Scientific Forecaster Discussion

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Area forecast discussion 
National Weather Service Taunton Massachusetts
707 am EDT Thursday Apr 17 2014

Synopsis...
high pressure will bring dry...but seasonably cool weather to the
region today and tomorrow. Dry and slowly warming weather is
expected through Monday. The only exception will be a period of
cloudiness and possible drizzle along the southeast Massachusetts coast
Friday night. Slow moving low pressure could bring showers from
late Monday night into Wednesday of next week.

&&

Near term /until 6 PM this evening/...
7 am update....
visible satellite imagery shows scattered low clouds affecting
parts of east coastal Massachusetts early this morning. Otherwise...sunshine
will be the rule this morning. We were off to a very chilly start
with 7 am temperatures still in the 20s to lower 30s except middle to
upper 30s on Cape Cod and the islands. Strong high pressure to our
northeast was causing an increasingly tight gradient over
southeastern Massachusetts. Winds were already gusting to 30 miles per hour on
Nantucket.

Previous discussion for today...
high pressure will move towards the Maritimes resulting in a more
onshore flow across the Massachusetts coastline. This easterly flow will push
the cool maritime air onshore resulting in temperatures along the
coastline in the low 40s. A few scattered clouds may move onshore
as well as the moisture increasing within the column. Otherwise
across the interior...temperatures will warm into the upper 40s to low
50s...which is still below normal.

&&

Short term /6 PM this evening through 6 PM Friday/...
Thursday night into Friday...

Southern new england's weather will still be influenced by the
offshore high pressure over the Maritimes while a stalled front
south of the region will stay suppressed. This set-up will
continue the easterly flow keeping the maritime air onshore.
Throughout the night on Thursday and into Friday moisture will
increase in the low levels as cross sections show moisture
being trapped under the inversion. Friday especially looks to be
a cold and dreary day from the North Shore down to the
cape...including Boston...due to the increase of cloud cover and
drizzle.

Otherwise across the interior...temperatures will radiate out on
Thursday night due to clear skies and light winds. Temperatures will dip
again below the freezing mark but will hold off on any headlines
as the growing season begins on the 20th of April. On Friday the
interior will warm up well into the middle to upper 50s with the CT
valley being the warm spot which could make a run to 60f.

&&

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

* clouds/possible drizzle southeast areas Friday night
* dry and seasonable through Monday
* showers a good bet for Tuesday into Wednesday

In general there is very good model agreement through the extended
forecast period. From late in the week through early next
week...upper level split flow exists across the eastern USA.
Southern New England is influenced by the northern stream and a
cutoff low over the southeast states sneaking harmlessly out to
sea well to our south. On Tuesday...a new upper trough over the Great
Lakes deepens...forming a cutoff low off of Cape Cod by Wednesday.
Details...

Friday night and Saturday...

A storm system will be passing very far to the southeast of
New England Friday night. Its precipitation shield will remain
south of our waters. However the onshore flow between that
system and an approaching weak surface trough will likely keep
low cloudiness and perhaps fog and drizzle over Cape Cod and
the islands and perhaps as far north as Marshfield Massachusetts Friday
night...best indicated by the NAM low level relative humidity fields but also
seen on the GFS. Otherwise expect partly to mostly cloudy skies
farther inland with lows in the 30s.

A weak surface trough will pass across southern New England early
Sat. While a shower cannot be ruled out...its main impact will be
to put an end to the onshore flow...with light west to northwest
winds becoming established and sunshine returning for most of the
day. This will allow highs to reach the upper 50s to near 60.

Sunday and Monday...

High confidence of remaining dry through Sunday and Monday.
Very strong high pressure becomes centered over New England
Sunday and moves offshore Monday. Sunday will be bright and sunny
with highs again in the upper 50s to lower 60s...cooler near the
coast though. Light southwest flow around the departing high on
Monday will give temperatures another boost. 925 mb temperatures are
forecast to reach +8c to +10c by Monday evening. Have increased
forecast maximum temperatures a few degrees above guidance...reaching
the middle to perhaps upper 60s except 50s at the immediate coast.
Sunshine will fade behind increasing middle and high level cloudiness
Monday afternoon. However there no longer is any risk for
precipitation during the day.

Monday night through Wednesday...

This is an unsettled period. Models agree that another upper level
trough in the northern stream moves from the Great Lakes eastward
and amplifies Tuesday...eventually becoming a cutoff upper low
somewhere off the New England coast. Model consensus is that this
occurs east of Cape Cod/Nantucket on Wednesday although the GFS
operational run is farther north off of New Hampshire. Mild with
showers a good bet from late Monday night through at least Tuesday night.
Have extended this chance of showers through Wednesday based on the 00z
European model (ecmwf) model run. There is a chance that this could turn into a
soaking rain... especially Tuesday into Tuesday night...but this far out
in time our probabilities only reflect 30-40 percent chances of
rain. Model guidance shows highs in the middle 60s Tuesday and upper 50s
to near 60 Wednesday. Have gone with this...however the European model (ecmwf) 850 mb
temperatures are only +4c...which is colder than the GFS +8c...so it is
possible the Wednesday maximum temperatures may need to be adjusted downward.

&&

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

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

Today...high confidence...VFR. Increasing northeast to east
winds...strongest on the cape and islands. There is a risk of
ceilings in the 3000-3500 feet range across eastern Massachusetts coast.

Tonight...high confidence...VFR to start. Ceilings may build and drop
to MVFR conditions across the east coastline including the cape
and the islands due to onshore flow.

Friday...moderate confidence...onshore flow will continue
dropping the ceilings across both coastlines to MVFR. There is a low
probability of locally IFR as well as fog and drizzle.

Kbos terminal...high confidence.

Kbdl terminal...high confidence.

Outlook...Friday night through Monday...

Friday night into early Saturday morning...low to moderate
probability of IFR conditions in low clouds and fog over Cape Cod
and the islands. VFR expected inland with a low probability of
MVFR in an isolated shower.

Late Saturday morning through Monday...high confidence VFR.

&&

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.

Winds will continue to be gusty throughout the day and tonight
before dissipating by Friday. Because of the gusty winds...the
seas will take a bit to relax below 5 feet. Therefore have extended
Small Craft Advisory accordingly.

Outlook...Friday night through Monday...

Friday night through Sat morning...light but persistent east to
northeast flow will keep seas elevated above Small Craft Advisory
thresholds for waters south and east of New England.

Sat afternoon and night...a brief period of northwest flow behind a weak
low pressure trough. Seas may subside briefly to below 5 feet over the
outer waters.

Sunday...high pressure and a return of northeast wind flow.
Seas once again building to just above the 5 feet threshold.

Monday...as the high moves offshore...winds shift to the southwest
and become gusty...especially over the waters east of Massachusetts. They
could reach 20 to 25 knots at times. Seas expected to remain on the
order of 3 to 5 feet.

&&

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 on Tuesday 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 3 am EDT Friday for anz231>235-237.
Small Craft Advisory until 8 PM EDT Friday for anz250-254-255.
Small Craft Advisory until 2 PM EDT Friday for anz256.

&&

$$
Synopsis...dunten/field
near term...field/dunten
short term...dunten
long term...field
aviation...dunten/field
marine...dunten/field
hydrology...staff