Lexington Weather

Lexington, Massachusetts, USA

40°F
3/30/2020 9:20am 
  • Lexington Conditions: Mist, Overcast
  • Temperature: 39.9°F / 4.4°CWarmer 0.5°F than last hour.
  • Dew Point: 39.2°FIncreased 0.5°Fsince last hour.
  • Relative Humidity: 97
  • Wind: Wind from NNE NNE 4 mph, 10-min avg: 3 mph, gust: 5 mph
  • Barometer: 29.97 in Steady
  • Visibility: 2 miles
  • Rain Today: 0.02 in
  •   

Area Forecast Discussion
for Boston, MA

        
000
FXUS61 KBOX 301122
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
722 AM EDT Mon Mar 30 2020

.SYNOPSIS...

Another cool, wet late March day across southern New England. An
inverted trough will bring rain showers late this morning into
the afternoon. Rain showers will gradually change over to rain
and snow or all snow late this afternoon and tonight. Could see
up to an inch of snow accumulation across the higher elevations.
Precipitation tapers off tonight. Cloud cover gradually
diminishing on Tuesday. An ocean storm will result in rather 
cool temperatures continuing right through Friday especially 
across eastern Massachusetts. While most of Wednesday should be 
dry, a period of showers are likely sometime Thursday into 
Friday especially across eastern New England. We expect 
temperatures to moderate a bit by next weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...

7 AM Update...

Decreased precipitation chances across southern New England this
morning and added drizzle. This is a result of the lingering low
level stratus in combination with the lift associated with the
cutoff and easterly flow advecting air in off the ocean. Best
shot for any shower activity today will be during the afternoon
heading into the evening. The rest of the forecast remains on
track.

Previous discussion...

Highlights...

* Cool, wet southern New England day as rain showers develop late 
  this morning and afternoon. The higher elevations will see snow 
  begin to mix in late in the afternoon.

* Potential for isolated thunderstorms across the eastern slopes of 
  the Berkshires and the CT River River Valley this afternoon. Best 
  shot in these locations for the sun to break out for a bit.

A cutoff low will rotate across the eastern Great Lakes and far 
southeastern Ontario today. There are two areas of low pressure to 
keep an eye on. The first is the low in place where the cutoff is 
located and the second is lifting east of Cape Cod and the Islands. 
This will keep the majority of the region cloudy today under stratus 
with rain showers spreading in late this morning and this afternoon. 
Best shot for any sunshine is across western MA and the CT River 
Valley, but this will be short lived.

Expect dry weather for part of this morning as the secondary low 
lifts offshore and the cutoff/primary low slide into the eastern 
Great Lakes. If the sunshine can break out for a bit there may be 
enough instability that develops in combination with the lift of the 
cutoff that a few thunderstorms develop. This is hinted at by the 
HRRR and NAM guidance across western MA and parts of CT with up to 
100 J/kg of MUCAPE. Have held off from including in the latest 
forecast, but will be something to keep an eye on. 

The combination of the inverted trough, cutoff and diurnal heating 
will result in scattered shower activity developing across the 
region beginning late this morning. Good agreement amongst 
deterministic and ensemble guidance. Will be cool once again due to 
easterly/northeasterly flow at 925 hPa. As much colder air advects 
in during the afternoon, 0 to -4 degree Celsius air, will see rain 
showers begin changing over to snow across the higher elevations. 

With the low level stratus in place, expecting fairly similar highs 
today to Sunday. Knocked temperatures down toward the 5th percentile 
of guidance across much of the interior. Some uncertainty on 
temperatures across the CT River Valley into western MA where the 
sun may break out. Kept temperatures toward the 50th percentile over 
much of CT River Valley, but may need to be higher if sunshine lasts 
longer than currently anticipated. This yields readings in the upper 
30s across the higher elevations and 40s inland. The CT River Valley 
will see readings range from the mid 40s to the low 50s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...

Highlights

* Any rain showers changing over to rain/snow or all snow as 
  precipitation tapers off tonight. Could see up to an inch of snow 
  accumulation across the higher elevations. Rain will continue 
  across southeast MA, including Cape Cod and the Islands.

* Rain ending across Cape Cod and the Islands early on Tuesday. The 
  rest of southern New England will see decreasing cloud cover and 
  sunshine breaking out during the afternoon. Near normal 
  temperatures expected. 
  
The cutoff low will rotate through southern New England tonight and 
offshore on Tuesday. The primary low will dissipate while the 
secondary low lifts further offshore. The secondary lows inverted 
trough will rotate from southern New England to south of the region 
by Tuesday morning/afternoon. This will result in precipitation 
gradually tapering off across much of southern New England tonight, 
but may transition over to all snow before precipitation ends. Could 
see up to an inch of snow accumulation across the higher elevations. 
Interior areas across MA with the exception of the Boston Metro and 
southeast MA could see light snow accumulate on grassy surfaces.  

Tonight...

Precipitation transitioning from rain to rain/snow or all snow as 
precipitation tapers off. This is due to an inverted trough sliding 
through and -3 to -6 degree Celsius 925 hPa air advecting in. Good 
agreement amongst deterministic guidance. Utilized a blend of the 
GFS and HREF for precipitation timing. Expect northeasterly winds 
and it may be gusty at times along the coast due to the tight 
pressure gradient. Low temperatures range from the upper 20s to the 
mid 30s. 

Tuesday...

Any rain showers coming to an end across Cape Cod and the Islands 
during the morning. Will see decreasing cloud cover as drier air 
advects in due to northerly flow. May see the sunshine break out 
during the afternoon, but may be too optimistic given the proximity 
to the cutoff low nearby. If there are more clouds in place then 
current highs will be too warm. Right now expect temperatures in the 
40s, which is normal for this time of year. Still may be breezy 
across Cape Cod and the Islands throughout the day out of the 
north/north northeast.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...

Highlights... 

* Cool temperatures continue Wed through Fri particularly across 
  eastern MA 

* A period of showers likely Thu into Fri esp across eastern MA

* Temperatures moderate a bit by next weekend

Details....

Wednesday through Friday...

A classic upstream blocking pattern /-NAO/ will persist Wednesday 
through Friday. Vigorous northern stream energy across the northeast 
will allow surface low pressure to intensify off the Carolina coast 
Wed and slowly move east Thu into Fri. While guidance agrees that 
this ocean storm will remain well east of our region, the upstream 
blocking pattern keeps it meandering over ocean through Friday.

Despite the ocean storm being well to our east, potent closed upper 
level energy over New England would set up an inverted trough. 
While most of Wednesday will be dry, the inverted trough will likely 
bring a period of showers Thursday into Friday, especially across 
eastern MA. Low risk that a few wet snow flakes are mixed in 
briefly, but boundary layer looks mild so expecting mainly rain 
showers.

The ocean storm combined with upstream block will keep temperatures 
rather cool Wed/Thu and Fri. High temperatures should generally be 
in the 40s to the lower 50s. Best chance of breaking 50 will be in 
the CT River Valley with the coolest readings expected across 
eastern MA. 

Next Weekend...

The ocean storm should finally lose its grip over our region by next 
weekend. This should allow height fields to rise resulting in temps 
moderating a bit, but nothing too warm. High temps should recover 
into the 50s at least away from the immediate coast and perhaps 
approaching 60 by Sun. Dry weather looks to dominate next weekend, 
but a weak front may bring a few showers sometime on Sun but not 
expecting a washout at this point.

&&

.AVIATION /11Z MONDAY THROUGH FRIDAY/...

Forecaster Confidence Levels...

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

12Z TAF Update...

Monday...High confidence in trends. Moderate confidence in 
timing.

MVFR to IFR conditions expected today as low level stratus
lingers with continued NE winds. Expect it to remain shower
free this morning, but drizzle is expected due to the lift from
the cutoff from the west and ocean moisture advecting in.
Expecting LIFR conditions to persist at ORH through the forecast
per RAP/NAM/GLAMP and MOS guidance. Will have increasing 
chances of showers due to the combination of day time heating 
along with the cutoff low rotating in and interacting with an 
inverted trough from the secondary low. Still not out of the 
question that there are a few thunderstorms across far western 
areas, but confidence too low to include in the forecast at this
point in time. 

Colder air advects in this afternoon and into the evening. This
will change over precipitation to snow across the higher 
elevations. Expect visibility reductions in areas of heavier 
precipitation. Gusty winds expected along coastal terminals.

Monday Night...Moderate confidence

Precipitation tapering off as the inverted trough moves farther
offshore. Precipitation will linger across southeast MA, Cape 
Cod and the Islands as rain. Expecting some snowflakes that mix
in at BOS, BED, and BAF before precipitation comes to an end. 
Will see gradual improvement to high IFR or MVFR toward 
daybreak. Gusty northeast winds continue along coastal
terminals.

Tuesday...Moderate to high confidence

Gradual improvement to VFR as drier air filters in from the
north. May see skies scatter out during the afternoon. Light
north northeast winds. May still be a bit gusty across Cape Cod
and the Islands. 

KBOS Terminal...Moderate confidence in the TAF.

KBDL Terminal...Moderate to high confidence the TAF.

Outlook /Tuesday Night through Friday/... 

Tuesday Night through Wednesday: Mainly VFR, with local MVFR
possible. Breezy. 

Wednesday Night: Mainly VFR, with local MVFR possible. Breezy.
Slight chance SHRA.

Thursday: Mainly MVFR, with areas VFR possible. Breezy. Chance
SHRA.

Thursday Night: MVFR. Breezy. Chance SHRA.

Friday: Mainly MVFR, with local VFR possible. Windy with local
gusts up to 30 kt. Slight chance SHRA.

&&

.MARINE...
Northerly to northeasterly winds continue throughout the day. Speeds 
gradually increasing this afternoon into tonight as a secondary low 
deepens offshore. Expect rain showers to spread in from north to 
south as an inverted trough slides in. Will see some visibility 
reduction due to showers and fog. Rain continues tonight into early 
Tuesday as the trough gradually lifts out.

Wind speeds and gusts will gradually diminish on Tuesday as the low 
lifts further offshore. Seas will remain heightened through the day. 
Confident enough at this point in time to expand and extend Small 
Craft Advisories through Tuesday.

Outlook /Tuesday Night through Friday/...

Tuesday Night: Winds less than 25 kt. Areas of rough seas.
Slight chance of rain showers. 

Wednesday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Slight chance of rain
showers. 

Wednesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 25 kt. Rough seas up to 10 ft. Chance of rain
showers. 

Thursday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. Chance of rain showers.

Thursday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Areas of rough seas. Rain showers
likely. 

Friday: Moderate risk for Small Craft Advisory winds with local
gusts up to 30 kt. Rough seas up to 13 ft. Slight chance of
rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory from 8 PM this evening to 8 PM EDT 
     Tuesday for ANZ232>234.
     Small Craft Advisory from 5 PM this afternoon to 5 PM EDT 
     Tuesday for ANZ230.
     Small Craft Advisory from 5 PM this afternoon to 8 PM EDT 
     Tuesday for ANZ231.
     Small Craft Advisory until 8 AM EDT this morning for ANZ235-
     237.
     Small Craft Advisory until 8 PM EDT Tuesday for ANZ250-251-
     254>256.

&&

$$
SYNOPSIS...Frank/BL
NEAR TERM...BL
SHORT TERM...BL
LONG TERM...Frank
AVIATION...BL
MARINE...Frank/BL
      

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