Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 231054
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
654 AM EDT Thu Mar 23 2017

.SYNOPSIS...
Blustery and very cold conditions will moderate some today.
High pressure will move off the eastern seaboard Friday,
bringing windy and milder conditions. Unsettled weather this
weekend, with potential for a variety of precipitation types.

&&

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

Departing upper level trough and approaching ridge will result
in tight pressure gradient. 925 mb jet near 30 kts will mix down
this morning, but begin to relax as surface high pressure moves
overhead during the afternoon hours. Plenty of sunshine today
will help warm temperatures into the 30s with a low prob of a
site or two hitting 40F.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
Tonight...

High pressure will move off the Mid Atlantic coast. Expecting
winds to become light and variable for a time, before becoming
southwest late tonight. Not ideal radiational cooling
conditions, as mid and high level clouds should arrive late
this evening, and especially after midnight.

Friday...

High pressure continues to move offshore during the day. A
front is likely to stall just to our north Friday. A weak mid
level shortwave passing by will assist any overrunning to produce
light precipitation during the morning hours. Timing will be
everything. There is a window for some light snow early Friday
morning. Once temperatures start to rise after daybreak, snow
will transition to rain. There could also be a brief period of
sleet or freezing rain during this transition. Have high
confidence in the overall trend, but only moderate confidence in
the precipitation types. This will need to be monitored closely
over the next 24 hours.

Strong southwest low level jet will drive the overrunning
process, but also provide the momentum for gusty winds,
especially during the afternoon when mixing is greatest. It
still appears the greatest risk for gusts over 30 mph to be
along the Boston-Providence corridor and southeast from there.

While max temperatures should make a 5-10 degree rise from
today, they should still be slightly below normal.

&&

.LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/...
Highlights...

* Above average temps on Saturday with a few showers
* Low confidence next Sun-Tues with unsettled weather possible at
  times with some rain, ice and/or snow possible
* Moderating temperatures by mid-next week

Pattern Overview...

00z models and ensembles are in agreement with the general synoptic
pattern for the long term. Uncertainty increases in the extended do
to mesoscale and thermal issues. Split flow aloft with closed low
over the southern Plains and northern stream across southern Canada.
The initial closed 500 mb will slowly move into the Midwest over the
weekend. This low deamplifies into an open wave as it comes towards
the Northeast early next week. Due to the confluent flow aloft, high
pressure persists over northern New England keeping surface
temperatures cool, resulting in mixed precip at times for the
weekend into early next week. The models have slowed again compared
to 22.00z guidance but are similar in timing. Another open wave
moves through the flow during the mid-week with the GFS more
amplified versus the progressive EC. Still a lot of uncertainty with
this timeframe.

Details...

Friday night into Saturday...Moderate confidence.

A bit tricky forecast is in store for this timeframe. Used a non-
diurnal trend for the overnight hours thanks to increasing WAA. 850
mb temps Saturday morning will be close to 8C but drop through the
day as cold front begins to slide southward. Surface temperatures
will reach into the mid 50s, cannot rule out a few 60s if the mid-
level ridge continues to build and slows the timing of the front.
Along the front, there could be a few rain showers but not expecting
widespread rainfall as heights continue to build overhead.

Saturday night into Sunday...Moderate confidence.

Cold front will pass through southern New England dropping surface
temps below freezing. The timing of the cold air drainage from the
high pressure over northern New England will determine if precip
type remains all rain, or if snow and/or mixed precip develops. Mid-
level ridging could keep a warm layer around 850 mb which would aid
in the mixed p-type. This is something to watch in the coming days.

For Sunday, cold front will stall somewhere between southern New
England and the Mid-Atlantic as high pressure begins to move
southeast into the Gulf of Maine. Depending on how close the high
pressure gets, we could see a dry Sunday or a few showers. One thing
to keep an eye on is the easterly flow, which could keep the low
level moist resulting in drizzle. Still a lot of uncertainty with
this time frame.

Sunday night Monday into Wednesday...Low confidence.

While guidance is in agreement synoptically, still a lot of details
to work out for this portion of the forecast. Biggest uncertainties
will be the placement of the upper level low and how quickly it will
diffuse early next week.

Right now, the stalled front looks to return back north as a warm
front late Sunday into Monday, as surface low pressure moves into
the Great Lakes. Although warmer air aloft should move easily back
into the region, the low-level cold air may be a little tougher to
dislodge this time due to the nearby surface high pressure. Believe
this is the timeframe where we will see the heaviest precip due to
passage of the open wave. Another open wave right behind this one
will push through the flow developing around shot at precip on
Tuesday.

As mentioned before, still a lot of uncertainty as to the thermal
profiles. Continue to believe that there could be a period where the
region could see a mixed bag of precip with the highest confidence
Sunday night into Monday and another shot Monday night into Tuesday
due to surface temps falling overnight.  Still a lot of uncertainty
with this timeframe as thermal profiles will change. Will continue
the mentioning of snow, sleet, ice and/or rain for the forecast
until thermals come better in alignment.

Lastly, weak ridging inbetween waves may allow for temps to moderate
back to seasonable during the day light hours Monday and Tuesday.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels...

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

Short Term /through Friday/...

Today and Tonight...High confidence VFR. NW winds with gusts up
to 25 kt, becoming light and variable for a time tonight. Winds
become light south to southwest late tonight.

Friday...Moderate confidence. Mainly VFR. Patchy MVFR
CIGS/VSBYS in -SN, changing over to -RA by around midday. May
see some sleet or freezing rain early Fri across western
terminals. SW winds gusting up to 25-30 kt, highest along the
coast and higher terrain.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Friday Night through Monday/...

Saturday into Sunday...Moderate confidence.  A period or two of
showers along with some MVFR cigs are possible at times as cold
front sags southward over the region. Could see a period of mixed
precip overnight.

Sunday into Monday...Low confidence. Showery weather to start with
possible MVFR cigs. Precip chances increase overnight into Monday
which could result in mixed precip.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Friday/...

Today...High confidence. Still gusty NW winds in the morning
with gusts 25-30 kt diminishing this afternoon. Freezing spray
will subside this afternoon. Rough seas over outer waters
gradually subside, too.

Tonight...High confidence. Diminishing NW winds becoming light
SW overnight. Seas subsiding below 5 ft over outer waters.

Friday...Moderate confidence. Southwest winds increase,
especially during the afternoon. Wind gusts up to 30 kt
possible. Small Craft Advisories likely. Low chance for gale
force gusts on the eastern outer waters during the afternoon and
evening prior to frontal passage. Visibility restrictions
possible in patchy light rain.

Outlook /Friday Night through Monday/...

Friday night into Saturday...High confidence. Increased pressure
gradient with approaching systems may result in gales across the
eastern waters. Cold frontal passage on Saturday may bring some
showery weather for the waters.

Sunday...Moderate confidence. Cold front will be south of the waters
as surface high pressure moves northeast of the region. Conditions
should remain below SCA but if the front gets closer than seas and
winds may be a bit stronger.

Monday...Low confidence. Approaching upper level system and passing
warm front will increase precip as well as wind and seas of the
waters. SCA may be needed.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 10 AM EDT this morning for ANZ230-
     232>237.
     Freezing Spray Advisory until 10 AM EDT this morning for
     ANZ231>235-250-251-254>256.
     Small Craft Advisory until 2 PM EDT this afternoon for ANZ231-
     251-256.
     Small Craft Advisory until midnight EDT tonight for ANZ250-254.
     Small Craft Advisory until 8 PM EDT this evening for ANZ255.

&&

$$
SYNOPSIS...Belk/Dunten
NEAR TERM...Belk/Dunten
SHORT TERM...Belk
LONG TERM...Dunten
AVIATION...Belk/Dunten
MARINE...Belk/Dunten



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