning commute draws to a
close. Later shifts may be able to drop it early assuming this
weakening trend in the rainfall rates continue.

Previous discussion...

Cold front stalled offshore is providing one focus for lift as a
low level 20-25 knot south jet rides up over the top. But the
best lift has been with fgen forcing along the temperature
gradient at 925 mb and 900 mb...across western/central mass and
northern CT.

Radar observations from upstream show additional wet weather
moving up from New Jersey and Delaware-Maryland-Virginia. Wet weather continues to
move across southern New England today. Precipitable water values
are 1.50 to 1.75 inches along the coast and 1.25 inches over
western/central mass. Based on this we expect wet weather to
continue to move across southern New England today.

Northern stream shortwave moves over the region by this evening.
As it approaches it will push the forcing farther east this
afternoon. This should move the heavier showers over the coastal
plain at that time.

Extrapolating the back edge of the rain suggests it will end in
the west in the early afternoon...and in much of the east toward
evening. The rain may linger along the South Coast past this
evening.

We will continue to forecast categorical probability of precipitation for showers with a
cool northeast low level flow over the region. With that in mind
we will forecast temperatures to slowly climb into the 50s this
afternoon. That may be optimistic right along the east mass
coastline.

With additional rain of 1/2 inch to 1 inch expected today...we
will maintain a Flash Flood Watch through the day. The pre-event
dryness of the soil is probably helping US absorb the volume of
water. But poor drainage areas and small streams continue to be of
concern.

&&

Short term /6 PM this evening through 6 PM Wednesday/...
tonight...
the upper shortwave moves through and off to the east. This will
turn the upper flow northwest and push the last of the precipitation
offshore. We expect at least partial clearing from northwest to
southeast during the night. With dew points in the
40s...min temperatures should also be in the 40s.

Wednesday...
high temperatures today running about 20-25 degrees below normal!
Normal high today is 70-75.
High pressure over eastern Canada builds over New England with dry
air/sunshine. But the surface flow around the high will draw winds
back around out of the northeast off the water. With the wind
coming off water temperatures in the lower 50s...this natural air
conditioning should keep coastal temperatures in eastern mass
around 60...possibly just in the upper 50s. Meanwhile the CT
valley will be less inhibited by the marine air and should mix to
at least 900 mb. Temperatures at the top of that layer would support maximum
temperatures near 70.
High temperatures today running about 20-25 degrees below normal!
Normal high today is 70-75.

&&

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

* mainly dry with below normal temperatures Thursday
* a few showers possible Friday into Sat as a cold front approaches
* dry and seasonable sun then threat of showers returns Monday

Overview and model preferences...
although the 02/00z model guidance suite is in relatively good
agreement through the weekend...at least regarding the upper level
flow pattern...there some spatial/temporal differences in the
surface/low level features which will ultimately drive sensible weather Friday-
sun. Split flow regime across na with the weaker southern stream
dominating initially. Slow moving appalachian trough lies on the eastern
edge of moderate block through the S central Continental U.S.. this block
will favor ridging across New England through the latter half of
the week. By the weekend however...there is some suggestion that a
northern stream wave may phase somewhat with the weaker southern stream trough
in the middle Atlantic. This is where certainty in the forecast
decreases somewhat. Models are continuing to indicate a weak low
level baroclinic wave moving off the middle Atlantic on Friday...which may
allow for the forcing of some showers across the region as
moisture increases. Models now indicating a little more quantitative precipitation forecast Friday
than previous runs so will need to continue to monitor this trend.
This also leads to timing differences of a cold frontal passage for
Sat...but in either case...risk for showers remains until remnants
of the central Continental U.S. Block enhance ridging once again across the
NE.

Details...

Wednesday night into Thursday...
high pressure remains in control but will begin to slip back to the east
through the period. Expecting mainly dry weather...and even though some
models suggest quantitative precipitation forecast late Thursday and Thursday night...feel the forecast is
more dry than wet given BUFKIT data from the same model shows dry
subsidence inversion remains in place. Model quantitative precipitation forecast may be an
indication of the struggle with the weak baroclinic wave
development offshore late in the period. Temperatures are likely to
remain near or even possibly slightly below seasonal normals as
850 mb temperatures are generally below +10c.

Friday and Sat...
gradually deepening northern stream shortwave combines with leftover
energy from an appalachian wave to increase precipitation chances
through this period thanks to two primary mechanisms. 1. A weak
offshore low pressure system moving well S of the region...but
forcing an inverted trough across southern New England and 2. A cold
frontal passage. Precipitable Waters Peak late Friday and Friday night...just above
1.50 inches /about 1.5 Standard deviations above normal.
Therefore...expect a period with precipitation chances. Not a
washout here as forcing is relatively weak...and the column
somewhat stable. Slight-chance probability of precipitation still look reasonable.
Temperatures remain near seasonal normals in spite of return flow.
Mainly due to the expectation of more cloud cover than Thursday.

Sun...
return to brief riding as remnants of the central Continental U.S. Block
moves across the area behind the cold front which is likely to
stall offshore. Temperatures mainly just below normal due to 850 mb temperatures
prognosticated below +10c.

Early next week...
another possible threat for rainfall as a more robust northern stream
shortwave is prognosticated to dive S from Quebec/Ontario. Final outcomes
are likely to be dependent on timing/instability but given there
is a connection to Gulf moisture with this deeper wave...ensembles
support precipitable waters approaching 2 Standard deviations above normal.

&&

Aviation /12z Tuesday through Saturday/...
forecaster confidence levels...

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

Today...high confidence in trends...lower confidence in exact
timing.
IFR/MVFR conditions dominate in mix of rain/fog/low ceilings through
most of the morning. However...expect some improvement to mainly
MVFR/low VFR beginning around 16z. Some MVFR lingers especially southeast
of a bdl-orh-bvy line into the evening. Northwest of this line
improvement to VFR expected late in the day. Winds take on a more
northerly direction.

Tonight...moderate confidence.
Gradual improvement expected with rain ending everywhere.
However...some MVFR conditions possible in lingering low ceilings and
fog. Low confidence on exactly how widespread this is.

Wednesday...VFR. North winds trend northeast by afternoon
especially along the coast.

Kbos terminal...high confidence in overall taf trends...lower
confidence in exact timing. Also low confidence in low ceilings/fog
overnight tonight.

Kbdl terminal...high confidence in ceilings. Moderate confidence in
visibilities.

Outlook...Wednesday night through Saturday...

Thursday into Friday...high confidence.
Mainly VFR. Although occasional MVFR/IFR possible in fog/rain showers Friday night. This will be hit-or-miss. Winds mainly southerly.

Sat...high confidence.
Mainly VFR with some showers. Winds shift from S to north-northwest.

&&

Marine...
forecaster confidence levels...

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

Short term /through Tuesday night/...moderate to high confidence.

Today...northeast winds around 15 knots sustained and with gusts
up to 25 knots. This should maintain 5-6 foot seas on mass Bay and
the adjacent outer waters...with slightly lower seas west and
south. Showers will continue to move northeast up the coast across
the waters...with some locally heavy downpours possible. Low risk
of isolated thunder.

Tonight...high pressure builds from the north. Winds should
diminish and become northerly. Seas may linger around 5 feet on
the outer waters.

Wednesday...winds shift to east-northeast but with speeds under 15
knots. Seas will also diminish to 4 feet or lower.

Outlook...Wednesday night through Saturday...

Thursday into early Friday...high confidence.
Winds and seas will remain below small craft thresholds as high
pressure moves over the waters.

Late Friday into Sat...moderate confidence.
Low pressure passing well to the S and an approaching cold front will
lead to increased chances for precipitation/fog over the waters at times.
S winds will give way to northwest winds late Sat. Some wind gusts may
approach 20-25 knots mainly Sat. Seas however...should generally
remain below the 5 feet mark.

&&

Climate...
all four stations set or tied record low maximum temperatures for June 1.

Bos...49...old record was 53 in 1992.
Pvd...53...old record was 56 in 1984.
Bdl...53...old record was 57 in 1992.
Orh...48...old record was 52 in 2004.

How cold was it yesterday? Look at the average temperatures
yesterday and compare them to history.

Coldest average temperatures for June 1

Bos...48 ... lowest was 50 in 1946.
Pvd...50.5...previous lowest was 53 in 2004/1945/1917/1907.
Bdl...50.5...previous lowest was 52.5 in 1945.
Orh...46...previous lowest was 47.5 in 1992.

Coldest average temperatures for any June day

Bos...48...tied for 3rd. Coldest was 47 on June 5 1947.
Pvd...50.5 tied for 9th. Coldest was 45 on June 2 1907.
Bdl...50.5...tied for 6th. Coldest 47 on June 2 1946/June 2 1907.
Orh...46...2nd coldest. Coldest was 44.5 on June 2 1946.

&&

Box watches/warnings/advisories...
CT...Flash Flood Watch through this evening for ctz002>004.
Massachusetts...Flash Flood Watch through this evening for maz003>007-010>021-
026.
Rhode Island...Flash Flood Watch through this evening for riz001>007.
Marine...Small Craft Advisory until 8 PM EDT this evening for
anz230>235-237-250-251-255-256.
Small Craft Advisory until 10 am EDT Wednesday for anz254.

&&

$$
Synopsis...wtb/doody
near term...wtb/doody
short term...wtb
long term...doody
aviation...wtb/doody
marine...wtb/doody
climate...staff

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