Area Forecast Discussion
Issued by NWS Boston, MA

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000
FXUS61 KBOX 230254
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
1054 PM EDT Wed Mar 22 2017

.SYNOPSIS...
Blustery and very cold conditions will tonight will gradually
moderate Thursday with less wind. High pressure will move off
the eastern seaboard on Friday, bringing windy and milder
conditions. A cold front will push south across the region
Saturday, then stall south of New England early next week. Weak
low pressure waves forecast to push along this front, with the
potential for periods of rain and mixed precipitation.

&&

.NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
1054 PM Update...

Winds continue to slowly diminish late this evening. Clear and
dry, so mainly tweaked temperatures and winds to reflect
observed trends.

735 PM Update...

Winds have diminished over the last few hours, so have cancelled
the remaining wind advisory for RI/central and eastern Mass.
Will still see some gusts up to 30-40 mph through around
midnight, with the highest gusts along the immediate E coast of
Mass, Cape Cod and the islands.

Skies were mainly clear at 23Z, except for only a few mid level
clouds lingering near the coast. Temperatures have fallen
steadily through the day, down to the 20s across the region, but
feels much colder with the gusty winds.

Winds will continue to slowly diminish tonight as pressure
gradient slowly relaxes. Strong cold air advection will also
continue, with H85 temps dropping to -14C to -18C overnight.
Expect temps down to the teens across most areas, ranging to
20-25 on Cape Cod and the islands by around midnight.

Have updated near term forecast to bring conditions current.

Previous Discussion...

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...

* Light snow early Friday changes to rain as temps rise to the
  lower-mid 40s
* Mild temps on Saturday along with periods of light rain
* Low confidence Sunday-Tuesday with unsettled weather possible at
  times with some rain, sleet and/or snow possible
* Conditions may slowly improve during Wednesday, but low confidence
  continues

Overview...

12Z model suite and ensembles continue to signal general agreement
of a cold frontal passage during Saturday. Beyond this, a lot of
questions, first where this front stalls as it becomes parallel to
mid level northern stream steering flow. To complicate things, H5
cutoff low pressure over then central Mississippi valley late
Saturday is forecast to open up and move along into the northern
stream flow while large high pressure pushes across central and
eastern Canada keeping a cold air flow working southward.

Much will depend how far N the front stalls, and the timing of weak
low pressure waves that will move along this front. At this point,
looks like we will see periods of rain this weekend, with some
possible mixed precipitation during the nighttime hours as
temps fall close to or below freezing. Best chance for any
sleet/snow and/or freezing rain looks to occur main N of the
Mass Pike each night.

12Z models signaling the best shot for better organized precip with
be with the approaching open H5 wave late Mon into Tue. Models
showing general agreement on features, but exact timing and track
still very much in question. Could also see a better chance for
mixed precip Mon night further S with the established E-NE wind
flow, mainly for areas away from the coast. Lots of uncertainty
continues.

At this point, may see some improving conditions starting next
Wednesday, but remains a difficult call this far out.

Details...

Friday...Moderate confidence.

As large high pressure moves off the eastern seaboard Friday,
expect SW winds to bring milder temperatures across the region.
An approaching cold front will cause increasing pressure
gradient, along with SW low level jet up to 40-45 kt from H95
thru H9 moves across. While best LL mixing is limited to 925
hPa, could still see some gusts up to around 30 kt during Fri
afternoon, mainly from the Boston-Providence corridor SE to Cape
Cod and the islands.

Approaching cold front will bring the threat of light snow by
mid to late morning Friday, then will quickly mixing with sleet
and snow before changing to rain by early afternoon. With the
good SW wind flow in place, should see temps rise quickly. At
this point, freezing rain remains out of the forecast, but will
continue to monitor this aspect carefully. Temps should reach
the lower-mid 40s by late in the day, though a few spots across
the higher terrain may remain below 40 but likely above
freezing, at least at this point.

By Friday night, most of the precip should dissipate or remain
across northern New England, but still can not rule out the
threat for spotty light rain. Noting a non-diurnal temp trend
due to the milder air in place ahead of the approaching cold
front. Looks like front should push into the region after 05Z-
06Z. Current thinking suggests that temps should remain in the
35-40 degree range through the night.

Saturday-Saturday night...Moderate confidence.

Will see mild temps on Sat, actually close to seasonal normals
as warm air advection remains in place on W-SW winds. Looks like
the front should push off the S coast between mid morning to
midday on Saturday as winds start to shift to W-NW. Expect highs
in the mid- upper 40s along the N Mass border, ranging to the
mid 50s across N CT/RI/SE Mass, though would not be surprised to
see readings a few degrees milder before beginning to fall
during Sat afternoon. Short range models suggest that patchy
light rain may redevelop during the day and continue into Sat
night.

Colder air works in Sat night as winds become light northerly.
Weak low pres wave moves in, bringing another shot of light
precip. As the colder air filters in, looks like a wintry mix
could develop even as far S as the S coast after midnight. Lots
of uncertainty remains due to timing of the colder air and the
onset of precip, as well as how far south this will develop.
Will monitor this closely.

Sunday into Wednesday...Low confidence.

General forecast agreement continues during this timeframe, but
the big problem is the specific details for each day`s
forecast. Will need to see how each piece of the puzzle fits in,
such as the mid Mississippi upper low and how quickly it will
weaken and move NE in the northern stream flow, plus timing the
precip with each weak short wave. Another factor will be the
high over eastern Canada and how it will interact with these
lows as well as the intrusion of colder air affecting PTYPE
during each night and whether it will linger into the daytime
hours.

A lot to consider, especially with the thermal patterns each
day. At this point, could see mixed precip into Sunday morning,
then again Sunday night into Monday. Have kept rather general
mixed bag of precip each nighttime period for now, and possibly
into the morning both Sunday and Monday. However, this could all
change with the next forecast package.

&&

.AVIATION /03Z THURSDAY 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, mainly along the immediate E coastal
terminals, then will gradually diminish but still gusts to 25 kt
overnight. 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. Mainly VFR. Patchy MVFR
CIGS/VSBYS in -SN, changing over to -RA by around midday. May
see some sleet early Fri across western terminals. Light rain
ends from S-N Fri night, but may linger across E slopes of the
Berkshires. SW winds gusting up to 25-30 kt, highest along the
coast and higher terrain, lingering into Friday night across
Cape Cod and the islands before diminishing around midnight.
MVFR CIGS linger Fri night across higher terrain.

Saturday and Sunday...Low to moderate confidence. Periods of
light rain/showers through the weekend. May see mixed
sleet/freezing rain push across portions of the region Saturday
night into Sunday. Exact placement and timing in question.

Sunday night-Monday...Low confidence. Depending upon how far S
the colder air works in, could see areas of rain, sleet and
freezing rain Sun night into Mon morning which may linger most
of Mon across the higher terrain. Patchy MVFR CIGS/VSBYS mainly
at night/early morning hours.

&&

.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.

Began the process of converting Gale Warnings to Small Craft
Advisories. More such conversions expected overnight, with the
next set around midnight.

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.  SW wind gusts up to 25-30 kt,
shifting to W Fri night as cold front passes. Small crafts
likely. Low chance for gale force gusts on the eastern outer
waters Fri afternoon/evening prior to frontal passage.
Visibility restrictions possible in patchy light rain Fri into
Fri night.

Saturday...Moderate confidence. Leftover small crafts as W
winds gust to 25 kt early Sat, then should diminish. Light rain
redevelops as cold front pushes off the coast with some
visibility restrictions. May see mix of sleet and snow Sat night
as colder air works in on NE winds.

Sunday-Monday...Low confidence. Depending upon where the front
stalls, may see more periods of rain during each day, possibly
mixing with sleet and snow across the eastern waters Sun night.
E-NE winds gusting to 25-30 kt so small crafts may be needed
again.

&&

.CLIMATE...
Just sent out the latest CLI messages for our four long term
climate sites. Looks like the record mins and record cold max
temps will remain intact for today.

Record lows for today:

Boston     (BOS)  8/1885, forecast low of 20
Hartford   (BDL) 12/1934, forecast low of 19
Providence (PVD) 15/1988, forecast low of 20
Worcester  (ORH)  8/1988, forecast low of 14

Record cold highs for today:

Boston     (BOS) 24/1885, high was 43 set at 259 AM
Hartford   (BDL) 29/1960, high was 38 set at 251 AM
Providence (PVD) 28/1914, high was 42 set at 1207 AM
Worcester  (ORH) 25/2002, high was 36 set at 1234 AM

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...None.
MA...None.
RI...None.
MARINE...Freezing Spray Advisory until 11 AM EDT Thursday for
     ANZ231>235-250-251-254>256.
     Gale Warning until 2 AM EDT Thursday for ANZ231-232-251-255.
     Gale Warning until midnight EDT tonight for ANZ230-233-234.
     Small Craft Advisory until 6 AM EDT Thursday for ANZ236.
     Small Craft Advisory until 10 AM EDT Thursday for ANZ235-237.
     Gale Warning until 5 AM EDT Thursday for ANZ250-254.
     Small Craft Advisory until noon EDT Thursday for ANZ256.

&&

$$
SYNOPSIS...KJC/EVT
NEAR TERM...Belk/KJC/EVT
SHORT TERM...KJC
LONG TERM...EVT
AVIATION...KJC/EVT
MARINE...Belk/KJC/EVT
CLIMATE...Staff


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