Area Forecast Discussion
Issued by NWS Boston, MA

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FXUS61 KBOX 201127

Area Forecast Discussion
National Weather Service Taunton MA
627 AM EST Mon Feb 20 2017

A brief return to seasonably cool weather occurs today through
Tuesday with high pressure in control.  Strong low pressure
developing across the Central Plains slowly lifting towards the
Great Lakes will result in an extended period of  unseasonably mild
temperatures Wednesday through Saturday. A cold front will
cross the region Saturday, likely bringing some rain, followed
by more seasonable temperatures by Sunday.



Relatively quiet weather continues today. Only tweaked the
forecast to reflect observed trends.

Previous discussion...

Mid level trough axis amplifies east of southern New England as
additional shortwave energy crosses the region. This will result
in dry northwest flow today, but decent cold air advection will
allow 850T drop to between -8C and -10C by afternoon. Column is
fairly dry so plenty of sunshine. This combined with a rather
mild start should allow highs in the upper 30s across the higher mainly the lower to middle 40s elsewhere. Bufkit
soundings show 20 to 25 mph wind gusts developing later this
morning and afternoon as mixing increases.



Large high pressure builds across southern New England tonight.
The result will be mainly clear skies, except for some ocean-
effect clouds across the Cape/Nantucket as winds become
northerly. Otherwise, light winds/mainly clear skies elsewhere
should allow for overnight lows in the teens across the outlying
locations with lower to middle 20s in the urban heat islands of
downtown Boston/Providence.


High pressure overhead Tuesday morning will slowly shift
offshore by late in the afternoon. Plenty of sun expected during
the morning...but some mid/high level cloudiness should move
across the region from west to east during the afternoon. Mid
level temperatures will be warming as height fields rise, but a
chilly start and relatively weak mixing will keep high temps
mainly in the lower to middle 40s. Weak pressure gradient should
allow sea breezes to develop along the eastern MA coast and may
keep highs in the upper 30s for those locations.



* Light rain/pockets of freezing rain Tue night into Wed
* Thursday looks to be our warmest day
* More likely for widespread rain Friday night into Saturday

Overview and model preferences...20/00z guidance was is good
agreement with overall trends through Thursday. Even beyond
Thursday there is some agreement on a similar pattern, just a
lot of uncertainty with the details. The main uncertainty
derives from a potent shortwave moving east from the West Coast
about mid week. How this shortwave amplifies a downstream trough
toward the end of this week, will determine the timing of a
more widespread precipitation event.

Preferred a consensus approach for this period to smooth over
the less predictable mesoscale details. Above average confidence
in the forecast through Thursday. Low confidence in the details
beyond Thursday.


Tuesday night into Wednesday...

High pressure off the East Coast holds on strong.  With the core of
this high pressure well to our south, expecting a persistent south
wind to develop. The resulting rising heights should lead to a
predominantly rain event as a cold front tries to push south through
our region. The issue will be surface temperatures. There is still a
risk of patchy freezing rain Tuesday night, mainly across the
normally colder spots in north central and western MA. Not expecting
much in the way of ice, but enough that overnight, early AM commutes
could be slippery on untreated roadways.

Still expecting improvement to drier and warmer weather Wednesday,
as a a front moves back north as a warm front. With a strong high
pressure offshore, the current timing of the forecast for this
period may be too fast. Something to be monitored over the next day.

Thursday and Friday...

Modest clipper-like low pressure should move through the Great Lakes
Thursday.  This appears to be the favored storm track for the next
series of storms. Increasing south to southwest flow should
make Thursday the warmest day we`ve had in a while. Just a
slight chance of a shower as this low passes by.

Some slight cooling for Friday, especially with increasing clouds
ahead of a warm front. Timing of overrunning precipitation still
looks to hold until Friday night.

Next weekend...As previously mentioned, have low confidence in
the details in this portion of the forecast, mainly due to
timing issues. Have greater confidence in another low pressure
moving through the Great Lakes Saturday. Precipitable water
values anticipated to be greater than 1 inch, which should mean
the risk for moderate to heavy rainfall at times.

Within the warm sector of the Great Lakes low pressure, the
combination of a strong low level jet at 925 mb, and modest
instability, could lead to isolated thunderstorms if everything
lines up.

Conditions improve Sunday, with a return to much more seasonable
temperatures in the wake of this stronger system.


Forecaster Confidence Levels...

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

Short Term /through Tuesday/...

Today...High confidence. Mainly VFR, but some brief marginal
MVFR CIGS are possible, with the highest risk across Cape Cod.
Northwest winds will gust to 20 knots later this morning and
afternoon, with up to 25 knots across portions of the

Tonight and Tuesday...High confidence. VFR except some marginal
MVFR CIGS possible into Tuesday morning across portions of Cape

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Tuesday Night through Friday/...

Tuesday night into Wednesday...Moderate confidence.

Overnight low-moderate risk for some MVFR/IFR CIGS along with
occasional MVFR vsbys in light rainfall. Low risk for some light
freezing rain, mainly Worcester Hills and western MA. Improvement
to VFR gradually after sunrise Wednesday. Winds shift to the

Thursday and Friday...High confidence.
Mainly VFR. Low risk for some mixed MVFR CIGS by late day Friday,
but these may hold off until Friday night.


Forecaster Confidence Levels...

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

Short Term /through Tuesday/...

Today...High confidence. Northwest wind gusts of 20 to 30 knots
in the cold air advection pattern. The strongest of those winds
gusts will occur across our eastern waters. Small craft
headlines posted for all waters except Boston Harbor and
Narragansett Bay.

Tonight...High confidence.  Lingering marginal small craft wind
gusts/seas across our eastern waters this evening should diminish
after midnight as high pressure builds in from the west.

Tuesday...High confidence.  High pressure overhead will result in
light winds and flat seas.

Outlook /Tuesday Night through Friday/...

Winds and seas expected to remain below Small Craft Advisory
thresholds through this period. Winds mainly south to southwest
through Thursday.


MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ231-
     Small Craft Advisory until 1 PM EST this afternoon for
     Small Craft Advisory until 4 AM EST Tuesday for ANZ250-254-255.
     Small Craft Advisory until 3 PM EST this afternoon for ANZ256.


NEAR TERM...Belk/Frank
MARINE...Belk/Frank is the U.S. government's official web portal to all federal, state and local government web resources and services.