Area Forecast Discussion
Issued by NWS Boston, MA

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857
FXUS61 KBOX 271103
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
603 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 /UNTIL 6 PM THIS EVENING/...

6 AM Update...

Chilly start to the day as temperatures are back to seasonable
for this time of year. Plenty of sunshine will help temps
rebound in the 50s. Aside from a few minor updates the overall
forecast remains on track for today.

Previous Discussion...
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 /6 PM THIS EVENING 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 Wednesday
* Showers and thunderstorms Wednesday into Thursday
* More seasonable conditions return on Friday

Pattern Overview...

00z models and ensembles remain in generally good agreement and a
consensus approach was used. Overall, frontal boundary is forecast
to progress through the East during the Wed-Thur timeframe. Upper
level trough will remain over the region in the weekend resulting in
more seasonable conditions. The pattern will then begin to transition
to a more quasi-zonal flow by the beginning of next week.

Details...

Tuesday night...High Confidence.

Warm sector will begin to push through the region as upper level
warm front passes northward. This pushes southern New England into a
higher theta-e region. A weak mid-level wave will develop and bring
showers to the area overnight. Temperatures will remain steady
and/or rise a few degrees by morning. Low confidence on any thunder
for Tuesday night as some models are indicating elevated
instability.

Wednesday into Thursday... Moderate confidence.

Main weather producer will occur Wednesday into Thursday. Still some
issues on the timing of the cold frontal passage. The NAM appears to
be on the slower end of the guidance compared to the rest of the
solutions. Will need to watch if this slow down will continue as
some of the ensemble members are also hinting at this as well.

Temperatures will be well above normal on Wednesday and thus went
above guidance by several degrees. If full mixing occurred some
locations would be in the mid-70s. However lots of low and mid-level
moisture due to clouds so have gone down the middle for temperatures
with highs nearing 70F.

Overall, southern New England will remain in the warm sector
starting Wednesday as upper level trough approaches from the west.
This low pressure system will drag a cold front across the region by
Thursday. There is the potential for a few waves to develop along
the front. A head of the system, stout southwesterly LLJ near 60-70
kts will develop. This southwest flow will tap into Gulf moisture,
pushing PWAT values 3 STD above normal for this time of year.
Moisture flux will be on the increase as the frontal system
approaches so anticipate a period of moderate to perhaps heavy rain
on sometime Wednesday into early Thursday.

There is a risk for thunderstorms on Wednesday into Wednesday night
as lapse rates will steepen to 7 C/KM as well as LI dropping below
0. Models are even producing some surface CAPE near the area and so
have upped the chances for thunderstorms. Can`t rule out a few
strong storms as 0-6 km shear values will be close to 40-50 kts.
While the entire period don`t be wet, as dry air intrudes in the mid-
levels at times, appears that a good slug of rain can fall
especially within any thunderstorms. Main threat for these storms
will be heavy rain and strong gusty winds.

The cold front will sweep through during the first half of the day
on Thursday resulting in temperatures falling. Looks like another
scenario of high temps occurring at midnight. There is still some
timing issues on FROPA but appears that gusty winds will follow
suite as model sounding indicating good mixing behind the front.

Friday and beyond... Moderate confidence.

As the cold front passes through, northwest winds take a hold of the
region. Models continue to indicate the potential for a clipper
system on Friday/Saturday. This will bring reinforcing cold air to
the region allowing temperatures to fall back towards seasonable.
The GFS is a bit more robust then other guidance with the clipper so
leaned towards an ensemble approach. Good mixing and cold air over
the ocean may result in ocean effect snow showers over the weekend
before another clipper system comes through towards the end of the
weekend.

&&

.AVIATION /12Z 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/...

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.

Friday...Moderate confidence. Mainly VFR, with MVFR possible
toward the south coast in -SHSN.

&&

.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, with
the better chance for 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 8 PM EST this evening for
     ANZ231>235-237-251.
     Small Craft Advisory until 6 PM EST this evening for ANZ230-
     236.
     Small Craft Advisory until midnight EST tonight for ANZ250-254.
     Small Craft Advisory until 8 PM EST this evening for ANZ255-
     256.

&&

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



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