Area Forecast Discussion
Issued by NWS Boston, MA

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS61 KBOX 260017
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
709 PM EST Sun Feb 25 2018

.SYNOPSIS...

The rain has ended but areas of ground fog and patchy black ice may
impact motorists later tonight into early Monday morning. High
pressure will then bring dry weather with cool nights and mild
afternoons through mid week. The potential continues for a
significant coastal storm late this week with several possible
weather hazards...but it is not a certainty this far out.

&&

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

710 pm update...

Tricky forecast overnight into early Monday morning regarding the
extent of fog and potential for patchy black ice developing.

Early this evening...the rain has exited the region as departing
low pressure has taken the deeper moisture/forcing with it.
However...there has not been a real push of dry low level air so
an abundance of low clouds remained in place. Some data
suggesting that enough drier air will eventually work into the
region to allow some breaks in the low clouds. If this
occurs...given wet ground/boundary layer moisture areas of fog
will become more widespread and perhaps dense in the typical
spots. Greatest risk for this is after midnight through around
daybreak Monday. In addition...that would also allow many
locations to drop into the upper 20s to the lower 30s leading to
the risk of patchy black ice for the early Monday morning
commute. Greatest risk for that will be northwest of the Boston
to Providence corridor.

A lot of the fog/patchy black ice potential hinges on how much
of the lower clouds scour out. This remains uncertain...but
motorists planning travel overnight into early Monday morning
should be prepared for locally dense ground fog and patchy black
ice.

&&

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

Mon...
Low and mid lvl baroclinicity wedged between the low pres
moving E of the Maritimes and sfc 1030hPa high pres slackens
through the early AM hours. This both raises the H92 temps in
the NW interior and cools these same temps across the SE,
yielding a nearly uniform +1C to +2C. Early AM lingering clouds
should dissipate through mid day, so expect that mixing should
reach and more likely exceed H92, allowing temps to reach the
mid-upper 40s. Highs may peak out in the low 50s however across
portions of E MA/RI thanks to a W-downsloping component to the
flow. Overall dry but a bit breezy with winds gusting to 20mph
at times.

Mon night...
High pres in control with continued clearing overnight. Although
still not perfectly ideal for radiational cooling as pres
gradient remains elevated enough to keep some light winds at the
sfc. Only caveat may be the more sheltered valleys of NW MA.
Seasonably cool overnight, mins mainly in the upper 20s and low
30s. Slightly cooler where isolated decoupling occurs.

&&

.LONG TERM /TUESDAY THROUGH SUNDAY/...

Highlights...

* Dry/mild with above normal temperatures Tue and especially Wed

* Significant coastal storm possible late this week with several
  "potential" weather hazards but it is not a certainty this far out

Details...

Tuesday and Wednesday...

Westerly flow aloft with above normal height fields coupled with a
surface high pressure to the south will keep our weather dry and
mild. High temps should reach into the upper 40s to lower 50s Tue
afternoon.  Even milder temperatures on Wed as the high moves off
the mid Atlantic coast allowing high temps to recover well into the
50s to near 60...away from the cooling marine influence of the south
coast.

Thursday through Saturday...

The potential continues for a significant/long duration coastal
storm late this week...but there remains plenty of uncertainty. This
event is still 4-5 days out in the model world...where track errors
over 150 miles are quite common. Therefore...it really is
impossible to lock in any particular solutions or outcomes.
Nonetheless...there are several ingredients in place that still have
us concerned for the threat of a significant/long duration coastal
storm with several weather hazards possible.

What exactly unfolds late this week will have to do with
timing/strength of many features. A couple main players involve
shortwave energy emerging from the southwest and another across
the north central plains. Their specific strength/timing will
have a large impact on the developing storm that will occur in
the Ohio Valley. A strong -NAO/Greenland Block should prevent
the storm from cutting to our west and force it eastward...at
least secondary coastal development. As previous forecaster
mentioned...a highly anomalous -NAO can sometimes suppress the
storm track well south of our region but that is not always the
case. There have been plenty of big storms in New England with
very strong -NAO/s...but a lot of that is a function of where
the block sets up along with where exactly the storm develops
and intensifies.

While it is way too early to get into specifics about this potential
strong coastal storm...there are several possible weather hazards.
These include significant amounts of rain and/or snow depending on
thermal profiles...which are impossible to say at this point.  If
ptype favored rain there would be a concern for fresh water
flooding.  A period of strong to damaging winds especially along the
coast. The GEFS ensembles are already indicating an easterly LLJ 4+
standard deviations above normal at 12Z Friday...which is quite
a strong signal to see in an ensemble 120 hours out. Lastly...a
persistent and potentially strong onshore flow may result in
significant coastal flooding/beach erosion during several high
tide cycles along the eastern MA coast given high astro tides.

In a nutshell...the potential hazards listed above are if this storm
comes to fruition but we are still 4 to 5 days out.  If shortwave
timing/strength changes a weaker storm suppressed further to
the south could spare the region many issues. Nonetheless...this
system does have significant potential and bears watching.

Sunday...

Low confidence this far out...but looks like bulk of the
precipitation will have departed with seasonable temperatures.

&&

.AVIATION /00Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

Short Term /through Monday Night/...

Through 11Z Mon morning...Low to Moderate confidence. Mainly IFR
to low end MVFR conditions across the interior early this
evening. Ceilings may lift a bit or even scour out from a
time...especially from west to east after midnight.
However...this may lead to more fog perhaps becoming locally
dense in spots late. Therefore...a wide variety of conditions
may be seen in the terminals after midnight. Some areas may
lower LIFR conditions in fog developing which may be locally
dense with the best chance in low lying areas. Other locations
may see MVFR to even localized VFR conditions develop near
overnight.

After 11Z and into Mon night...High confidence. Winds settle NW
around 10 kt. Lingering IFR/fog conditions dissipate through
the early AM, with VFR then remaining through Mon night.

KBOS Terminal...Moderate confidence in TAF. IFR conditions early
this evening may improve to MVFR conditions after midnight and
perhaps even VFR towards 12z.

KBDL Terminal...Low confidence. MVFR conditions early this
evening may see brief improvement to VFR. However...if this
occurs areas of fog perhaps locally dense may develop. This
remains uncertain...but if any dense fog develops it should
scour our shortly after daybreak Monday.

Outlook /Tuesday through Friday/...

Tuesday through Wednesday...High confidence in mainly VFR
conditions.

Thursday: Increasing threat for MVFR to perhaps even IFR
conditions as the day wears on Thu...but that will depend on the
timing of a developing coastal storm.

Thursday Night and Friday: MVFR-IFR conditions likely. Windy
with gusts to 40 to 50 knots possible along the coast depending
on track/timing/strength of coastal storm. RA and/or SN likely.

&&

.MARINE...
Forecaster Confidence Levels...

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

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

Through tonight...
All gales have been converted to small craft headlines. While
the winds dissipate and back to the N-NW, seas remain elevated
through the early AM hours. Therefore small craft advisories may
have to linger through early Mon across the outer most waters.
Otherwise, fog through the evening expected with reduced vsby.

Mon and Mon night...
Brief lull in conditions Mon morning. By Mon afternoon, wind
gusts should once again reach around 25 kt offshore out of the
NW and linger through the evening, seas only build to about 5
ft, but some Small Craft Advisories will likely be needed even
for the marginal conditions.

Outlook /Tuesday through Friday/...

***Potentially dangerous storm for Mariners late Thursday into
 Saturday with strong winds and high seas which are dependent
 on the track/strength of a potential strong coastal storm***

Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft.

Tuesday Night: Winds less than 25 kt.

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

Wednesday Night: Winds less than 25 kt. Seas locally
approaching 5 ft.

Thursday: Winds less than 25 kt. Seas locally approaching 5 ft.
Chance of rain.

Thursday Night and Friday: Gale to storm force wind gusts
between 40 and 50 knots may develop depending on track/strength
timing of coastal storm. Seas may approach or exceed 20 feet!

&&

.TIDES/COASTAL FLOODING...

Thursday through Saturday...

The potential exists for significant coastal flooding/beach erosion
over several high tide cycles late this week...particularly along
the eastern MA coast.  While this is far from a certainty given the
potential event is 4 to 6 days in the future...there are several
ingredients in place coupled with high astronomical tides that this
will need to be watched closely.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 10 PM EST this evening for
ANZ235-     237.
     Small Craft Advisory until 7 AM EST Monday for ANZ250-251-
     254>256.

&&

$$
SYNOPSIS...Doody/Frank
NEAR TERM...Frank
SHORT TERM...Doody
LONG TERM...Frank
AVIATION...Doody/Frank
MARINE...Doody/Frank
TIDES/COASTAL FLOODING...Frank



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.