Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 122113
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
413 PM EST Mon Nov 12 2018

.SYNOPSIS...
Potent low pressure tracks up the eastern Seaboard later tonight and
across southeast MA Tue afternoon resulting in a windswept soaking
rain, with potentially damaging winds over Cape Cod and the Islands.
Blustery and colder conditions return Tuesday night into Wednesday
with diminishing Thursday but remaining cold. Another storm will
impact the region late Thursday into Friday, which may be
accompanied by some wintry weather at the start. Colder and drier
weather follows next weekend.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...

4 PM update...

1030 mb high just southeast of Nantucket at 4 pm will support light
SSW winds diminishing this evening especially inland. This combined
with dew pts in the 20s and the absence of low/mid clouds, temps
will fall fairly quickly with sunset especially inland where winds
decouple. However by late evening and especially after midnight
southeast will increase and clouds will lower and thicken,
precluding temps from falling much more.

Model consensus including the 12z HREF have rain overspreading the
region from 12 am to 3 pm from west to east. Inland temps will fall
into the 30s from evaporative cooling. Model soundings do support a
few hours of wet snow possible across northwest MA including
Franklin county where a coating to 2 inches is possible. However
this will be short lived and will wash away by the morning commute
as snow changes to rain.

Elsewhere, temperatures will rise toward morning in response to
increasing southeast winds off the ocean as low pressure tracks into
southern NJ.


&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...

4 PM update...

* Highlights...

 - Intensifying coastal low tracks near the I-95 corridor

 - Strong to damaging winds possible Cape Cod & Islands Tue

 - 3-6 hour window of heavy rain approximately 8 am to noon

 - Minor flooding of small rivers & streams possible including
   the Sudbury river at Saxonville and Pawtuxet River at
   Cranston along with minor street & Highway flooding

Strong/Damaging Winds...

Very strong low level southerly jet moves across Cape Cod and the
Islands between 15z-18z accompanying intensifying low tracking thru
I-95 corridor of CT-RI into into Cape Cod Bay. Highest risk of
damaging winds will be in the warm sector. Some uncertainty on the
exact track of the surface low which will dictate areal extent of
warm sector. Highest confidence for damaging winds is across
Nantucket with the threat diminishing northward. Thus will convert
High Wind Watch to a High Wind Warning for Nantucket and go with a
High Wind Watch for Cape Cod and Marthas Vineyard. Model soundings
in the low levels become neutral here with 60 kt of wind below a 1
kft at Nantucket. So even if higher winds aloft don`t transfer to the
surface, sustained winds may reach warning criteria of 35 kt/40 mph.
Some increased forecast certainty regarding strong winds comes from
12z models trending upward with intensity of low level jet along
with a very impressive rise/fall pres couplet with 17mb pres fall
from 12z-18z centered over Cape Cod and the Islands. This will
enhance the isallobaric wind component and increase the threat for
damaging winds. Elsewhere winds will be considerable less given the
cooler/stable surface temperatures on the NW side of the low track.

Heavy Rain/Flood Risk...

Rain will be across the entire region at daybreak with rain
intensity increasing 7 am to 10 am from west to east across the area
as 90 kt low level southerly jet acts on PWATs surging upward to 1.5
inches. Thus heavy rain will impact the morning commute but the
heaviest rain may wait until the tail end of the morning rush, say 9
am to noon-ish. Good model agreement now on qpf with a widespread
0.75-1.5 inches with heaviest totals across CT-RI and southeast MA,
with low prob of isolated 2 inch amounts along the south coast. The
progressive nature of this system will limit the flood threat, thus
decided to hold off on a flood watch.

As for rivers and streams, the Sudbury river at Saxonville and the
Pawtuxet River at Cranston may experience minor flooding. However
both of these sites may remain below flood stage. Thus given the low
probability here of flooding will hold off on any river flood
watches.

The low quickly exits the eastern MA coast after 18z so expecting a
drying trend during the afternoon along with gusty west winds and
cooler temps.

Tuesday night...

Blustery and turning much colder with 850 temps crashing from +2C at
00z to -13C by 12z Wed! Gusty NW winds up to 40-45 mph will make it
feel even colder with air temps falling into the 20s but wind chills
in the teens!

&&

.LONG TERM /WEDNESDAY THROUGH MONDAY/...

Highlights...

* Windy and cold Wed, then coldest air of the season Wed night
* Another storm late Thu into Fri with rain/snow/ice possible
* Mainly dry and colder next weekend into early next week

Wednesday into Wednesday night...

Windy and cold day Wed with strong W/NW flow. Soundings show a deep
and well mixed boundary layer which supports gusts to 40-50 mph,
especially across central and NE MA, with 30-40 mph gusts elsewhere.
Wind advisories will likely be needed for a portion of SNE.
Strongest wind gusts through early afternoon then slowly
diminishing.  Expect lots of sunshine Wed, although lake effect
moisture may result in clouds spilling into northern CT and SW MA.
850 mb temps down to -12 to -14C Wed so highs will only reach
mid/upper 30s with lower 30s higher terrain. Wind chills in the 20s
with upper teens higher terrain.

Coldest night of the season by far Wed night as strong high pres
builds into New Eng with clear skies and diminishing winds and very
dry airmass in place. Excellent radiational cooling will result in
lows dropping into the teens for much of the region, a little milder
in Boston and outer Cape/Islands. Some single numbers possible in
the CT valley in northern MA.

Thursday into Friday...

Dry weather and sunshine to start the day with high pres in control.
But clouds will overspread region during the day as the high moves
offshore. Model guidance indicating a rather potent southern stream
closed low lifting NE into New Eng Fri. While system is de-
amplifying and opening up, it still moves through as a robust
negative tilt trough, ensuring a period of heavy precip and strong
winds. Timing brings onset of precip north across the region Thu
afternoon/evening with precip persisting through Thu night and into
Friday as the potent negative tilt trough moves across the region.

Strong high pres north of the region will provide enough cold air at
the start for some snow/mixed precip, especially interior. How long
snow/ice/mixed precip hangs on in the interior and specific
accumulations will depend on the low track and details of thermal
profile. However, some snow and/or ice accum is likely in the
interior. Looking at mostly rain by Friday.

Saturday into Monday...

Turning colder, especially Sun into Mon as departing shortwave
brings reinforcing shot of colder air. Expect temps well below
normal Sun/Mon. Saturday will be transition day with temps close to
seasonable. Mainly dry during this period, although some rain/snow
showers possible with shortwave passage Sat night.

&&

.AVIATION /21Z MONDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...

1830z update...

Thru This Evening...VFR, dry weather and modest SSW winds. High
confidence.

Overnight...rain overspreads the area from west to east 05z to
08z. VFR conditions quickly becoming MVFR with areas of IFR in
the Worcester Hills. High confidence.

Tuesday...MVFR to start but then lowering to IFR in periods of
heavy rain beginning around 13z thru 17z from west to east. Then
rapidly improving after 17z from west to east with rain exiting
and improving to MVFR then VFR. LLWS 12z-17z southeast MA
including Cape Cod and the Islands with 90 kt low level
southerly jet. Sharp wind shift 16z-19z to the NW 20-30G40 kt.
High confidence on overall theme but lower confidence on
specific timing.

Tuesday night...strong NW winds 25-35G45 kt. VFR and dry
weather.

KBOS Terminal...
Strong surface wind and LLWS south of Boston over Cape Cod and
Islands. Heaviest rain 14z-17z then sharp wind shift to the NW.

KBDL Terminal...
Potential LLWS with SSE low level jet 09z-12z Tue. Heaviest rain
12z-15z.

Outlook /Wednesday through Saturday/...

Wednesday: VFR. Strong winds with gusts to 40 kt.

Wednesday Night: VFR. Windy with local gusts to 30 kt.

Thursday: Mainly VFR, with local IFR possible late with chance
PL, chance SN, chance RA.

Thursday Night: Mainly MVFR, with areas IFR possible. Windy
with gusts to 35 kt. PL likely, RA likely, FZRA likely, SN
likely.

Friday: Mainly MVFR, with local IFR possible. Strong winds with
local gusts to 40 kt. RA likely, FZRA likely.

Friday Night: Mainly VFR, with local IFR possible. Windy with
areas gusts to 30 kt. Slight chance RA, slight chance SHSN.

Saturday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels...

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

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

Tonight...

Light winds to start but SE gales toward morning along with rain and
fog lowering vsby.

Tuesday...

SE gales with strongest winds near 50 kt possible across the waters
of Cape Cod and the Islands between 10 am and 1 pm, as intensifying
low pres tracks near the I-95 corridor of CT-RI into Cape Cod Bay.
Rain and fog reduce vsby but improving in the afternoon with a wind
shift to the west.

Tuesday night...

West gales likely along with improving vsby.

Outlook /Wednesday through Saturday/...

Wednesday: Moderate risk for gale force winds with gusts up to
45 kt. Rough seas up to 14 ft.

Wednesday Night: Low risk for Small Craft Advisory winds with
gusts up to 30 kt. Local rough seas.

Thursday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain. Local visibility 1 to 3 nm.

Thursday Night: Low risk for gale force winds with gusts up to
40 kt. Areas of rough seas. Rain likely.

Friday: Moderate risk for gale force winds with gusts up to
40 kt. Rough seas up to 13 ft. Rain likely.

Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Rough seas up to 12 ft.

Saturday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...High Wind Watch from Tuesday morning through Tuesday afternoon
     for MAZ022-023.
     High Wind Warning from 10 AM to 2 PM EST Tuesday for MAZ024.
RI...None.
MARINE...Gale Warning from 7 AM Tuesday to 6 AM EST Wednesday for
     ANZ231>235-237-250-251-254>256.
     Gale Warning from 1 AM to 6 AM EST Wednesday for ANZ230.
     Small Craft Advisory from 4 AM Tuesday to 6 AM EST Wednesday
     for ANZ236.

&&

$$
SYNOPSIS...KJC/Nocera
NEAR TERM...Nocera
SHORT TERM...Nocera
LONG TERM...KJC
AVIATION...KJC/Nocera
MARINE...KJC/Nocera


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