Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 221740

Area Forecast Discussion
National Weather Service Taunton MA
1240 PM EST Wed Nov 22 2017

A cold front approaches the region today, and with moisture
working up the eastern seaboard to bring a period of rain this
morning, especially SE New England. Quiet weather Thursday and
Friday. Another shot of wet weather and breezy conditions this
weekend. Drier and milder toward the middle of next week.


10am update...
OBs and MSAS mass/thermal fields suggest cold front has moved
into W MA/CT but remains somewhat dammed against the
Berkshires/Litchfield hills. As the peak moisture plume across E
MA/RI continues a slow shift to the E with attendant coastal low
pres offshore, this should allow the front to begin to make a
slow transition E. Initially, the added f-gen provided by the
front should lead to a net increase in RA across W MA/CT so will
actually feature rising POPs over the next few hours. However,
thereafter as CAA/dry air begins to entrain through the column,
this RA will end mid-day through the afternoon W-E across S New
England. Will maintain a low risk for occasional TSRA as KDP/CC
before the radar equipment issue showed good ice signatures

Have slowed the E progress of the higher POPs this afternoon as
confluence of higher theta-e and phasing of the approaching
front looks to generate a weak meso-low pres which will slow the
drier air moving in. Still, most locations should see the end of
rainfall by sunset.

Previous discussion...

Split flow across the region early this morning as northern
stream cold front approaches from the Great Lakes. Southern
stream shortwave/coastal low off the Carolina coast will move
northward up the east coast. This system will remain well
offshore but its moisture plume will impact the region.

Currently, surface cold front is making its way into upstate
NY. Radar imagery shows some showers along this front, but
overall moisture is pretty meager. Southern New England remains
in the warm sector ahead of this approaching front thus temps
early this morning have reside above average. In fact, the
office is currently a balmy 51 degrees with Nantucket at 56F.

Focusing south, latest GOES-16 satellite shows moisture
beginning to stream northwards towards New England thanks to
Bermuda high pressure. Current radar imagery shows widespread
showers across the Carolina coast, with scattered showers
developing across Long Island and into southeast Massachusetts.
These showers are associated with the upper level jet and mid-
level moisture at 700mb. At the surface, theta-e gradient has
set-up with a 1000-925mb frontogenesis which has help aided the
showers in southern New England. The profile has moisten up as
guidance suggested as rainfall is being reported from WST to

Over the next few hours, moisture will continue to stream into
the region as surface cold front from the West approaches. This
will help pool the moisture into the area and push PWAT values
to above 1.0 inch by the mid-morning hours. Showers will begin
to overspread the rest of the region after 7AM. The combination
of the upper level jet and LLJ will help aid in strong lift for
the region. In fact, guidance continues to hint at strong omega
during the mid-morning hours especially along and points east of
I-95. This combined with the high PWATs will lead to heavy
downpours across RI and eastern MA. NCAR ensembles continue to
show the potential for 40dbz during the 7Am to noon time-frame.
Also cannot rule out a rumble or thunder as guidance continues
to hint as SB Cape thanks to higher dewpoints.

Continued to trend QPF towards the EC but with the Hi-res
guidance mix in as well. Appears that heavy precip axis will be
along of just east of the I-95 corridor. This is also supported
by the HREF, NCAR ensembles and HRRR. Generally 0.5 to 1 inch
QPF will fall across a line east of IJD to BVY. Highest amounts
will occur just east of I- 95. Areas west of the Worcester Hills
will see rainfall amounts less than 0.25 inches.

As the front pushes through southern New England, precip will
exit the region by the mid-afternoon. Behind the front, dry but
cooler air will quickly usher into the region leading to temps
dropping through the afternoon hours and winds beginning to pick
up. Overall anticipate a rainy morning leading to heavy
downpours slowing the morning commute. Conditions will improve
by the afternoon hours leading to a great, but chilly start to
the Holiday travel.


Tonight into Thanksgiving Day...

Cold front will be offshore by this evening as strong CAA usher
into the region. Good mixing with this cold air aloft resulting
in gusty NW winds near 20-25 MPH during the overnight hours.
Surface high pressure approaching from the west may be enough to
allow for the winds to slacken off resulting in radiational
cooling before daybreak. Highest confidence is across the
interior. Thus will keep temps cooler than MAV/MET guidance.

Chilly start to the Thanksgiving Holiday as high pressure from
the west builds into the region. Weak shortwave aloft will
increase cloud cover during the afternoon. Moisture associated
with this wave looks meager enough to keep the forecast dry.
Westerly winds at the surface as temperatures in the upper 30s
to low 40s across the region. Overall, a chilly but dry Turkey
day as temperatures will remain 5 to 10 degrees below normal.


*/ Highlights...

 - Quiet weather through Friday
 - Showers possible at times this weekend, could be breezy
 - Turning mild Tuesday into Wednesday, could also be breezy

*/ Overview...

22/00Z guidance suite is rather good overall agreement into
Sunday. More detail differences become more prevalent early next
week. Continue to favor a consensus approach to smooth over the
less predictable details, particularly with timing and amplitude
of various shortwaves moving through the larger synoptic pattern.

In general, expecting a mid level longwave trough to linger
near our region Friday into Saturday. As previously note, this
is more of a split flow during this time. Majority of the
guidance merges this flow into a deeper mid level trough Sunday
into Monday. This mid level trough expected to finally move
over the Maritimes toward the middle of next week.

Only concern for precipitation during this time will be this
weekend. Besides a series of front Saturday, will need to
monitor the progress of an offshore low pressure. At this time,
thinking this coastal low remains far enough east to not have a
major impact other than increasing the pressure gradient,
especially Sunday.


Forecaster Confidence Levels...

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

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

Through 00Z this evening..
Mixed IFR to VFR conditions continue with most VFR W of the
Worcester Hills and mixed MVFR/IFR east through about 21Z. After
this point, rapid improvement to VFR all sites from W-E through
the remainder of the evening as winds shift to 320. Gusts to
around 25-30 kt possible also with this wind shift.

Tonight into tomorrow night...
Mainly VFR after this evening. NW winds continue to gust around
25 kt through the overnight hours but then drop off during the
early morning. These winds shift to mainly W tomorrow and
tomorrow night.

KBOS Terminal...
Mixed VFR/MVFR conditions with last batch of rain through about
21Z along with E-NE flow. Once winds shift to 320 conditions
improve rapidly thereafter. With the wind shift, gust 25-30 kt
are possible at times, which linger into the overnight.

KBDL Terminal...
Mainly VFR, winds will shift to NW no later than 20Z with gusts
to around 25 kt at times lingering into the evening.

Outlook /Friday through Sunday/...

Saturday: VFR. Breezy. Slight chance SHRA.

Saturday Night: VFR. Slight chance SHRA.

Sunday: VFR. Breezy.


Forecaster Confidence Levels...

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

Short Term /through Thursday/...

Today...High confidence.

Passing cold front during the day and passing coastal low well east
of the waters will lead to widespread rainfall today which could
limit VSBYS. Seas will remain near 5 feet for the outer waters but
SCA have been let go elsewhere.

Tonight into Tomorrow...High confidence.

Strong CAA across the relatively warm waters will result in gusts NW
winds between 25-30 kts. Seas will also build in response. SCA have
been reissued to account for this trend. Low confidence on gales for
the eastern ocean waters. Conditions will improve on Thanksgiving,
but seas will remain choppy into the afternoon.

Outlook /Thursday Night through Sunday/...

Thanksgiving Day: Winds less than 25 kt. Local rough seas.

Thursday Night: Winds less than 25 kt. Seas up to 5 ft.

Friday through Friday Night: Winds less than 25 kt. Areas of
seas approaching 5 ft.

Saturday through Saturday Night: Winds less than 25 kt. Areas
of seas approaching 5 ft. Chance of rain showers.

Sunday: Moderate risk for Small Craft Advisory winds with gusts
up to 30 kt. Seas up to 5 ft. Slight chance of rain showers.


MARINE...Small Craft Advisory from 4 PM this afternoon to 4 AM EST
     Thursday for ANZ230>234-251.
     Small Craft Advisory from 4 PM this afternoon to 1 AM EST
     Thursday for ANZ236.
     Small Craft Advisory from 4 PM this afternoon to 2 PM EST
     Thursday for ANZ235-237.
     Small Craft Advisory from 4 PM this afternoon to 8 PM EST
     Thursday for ANZ250.
     Small Craft Advisory until 8 PM EST Thursday for ANZ254>256.


NEAR TERM...Doody/Dunten
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