Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 251957
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
357 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 QPF ranges between 1 to 1.5 inches for much of the
area, with locally higher totals closer to 2 inches.

Deeper moisture plume looks to move northeast of our area towards
12Z Wed, so precip quantity should be diminishing towards 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 /20Z 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. E wind gusts 25 to 30 kt over Cape/Islands
with winds veering to SE tonight with similar gusts. LLWS
developing Cape/Islands tonight as SE/S low level jet at 50+ kt
develops, especially after midnight. LLWS may extend as far
north as BOS. Isolated TSRA possible tonight.

Wednesday...Moderate confidence. MVFR-IFR CIGS continue with
areas of -RA/RA and patchy fog, especially across the eastern
half of southern New England. Reduced VSBYS likely, down to IFR
in spots. May see areas of LIFR CIGS across the higher inland
terrain and along the coast. SE winds gusting up to around 25 kt
across Cape Cod and the islands. Low risk of TSRA early in the
day, especially the S coastal terminals. LLWS 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 LLWS 08Z-
14Z with SE 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.

Persistent easterly flow across the coastal waters this
afternoon into tonight. Gusts 25 to 30 kt possible, especially
across the southern coastal waters. Widespread rain continues
this afternoon, and is expected to be heaviest tonight into
Wednesday morning. Plenty of visibility restrictions in both
rain and fog expected. Low risk of thunderstorms, mainly on the
southern waters.

Extended Small Craft Advisories across most waters through
Wednesday.

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...
* Potential minor flooding impacts during astronomically high
  tides Tonight through Wednesday along the east and south
  coasts

Not anticipating any flooding impacts for the high tide later
today, as winds, surge and seas will not have built up enough.

Minor flooding possible during the high tide cycles tonight and
Wednesday along both coastlines. A storm surge around 1 ft with
low risk of 1.5 ft surge on top of high astronomical tides and
building seas may lead to minor inundation of vulnerable
shoreline roads. Some beach erosion is also possible, especially
for east and southeast facing beaches.

Boston High Tides (flood stage 12.5 feet)...

11.47 feet / Tuesday 11:20 pm
11.15 feet / Wednesday 11:50 am

Providence High Tides (flood stage 7 feet)...

5.98 feet / Tuesday 8:11 pm
5.53 feet / Wednesday 841 am

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...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
SHORT TERM...NMB
LONG TERM...Frank
AVIATION...Frank/NMB
MARINE...Belk/Frank
TIDES/COASTAL FLOODING...


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