Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Taunton Massachusetts
705 am EDT Friday Apr 18 2014

Synopsis...
east to northeast flow will keep temperatures cool along coastal
areas...along with the possibility of gray skies through the
afternoon. A weakening front will push across the region on
Saturday. High pressure will result in dry and pleasant weather Sunday and
Monday. Low pressure will likely bring a period of wet weather to
the region sometime late Tuesday into Wednesday.

&&

Near term /until 6 PM this evening/...

705 am update...

A scattered to broken deck of low clouds have moved into eastern New
England early this morning. The main uncertainty today will be the
extent of low clouds and how far west they progress. Forecast
confidence is below normal in cloud cover today. We do think
there will be a fair amount of clouds along the coast with more in
the way of sunshine across the CT River Valley. This is supported
by latest model cross sections...but low clouds can often be a
challenge for the models so later shifts will have to monitor closely.

Inverted ridging from high pressure center in the Canadian Maritimes
continues to yield a deep dry layer above some trapped moisture
from the Delaware-Maryland-Virginia to New England. This is combining with east to NE
flow...drawing air across the waters where SSTs are only in the
low 40s. With this flow expected to continue until the ridge
shifts east late today...the trajectory is expected to keep areas
within both the I-495 and I-95 corridors much colder than areas
further west. Therefore...expect highs only in the low-middle 40s mainly
east of these highways while highs further west will break into the low-
middle 50s in the lower CT River Valley.

&&

Short term /6 PM this evening through 6 PM Saturday/...

Tonight...
surface cold front will be rapidly sliding across the area during the
overnight hours. However...soundings show moisture layer remains
mainly above h6...with dewpoint depressions exceeding 10c from the surface
to h6. Low-middle level f-general is also very weak as it arrives given it
is trying to push through ridging. Therefore...expect little
fanfare with this frontal passage except middle-high cloudiness and west
winds increasing through sunrise. Continue to suggest none probability of precipitation.
Broken-overcast clouds will keep mins warmer than previous nights...but
anomalously cool airmass suggests temperatures still drop to the low-middle
30s.

Sat...
high pressure regains control with cold advection to start the day.
This cold advection will allow mixing under only partly cloudy
skies to reach higher than 800 mb...where temperatures only dip to around
-1c. Combine this with west downslope flow...and temperatures should be able
to rebound into the low 60s. Low chance of a sea breeze given h92
winds reach around 20-25 knots. Therefore...also expect winds around
20 miles per hour through the day.

&&

Long term /Saturday night through Thursday/...

Highlights...

* dry Sunday and Monday with chilly nights/mild days
* wet weather likely sometime late Tuesday into Wednesday

Details...

Saturday night and Sunday...

High pressure overhead will result in dry weather with a chilly
Saturday night being replaced by a mild Sunday afternoon. Light
winds/mainly clear skies will allow for excellent radiational
cooling conditions Sat night. Low temperatures should bottom out in the
middle to upper 20s across the normally colder outlying locations of
southwest New Hampshire/northwest Massachusetts...to mainly the 30s elsewhere. On
Sunday...plenty of sunshine will allow for highs to reach into the
upper 50s and lower 60s just inland from the coast. However...weak
pressure gradient will allow for sea breezes on the immediate coast
probably holding highs in the upper 40s to lower 50s.

Sunday night...

High pressure will remain anchored over the region allowing for
another good night of radiational cooling. Low temperatures will be mainly
in the 30s.

Monday...

High pressure will still be in control of our weather with a mixture
of sun and clouds. 850 mb temperatures moderate considerably from Sunday/S
values reaching between +6c to +8c. This should allow high temperatures to
reach well into the 60s across much of the region...to perhaps even
near 70 in a few locales. Along the immediate coast including
Boston...its uncertain if sea breezes will develop in this time
range. If sea breezes are able to develop...it would probably keep
high temperatures in the 50s...but they may end up very localized just
affecting areas within a few miles of the coast.

Tuesday and Wednesday...

A potentially strong upper level shortwave will dive southeastward
from Canada. This will spawn a surface low pressure system
approaching our region from the west. At this time range...there is
low confidence on strength/timing of shortwave and track/intensity
of surface low pressure. It does look like a decent shot for at
least period of wet weather sometime late Tuesday into Wednesday.

Thursday...

Dry weather should follow behind the departing low pressure system.
Some indications are that it may be windy behind the system with
near or below normal temperatures.

&&

Aviation /12z Friday through Tuesday/...
low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.

Moderate confidence through early evening...higher confidence into
Sat...

Scattered to broken MVFR ceilings have overspread eastern sections of New England
early this morning. There is a bit of uncertainty in extent of low
clouds and how far west they will venture. For now we may see them
advance west of a Worcester to Providence line for a time...but
probably stay east of the CT River Valley. Again...confidence is
below normal and later shifts will have to monitor closely.

By early evening...winds west of the line shift from the S to west and
winds east of the line begin to shift to the S...so any lingering MVFR
ceilings should begin to scattered out.

After that mainly VFR is expected overnight into Sat although with
increasing high and middle clouds during the overnight and early
morning hours. Although there is the low probability of some
MVFR/IFR fog before winds shift to the west at coastal terminals
early Sat morning. Winds then shift to the west Sat morning with west-northwest
wind gusts around 20 knots by middle day Sat.

Kbos terminal...moderate confidence. Main issue is extent and
duration of MVFR ceilings through the afternoon.

Kbdl terminal...high confidence.

Saturday night through Monday...high confidence in VFR conditions.

Tuesday...low to moderate confidence. VFR conditions may
deteriorate to MVFR-IFR thresholds late Tuesday or Tuesday night in rain
showers.

&&

Marine...
forecaster confidence levels...

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

Short term /through Saturday/...high confidence.

Although winds each day are expected to remain below the 25 knots
threshold for Small Craft Advisory...a lingering swell will keep
seas at least 5-7ft through the day on Sat on the ocean waters
especially. Therefore will transition to small craft for hazard seas
across the waters into 12z Sat at least...with near shore waters
dropping earlier.

Winds today being out of the N-NE...shifting to the SW tonight
then west during the day on Sat.

Outlook...Saturday night through Tuesday...

Saturday night and Sunday...moderate to high confidence. High
pressure over northern New England and low pressure well to the
south of the waters will result in north to northeast winds. Wind
gusts of 20 to 25 knots along with 3 to 5 foot seas are possible
across the outer-waters. This may result in marginal Small Craft Advisory conditions.

Monday and Tuesday...moderate to high confidence. Weak pressure
gradient should keep winds/seas generally below Small Craft Advisory thresholds. We
may see marginal Small Craft Advisory seas develop late Tuesday/Tuesday night as a result of
southeast swell from low pressure well east of the waters.

&&

Fire weather...
Saturday is the three day mark since last appreciable rainfall
across southern New England. Given this fact...with temperatures
rising into the low 60s and low dewpoints in the 20s...min relative humidity values
should dip to around 30 percent in the afternoon. This will
combine with west wind gusts of 20 to 25 miles per hour...with occasional gusts
to 30 miles per hour. Confidence is high that these conditions will be
realized.

&&

Hydrology...
minor flooding continues along portions of the main Stem CT river.
Most points have reached crest...but will take more time to drop
below flood stage. The river has dropped below flood stage at
Montague...and is not expected to reach moderate flood any longer
at Middle Haddam.

Flood warnings remain posted along CT river at...

Northampton
Thompsonville
Hartford
Middle Haddam

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
New Hampshire...none.
Rhode Island...none.
Marine...Small Craft Advisory for hazardous seas until 2 PM EDT this
afternoon for anz232.
Small Craft Advisory for hazardous seas until 5 PM EDT this
afternoon for anz235-237.
Small Craft Advisory for hazardous seas until 8 am EDT
Saturday for anz250-251-254>256.

&&

$$
Synopsis...doody/Frank
near term...Frank/doody
short term...doody
long term...Frank
aviation...Frank/doody
marine...doody/Frank
fire weather...doody
hydrology...doody