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Area forecast discussion
National Weather Service Taunton Massachusetts
430 PM EDT Tue Apr 25 2017

Synopsis...
low pressure will slowly track up the East Coast tonight into
Wednesday morning bringing periods of rain along with a few
embedded thunderstorms. Low clouds along with some drizzle and
fog are expected to linger Wednesday night into Thursday
especially along the coast. Very mild to warm afternoons should
return Friday and Saturday with the low risk for a few
showers/thunderstorms. Much cooler weather follows Sunday
especially on the coast. Another cold front will likely bring
more showers to the region sometime Monday into Tuesday.

&&

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

Tonight...high confidence. A widespread soaking rain is expected to
continue through the overnight hours. Vertically stacked low
pressure has been lingering along the coast of the Carolinas today,
with high pressure well to our northeast in the Canadian Maritimes.
The low makes little northward progress tonight, filling some as it
meanders into the coastal mid Atlantic region.

Southern New England has seen a steady feed of moisture from the
south/southeast aloft, and east at the surface, which continues
tonight. NAM/GFS show plume of 1.25 to 1.5 inch precipitable water
feeding into our area during tonight, accompanied by a 50 kt
h850 jet. A low level inversion is in place near the surface,
could see some gusts 25 to 30 mph along the coastline. Models
showing some marginal elevated instability tonight, with k
indices in the low 30s, isolated rumbles of thunder are
possible. Including lingering lighter precip on Wed, thinking
event total quantitative precipitation forecast ranges between 1 to 1.5 inches for much of the
area, with locally higher totals closer to 2 inches.

While rivers and streams are expected to remain in their banks,
we could see some minor urban and poor drainage flooding
tonight into early Wednesday morning. Deeper moisture plume
looks to move northeast of our area towards 12z Wed, so precip
quantity should be diminishing towards or after daybreak.

With surface dewpoints in the 40s and low 50s, temps overnight will
not drop much/remain nearly steady.

&&

Short term /6 PM this evening through 6 PM Wednesday/...
models show the low pressure center to our south slowly moving
northward during the day, heading south of Long Island. The surface
low continues to weaken/fill. With the deeper moisture plume begins
to shift northeast of our area. May see an isolated rumble of
thunder early in the morning, otherwise anticipating some lighter
rain and perhaps drizzle for much of the day. Highest pops during
the morning, but precip chances persist thru the afternoon.

&&

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

* low clouds/spotty drizzle Wed night+thu with cool temps on coast
* mild to warm afternoons Fri/Sat with a low risk for a few T-storms
* backdoor cold front brings much cooler temps by sun
* period of showers which may be briefly heavy sometime Mon/Tue

Details...

Wednesday night and Thursday...

Closed upper level low will linger off the southern New England
coast Wed night into Thu. Model cross sections indicate a fair
amount of low level moisture lingering below the subsidence
inversion. Given overall setup and time of year, feel low clouds
will linger Wed night into Thu afternoon even across much of the
interior. There also should be areas of fog and drizzle, especially
on the coast Wed night and Thu am along with the risk for a spot
shower or two.

With that said, guidance is probably too warm with forecasted high
temps on Thu given expected low cloud cover. High probably remain
in the 60s for most of the region and perhaps stuck in the mid to
upper 50s along the coast. Now if more sun is realized than expected
it still would be possible for portions of the interior to break 70,
but hedging cooler for now.

Friday and Saturday...

Upper level ridge of high pressure building off the southeast coast
will be pumping higher height fields into southern New England.
Decent shot for high temps to reach the 70s to lower 80s away from
any marine influence along the coastline, especially the South Coast
with south to southwest flow. Most of this time should feature dry
weather, but a few shortwaves will result in the low risk for a
couple of showers/T-storms. Greater chance of development would
occur if energy moves through closer to the time of peak
heating on Fri and Sat.

Saturday night and Sunday...

Despite abnormally high height fields, strong high pressure will be
building across eastern Canada. This will likely send a backdoor
cold front south of the region late Sat or Sat night. Much cooler
temps are likely for Sunday especially along the coast where they
should remain in the 50s. Perhaps a few spot showers, but high
pressure may suppress most of the activity to our southwest.

Monday and Tuesday...

Timing uncertain, but an approaching cold front will likely bring a
period of showers. Gefs anomalies signaling decent low level jet
coupled with fairly high pwats so the showers may be heavy for a
brief period of time. Again, timing uncertain and not expecting
both days to be total washouts. Temperatures also uncertain
given timing/wind direction.

&&

Aviation /21z Tuesday through Sunday/...
forecaster confidence levels...

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

Short term /through Wednesday/...

Late this afternoon and tonight...high confidence in trends,
moderate confidence in timing. For most of the area, conditions
continue to deteriorate to IFR/LIFR during late this afternoon
and evening with rain/showers and fog. In bdl/baf vicinity,
where MVFR conditions are expected into early evening, then
deteriorating to IFR. East wind gusts 25 to 30 kt over cape/islands
with winds veering to southeast tonight with similar gusts. Low level wind shear
developing cape/islands tonight as southeast/S low level jet at 50+ kt
develops, especially after midnight. Low level wind shear may extend as far
north as bos. Isolated thunderstorms and rain possible tonight.

Wednesday...moderate confidence. MVFR-IFR ceilings continue with
areas of -ra/rain and patchy fog, especially across the eastern
half of southern New England. Reduced visibilities likely, down to IFR
in spots. May see areas of LIFR ceilings across the higher inland
terrain and along the coast. Southeast winds gusting up to around 25 kt
across Cape Cod and the islands. Low risk of thunderstorms and rain early in the
day, especially the S coastal terminals. Low level wind shear impacts for the
cape and islands, and possibly as far north as bos, during the
morning hours.

Kbos taf...moderate confidence in taf. Potential for low level wind shear 08z-
14z with southeast low level jet.

Kbdl taf...moderate confidence in taf.

Outlook /Wednesday night through Sunday/...

Wednesday night into Thursday...moderate to high confidence. IFR to
even LIFR conditions likely Wed night into part of Thu am along with
some fog, drizzle and a spot shower. Lower conditions most likely
on the coast. Conditions may improve to mainly MVFR by late Thu
morning and afternoon.

Thursday night and Friday...moderate confidence. MVFR/IFR
conditions likely in areas of low clouds and fog patches Thu night
into early Fri am. Improvement to VFR likely by Fri afternoon with
the low risk for a few showers and perhaps a T-storm.

Saturday and Sunday...moderate confidence. VFR conditions probably
dominate.

&&

Marine...
forecaster confidence levels...

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

Short term /through Wednesday/...high confidence.

Small craft advisories remain in effect across all waters for
tonight into Wednesday. Low level jet of 50 to 60 knots lifts across
most of the waters tonight, but the mixing of those winds to the sea
surface is tempered by a strong temperature inversion. Hence, we
anticipate most wind gusts will top at around 30 knots. There is a
broad southeast to east-southeast fetch which due to its length and breadth may bring
8 to 10 foot seas into Rhode Island and Block Island sounds by late
evening even though the inversion will likely inhibit gusts much
higher than 30 knots. Winds and seas will gradually subside
Wednesday afternoon as the tighter gradient moves into the Gulf of
Maine and the coastal low gradually weakens as it drifts north.

Outlook /Wednesday night through Sunday/...

Wednesday night through Friday...moderate to high confidence.
Despite wind gusts mainly 20 knots or less, left over southeast
swell will result in small craft seas persisting through Friday
across many of our outer and southern waters. In addition, areas of
fog may result in poor vsbys for mariners especially during the
overnight and early morning hours.

Saturday and Sunday...moderate to high confidence. West to
southwest wind gusts to 20 knots Saturday will shift to the
northeast by late Sat or Sat night behind a backdoor cold front.
Overall, expect winds and seas to remain below Small Craft Advisory
thresholds.

&&

Tides/coastal flooding...
* isolated minor coastal flooding impacts during astronomically
high tides tonight through Wednesday night along the east and
south coasts

We are entering a Spring tide cycle with high tides that are
astronomically high. This combined with an anticipated storm surge
of around 1 foot may set the stage for isolated pockets of minor
coastal flooding along both south and east coasts around the time of
high tide this evening as well as possibly for the Wednesday day and
night tides as well. Have opted to renew the coastal flood
statement issued early this morning. One area that we are
watching a little more closely is the Charlestown and westerly
shorelines along the Rhode Island southwest coast where the storm surge
may reach 1.5 feet by the time of the evening high tide near 8
PM. This reach of coastline can be vulnerable to an east-southeast fetch,
although it looks like the highest surge and wave action will
occur after the evening high tide.

The combination of runoff from heavy rain and elevated water
levels near high tide this evening could exacerbate drainage of
fresh water in some coastal urban areas and near the mouths of
streams and small rivers.

We will need to continue to monitor The Tides through at least
Wednesday night as there is not a significant offshore flow or
pressure rises to help evacuate a lingering surge. The astronomical
high tides remain very elevated through the end of the week.

Due to the breadth of the fetch, we may encounter enough wave action
with lengthening periods on top of an elevated tide to cause pockets
of erosion tonight through Wednesday night along the Martha's
Vineyard South Coast, Nantucket south and east coasts, and the Outer
Cape ocean side from Truro to Chatham.

Boston high tides (flood stage at Boston 12.5 feet)...

11.47 feet / Tuesday 11:20 PM
11.15 feet / Wednesday 11:50 am
11.92 feet / Thursday 12:07 am

Providence high tides (flood stage at Providence 7 feet)...

5.98 feet / Tuesday 8:11 PM
5.53 feet / Wednesday 8:41 am
6.21 feet / Wednesday 9:00 PM

&&

Box watches/warnings/advisories...
CT...none.
Massachusetts...none.
Rhode Island...none.
Marine...Small Craft Advisory until 3 PM EDT Wednesday for anz231>234.
Small Craft Advisory until 8 PM EDT this evening for anz230-
236.
Small Craft Advisory until 8 PM EDT Wednesday for anz235-237-
250-251-254>256.

&&

$$
Synopsis...Frank/nmb
near term...nmb

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