Area Forecast Discussion
Issued by NWS Boston, MA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS61 KBOX 212336
AFDBOX

Area Forecast Discussion
National Weather Service Taunton MA
736 PM EDT Tue Mar 21 2017

.SYNOPSIS...
An arctic cold front crosses the region early Wednesday
morning, followed by dry, windy conditions as well as very cold
temperatures into Thursday. Wind chills will drop to between 0
and 10 below zero Wednesday night into early Thursday morning.
High pressure will build west of New England on Thursday, then
push off the mid Atlantic coast Thursday night. Milder weather
returns Friday with the chance for a period of light
precipitation. A cold front crosses the region Saturday with a
period or two of rain, ice and/or snow possible into early next
week, but confidence is low.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...

715 PM Update...

Area of clouds across northern New England tending to dissipate
at its southern edge across S NH/VT, while another band of high
clouds crossing N PA/S central NY may reach across the region by
02Z-03Z as seen on latest IR satellite imagery.

Light/variable winds are starting to shift to W-NW across NW
Mass into S VT and the mid Hudson valley of NY as seen on 23Z
observations. Noting a weak high pres ridge that will cross the
region this evening. Arctic front should push across the region
between 08Z and 12Z Wed. NW winds will quickly increase not
long after frontal passage. Wind chill values will drop quickly
through the early morning hours, probably down to the single
digits and teens across the higher inland terrain by 09Z-10Z,
and in the 20s elsewhere by 12Z.

Forecast pretty much on track. Have updated near term forecast
to bring conditions current and incorporate trends into the
remainder of the overnight forecast.

Previous Discussion...

Departing shortwave to our north will allow skies to become
mostly clear early this evening. The result will be dry and
tranquil weather across southern New England for the majority of
the night.

An arctic cold front will sweep through the region toward
daybreak. The very cold air will just be entering our areas
towards 12z Wednesday...so expect temps to range form the middle
20s in northwest MA and lower to middle 30s across southeast MA
at that time. Not much moisture associated with the arctic
front...so expect mainly a dry passage other than perhaps a few
brief passing flurries generally along the east slopes of the
Berkshires.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH WEDNESDAY NIGHT/...
***Windy and very cold Wednesday with wind chills dropping to
between 0 and 10 below zero Wednesday night***

Wednesday...

An anomalously cold airmass for late March will invade the
region. 850T will drop to between -16C and -20C by mid to late
Wednesday afternoon. Plenty of strong March sunshine will be
fighting the strong cold advection into mid afternoon...so
expect temps through early afternoon to be in the 20s across the
interior to the lower 30s across southeast New England. The
strong cold advection will begin to win out by late afternoon
and by early evening temps should mainly be in the teens to
lower 20s. Wind chills will have dropped into the single digits
by early Wednesday evening...so quite a change from today`s mild
weather.

The other concern will be the strong winds that are expected.
Super adiabatic low level lapse rates combined with lots of late
March sunshine will probably allow winds to over achieve on
Wednesday. Northwest wind gusts of 35 to 45 mph are anticipated
with a few gusts up to 50 mph possible. Will hoist a wind
advisory for central and eastern MA as well as Rhode Island.
This may need to be expanded across our western zones, but will
let later shifts examine more closely.

Wednesday night...

Strong northwest wind gusts will continue to usher very cold
air into southern New England under mostly clear skies. Winds
should start to gradually subside by late evening, but it still
will be gusty well into the overnight hours. Low temps will
range from 5 to 15 above. This will result in wind chills of 0
to 10 below zero, which is quite impressive for late March
standards.

&&

.LONG TERM /THURSDAY THROUGH TUESDAY/...
Highlights...

* Cold and blustery Wednesday night and early Thursday, then
  winds diminish
* Mixed snow and rain showers to start Friday, then temps rise
  with mainly scattered rain showers
* Gusty SW winds late Friday, then cold front passes before
  stalling across the region Friday night
* Low confidence next Sat-Mon with unsettled weather possible at
  times with some rain, ice and/or snow possible

Details...

Thursday-Thursday night...High confidence.

Large high pressure will build SE out of NY state/PA during
Thursday, settling off the mid Atlantic coast by Thursday night.
After blustery and cold conditions during Thursday, with gusts
up to 20-25 kt inland, the winds will diminish before backing to
W-SW Thursday night as H5 ridging breaks down over the Great
Lakes and northern Plains states. Cutoff H5 low pres works E
across the southern stream, which will help to bring warm air
advection pattern eastward during Friday.

Good isentropic lift will push into western areas late Thu
night. With an approaching front out of central Canada, will
see some scattered snow showers develop toward daybreak across
the E slopes of the Berkshires into portions of the CT valley.

Core of cold air sits across the region Thu, so expect highs
only in the lower-mid 30s (running up to 15 degrees below
normal), with temps bottoming out in the upper teens and 20s
Thu night.

Friday-Friday night...Moderate confidence.

Snow showers will continue to spread across the region Fri
morning, then SW winds will quickly freshen. Noting a strong SW
low level jet (on order of 40-50 kt from H925 through H85) and
decent mixing mainly along the coast Fri afternoon. Will see
wind gusts increase to 25-30 kt by midday Fri, highest along the
S coast, Cape Cod and the islands. This will help temps rise
quickly to the 40s by midday, which will still run around 5
degrees below seasonal normals. So, any leftover snow will
quickly change to rain showers. May see a brief period of sleet
and/or freezing rain well inland, mainly across the higher
terrain in N central and NW Mass Fri morning, but even there it
will change over to rain by midday.

Will see cold front push SE out of central Canada during Fri
night, so will continue to see scattered showers across the
region. H5 ridging across the Great Lakes into the northern
Plains will continue to de-amplify, flattening out the northern
stream flow. So, the front looks to slow or even stall somewhere
either across or just S of the region during Fri night. Kept
chance POPs going through the night, but expect temps to remain
above freezing through the night, at least for now. Lower
confidence due to exact placement of the stalling front.

Saturday into Monday...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. Also the location
of the stalled front which will be the focus on where the precip
will be orientated as well as the thermal profiles.

Saturday afternoon...Temperatures will be in the upper 40s, with
the southern coast reaching into the low 50s. Widespread rain
showers are expected to continue through Saturday due to the
above freezing temperatures, with a change of precipitation late
that evening.

As temperatures continue to drop below freezing early Sunday
morning, rain will change over to snow as the arctic cold front
moves from north to south. Snow will creep down into Rhode Island
and Connecticut that morning. There is the possibility of snow
changing over to freezing rain or sleet depending on the thermal
profile as temperatures warm throughout the day Sunday. Afternoon
temperatures Sunday will struggle to reach into the 40s, with the
majority of the region remaining in the upper 30s. Despite
temperatures reaching above freezing Sunday, the surging cold
arctic air aloft will pose several problems for precip type
throughout the day.

Both the GFS and ECMWF suggest that mixed precipitation will
continue through Sunday across the region, and even into Monday
evening. The system will move offshore by 00z Tuesday with
possible lingering snow or rain showers.

With an approaching short wave, another round of mixed
precipitation is possible Tuesday afternoon. Sites at higher
elevations having the greatest chance of seeing freezing rain or
snow as temperatures drop below freezing. Most areas south of
the Mass Pike should remain above freezing overnight.

Below average temperatures are expected to prevail through next
week.

&&

.AVIATION /23Z TUESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels...

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

Short Term /through Wednesday Night/...

2330Z update...

Tonight...High confidence. VFR. May see a brief band of
CIGS around 3-4Kft in association with an arctic front toward
daybreak Wednesday.

Wednesday...High confidence. A few brief marginal MVFR cigs
possible into mid morning, but otherwise VFR. Main story will be
northwest wind gusts of 30 to 40 knots.

Wednesday night...High confidence. VFR with gradually
diminishing winds although it will remain gusty into the
overnight hours.

KBOS TAF...High confidence in TAF. Sea breeze comes to an end
early by this evening.

KBDL TAF...High confidence in TAF.

Outlook /Thursday through Sunday/...

Thursday-Thursday night...High confidence. VFR conditions. May
see local MVFR-IFR VSBYS in scattered -SHSN after 06Z Fri across
E slopes of the Berkshires.

Friday and Friday night...Low to moderate confidence. Mainly
MVFR in scattered -SHSN early Fri, changing over to -SHRA. May
see brief -PL/-FZRA across higher terrain Fri afternoon/evening.
VFR CIGS lower to areas of MVFR from W-E during the day,
continue into Fri night.

Saturday and Sunday...Moderate confidence. Periods of rain or
snow showers along with some MVFR cigs are possible at times.

&&

.MARINE...
Forecaster Confidence Levels...

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

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

Tonight...Winds and seas will generally be below small craft
advisory thresholds for most of the night. However...NW winds
should rapidly increase towards 12z Wednesday with gusts up to
30 knots behind an arctic front.

Wednesday and Wednesday night...Northwest wind gusts of 30 to
40 knots expected under very strong cold advection. Strongest of
those wind gusts will occur through Wed evening. Gale warnings
are posted for all our waters. In addition...the anomalously
cold airmass has prompted the issuance of freezing spray
advisories for many of our waters Wed night into mid morning
Thursday.

Outlook /Thursday through Sunday/...

Thursday...Moderate to high confidence. NW winds gusting to
25-30 kt, highest over the outer waters, diminishing below small
craft criteria Thu evening. Light freezing spray will continues
through midday, then ends as winds drop off. Seas up to 5-6 ft
on the outer waters.

Thursday night...High confidence. NW winds continue to diminish,
then back to SW after 06Z Fri. Seas subside be low 5 ft by around
05Z-06Z Fri.

Friday-Friday night...Moderate confidence. SW winds increase
quickly Fri morning, gusting up to 25-30 kt. Small crafts
likely. Low risk of minimal gale force winds for a time Fri
afternoon-evening on portions of the outer waters. Expect winds
to diminish Fri night as cold front passes and shift to W. Seas
up to 4-6 ft, highest over the southern outer waters Fri
afternoon/night.

Saturday...Low confidence. N-NE wind gusts up to 20 knots and
seas under 5 feet. Conditions may vary significantly depending
upon the timing of the frontal passage.

Sunday...Low confidence. E-NE winds 20 kt or less. Seas 4 ft or
less. Gusts to small craft levels possible.

&&

.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...None.
MA...Wind Advisory from 8 AM to 8 PM EDT Wednesday for MAZ004>007-
     012>024-026.
RI...Wind Advisory from 8 AM to 8 PM EDT Wednesday for RIZ001>008.
MARINE...Freezing Spray Advisory from 7 PM Wednesday to 9 AM EDT
     Thursday for ANZ231>235-250-251-254>256.
     Gale Warning from 8 AM Wednesday to midnight EDT Wednesday
     night for ANZ230>237.
     Gale Warning from 8 AM Wednesday to 2 AM EDT Thursday for
     ANZ250-251-254>256.

&&

$$
SYNOPSIS...Frank/EVT/Correia
NEAR TERM...Frank/EVT
SHORT TERM...Frank
LONG TERM...EVT/Correia
AVIATION...Frank/EVT/Correia
MARINE...Frank/EVT/Correia
CLIMATE...Staff



USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.