Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 260816
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
416 AM EDT Fri May 26 2017

.SYNOPSIS...
Low pressure tracks across Rhode Island and eastern Massachusetts
this morning then offshore this afternoon. Periods of rain will
continue today with rain heavy at times across northern
Massachusetts this morning. High pressure builds into the region
beginning tonight and ushers in a drier airmass that lingers through
much of the holiday weekend. This high will provide mild days and
cool nights to the area Sat and Sun. The next chance of rain will
arrive Sun night into Mon as a trough of low pressure moves across
the region. Scattered showers possible much of next week, mainly
diurnal and by no means a washout. Temperatures will warm to near
normal values.

&&

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

Widespread showers will continue to move through the region early
this morning as vertically stacked system moves through southern New
England. Looking at satellite data, you can see the low pressure
circulation just south of Long Island. The systems weak warm sector
has pushed across the Islands as temps are near 60F with a southeast
wind. The reminder of the region continues to be on the cool side of
the low. This as well as due northerly winds/stable air will limit
any more thunder development. However, near the occlusion center of
the low we could see a rumble of thunder.

Over the next few hours, the focus shift towards the western half of
the region where the heaviest precipitation will fall. Guidance
continues to show a deformation zone/comma head set-up over this
region and with several guidance members showing over an inch of
precip, may need to watch for nuisance flooding. As the low
continues to approach, pressure gradient will tighten resulting in a
few gusts to near 20 mph.

Today...

The upper circulation slowly moves into the Gulf of Maine. This will
result in a diminishing trend in the precipitation. However with
moist, cyclonic flow aloft remaining overhead, anticipate plenty of
clouds and scattered showers for much of the day. Conditions will
begin to improve during the later half of the day.

Cloudy skies today will limit diurnal heating. Expect high temps to
run below average today remaining in the upper 50s to low 60s. The
possible exception could be across the southwest portion of the area
which stands the best chance to briefly break out of the overcast
later in the day.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...

Tonight...

Upper level low will continue to move into the North Atlantic
tonight. Heights will be rising as northwest flow continues. Passing
shortwave on the backside of the low may trigger a few showers
overnight but overall trend will be dry. Temperatures will remain
steady overnight with lows in the 50s.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...

*/ Highlights...

* Mainly dry weather w/mild days and cool nights Saturday and Sunday
* Risk of rain returns Sun night into Monday
* Temperatures warming to near normal Tue thru Thu along with a risk
  for scattered showers each day, although by no means a washout

Synoptic Overview...

Main large scale feature this period will be a building mean ridge
over western Canada which induces downstream troughing over the
Great Lakes. This will yield an active/amplified northern stream
with cyclonic flow into New England much of next week. This will
translate to a risk of showers each day (mainly diurnal) but also
temperatures warming to near seasonal levels.

Daily Details...

Saturday...

Dry weather prevails in response to NW flow aloft and weak high
pressure at the surface advecting across the area. Typically this
setup supports at least some sunshine however models are depicting
lots of low level moisture remaining trapped beneath the subsidence
inversion. Both the NAM and GFS moisture profiles suggest BKN-OVC
strato-cu much of Saturday. Thus mostly cloudy appears to be the
model consensus. Although the combination of light winds (weak high
pressure overhead) and temps warming into the upper 60s - low 70s
will yield very pleasant conditions.

Sunday...

Ensembles and deterministic guidance in very good agreement that
deep layer east coast ridge lingers long enough to provide mainly
dry weather here. Any showers likely hold off until after sunset.
Thus a fairly nice day with temps 70-75, 60s at the coast given
cooling seabreezes. Moisture profiles suggest more sunshine eastward
across RI and eastern MA.

Monday...

Still some uncertainty regarding the timing of next system. Model
consensus would support risk of showers Sunday night into Monday as
northern stream trough advects across the area. Cooler given cloud
cover, southeast onshore winds and risk of scattered showers with
highs only in the 60s.

Tuesday thru Thursday...

Long wave trough sets up across the Great Lakes with cyclonic flow
into New England. This setup supports isolated or scattered diurnal
showers each day but by no means a washout. Somewhat warmer low
level flow becoming southwest. This will support highs in the 70s,
60s for the south coast of MA/RI including Cape Cod and the Islands.

&&

.AVIATION /08Z FRIDAY THROUGH TUESDAY/...
Forecaster Confidence Levels...

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

Short Term /through Tonight/...High confidence.

Today...MVFR/IFR cigs and vsbys in rain and fog this morning
improving to MVFR by the afternoon. Heaviest rainfall in the morning
with -SHRA in the afternoon. Northeasterly winds could gust to 20
knots. Conditions may improve to VFR across western terminals in the
late afternoon.

Tonight...Any low cigs or vsbys should improve to VFR overnight.
Cannot rule out patchy fog in low lying regions. Northwest winds
with gusts to near 20 kts.

KBOS TAF...High confidence in trends, moderate confidence on timing.

KBDL TAF...High confidence in trends, moderate confidence on
timing.

Outlook /Saturday through Tuesday/...moderate confidence.

Saturday and Sunday...Mainly VFR. Light winds Saturday, with
seabreezes at the coasts. Light S-SE winds Sunday.

Sunday night through Monday...Cigs/vsbys trending to MVFR/IFR in
showers. Winds from the southeast, trending from the south Monday.

Tuesday...Mainly VFR, with scattered diurnal MVFR showers.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Tonight/...High confidence.

Today and Tonight...

Passing low pressure system will keep seas above 5 feet for most of
the period. Northerly winds will switch to the northwest by tonight.
A few gusts to near 25kts are possible across the near shores, but
confidence is to low to extend the adv.

Outlook /Saturday through Tuesday/...

Saturday...light and variable winds with seabreezes at the shore.
Dry weather and good vsby prevail with high pres overhead.

Sunday...light southeast winds expected with high pres just
offshore. Dry weather and good vsby during the daylight hours then
risk of rain and fog overnight.

Monday...another front sweeps across the area with the risk of
scattered showers. Modest SE winds develop.

Tuesday...winds becoming southwest. Low risk for a few afternoon
showers.

&&

.TIDES/COASTAL FLOODING...

A surge of 1 foot occurred with the past high tide resulting in
minor coastal flooding across the MA east coast. This surge remains
across most of the east coast thanks to persistent easterly flow from
passing low pressure system.

The focus turns to the high tide for tonight. Currently a surge of
0.2 to 0.4 feet is forecast and combined with the peak of
astronomical tides (Boston at 12.41 feet), should see at a minimum
coastal flooding of low-lying locations notorious for becoming
inundated during such tides (i.e., Morrissey Boulevard in Boston).
Additional coastal flood statements may be necessary but confidence
is to low. Especially as heights are beginning to rise and surface
low turns to the northwest.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 6 AM EDT Saturday for ANZ235-237-
     250-254>256.
     Small Craft Advisory until 6 PM EDT this evening for ANZ251.

&&

$$
SYNOPSIS...Nocera/Dunten
NEAR TERM...Dunten
SHORT TERM...Dunten
LONG TERM...Nocera
AVIATION...Nocera/Dunten
MARINE...Nocera/Dunten
TIDES/COASTAL FLOODING...Staff



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