Area Forecast Discussion
Issued by NWS Boston, MA

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850
FXUS61 KBOX 241150
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
650 AM EST Fri Nov 24 2017

.SYNOPSIS...
Dry and seasonably cool weather will prevail today. Milder air
returns Saturday ahead of a cold front. The cold front moves
through southern New England Saturday night accompanied by
scattered showers. Blustery weather follows on Sunday. Milder
temperatures may return for Tuesday and Wednesday of next week.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

7 AM Update...

Area of mid to high clouds should pass offshore by around 8 AM.
Mostly clear skies are expected today with near normal
temperatures. Prior forecast is on track with only very minor
adjustements needed.

Prior discussion...

Mid and high level clouds continue to dissipate as they move
east across southern New England this morning. The thicker mid
level clouds towards the Berkshires will be more stubborn to
erode as there is some connection to the Great Lakes to keep the
humidity higher, along with the upslope over the Berkshires
themselves.

Adjusted the forecast through daybreak to reflect observed
trends.

For today, high pressure to our south will dominate our
weather. Dry conditions with relatively light west winds
shifting southwest as the day progresses. Abundant sunshine with
only a few higher clouds from time to time. This sunshine will
permit higher temperatures than Thursday, and close to normal
values for late November.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM SATURDAY/...
Southwest winds should increase slightly tonight, setting the
stage for a warmup Saturday. As noted by prior shift, dewpoints
also increase with the southwest flow, but not expecting fog to
be an issue. Low stratus is likely across the Cape and islands
late tonight. Dry conditions continue.

Saturday should be above normal temperature-wise as modest
southwest winds continue ahead of a cold front. Latest model
suite continues to show pretty good lift and humidity within the
850-700 mb layer, but more drier air beneath it to be overcome.
Envisioning a scenario where clouds increase through the day,
with dry weather into mid-late afternoon.

Since this is a cold frontal passage, and BUFR soundings
continue to show the column saturating from the top down, will
continue the idea of a slight chance for showers, becoming a
greater risk towards the east coast very late in the day
Saturday due to proximity to more humid low levels.

&&

.LONG TERM /SATURDAY NIGHT THROUGH THURSDAY/...
Highlights...

* Scattered showers Saturday night and then mainly dry rest of the
  forecast period
* Blustery behind cold front on Sunday
* Milder temperatures may be in store for Tuesday and Wednesday

Discussion...

Forecast area will be subject to a series of fairly low amplitude
upper short wave trough passages for the next 7 days. At the
surface, these will be reflected by mainly dry frontal passages.
After Sunday and Monday, it looks to be mainly dry, but some
uncertainty in temperatures due to uncertainty in whether the
southern and northern stream flow is the more dominant over the
region. As is typically the case in a pattern with progressive short
wave troughs, there are uncertainties especially in the timing.
However, the impact on the forecast is mitigated by the fact that
there is limited moisture available. Most of the focus for this
forecast period is early on with the cold front passage Saturday
night followed by a rather blustery day on Sunday.

A fairly sharp upper short wave trough and moderately strong surface
cold front affect the region Saturday night. Moisture is expected to
be fairly limited given the trajectory of this feature, but bufkit
soundings do show a brief period of fairly deep moisture especially
closer to the coast where there is some marine influence in the
lower levels. This looks to be enough to support at least scattered
light showers.

Moderately strong cold air advection follows on Sunday with 850 mb
temperatures +2C to +4C Saturday evening dropping to about -5C to -
8C by midday Sunday. Upper trough axis probably does not pass
through southern New England until midday Sunday and so cannot rule
out a few flurries at least across the higher terrain. The surface
pressure gradient and cold air advection will likely produce mixing
of 25 knots or slightly higher gusts to the surface during the day
Sunday over land and perhaps closer to 30 knots over the water.

Medium range models suggest another upper short wave trough in the
NW flow moving across New England Sunday night. This looks to be dry
other than a chance of a few flurries over the east slopes of the
Berkshires.

For Tuesday through Wednesday, 500 mb heights rise in response to a
southern stream trough ejecting from the 4 corners area, and this
should be reflected in milder temperatures. A fly in the ointment,
however, could be a northern stream short wave trough that may hold
back warm air advection in to New England. For now have gone with a
model blend with a somewhat greater temperature gradient than
average from north to south. Given uncertainty in timing and
strength of this northern shortwave, there is below average
confidence in mid week temperatures.

Operational and ensemble runs suggest upper level ridging over our
area ahead of a somewhat more amplified trough moving across the
Mississippi Valley on Thursday with possibly an approaching warm
front late in the day or Thursday night.

&&

.AVIATION /12Z FRIDAY THROUGH TUESDAY/...
Forecaster Confidence Levels...

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

Short Term /through Saturday/...High confidence.

VFR. WSW winds will become SW this afternoon and increase some
in speed on Saturday.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Saturday Night through Tuesday/...

Saturday night...High confidence. Mostly VFR with local areas
of MVFR ceiling and visibilities in scattered showers.

Sunday...High confidence. VFR but surface wind gusts 25 to 30 kt.

Sunday night through Tuesday...High confidence. Mainly VFR.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Saturday/...

Small Craft Advisories adjusted to account for trends in
observed seas. Expecting all advisories for the outer coastal
waters to be down by daybreak this morning. Will adjust timing
as needed. High pressure in control with good boating weather
for a time today.

Increasing southwest winds tonight into Saturday will likely
build seas once more across portions of the outer coastal
waters. Additional Small Craft Advisories may be needed for
marginal rough seas.

Outlook /Saturday Night through Tuesday/...

Confidence...Moderate

NW winds will likely gust to between 25 and 30 kts across the
waters on Sunday. Isolated gale gusts, especially east of Cape
Cod and Nantucket, cannot be ruled out.

May be enough gradient and lingering seas to result in Small
Craft Advisory conditions persisting through the early part of
next week across the outer waters.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 5 PM this afternoon to 7 PM EST
     Saturday for ANZ250.
     Small Craft Advisory from 5 PM this afternoon to 2 PM EST
     Saturday for ANZ251.
     Small Craft Advisory for hazardous seas until 7 AM EST this
     morning for ANZ254.

&&

$$
SYNOPSIS...Belk/Thompson
NEAR TERM...Belk/Thompson
SHORT TERM...Belk
LONG TERM...Thompson
AVIATION...Belk/Thompson
MARINE...Belk/Thompson



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