Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 191935

Area Forecast Discussion
National Weather Service Taunton MA
335 PM EDT Wed Oct 19 2016


Cold front settles south of the region tonight. High pressure
builds across Northern New England and brings us dry weather.
Warm moist air moves back to the north and brings a chance of
showers Thursday afternoon and night. A more widespread heavier
rainfall possible sometime Friday into Friday night as low
pressure tracks across the region. Cooler and mainly dry weather
will follow Sunday into early next week.



Cold front moves off the South Coast this evening. This may serve
as a focus for some clouds, but offshore. High pressure builds
over New England with center over Northern New England. Cool dry
airmass with dew points in the 40s north of the Mass Pike and 50s
to the south. The high will eventually bring low level winds
around from NW to E, although nighttime speeds may be too light to
notice the change during the night. The light winds will allow for
some radiational cooling in the interior with min temps in the 40s
north and 50s south. The low Temp/Dewpt differences may also allow
areas of fog.




High pressure moves off through the Maritimes Thursday morning.
Upper flow turns from the southwest, bringing increasing mid and
high clouds during the morning. Ohio Valley low pressure draws a
40-knot low level S-SW jet up through the Apppalachians, but
aimed at PA and NY. The eastern edge of this jet will slide into
New England during the afternoon/evening, and as it rides up over
the stalled front to our south it will bring increasing chance of
showers, mostly to CT and Western MA. The best lift will remain
along the jet axis to our west. And the upper jet will remain over
the Great Lakes, so upper dynamics will also linger well to our

The low level east winds will keep daytime temps cooler. Water
temperatures in the lower 60s supports air temps Thursday in the
low to mid 60s.

Thursday night...

Upper level shortwave will continue to dig over the Great Lakes,
further slowing the eastward progress of this weather system.
Models agree on the low level jet continuing to shift east with
time during the night, which should increase the probability of
precip in our area with highest values in the west. A cool night
but with clouds keeping temps a little milder than tonight.
Forecast will mostly show mins in the 50s.



 * Rainy and unsettled Friday.
 * Cooler and dry by the weekend.
 * Seasonable early next week.

Overview and model preferences... Still noting fairly good agreement
at the synoptic scale through much of the long term, even with the
latest 00Z updates.  Gradual deepening wave across the NE and Canada
becomes cutoff by the later portions of the work week and the
weekend.  While there is fairly good agreement in this setup in the
upper lvls, there continues to be some issues at hand near the sfc,
regarding the interaction with a tropical disturbance currently in
the Bahamas.  While there is generally good agreement that these
features will in fact phase at some point, exactly when will define
how wet conditions will be and for how long at the end of the week.
GFS/ECMWF have switched from last night, with the GFS now the most
progressive (phasing late and well offshore) while the ECMWF is now
slower, although still not as slow as the CMC.  Noting that both
GEFs and ECENS ensemble members are generally in better agreement
with the ECMWF, so this update will add more weight to the ECMWF and
carry this weight through the remainder of the forecast period.


Friday into Fri night... As upper lvl wave deepens into stacked
low pres in the OH Valley, warm front will shift N into N New
England and Canada. Noting RRQ of upper lvl jet is setup mainly to
the NW, along with the sfc low pres. Therefore, bulk of precip
initially early Fri, will remain to the NW although warm
advection in the warm front (with low lvl moisture increasing)
could yield a few shra across the region.

Fri and Fri night however, will see moisture increase as tropical
influence approaches from the S.  PWATs increase to near 2.0 inches
(nearly 2 std deviations above seasonal normals).  Slow phasing
process occurs as the upper lvl jet shifts it`s RRQ to the SE.
Secondary low pres development within the deep moisture plume could
allow for more widespread rainfall, however it depends on how far SE-
E it deepens.  The ECMWF weighted solution suggests nearly 70
percent probability of at least 0.5 inches QPF in 245 hours, so some
ares could see as much as 0.5-1.0 inches of total rain as the
tropically influenced low pres passes over or near S New England.
The deepening process continues as it shifts int N New England, so
wrap-around comma-head precip could linger into the morning hours
Sat.  All-in-all, watch for 0.5-1.0 inches of precip, not a drought
buster, but certainly a help.  Temps mainly above normal thanks to
H85 temps hovering near +14C.  Expect highs in the low 70s and lows
only dipping into the 60s.

Also of note, the secondary low pres deepening could impact coastal
areas as we are still dropping from King Tide, see coastal flooding
section below for more information.

Sat and Sun... Return to fall thanks to strong cold advection and
brisk NW flow between deep low pres across the Maritimes and High
pres approaching from the SW.  H85 temps drop as low as -5C to -7C
while H92 temps hover near 0C.  This suggests highs only in the mid
50s to low 60s at best, while overnight mins should drop into the
upper 30s even with a strong pres gradient.  If the gradient weakens
enough (mainly Sun night) could see more widespread areas near or
below freezing.  Winds on Sat will be strongest, possibly
approaching 30-40 mph out of the NW.  Low risk for some wind

Mon... Brisk secondary shortwave pushes through the region.  Noting
enough diff vorticity for some lift as the wave moves through,
however dry NW flow will have been ongoing for almost 48 hours.  So,
risk for showers will be dependent on local instability, lapse rates
through the moisture between sfc-H7 approach 6.0C/km, so could see
some shra with the wave passage.  Some ocean effect clouds and even
shra possible after the wave passage as H85 temps drop to near -4C
with SSTs still near or above 10C.  Reinforcing brisk N flow.

Tue into Wed... More seasonable wx follows with high pres and temps
falling near normal.


Forecaster Confidence Levels.

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

Short Term /through Thursday Night/...

Tonight...High confidence.

Mainly VFR. Low confidence on potential for fog formation after
midnight. The best chance will be in the CT Valley.

Thursday...High confidence.

VFR through mid afternoon with patches of MVFR cigs toward
evening in the south and west.

Thursday night...Moderate to High confidence.

Developing MVFR cigs/vsbys in showers early night. Mixed MVFR/IFR
cigs and vsbys in showers and fog overnight. South winds of 40
knots will move in at 2000 feet AGL over Western MA and CT late at
night and may contribute to some low level wind shear in those
areas. East winds at the surface, South-Southwest winds above 2000

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Friday through Monday/...

Fri into Fri night...High confidence. Mix of IFR/MVFR as rain and
fog develop across the region. Easterly to southeaster flow.

Sat and Sun...High confidence.
Mainly VFR early Sat as winds shift to the W.  Wind gusts,
especially during the day could reach 25-35 kt.

Mon...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 Thursday Night/...Moderate-High confidence.

Tonight...Cold front stalls over the southern waters tonight.
Winds will remain less than 20 knots. Still a couple reports on
the Southern Outer Waters for 5 foot seas, most of it in a SW
swell. But waves and swell are both diminishing so we will allow
the SCA on the Southern Outer waters to expire. Northeast winds
start to increase again late tonight with gusts to 20 knots.

Thursday and Thursday night...East winds during the day will turn
Southeast Thursday night as a warm front moves north. Wind speeds
will remain below 25 knots. Seas will build, especially Thursday
night, with heights reaching 5-6 feet on the outer waters Thursday
night. A Small Craft Advisory may be needed for those seas.

Outlook /Friday through Monday/...

Fri...High confidence.
SE flow remains generally 20 kt or below, however, swell will be
building offshore reaching 5 ft by the overnight hours.  Small craft
advisories may be needed late.

Sat and Sun...Moderate confidence.
Winds shift to the W early Sat morning, and increase with gusts 25-
35 kt possible at times through the whole period.  This suggests
occasional Gales possible, but at the very least, expect strong
Small Craft advisories through the period.  Seas build to 6-8 ft
along the SE ocean waters by late Sat and Sat night.

Mon...Moderate confidence.
Winds and seas diminish through the day on Mon, but seas will likely
remain above 5 ft.  Therefore, small craft advisories will continue
even as winds drop below 20 kt.



Astronomical high tides are subsiding with each tidal cycle. There
may still one or two high tides Thursday and Friday that threaten
minor splashover at the more vulnerable spots on the coastline,
but the general trend is now moving away from that.

Much uncertainty remains for Fri and will depend upon the
interaction of a fairly high amplitude short wave trof and a
possible low center with subtropical origins off the coast. Latest
guidance is suggesting more southerly winds Fri which would limit
surge and potential coastal flooding for the east coast. However,
the range of possibilities are wide and we will need to monitor
trends with later computer model operational and ensemble runs.


Record High Temperatures:

Wednesday October 19th

Boston 84 in 1945
Worcester 81 in 1963
Providence 81 in 1945
Hartford 82 in 1963




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