Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 130301
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
1001 PM EST Thu Jan 12 2017

.SYNOPSIS...
A cold front moves through Southern New England tonight, followed by
a drying and cooling trend overnight. Arctic high pressure builds
into the Great Lakes Friday and then into New England Saturday. This
will support a return to colder than normal weather across the
region Friday night and Saturday. A reinforcing surge of cold dry
air arrives Sunday as High Pressure exits Quebec into Maine. A cold
start to the week Monday morning but a warming trend for the
remainder of next week along with showery weather from time to
time.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
10pm update...
MSAS/Sfc obs suggest that the cold front is right on the doorstep
of the Hudson valley, having just passed through ALB and holding
near the Catskills. Therefore, expecting it to arrive in W New
England by about 4Z and continue E, likely being offshore by about
09Z or so per current speed. Precip already ending and drier air
should arrive fairly quickly to fill the void from NW-SE as the
front moves through. High clouds will be the last to dissipate
toward early morning. Most of the forecast parameters are on track
this evening, so only minor adjustments in the trend are being
made.

Previous discussion...

Low pressure mid afternoon was moving off toward Newfoundland, and
swinging a cold front through the St Lawrence Valley and
Northern/Western New York. The upper flow will continue to move
this east and southeast this evening and tonight. Movement of the
front would extrapolate it to the Connecticut River Valley around
9 PM/02Z, Worcester/Central Hills 1030 PM/0330Z, and the BOS-PVD
corridor around midnight/05Z.

Expect wet weather in much of Southern New England through the
early night. Radar mosaics show a broad area of rain across NY
and NW Pennsylvania. This is moving ENE into New England. Within
this rain is a line of convection over western PA moving ENE
leading the front. Several lightning strikes along this line in
Western PA and Central Ohio. This line, if it holds together,
extrapolates to the CT Valley about 7 pm and to the coast by 9 pm.

Still strong winds overhead at 2000-3000 feet AGL, so we will
continue to be concerned with gusts 30-35 knots in any heavier
rain through the evening.

Once the cold front moves through... the rain will end, the winds
will shift from the west and eventually the northwest. Skies will
clear, mainly after midnight.

Temperatures should remain mild this evening, but then turn colder
after the cold front moves through. Temperatures upstream early
this morning were in the 30s and low 40s, which will be our
min temp forecast for us tonight.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
Friday... High confidence.

Northwest winds will bring cold advection to the region through
the day. Mixing is forecast to 925 mb. Temps in the mixed layer
at 12Z would support max sfc temps of 40s except mid to upper 30s
in western MA. Temps aloft at 18Z would support max sfc temps in
the upper 20s and 30s. So we expect max temps to occur during the
morning with falling temps much of the day. Cold advection mixing
will also bring wind gusts of 25 to 30 knots to the surface.

The airmass will be dry, but with some lingering moisture around
900 mb. That should be enough for a few diurnal clouds. Otherwise
a sunny day with the aforementioned wind and falling temps.

Friday night... High confidence.

High pressure builds over the region with clear skies and light
winds. Increasing high-level moisture suggests some increasing
cirrus late at night. For the most part it will be a good
radiational cooling night. With dew points in the single numbers,
plenty of room for min temps of 5F to 15F. We undercut guidance by
about 3 degrees.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
Updated 445 pm...

Highlights...

* Mainly dry but cold this holiday weekend
* Warning trend next week but showery weather at times
* Winter on spring break until the end of the month?

Saturday/Sunday/Monday...

Cold start to the weekend as 1040 mb arctic high pressure settles
over the region Sat. -12C air at 925 mb over the area combined with
subsidence inversion will preclude much if any adiabatic warming.
Only good news is that weak pressure gradient will support light
winds, thus no wind chills to speak of. Sided with the coldest
guidance given these factors which will limit highs Sat to the mid
and upper 20s.

As for late Sat into Sat night...all model guidance has confluent
flow over New England suppressing deep layer moisture to the south
coast and offshore with next system. 12z ECMWF is farthest south,
12z farthest north and GFS in between. FWIW new 18z has shifted
farther south. Perhaps more importantly both ensemble systems...12z
GEFS and 12z EPS have trended farther south too. Thus our new pops
reflect this trend with mainly a dry forecast Sat aftn and evening
with just a low risk of flurries or a period of light snow from
BID/MVY to ACK.

Another northern stream trough zips across southern Quebec into New
Brunswick Sunday with corresponding 1033 mb High advecting into
Maine. This will deliver a reinforcing surge of cold air into the
region for Sunday/Sunday night...then lingering into Monday.
However this will support dry weather both Sun and Mon. As for
temps, given radiational cooling potential both Sat ngt and Sun ngt
have sided with the colder MOS temps.

Tuesday thru Friday...

The Southeast/Subtropical Ridge builds up the eastern seaboard next
week. This shifts the storm track west of New England...supporting
warm sector airmasses to overspread southern New England. FWIW 12z
EPS has up to 50% of highs 50+ Wed/Thu and Fri. Interestingly a
blend of all guid supports highs near 50 each of these days. Thus
well above normal temps likely mid to late next week.  As for
precip, impossible to time individual waves but deterministic and
ensemble guidance supports multiple precip events next Tue thru Fri.
Given amplitude of southeast ridge and thermal profiles ptype looks
wet and not white.  In fact Euro ensembles (EPS) indicate warm
southeast ridge influencing our weather at least thru day-10 and
the ridge not eroding until late in the month!

&&

.AVIATION /03Z FRIDAY THROUGH TUESDAY/...
Forecaster Confidence Levels...

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

Short Term /through Friday Night/...

730 pm Update...

Not much change from 18z and 21z TAF updates. Showers will sweep
across the region thru about 03z with mainly VFR conditions.
Abrupt wind shift with the frontal passage after midnight with
winds going from SSW to WNW and gusty. Earlier discussion below.

===================================================================

Tonight... Moderate confidence.

Broad zone of light rain from Southern Vermont through NY and NW
PA. Movement along the line is toward the northeast, but with time
later this afternoon and evening it will slide southeast across
MA-RI-CT. Cloud bases ahead of this rain are VFR, but in the cloud
layer we note a lower cloud layer around 1500-2500 feet and
expect this to move through with the rain during the evening and
early night. In addition, strong winds continue around 2000 feet
AGL with speeds of 40-50 knots. This will continue to create low
level wind shear through early tonight.

A cold front trails the rain, and will sweep across MA-RI-CT
tonight after 10 pm. Winds will shift from the west behind the
front. Ceilings/vsbys will then improve to VFR for the remainder
of the night.

Friday-Friday night... High confidence.

High pressure builds over the region. The increasing air pressure
and movement of cold air into New England will cause brisk wind
and will draw stronger winds to the surface from 3000 feet AGL.
Expect NW wind with gusts 25 to 30 knots during the late morning
and afternoon.  Winds will diminish at night.

KBOS TAF...VFR with LLWS. Ceilings will lower to MVFR levels this
evening and early night as an area of rain moves through. Timing
of the end of the rain is approximately 11 PM but with low
confidence. A cold front follows, with wind shift and improvement
to VFR.

KBDL TAF...VFR. Ceilings will lower to MVFR levels late this
afternoon and evening as an area of rain moves through. Timing of
the end of the rain is approximately 10 PM, but with low
confidence. A cold front follows, with wind shift and improvement
to VFR.

Outlook /Saturday through Tuesday/...Moderate confidence.

Updated 445 pm...

Saturday/Sunday/Monday...VFR and light winds.

Tuesday and Wednesday...MVFR and/or IFR likely along with scattered
showers and patchy fog.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Friday Night/...

Tonight...

Southwest winds have had observed winds in the 20s and around 30
knots. Expect the gusty winds to continue through the evening as a
cold front approaches. This front will bring a period of reduced
vsbys in rain, although with the best chance on Massachusetts Bay
and Ipswich Bay and the outer waters to the east. The cold front
will move across during around midnight, at which point the winds
will shift from the west and northwest and diminish.

Seas of 5 to 10 feet the first part of the night on the exposed
waters, but these will subside overnight after the cold front and
wind shift move past. Small Craft Advisory continues.

Friday...

Northwest winds will have potential gusts to 30 knots through much
of the day. Lingering 5 to 7 foot seas, mainly on the outer waters
and also on RI Sound. Small Craft Advisory in effect on all
waters.

Friday night...

Winds and seas diminish Friday night as high pressure builds over
Southern New England and the waters. Small Craft Advisory coverage
will diminish through the night.

Outlook /Saturday through Tuesday/...Moderate confidence.

Updated 445 pm...

Saturday thru Monday...

Fairly light winds with high pres over or near the region. Dry
weather and good vsby.

Tue and Wed...

Low pres tracking west of New England will bring a return to SSW
winds to the coastal waters. Vsby limited at times in scattered
showers and patchy fog.

&&

.CLIMATE...
The following climate records have been tied or broken...

BOS 61 tied old record 61 set in 1975 and 1913.
ORH 57 broke old record 55 set in 1980.
PVD 60 broke old record 59 set in 1975.

Meanwhile...
BDL 56 at 2 pm...record is 57 set in 1913.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 2 AM EST Saturday for ANZ231>234-
     251.
     Small Craft Advisory from 10 AM to 7 PM EST Friday for ANZ230-
     236.
     Small Craft Advisory until 10 PM EST Friday for ANZ235-237.
     Small Craft Advisory until 5 AM EST Saturday for ANZ250-
     254>256.

&&

$$
SYNOPSIS...WTB/Nocera
NEAR TERM...WTB/Doody
SHORT TERM...WTB
LONG TERM...Nocera
AVIATION...WTB/Nocera
MARINE...WTB/Nocera
CLIMATE...



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