Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 222012

Area Forecast Discussion
National Weather Service Taunton MA
412 PM EDT Sun Oct 22 2017

High pressure south of New England will result in unseasonably
mild and dry weather into Monday. Sea breezes along both coasts
today will make it a little cooler there. A slow moving cold
front will bring rounds of heavy rain Tuesday into Wednesday
with a period of strong to damaging wind gusts possible. A few
lingering showers are possible Thursday, but the trend towards
drier and more seasonable temperatures are expected Thursday
into Friday. Above normal temperatures may return by next


1005 AM Update...

Good visibility reported from all observation sites at 14Z, as
patchy fog has burned off. Still noting bands of high clouds
crossing the region from the NW as seen on both GOES-13 and
GOES-16 (prelim, non operational) visible satellite imagery
after sunrise through 14Z. Tough to see if any low ocean clouds
are trying to develop/push toward E coastal areas as some short
range high resolution models continue to suggest. Still believe,
as previous forecaster mentioned, that this is still too fast
and overdone, so kept the low clouds out for now. Will continue
to monitor.

Bubble high pressure noted across E Mass at 14Z as main center
sits across New Brunswick. Light/variable or calm winds
continue for most locations, with light W-SW winds along the S
coast. Noting some N-NE light winds across Cape Ann into Boston,
and believe that the light E-NE winds will continue to work
across most if not the entire region during this afternoon with
very light pressure gradient in place.

Other than adjustments on near term conditions to bring current,
forecast pretty much on track. Have incorporated near term
trends into the updated forecast.

Previous Discussion...

Only potential problem is the continued forecasted low clouds
moving in off the ocean across E coastal areas during this
afternoon as depicted by some high resolution model guidance.
Believe this aspect is overdone and too fast, so did not bite at
this point.

High pressure will remain in control of our weather today, but
will be centered more to our northeast today. The resulting
light winds will set the stage for a seabreezes along both
coasts, which in turn will mean lower max temperatures today.
Highs across the eastern MA coast will reach between 65 and 70,
while portions of the Connecticut River valley will see highs
reach into the upper 70s to near 80.


Seabreezes diminish early this evening, to be replaced with a
light south synoptic flow. Another mild night in store, with
slowly increasing dew points. Dry weather continues. Still some
concern for low clouds and patchy fog across portions of
southeast MA, as dew points may get close to the water
temperatures just offshore. Just don`t have much confidence in
that outcome, yet.

Monday is still expected to be mostly dry. Overrunning lift
should get underway by the afternoon. The main limitation for
rainfall will by the abundant relatively dry air near the
ground. Many members of the 22/00Z guidance suite bring light
rainfall into southern New England during the daytime Monday.
Thinking this is likely a bit overdone, especially across the
eastern half of southern New England.

Will continue to have a chance of showers during the afternoon
into evening hours across the western half of southern New
England, owing to the proximity to the approaching cold front.
There should be better low level moisture convergence to help
overcome the drier air a little quicker.

Temperatures should be a little lower with increasing clouds,
but still well above normal.



* Period of strong to damaging wind gusts possible Tue into Wed am
* Heavy rain will result in an urban/street flooding threat Tue-Wed
* More seasonable late October temps finally return Thu/Fri

Overview and model preferences...
Strong and acute blocking high pres now looks to cutoff
completely near Labrador based on 22.12Z guidance. This promotes
deepening, and redevelopment of upstream longwave trof/cutoff
across the CONUS, yielding a highly meridional flow pattern
through much of the week. The first longwave trof begins
negative tilt process through Wednesday, and is progged to be a
bit closer to the downstream ridge. The trof is linked to
gradually occluding low pres which will slide into Canada but
drag a slow moving front into New England through mid week,
coupled with Gulf of Mexico moisture. Lifting N late week thanks
to a slight resurgence of the subtropical high, a second trof,
deepens in response to arctic influenced phasing near the
continental divide. With blocking remaining firmly entrenched
across the W Atlantic, this second trof deepens in place through
the weekend. Overall, a complex pattern with some disagreements
in the mass fields particularly beyond Wed. Will continue to
lean most heavily on the ensembles at this time, although with a
little weight on the ECMWF given its overall slower progression
which is favorable in such an amplified pattern.


Tue and Wed...

Met. Overview...
Slow cold front becomes parallel to upper flow as trof takes on
negative tilt near the OH valley and parent low pres moves into
Quebec. Guidance continues to favor the front slowly drifting
across the region Tue into Wed. This front will be associated
with very deep layer moisture, with PWATs near the 2.00 inch
mark, or nearly 3 std deviations above normal. A series of weak
LLJ impulses will also traverse the front. Mean H92 S wind
speeds rest mainly around 40 kt, however, with each impulse
50-60 kt are also forecast, especially early Wed as the front
shifts E. The increase in low lvl moisture and anomalously warm
airmass associated with the high downstream (temps mainly in the
upper 60s to low 70s by day) combined with dwpts in the mid-
upper 60s as well and a conditionally unstable profile, do
indicate some modest CAPE values near 500j/kg especially late
Tue into early Wed. All ingredients point to a wet and highly
unsettled environment. It is interesting to note that both
ensemble probabilities, and latest runs of the CIPS analogs
support heavy rain and strong winds as has been advertised.

Wind risk...
With 40-45 kt steady and impulses reaching near 60 kt at H92 as
modest BL destabilization occurs late Tue into early Wed, at
least some of this momentum is expected to reach the sfc. The
peak will be along E MA/coastal plain, as the jet increases
early Wed morning across this area. 35-45 mph gusts are
possible, potentially as far inland as the Worcester hills and
central CT, with gusts 50+ mph possible overnight Tue night into
Wed mainly in the coastal plain mentioned above. Will need to
especially monitor the potential for a fine convective line
along the frontal boundary as this could more efficiently yield
the strong-damaging gusts. With leaves still on most trees, this
will exacerbate the risk for downed limbs or even some trees
with localized power outages. Wind headlines will likely be
needed. This risk coincides with the latest SPC SWODY3.

Heavy rain...
With very high PWATs, a strong frontal boundary and LLJ,
combined with modest instability, pockets of convectively driven
heavy rain is possible. Widespread shield of light-mod rain
begins early Tue, but pockets of rainfall with 1+ inch/hr
rainfall rates are likely late Tue into early Wed as the front
gradually shifts E. Any thunderstorms will enhance these
rainfall rates. Given the winds, some stripped leaves could clog
area storm drains as well, exacerbating issues with the
rainfall. At this time, the primary risk will be pockets of
urban/poor drainage flooding. Overall totals above 2.00 inches
are looking more likely given good agreement on GEFS/EPS and
CIPS. However, with the potential for high rainfall rates
locally, some areas of 3-4 inches cannot be ruled out.

Transitional day as secondary frontal wave is able to shift N
of the region, allowing for mid-upper lvl dry slot to begin to
shift in from the S. This is likely to trap some lower lvl
moisture, given PWATs remain elevated. Therefore, risk for
drizzle and continued SHRA activity through the day on Thu even
as heavier precip shield shifts into N New England. POPs will
gradually decline because of this. The introduction of colder
air within the trof lifting NNE will allow temps to drop closer
to seasonal normals, mainly the upper 50s and low 60s as drier
air slowly mixes to the sfc. Dwpts drop through the day as well.

Fri through the weekend...
Weak mid lvl ridging replaces the tilted trof as its axis
shifts well NNE of S New England. High pres 1020+ hPa shifts
over Fri into the weekend with drier air expected. The cool
airmass is short lived however as H92 temps warm to +9C on Fri,
then +12C by Sat and Sun. This suggests temps remain generally
above normal for highs with near normal lows thanks to
radiational cooling. Regarding the influence of the secondary
longwave trof developing late week, the highly meridional
pattern favors a slower progression than the current GFS/CMC and
some ensemble members suggest. Will lean on a slower/drier
period through the weekend based on other guidance sources than
those listed previously.


Forecaster Confidence Levels...

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

Short Term /through Monday Night/....

Through this afternoon...Moderate to high confidence.
Sea breezes develop by midday along both coasts. Some high
resolution guidance continues to have IFR CIGS moving onto the
eastern MA coast during the afternoon. No evidence seen on both
GOES-13 and GOES-16, though tough to see with bands of high
clouds moving across. Continue to feel the low clouds are too
fast and overdone, but can not rule out a low risk for
development. Will continue to monitor

Tonight...Moderate confidence.
Uncertainty on how quickly MVFR-IFR conditions overspread the
area from the south. Mainly dry conditions prevail along with
light south winds.

Monday...High confidence.
Mainly VFR, although with a low risk for early AM fog and lower
clouds with isolated IFR conditions possible.

KBOS Terminal...Moderate to high confidence in TAF. We think
northeast winds develop at the terminal by around 15Z or so. Low
risk of IFR CIGS moving in off the ocean sometime this
afternoon. Still feel this is too fast and overdone, but will
continue to monitor.

KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Friday/...

Tue and Wed...High confidence.
Mainly IFR with occasional MVFR in low CIGS rain/fog. Some
occasional TS also possible with heavy RA at times. Winds gust
20-30 kt most of the region out of the S-SE with a few gusts
30-40 kt mainly SE MA/Cape/Islands. Cannot rule out stronger
gusts everywhere in heavier rainfall/thunderstorms. LLWS likely,
with winds as high as 50 kt at 2kft.

Thu...Moderate confidence.
Gradual improvement as winds shift to the west and diminish.
Some lingering SHRA and IFR/MVFR conditions but with improvement
to VFR into the overnight hours.

Fri...High confidence.
Mainly VFR.


Forecaster Confidence Levels...

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

Short Term /through Monday Night/...High confidence.

Very tranquil boating weather for late Oct continues this period
with light winds, dry weather and good vsby. Local seabreezes
develop by midday today. Seas down to around 2 ft on the open
waters, with some 3 foot seas E of Cape Ann which should subside
by this evening.

Light south winds tonight into Monday.

Outlook /Tuesday through Friday/...Tue and Wed...High
confidence. S-SE Gales developing through the day Tue and
continuing into the early half of the day on Wed. Wind gusts up
to 40 kt, with a few gusts higher possible at times. Seas build
to 12-14 ft on the SE outer waters. Rain, fog and occasional
thunderstorms possible. Overall, dangerous boating conditions.

Thu and Fri...High confidence.
Winds shift to the W, and gradually diminish although gusts to
20 kt possible both Thu and Fri afternoon. Seas will take a long
time to diminish with a lingering swell, and may require small
crafts on the outer waters at least well into Fri. Otherwise
improving weather, with dry conditions overall by Fri.


Dry weather continues through at least tonight with minimum RH
values 25 to 35 percent today, lowest values over CT and western
MA. However, with high pressure nearby winds will be very light.
Thus fire weather parameters remaining below Red Flag Warning


MARINE...Small Craft Advisory from 6 AM to 6 PM EDT Tuesday for
     Small Craft Advisory from 8 AM to 6 PM EDT Tuesday for ANZ230-
     Small Craft Advisory from 2 AM to 6 PM EDT Tuesday for ANZ235-
     Small Craft Advisory from 4 AM to 6 PM EDT Tuesday for ANZ250-
     Small Craft Advisory from 11 PM Monday to 6 PM EDT Tuesday for


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