Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 221952
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
352 PM EDT Wed Mar 22 2017

.SYNOPSIS...
Blustery and very cold conditions will tonight will gradually
moderate Thursday with less wind. Becoming windy and milder
Friday. A cold front will move through Saturday then stall
south of New England into early next week which will the
potential for periods of rain and mixed precipitation.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
Cold and very dry airmass across SNE with dewpoints in the
single numbers below zero for much of the region. Gusty NW winds
will continue in strong cold advection pattern with near dry
adiabatic low level lapse rates promoting excellent momentum
transfer with mixing likely to the top of the PBL. Soundings
suggest peak of the wind will continue into early evening with
gusts to 40-50 mph then gradually diminishing. However, winds
will remain somewhat gusty through the night, especially along
the coast as strong pressure gradient remains.

Mid level trof axis moves east of New Eng this evening, as one
last shortwave rotates through the NW flow. Column is very dry
so mainly clear skies tonight and very cold. Used a blend of
MOS and model temps for lows tonight which yields 5 to 15
degrees across much of SNE. Wind chills single numbers above
and below zero.

&&

.SHORT TERM /6 AM THURSDAY MORNING THROUGH THURSDAY NIGHT/...
Thursday...

Still some gusty winds in the morning along the coast but trend
will be for diminishing wind in the afternoon as high pres
builds east into New Eng. Under sunny skies, temps will
moderate as low and mid level temps rise, with highs reaching
mid/upper 30s which is still well below normal.

Thursday night...

High pres shifts south of New Eng with developing SW flow warm
advection yielding increasing mid/high clouds. There should be a
window for good radiational cooling in the evening before
clouds thicken which will result in a cold night. Lows ranging
from mid/upper teens to mid 20s across the region with temps
stabilizing or slowly rising late.

&&

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

* Snow to rain showers on Friday as temps warm near average
* 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

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. Mid-level ridge axis will move
through the region on Friday as high pressure slides to the south.
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. The low comes
into confluent flow and weakens 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 compared to
21.00z guidance. However, the EC is a bit faster compared to the
GFS/GEFS mean in the forward progression of the upper trough for
early next week. Still a lot of uncertainty with this timeframe.

Details...

Thursday night...High confidence.

Mid-level ridge will build overhead Thursday night allowing for WAA
to develop. Temps will radiate out during the first half of the
night thanks to light winds and clear skies. Clouds will build into
the area during the later half limiting radiational cooling. While
overnight lows will fall, appears that they may hold steady during
the later half of the night within the strong WAA pattern.

Friday...Moderate confidence.

Surface high pressure shifts eastward resulting in warm/moist
advection in the mid-levels. Tighten pressure gradient will result
in gusty winds near 30 MPH. Ascent due to isentropic lift will
eventually saturate the column, resulting in periods of
precipitation during the day and into the night. A weak shortwave in
the mid-levels will help increase precipitation chances. P-type will
be dependent on timing of precip as well as mid-level warmth as
surface temps will start out below freezing especially across the
higher terrain. Model guidance and BUFKIT data shows warm nose
inching in at 800 and 850 mb with cooling at 925mb. This will help
support a transition from snow to sleet to eventually rain during
the day on Friday. Low confidence on if freezing rain will occur,
something to watching in the coming days.

Saturday...Moderate confidence.

A bit tricky forecast is in store for this timeframe. Used a non-
diurnal trend in the Friday night into Sat morning forecast thanks
to increasing WAA. 850 mb temps Saturday morning will be close to 8C
but drop through the day. Surface temperatures will reach into the
mid 50s, cannot rule out a few 60s if the mid-level ridge continues
to build. Surface cold front will push through the region during the
day. Could see a few rain showers but not expecting widespread
rainfall as heights continue to build overhead.

Sunday into Tuesday...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 over the weekend into early next week. Already have seen a
slower track and could see northern High pressure strengthen moreso
leaning towards a slower precip time on Sunday.

Right now, 00z guidance shows stalled boundary draped across
southern New England on Sunday with a few shortwaves moving through
the flow. High pressure building in from the north has the potential
to push the front farther southward on Sunday which could leave the
first half of it dry. Diffusing closed low will become an open wave
and track through southern New England early next week with another
wave right behind it. Believe timeframe where we will see the
heaviest precip is when the open wave approaches Sunday night into
Monday.

As mentioned before, still a lot of uncertainty as to the thermal
profiles. Looking at the latest EC, it has trended a warmer in the
mid-levels versus the GFS with both models indicating surface temps
near freezing. Believe that there could be a period where the region
could see a mixed bag of precip. 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.

&&

.AVIATION /19Z WEDNESDAY THROUGH MONDAY/...
Forecaster Confidence Levels...

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

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

VFR. NW gusts to 30-40 kt into early evening will gradually
diminish but still gusts to 25 kt overnight along the coast.
NW wind gusts to 20 kt Thu becoming light Thu night.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Friday through Monday/...

Friday...Moderate confidence. VFR to MVFR conditions in snow to
rain showers during the day. Cannot rule out the potential for
sleet across western terminals in the morning. Gusty southwest
winds near 30 kts are possible.

Saturday into Sunday...Low to moderate confidence. A period or
two of showers along with some MVFR cigs are possible at times.
Saturday night into Sunday has the better chance for wintry
precip.

&&

.MARINE...
Forecaster Confidence Levels...

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

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

Tonight...NW gales continue into the evening before gradually
diminishing from west to east. Freezing spray will also
continue. Seas building to 12-15 ft over outer waters east of
Cape Cod this evening before slowly subsiding.

Thursday...Still gusty NW winds in the morning with gusts 25-30
kt diminishing a bit in the afternoon. Freezing spray will
subside in the afternoon. Hazardous seas over outer waters but
gradually subsiding.

Thursday night...Diminishing NW winds becoming light SW
overnight. Seas subsiding below 5 ft over outer waters.

Outlook /Friday through Monday/...

Friday...Moderate confidence.  Southwest wind gusts of 20 to 30
knots may develop ahead of frontal passage.  Small craft headlines
may be required. Low chance for gales across the outer eastern
waters.

Saturday...Moderate confidence. Cold frontal passage Saturday will
help increase seas and winds. SCA may be needed.

Sunday...Low confidence. Cold front will be south of the waters as
surface high pressure moves northeast of the region.

&&

.CLIMATE...
Record lows for Wednesday, March 22:

Boston     (BOS)  8/1885
Hartford   (BDL) 12/1934
Providence (PVD) 15/1988
Worcester  (ORH)  8/1988

Record cold highs for Wednesday, March 22:

Boston     (BOS) 24/1885
Hartford   (BDL) 29/1960
Providence (PVD) 28/1914
Worcester  (ORH) 25/2002

Record lows for Thursday, March 23:

Boston     (BOS)  6/1934
Hartford   (BDL)  9/1934
Providence (PVD)  8/1934
Worcester  (ORH)  4/1934

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Wind Advisory until 6 PM EDT this evening for CTZ002>004.
MA...Wind Advisory until 8 PM EDT this evening for MAZ004>007-
     012>024-026.
     Wind Advisory until 6 PM EDT this evening for MAZ002-003-
     008>011.
RI...Wind Advisory until 8 PM EDT this evening for RIZ001>008.
MARINE...Freezing Spray Advisory from 7 PM this evening to 11 AM EDT
     Thursday for ANZ231>235-250-251-254>256.
     Gale Warning until 2 AM EDT Thursday for ANZ231-232-251-255-
     256.
     Gale Warning until midnight EDT tonight for ANZ230-233>235-237.
     Gale Warning until 10 PM EDT this evening for ANZ236.
     Gale Warning until 5 AM EDT Thursday for ANZ250-254.

&&

$$
SYNOPSIS...KJC
NEAR TERM...KJC
SHORT TERM...KJC
LONG TERM...Dunten
AVIATION...KJC/Dunten
MARINE...KJC/Dunten
CLIMATE...


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