Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 270817
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
317 AM EST Mon Feb 27 2017

.SYNOPSIS...
High pressure centererd south of New England today moves out to
sea Tuesday. This brings back a mild flow of air with above
normal temperatures. A couple of weather systems will bring
periods of wet weather later Tuesday into Wednesday night.
Colder air returns late this week into next weekend.

&&

.NEAR TERM /THROUGH TODAY/...

High pressure centered south of New England. Flow around the
high has brought west-southwest winds to our area, which will
continue through the day. Dry airmass will mean mostly sunny
skies, possibly some thin cirrus.

Vertical profile shows potential for mixing up to 850 mb. Winds
aloft in this mixed layer are 25-30 knots. So this means
potential surface wind gusts reaching 25-30 knots. The mixing
will tap temps aloft of -3C to -4C, which would support max sfc
temps in the low to mid 50s. Given past behavior of model
temperatures and the potential for mixing higher than model
forecast, we added 2-3F to the max temps.

&&

.SHORT TERM /TONIGHT THROUGH 6 PM TUESDAY/...

Tonight...Moderate-High confidence.

West-southwest flow diminishes near the surface. But high
pressure offshore maintains dry weather for much of the night.

Weak cold front is indicated moving south from Canada into
Northern New England. A weak airflow makes it difficult to
determine how far south the front makes it, but pressure pattern
suggests it gets no farther south than the Massachusetts border.

Shortwave ejecting from a trough over the Pacific Southwest
reaches the Great Lakes by Tuesday morning. Models do show a
broad cloud area moving across New England, and the GFS is
aggressive with measureable pcpn while the ECMWF is generally
dry. We agree with increasing clouds, but tend more toward the
drier ECMWF solution for pcpn. Most of the dynamics and low
level inflow remain well to our west. Temperatures should cool
off early, but warm advection remains weak through the night so
at most temps would level off overnight with a range in the mid
20s NW to mid 30s coast.

Tuesday...Moderate-High confidence.

Increasing southwest flow, especially during the afternoon. This
will bring an increasing potential for lift over us and so a
chance of pcpn especially in the afternoon/evening. The airmass
looks similar to today but with a few more clouds in place. So
we expect another mild day with temperatures near 50 or in the
low to mid 50s.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Highlights...

* Above average temperatures for most of this week
* Widespread showers possible Tuesday night through late
Wednesday night
* More seasonable conditions return Friday into Saturday

Overview...

26/12z guidance continues to show rather good agreement on the
overall pattern through Friday. That said, there are the
typical discrepancies in the timing and amplitude of shorter
wavelength features toward the end of this week. Since these
sorts of details are usually less predictable at this time
range, still prefer a consensus approach.

Details...

Wednesday into Thursday...Moderate confidence.

Main weather producer will occur Wednesday into Thursday. Still
some  uncertainty on the timing and location of the surface
low.

Our region should remain in the warm sector of a low pressure
moving through the Great Lakes. Strong southwest winds aloft
are likely to bring an unseasonable amount of moisture our way.
This expecting plenty of clouds. Rainfall amounts however are
generally expected to be less than one half inch for most of our
region.

Convective instability will be the wildcard. Most convective
indices are rather marginal. However, if we could get some low
level instability to go along with the wind shear, then a few
thunderstorms may develop. This has been consistent, weak signal
the past couple of days. By no means is this a lock, but will
keep the mention of isolated thunderstorms in the forecast.

Still have high confidence that at least some precipitation
will fall, and temperatures will be above average Wednesday
into Wednesday night.

Cold front will sweep through early Thursday morning, resulting
in drying conditions with falling temperatures falling through
the day. Strong cold air advection likely to mean gusty west to
northwest winds.

Friday and beyond...Moderate confidence.

26/12Z GFS remains the model with the strongest hint of a
clipper-like low pressure passing by to our south Friday
morning. The other models are neither as aggressive, nor as
humid. Favored the drier consensus solution for now. This will
be something to watch over the course of this week.

High pressure remains to our south next weekend. After a period
of more seasonable temperatures Friday and Saturday, it appears
we get back into more of a warmup next Sunday.

Good mixing and cold air over the ocean may result in ocean
effect snow showers next weekend, before another clipper system
possibly approaches towards late Sunday.

&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
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.

VFR. Increasing high clouds especially in the afternoon/evening.
W-SW winds start the day light near the surface and at 25-30
knots in the lowest 5000 feet AGL. Expect some of this wind to
mix to the surface in gusts during late morning and afternoon,
then diminish toward evening.

Tonight... High confidence.

VFR. Increasing high clouds before midnight. Cloud bases lower
to around 4500 feet overnight.

Tuesday...Moderate confidence.

VFR most of the day. Chance of MVFR cigs developing during the
afternoon, but this could hold off until evening. There is a
chance of reduced vsbys in showers in the afternoon but the
better chances will hold off until night.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Tuesday Night through Friday/...

Tuesday night into Wednesday...Moderate confidence. Periods of
-RA through the period will result in MVFR/IFR conditions.
Cannot rule out LIFR in fog during the overnight hours.

Thursday...Moderate confidence. VFR conditions from west to
east during the morning. Blustery westerly winds are possible.

Friday...Moderate confidence. Mainly VFR, with MVFR possible
toward the south coast, including the Cape and islands.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Tuesday/...High confidence.

Today...

High pressure offshore moves east tonight and Tuesday.
West southwest flow actually increases for a time late morning
and afternoon, bringing a chance of 25-30 knot winds during that
time. Winds then diminish this evening. A Small Craft Advisory
will be in effect on all waters for this wind. Meanwhile 5 foot
seas will linger on the outer waters.

Tonight and Tuesday...

Winds and seas remain below Small Craft Advisory levels. Clouds
do move in from the west later tonight. Vsbys may lower below 3
miles in showers along the southern waters, mostly Tuesday
afternoon/evening.

Outlook /Tuesday Night through Friday/...

Tuesday night...Moderate confidence. Warm frontal passage
Tuesday night could drop vsbys in rain and fog.

Wednesday into Thursday...Moderate confidence.  Approaching system
from the west will push a cold front through on Thursday, increasing
both seas and winds during this period. Heavy rain and a few
thunderstorms are possible, lowering vsbys. There is the
potential for southerly gales across the waters Wed night, and
northwesterly gales on Thursday behind a cold front.

Friday...Moderate confidence. Gusty west winds continue. Small
Craft Advisories likely will be needed for some of the coastal
waters.

&&

.FIRE WEATHER...
Dry and blustery conditions will persist today pushing minimum
relative humidity values at or below 30 percent for a good
portion of interior Southern New England as southwesterly flow
gusts 25 to 30 mph.

Over the weekend much of Western and Central MA and CT saw
around 0.50-0.75" of liquid, with around 0.10-0.25" to the east,
there`s some concern of potential fire weather conditions over
Northeast CT, RI and Eastern MA as temperatures warm into the
mid and possibly upper 50s.

&&

.HYDROLOGY...
Rising water levels, partly from weekend rain but also from
snowmelt in Northern New England. There is still plenty of
water moving downriver from the snowpack. We will need to
monitor water levels across southern New England for a while
this week.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 1 AM EST Tuesday for ANZ250-254.
     Small Craft Advisory until 10 PM EST this evening for ANZ255-
     256.

&&

$$
SYNOPSIS...WTB/Belk
NEAR TERM...WTB
SHORT TERM...WTB
LONG TERM...Belk
AVIATION...WTB/Belk
MARINE...WTB/Belk
FIRE WEATHER...
HYDROLOGY...


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