Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Taunton Massachusetts
957 PM EDT Wednesday Apr 16 2014

Synopsis...
high pressure will bring dry...but seasonably cool weather to the
region through Friday. Weak offshore low pressure may bring a
shower or two late Friday night into early Saturday across the
South Coast. Otherwise...it should remain dry through Monday. A
cold front could trigger showers Monday night through Tuesday
evening.

&&

Near term /until 6 am Thursday morning/...

Updated at 1000 PM...

Forecast remains on track for this evening. Winds are dropping
across the interior as high pressure crest over northern New
England. However winds along the coastline remain up keeping the
usual radiational cooling sites from dropping as quickly as
thought. Regardless clear skies and dry weather will prevail.

Tonight...

Surface high pressure sweeping east across northern New England. In
response...surface winds gradually back towards the northeast.
Onshore flow off the Gulf of Maine anticipated for the eastern
shoreline with the possibility of a few scattered clouds...whereas
across the interior under clear skies light and variable winds will
allow for effective nocturnal cooling beneath an unseasonably cold
airmass. Could plausibly see temperatures fall to near record lows
/mainly for Worcester and Hartford/. Lows around the low- to middle-20s
for the interior...warmer around the freezing mark for the shores.

Keep in mind that the growing season for areas along the South-
Coast does not begin until April 20th...so there will be no freeze
headlines with this forecast package.

&&

Short term /6 am Thursday morning through Thursday night/...
Thursday...

Surface high pressure shifts northeast as an elongated area of low pressure
and accompanying stalled frontal boundary shift back to the north.
Tightening pressure-gradient lends to increasing easterly onshore flow.
The long fetch off the colder waters will result in a chilly day for
the eastern-coast of New England. Moisture pooling beneath a dry-air
inversion coupled with boundary-layer mixing per sunshine should
result in scattered to broken decks for a brief period. Otherwise
across the interior expect a milder day as the colder airmass aloft
retreats north with the surface high pressure. Highs in the upper-40s to
low-50s.

Thursday night...

Stalled offshore front to the south shifts further north in response
to an area of low pressure along the boundary. Along with a continued
breezy onshore easterly flow...clouds begin to increase across the
region keeps lows along the coastline around the freezing mark while
elsewhere lows will fall into the middle- to upper-20s. Easterly winds
will limit effective radiational cooling though sheltered valleys
over north/west New England may drop a few degrees lower.

&&

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

* cool near the coast on Friday...otherwise seasonable temperatures return
* few showers could brush the cape and islands Sat
morning...otherwise dry through Monday
* chance of showers Monday night through Tuesday evening

Split flow continues across the conterminous USA with southern New
England influenced mostly by the northern stream. Medium range
models depict reasonable agreement in large scale pattern but with
some differences on timing and configuration of short wave energy.
Operational models and ensembles suggest an amplification to the
flow toward the middle part of next week. Both the 12z European model (ecmwf) and
GFS depict milder 850 mb temperatures compared with the last few prior
runs.

Details...

Friday...

High pressure slides over region but sea breezes should keep both
east and south coasts quite chilly given ocean temperatures still in the
lower 40s across adjacent coastal waters.

Friday night and Saturday...

Southern New England remains sandwiched between northern and
southern stream energy. Cannot rule out a sprinkle or light shower
here and there but kept probability of precipitation in slight chance range most area.
There does seem to be just enough of a risk for a southern stream
system to brush the South Coast and islands and did keep a low
chance pop there. However...low confidence on whether the rain
shield will actually make it to the South Coast. As both the
northern and southern stream short wave energy gets embedded into
the denser upper air network...confidence should grow on the
eventual solution.

Sunday and Monday...

High confidence of remaining dry through Sunday into Monday morning
and moderate confidence of still remaining dry through Monday
afternoon. Overrunning warm air ahead of next system will likely
bring middle to high clouds into forecast area Monday
afternoon...especially across northern zones...but likely
remaining dry in our area. Southwest surface flow combined with
850 mb temperatures in the neighborhood of 6c to 8c may allow afternoon
temperatures into the lower 60s to the East Coast.

Monday night through Tuesday evening...

The northern stream flow brings a cold front across the region
Tuesday. There is also some southern stream energy that may or may
not remain detached from the northern flow. For now think quantitative precipitation forecast will
be fairly light but this could change if the southern stream
should end up phasing with the northern stream.

Wednesday...

Dry and considerably cooler air follows in the north to northwest flow
behind the cold front...although the April sun and downsloping should
temper the impact from cooler temperatures aloft with highs probably near
seasonable levels.

&&

Aviation /02z Thursday through Monday/...
low...less than 30 percent.
Moderate...30 to 60 percent.
High...greater than 60 percent.

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

Tonight through Thursday...VFR. Northwest winds continuing to diminish but
probably remain light from north and then NE toward daybreak. Will see
winds on the increase out of the east through Thursday. There is a
risk of scattered low-VFR ceilings.

Thursday night...bkn-ovc low-VFR to MVFR ceilings will develop across
southeast New England with continued breezy easterly
winds...especially vicinity of the South Coast.

Kbos terminal...high confidence.

Kbdl terminal...high confidence.

Outlook...Friday through Monday...

Friday...VFR.

Friday night into Saturday morning...VFR. Low probability of MVFR
in scattered showers S of a pym-wst line.

Saturday afternoon through Monday...VFR.

&&

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.

Winds will slowly diminish over the coastal waters but seas will
take long to subside and Small Craft Advisory likely needed to
remain through Thursday and possibly into Thursday evening outside of
harbors...bays and some sounds. Seas expected to persist 6 to 8
feet across outer waters into Thursday. Surface gradient tightens some
in response to especially strong surface high moving into
Maritimes and surface low development off middle Atlantic coast.

Outlook...Friday through Monday...

Friday through Sat morning...persistent easterly flow due to offshore
low pressure may keep seas elevated into Small Craft Advisory for
waters south of New England.

Sat afternoon and night...northwest flow behind low pressure that forms on
cold front may be enough to generate Small Craft Advisory
headlines.

Sunday through Monday morning...light winds and subsiding seas
anticipated.

Monday afternoon...increasing SW flow and fetch may cause winds and
seas to reach Small Craft Advisory thresholds of 25 knots gusts at
least across the near shore waters. There may be enough fetch to
build seas to 5 feet or more across the coastal waters south of
New England.

&&

Hydrology...
several points along the CT river are flooding or will be in minor
flood soon. Warnings continue for the CT river at...

Thompsonville
Hartford
Middle Haddam
Montague
Northampton

Rainfall yesterday and snowmelt over the last few days has the
mainstem CT river in minor flood...although projected to go into
moderate flood at Middle Haddam.

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
New Hampshire...none.
Rhode Island...none.
Marine...Small Craft Advisory until 2 am EDT Friday for anz235-237.
Small Craft Advisory until 8 am EDT Friday for anz250-254>256.

&&

$$
Synopsis...sipprell/Thompson
near term...dunten/sipprell
short term...sipprell
long term...Thompson
aviation...sipprell/Thompson
marine...sipprell/Thompson
hydrology...