fxus61 kbox 222042 

Area forecast discussion 
National Weather Service Boston/Norton Massachusetts 
342 PM EST Tue Jan 22 2019 

low pressure lifting across the Great Lakes into Quebec will 
result in considerably milder temperatures Wednesday. The risk 
for showers will increase later Wednesday into Wednesday night. 
Heavy rainfall and possible flooding, strong coastal winds and 
unseasonably mild temperatures expected on Thursday ahead of a 
cold front. Mainly dry and more seasonable temperatures Friday 
then turning colder Saturday. Snow showers are possible Sunday 
then another frontal system may impact the region Tuesday. 


Near term /until 6 am Wednesday morning/... 

340 PM update... 

High pressure will continue to move off the mid Atlantic coast 
tonight. The pressure gradient will be quite weak, so light 
winds and snow cover would result in a good night of radiational 
cooling. The issue is model cross sections indicate a fair 
amount of mid/high level cloudiness overspreading the region. 
Therefore...a rather tricky forecast in regards to overnight low 
temps. Given the uncertainty...have low temps falling well down 
into the teens in many locations with some single digits across 
western Massachusetts. 


Short term /6 am Wednesday morning through Wednesday night/... 

Intensifying low pressure will be lifting towards the Great 
Lakes as high pressure continues to move east of the mid 
Atlantic states. This will result in an abundance of mid level 
cloudiness and significantly milder temperatures. Despite a lot 
of clouds, expect high temperatures to top out in the lower to 
middle 40s in most locations with some upper 30s in the highest 
terrain. A developing strong southwest low level jet should also 
result in 20 to 30 mph wind gusts by Wed afternoon, perhaps up 
to 35 mph along the southeast New England coast. 

Dry weather should prevail through early afternoon. The 
strengthening low level jet will increase the forcing for 
ascent...so some light rain showers may develop by mid-late 
afternoon across the interior. It may be just cold enough to 
support a bit of light sleet/freezing rain at the onset across 
the interior high terrain. Greatest risk the east slopes of the 
Berks and northern Worcester Hills. Confidence not high enough 
to issue an advisory at this time...but will highlight the 
potential in a Special Weather Statement. It is one of those 
cases, where there could be some icing with temperature a few 
degrees above freezing given the very cold ground from the past 
two days. 

Wednesday night... 

The low level jet/pwat axis will continue to increase across 
southern New England Wednesday night. This a result of low pressure 
lifting northeast from the Great Lakes into Quebec. Therefore...the 
forcing for ascent will increase and expect rain to increase in 
areal coverage/intensity from west to east, particularly after 
midnight. In addition...also expect areas of fog to develop as 
anomalously high dewpoint air advects in over the snowpack. 

Temperatures should rise overnight and probably be 50+ degrees 
across portions of Rhode Island/southeast Massachusetts by daybreak Thu. Even across most of 
the interior, there is not any mechanism to hold the cold air in 
place so expect temps may be at or above 40 by daybreak. The strong 
low level jet should also result in southwest wind gusts of 30 to 40 
mph across the cape/islands by daybreak. 


Long term /Thursday through Tuesday/... 

* heavy rainfall/possible flooding Thu and strong winds southeast new eng 
* mainly dry and turning colder Fri into Sat 
* snow showers possible Sunday 
* another round of snow/rain showers possible next Tue 


Heavy rain: 
strong heavy rainfall and wind signal for Thu. Approaching mid level 
shortwave and sharp frontal boundary with anomalous low level jet 80- 
90 kts advecting high pwats into southern New England. Precipitable water anomalies are 3-4 South Dakota 
above normal with wind anomalies +4sd across southeast new eng. This will 
result in a period of heavy rain, which will be focused along and 
just ahead of the frontal boundary within the low level jet axis. 
Given strong forcing and some elevated instability, cant rule out 
isolated T-storms which may organize into a fine line of convection 
along the front. Additional rainfall on Thu 0.75-1.50" with locally 
2+" possible across Rhode Island and southeast Massachusetts especially with any convection. 
This rainfall combined with Wed night's rain will likely lead to 
areas of urban and poor drainage flooding and flood watches may be 
needed for portions of southern New England. In additions, some river flooding is 
possible across portions of Rhode Island and southeast Massachusetts. 

Strong winds: 
80-90 kt low level jet moves across southeast new eng and especially 
cape/islands around midday into early afternoon. Soundings show an 
inverted profile, but temps may soar well into the 50s across 
portions of Rhode Island and southeast Massachusetts which will weaken inversion and enhance 
mixing potential, especially with any convective elements. 
Fairly high confidence that at least wind advisories for 50 mph 
gusts will be needed for southeast new eng with a lower risk for high wind 
warnings. If fine line does develop, high wind risk will 
significantly increase with strongest winds focused along the fine 

Tides/coastal flooding: 
astronomical tides are elevated Tue, which is cause for concern 
along the South Coast, but strongest winds and surge expected to 
occur after the Thu morning high tides which will minimize risk. 

Friday into Sunday... 

Turning colder as piece of polar vortex drops south to Hudson Bay 
with series of shortwaves reinforcing gt lakes to new eng trough. 
Mainly seasonable temps Fri and sun with coldest day on Sat with 
intrusion of modified Arctic air. Dry weather Fri/Sat, then 
increasing risk for snow showers sun as warm advection and onshore 
easterly flow develops. 

Monday into Tuesday... 

High uncertainty. Additional shortwave energy rotates around the 
vortex to the north but timing, amplitude and location uncertain. 
May be dealing with an inverted trough sometime Monday/Mon night but 
location uncertain, then a possible clipper tracking to the north 
Tue with secondary development to the south. Something to watch. 


Aviation /21z 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/... 

Tonight...high confidence. VFR despite an increase in some 
mid/high level cloudiness. A light south-southwest will develop. 

Wednesday...moderate to high confidence. VFR conditions through 
early afternoon but with plenty of mid level cloudiness. Some 
MVFR conditions may develop across western Massachusetts/northern CT 
by late afternoon/early evening. Scattered light rain showers 
are also expected to develop by late afternoon/early evening 
across the interior, which may begin as a brief period of light 
sleet/freezing rain in a few locations. Greatest risk for that 
will be along the east slopes of the Berkshires. SW wind gusts 
of 20 to 30 mph develop during the afternoon, perhaps up to 35 
mph across the southeast New England coast. 

Wednesday night...moderate to high confidence. Widespread low 
end MVFR to IFR conditions develop from west to east as the 
night progresses. Rain along with areas of fog will also become 
more widespread from west to east. Southwest wind gusts of 25 to 
35 knots expected across the southeast New England coast. 
Lastly...low level wind shear will become a concern across much of the region by 
daybreak Thursday. 

Kbos terminal...high confidence in taf. 

Kbdl terminal...high confidence in taf 

Outlook /Thursday through Sunday/... 

Thursday: mainly MVFR, with areas IFR possible. Strong winds 
with gusts to 45 kt southeast new eng. Rain. 

Thursday night through saturday: VFR. Breezy. 

Saturday night: VFR. 

Sunday: MVFR/IFR conditions possible. Breezy. Chance shsn. 


forecaster confidence levels... 

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

Short term /through Wednesday night/... 

Tonight...high confidence. High pressure sliding off the mid 
Atlantic coast will result in winds/seas continuing to diminish. 
Will need to small craft headlines for a time this evening for left 
over seas across the outer-waters, but these should diminish by mid 
to late evening. 

Wednesday...moderate to high confidence. Increasing low level jet 
should result in southwest wind gusts of 25 to 35 knots across the 
waters during the day Wed. Strongest of those winds look to be 
across our northern waters, where a gale watch GOES into effect 
during the afternoon. 

Wednesday night...moderate confidence. Strong southwest low level 
jet will be fighting a growing inversion over the waters. 
Nonetheless...the low level jet is strong enough to support 30 to 35 
knot wind gusts. It is always uncertain how much of that mixes down 
in these cases, given its magnitude certainly Worth a watch 
especially approaching 12z. The long southwest fetch should also 
build seas to between 6 and 12 feet across our open waters. Areas 
of fog may also develop too, given the high dewpoint air 
overspreading the colder ocean. 

Outlook /Thursday through Sunday/... 

Thursday: moderate risk for gale force winds with gusts up to 
45 kt. Rough seas up to 17 ft. Rain, isolated thunderstorms. 
Local visibility 1 nm or less. 

Thursday night: moderate risk for Small Craft Advisory winds 
with gusts up to 30 kt. Rough seas up to 14 ft. Slight chance 
of rain showers. 

Friday: moderate risk for Small Craft Advisory winds with local 
gusts up to 30 kt. Rough seas up to 11 ft. 

Friday night: low risk for Small Craft Advisory winds with 
gusts up to 25 kt. Rough seas up to 9 ft. 

Saturday: winds less than 25 kt. Local rough seas. 

Saturday night: winds less than 25 kt. Seas up to 5 ft. Local 
visibility 1 to 3 nm. 

Sunday: low risk for Small Craft Advisory winds with gusts up 
to 25 kt. Seas up to 5 ft. Chance of rain showers, chance of 
snow showers. Visibility 1 to 3 nm. 


Box watches/warnings/advisories... 
Rhode Island...none. 
Marine...gale watch from late Wednesday night through Thursday 
afternoon for anz231>237-251-254>256. 
Gale watch from Thursday morning through Thursday afternoon 
for anz230. 
Gale watch from Wednesday afternoon through Thursday afternoon 
for anz250. 
Small Craft Advisory until 7 PM EST this evening for anz250- 
Small Craft Advisory until 10 PM EST this evening for anz254. 



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