Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 190934
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
434 AM EST Sun Nov 19 2017

.SYNOPSIS...
Strengthening low pressure over western NY state at predawn
continues to intensify as it moves across northern New England
this afternoon. Its attending cold front sweeps through the
region late this morning into early afternoon. Behind the front,
mild air this morning is replaced by much colder weather on
blustery west winds this afternoon into Monday. Winds shift to
southwest bringing milder temperatures on Tuesday, followed by a
cold front sweeping across the region late Tuesday night and
Wednesday morning bringing showers. Dry and colder conditions
expected late Wednesday through the end of the week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
4 AM update...

*** Strong Southwest Winds Along The South Coast This Morning
Followed By Strong West Winds This Afternoon All Areas ***

This Morning...

983 mb low over western NY at 4 am and will continue to intensify as
mid level short wave approaching from the west takes on a negative
tilt. Strong 130 kt upper level jet streak associated with this
feature with its LFQ overspreading southern New England this
morning, enhancing QG forcing. This combined with a plume of
subtropical PWATs of 1.5 inches (+2 STD) will yield in some locally
heavy downpours.

Some support from 00z meso guidance that a broken fine line of low
top convection may try to develop along and ahead of the approaching
cold front from about 10z-15z. Dew pts rising into the mid and upper
50s this morning providing a few hundred joules of SB cape. Thus
could be enough instability coupled with the very strong forcing for
ascent to yield some embedded convective elements. These heavier
showers may transport strong winds aloft down to the surface.
Greatest risk of this occurring will be along the south coast, Cape
Cod and Islands where core of low level jet traverses this morning.

Low level jet (925 mb) peaks at 60-65 kt around 12z, however model
soundings indicate steep inversion precluding much mixing and will
likely keep winds below High Wind Warning criteria. Thus after
collaboration with OKX High Wind Warnings for south coastal MA/RI
and coastal CT will be downgraded to wind advisory. Thus thinking
wind damage will not be widespread but rather more localized. At 4
am highest wind gusts so far 37 kt at EWB. So capped gusts to
about 45 kt and sustained to 25-30 kt.

As for temperatures, impressive thermal advection ahead of the
approaching cold front into southern New England with 4 am temps in
the low 60s across RI and southeast MA! Shallow cool air in the CT
river valley finally getting scoured out by heavier showers.

Rainfall amounts will average 0.25 to 0.50 inches but could locally
have amounts up to 0.75 inches in heavier downpours given PWATs up
to 1.5 inches. Not expecting any flood issues.

This Afternoon...

Strong cold front moving offshore around midday. Intensifying 979 mb
low over ME will provide strong pres gradient and combine with CAA
to steepen low level lapse rates and good pres rise-fall couplet to
support WNW post frontal winds up to 40 kt. Thus will continue wind
advisories for the entire region, as there could be isolated wind
damage behind the front. Morning clouds and showers will give way to
partial afternoon sunshine with temps falling behind the front.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/...
4 AM update...

Tonight...

Chilly night with good CAA as 850 mb temps drop to about -10C by 12z
Monday. Lows in the 30s with 20s inland but will feel much colder
given gusty WNW winds. Other issue will be potential lake effect
snow showers from NY state moving into western MA/CT and possibly
RI. All mesoscale guid advects low level moisture from the lakes and
steepening low level lapse rates into the region. Will have to
monitor later model trends to be more specific on these potential
mesoscale snow bands. For now just inserted slight chance pops into
the forecast.

&&

.LONG TERM /MONDAY THROUGH SATURDAY/...

Highlights...

* Dry conditions and blustery NW winds Monday
* Moderating temperatures Tuesday into early Wednesday
* Dry but chilly for Thanksgiving day and Friday

Overview...

Overall progressive mid level pattern continues across North
America through most of the long term period, with a few fast
moving H5 short waves in the northern stream flow. There may be
scattered showers with milder temperatures ahead of the short
wave and surface frontal passages, followed by colder temps and
some gusty winds especially on Monday. May see some
amplification of the mid level flow across the eastern half of
the U.S. around mid week, which continues to show some signs of
model solution spread giving a bit lower confidence in timing
the surface front through. Models in better agreement in
bringing some southern stream moisture up the eastern seaboard
as cold front approaches around the Wednesday timeframe. The
front remains progressive, and should push offshore Wed night,
just in time for dry but cooler conditions for the Thanksgiving
day HS football games. Temps look to remain on the cool side at
the end of the week.

Details...

Monday into Tuesday...High confidence.
Another weak disturbance in the W-NW flow should remain dry but
will bring colder air across the region as it moves through the
northern extent of the large high pressure are settling across
the southern Appalachians and SE U.S. on Monday.

May see some lake effect snow shower streamers try to cross the
Berkshires into western areas, mainly near the E slopes and the
northern CT Valley especially late morning into the early
evening hours. At this point, should see only light activity.

Not expecting temps to recover much during the day with W-NW
winds gusting up to 30-40 mph, highest across the higher terrain
and east coastal areas through midday, then should slowly
diminish. Excellent cold air advection with H85 temps down to
-10C to -12C through midday with little change in the afternoon.
Expect highs only in the lower-mid 30s across the higher
terrain ranging to the lower 40s along the immediate coast.

NW flow early Tuesday will back to SW as the large high
pressure center shifts E during the day. Will see return of
milder temps as readings top off in the mid 40s to mid 50s, with
a few upper 50 degree readings possible across S coastal areas.
A cold front will approach late in the day but will remain dry.

Tuesday night and Wednesday...Moderate confidence.
Expect the cold front to push quickly across, but most of the
energy and moisture will remain across northern New England into
southern Quebec. Good pressure gradient sets up between the
high exiting to the E and the approaching front. Plus, models
continue to signal moisture working up the eastern seaboard from
developing southern stream mid level system across S GA/FL into
the eastern Gulf of Mexico.

Still some timing issues amongst the model suite, but showing a
bit better continuity in bringing precip across most areas
except N central and NW Mass Tue night, then will push E Wed.
May see a decent shot of QPF amounts during Wed as the moisture
feed moves across eastern areas with 0.2 to 0.3 inches possible
before ending. Kept CHC POPs going, with best chances across S
coastal areas. High temps Wed will top off a few degrees either
side of seasonal normals.

Winds shift to W as the front exits late Wed into Wed night,
bringing yet another shot of colder air from central Canada.

Thanksgiving and Friday...Moderate to high confidence.
High pressure sets up from New England southwestward through
the Ohio Valley into the mid Mississippi Valley by midday
Thanksgiving day, then slowly shifts S Thu night and Friday.
Models trying to bring another low toward the region from
Manitoba and western Ontario late Friday, but model solution
spread on timing and track of this system. Have kept a dry but
cold forecast going through Black Friday.

&&

.AVIATION /10Z SUNDAY THROUGH THURSDAY/...
Forecaster Confidence Levels...

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

Short Term /through Tonight/...

3 AM Update...

Thru 17z/Noon...

Widespread MVFR with areas of IFR across the interior in showers
with embedded heavy downpours. Strongest/gusty SSW winds 09z-16z
from west to east along the south coast of MA/RI. Strongest
winds may occur in these heavy downpours. Elsewhere, LLWS thru
15z-16z, then low level jet moves offshore.

After 17z...

Cold front exits the area with a wind shift from SSW to WNW with
gusts up to 40 kt. Any leftover MVFR at midday will quickly
improve to VFR and dry weather. The only exception may be in the
hills of western MA/CT where MVFR is possible behind the front.

Tonight...

VFR cigs SCT-BKN040 with possible -SHSN from Lake Effect snow
showers coming across NY state into western MA/CT and possibly
RI. WNW winds will remain gusty up to 35 kt.

KBOS Terminal...
MVFR with periods of showers, embedded heavier downpours thru
about 16z. SSW winds may briefly gusts up to 40 kt in the
heavier showers. LLWS til 16z then becoming VFR as a cold front
sweeps across the terminal with a wind shift from SSW to WNW
with gusts up to 40 kt.

KBDL Terminal...
Mainly IFR but trending toward MVFR. Periods of showers with
locally heavy downpours. Light winds becoming SSW toward
daybreak. Although winds may become gusty in heavier showers.
Strong cold frontal passage around 15z with wind shift from SSW
to WNW. MVFR improving to VFR with the wind shift.

Outlook /Monday through Thursday/...

Monday: VFR. Windy with gusts to 35 kt.

Monday Night through Tuesday: VFR. Windy with gusts to 30 kt.

Tuesday Night: VFR. Windy with local gusts to 30 kt. Chance
SHRA.

Wednesday: VFR. Chance SHRA.

Wednesday Night: VFR. Breezy.

Thanksgiving Day: VFR.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Tonight/...

This morning...

SSW gales except storm force winds south coastal waters of MA/RI.
Heavy showers and fog will result in poor vsby at times.

This Afternoon...

WNW gales all waters behind cold front which crosses the waters late
this morning into early afternoon. Improving vsbys with the wind
shift.

Tonight...

WNW gales continue much of the night. Mainly dry weather but
rain/snow showers well offshore.

Outlook /Monday through Thursday/...

Moderate to high confidence.

Monday: Moderate risk for gale force winds with gusts up to
35 kt. Rough seas up to 11 ft.

Monday Night: Low risk for gale force winds with gusts up to
35 kt. Areas of rough seas.

Tuesday: Low risk for gale force winds with gusts up to 35 kt.
Local rough seas.

Tuesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Areas of rough seas. Chance of rain
showers.

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

Wednesday Night through Thanksgiving Day: Winds less than
25 kt. Areas of seas approaching 5 ft.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Wind Advisory from noon today to 10 PM EST this evening for
     CTZ002>004.
MA...Wind Advisory until 10 PM EST this evening for MAZ017>024.
     Wind Advisory from noon today to 10 PM EST this evening for
     MAZ002>016-026.
RI...Wind Advisory until 10 PM EST this evening for RIZ002>004-
     006>008.
     Wind Advisory from noon today to 10 PM EST this evening for
     RIZ001.
MARINE...Storm Warning until 10 AM EST this morning for ANZ232>234.
     Gale Warning until 10 PM EST this evening for ANZ230-236.
     Gale Warning until 6 AM EST Monday for ANZ231-250-251-254.
     Storm Warning until noon EST today for ANZ235-237-255-256.

&&

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



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