Old Res Weather

Lexington, Massachusetts, USA

43°F

4/19/2024 6:35am

Lexington Conditions: Overcast
Temperature: 43.3°F / 6.3°C
Dew Point: 40.8°F
Relative Humidity: 91%
Wind: Calm, 10-min avg: Calm, gust: None
Barometer: 30.21 in Steady
Visibility: 10 miles
Rain Today: 0.00 in
UV Index: $VPuv None

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 182327
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
727 PM EDT Thu Apr 18 2024

.SYNOPSIS...
Cool with a few showers into the evening. A more seasonable day
on Friday, along with dry conditions during the daytime hours. 
A cold front brings another round of showers overnight into 
early Saturday morning. Dry for the rest of Saturday and all day
Sunday with breezy conditions both days. The dry stretch of 
weather continues as we head into early next week, with the next
chance for unsettled weather being Wednesday.

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
715 pm update...

area of light rain is across RI and eastern MA and trying to
move east, but it is running into a wall of very dry air. Expect
the precip to dissipate within the next 2-3 hours. Noted that
the latest hi-res models are all too quick with dissipation, so
updated hourly PoPs more on radar extrapolation, but it doesn't
substantially change the forecast. 

345 pm update...

Highlights: 

* Raw afternoon with areas of light rain, turning drier overnight, 
  but can not rule out a spot shower across eastern Massachusetts 
  and Rhode Island.

Southern New England stuck under a blanket of thick clouds while 
just to the north, people of Maine are enjoying lots of sunshine. A 
shortwave passing through continues to produce areas of light rain. 
Most of the day has been largely dry, thanks to drier air to the 
northeast. This light rain continues to move east this afternoon, 
ending early this evening. Overall a cool and raw rest of the 
afternoon for southern New England with temperatures in the 40s. 

Overnight, southern New England is between surface high pressure to 
the north over Nova Scotia and low pressure to the south over the 
outer waters. This set up will allows for on shore flow tonight. A 
few showers are possible, though do think much of tonight remains 
dry. A mid-level shortwave drops down out of northern New England 
and will help in producing scattered light rain mainly over the 
eastern half of the CWA. Though, with this afternoon, the high 
pressure to the north does provide a fair amount of dry air and that 
will limit the coverage. This is a slight change from the previous 
forecast, did add slight chance POPs for the overnight period for 
parts of eastern Massachusetts and Rhode Island. 

East/northeast winds, strongest at the south coast with gusts to 20 
MPH, while further north winds are fairly light and at times 
variable in direction. 

Night time lows are seasonable, upper 30s across the interior and 
low 40s by the coast.

&&

.SHORT TERM /6 AM FRIDAY MORNING THROUGH FRIDAY NIGHT/...
345 pm update...

Highlights: 

* Slight improvement for Friday with drier weather for the daylight 
  hours and near seasonable temperatures. 

* Unsettled overnight with another chance for light rain, 
  especially along the south coast near daybreak on Saturday. 

Some improvement weatherwise on Friday with surface high pressure 
expanding into southern New England, along with mid-level ridging. A 
warmer, more seasonable day with highs in the upper 50s and low 60s 
are on tap. Where temperatures may struggle are along the immediate 
coast as the winds are still coming off of the water. Areas of low 
clouds to start gives way to breaks of sunshine late morning into 
early afternoon, short-lived as mid and high clouds move in from 
west to east ahead of a cold front. Winds are more or less out of 
the southeast due to the flow from the surface high based in eastern 
Quebec and surface low well off to the south near Bermuda. The 
pressure gradient eases allowing for gusts less than 20 MPH at the 
coast. 

Increasing clouds from west to east during the second-half of the 
day ahead of an approaching front. A prefrontal trough could set off 
a few showers across western Massachusetts and northern Connecticut 
late afternoon, but do think the bulk of any perception will come 
with the frontal passage overnight, then kick off shore shortly 
after sunrise on Saturday. That said, do not anticipate a soaking 
rain, much of southern New England receives a few hundredths of an 
inch, and the immediate south coast, Cape, and Island receive around 
a quarter to a third of an inch. 

Wind shifts overnight from southeast to southwest, no strong gusts 
are expected. Overnight lows dip into the middle 40s.

&&

.LONG TERM /SATURDAY THROUGH THURSDAY/...
345 pm update...

Key Point:
* Fire weather concerns this weekend through Tuesday

Fairly high consistency amongst the 12z global guidance runs as
well with prior runs. So that results in overall higher than
average confidence. In general, most of us will consider the
weather for most of the period to be pretty nice. A weak front
will be moving offshore during the first part of Saturday, only
bringing a few light showers. Behind the front, a much drier
airmass will be spreading in. So that will result in clearing
skies. Have again blended in the warmer side of guidance for
temperatures and lower side of guidance for dewpoints. Forecast
soundings still show excellent mixing (5000-6000ft) developing 
in the afternoon along with westerly winds. Being still a "pre- 
greenup" phase of vegetation, that usually means temperatures 
overachieve and humidity levels go lower than most guidance 
thanks to the combo of downsloping and deep boundary layer 
mixing. We should see widespread mid 60s for highs, perhaps 
making a run at 70F in the CT River Valley. 

Sunday will be similar, though with 850mb temperatures slightly
cooler (down around -1C vs +1C on Saturday), daytime highs will
be a few degrees cooler, primarily either side of 60F. Again
deep boundary layer mixing (6000-7000ft) will act to bring down
some of the 25kt winds aloft along with dry air. Thus winds will
be gustier than on Saturday and lower dewpoints. The combo will
mean we will be flirting with some of the fire weather
thresholds (RH <30%, Frequent gusts >25mph, less than 1/4" of
rain in 3 days). 

Monday, high pressure will move overhead and maintain the dry
weather. Still a dry airmass and deep mixing, but winds will be
weaker, so will still need to monitor fire weather aspects, but
don't think it's as significant a concern. Tuesday will still be
dry, but with high pressure moving off the east coast, winds
will start to turn southerly. 

Guidance showing another weak front coming through Wednesday, so
stuck with NBM PoPs. Rainfall amounts again will be light. Dry
weather should return for Thursday.

&&

.AVIATION /23Z THURSDAY THROUGH TUESDAY/...
Forecast Confidence Levels:

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

00z TAF update...

Overall moderate confidence. 

Currently VFR across the region. The rain across RI and SE MA
created brief periods of MVFR visibility conditions, but as the
rain is dissipating and expected to be nothing more than a few
sprinkles by 02z, it really has minimal impact to TAFs. Have
some VCSH for BOS, PVD, ACK and mention of -RA for FMH and HYA
through 01-02z. Otherwise VFR ceilings of 5000-7000ft are
expected to persist all night, as are the surface NE winds of
10kts or so. 

Should see BKN sky conditions develop Friday morning, eventually
becoming SCT for much of the region. Surface winds will
transition from NE in the morning to E by early afternoon and
then SE by late afternoon. This is in response to a front that
will be approaching from the west. 

Friday night expecting MVFR and some IFR conditions to develop
as the front and its associated band of showers moves into the
region. 

KBOS TAF...Moderate confidence. Any rain through 01z will be
very light. Winds tomorrow will be slowly changing direction
through the day, not suddenly like a sea breeze. Thus the FM
groups represent average conditions around that time. 

KBDL TAF...High confidence in TAF. 

Outlook /Saturday through Tuesday/... 

Saturday: VFR. Breezy. Slight chance SHRA.

Saturday Night through Sunday Night: VFR. Breezy. 

Monday through Monday Night: VFR. 

Tuesday: VFR. Breezy.

&&

.MARINE...
Forecaster Confidence Levels:

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

345pm update...

Tonight and Friday...High confidence. 

Pressure gradient weakens as the wave of low pressure continues to 
move further southeast and away from the region. Seas will also 
diminish, but some 5 foot seas to linger across our southern outer-
waters, extending small craft headlines in those locations through 
Friday late afternoon. Winds on Friday remain out of the east and 
less than 20 knots. 

Friday Night...High confidence. 

Wind direction from southeast to southwest with the passage of a 
frontal boundary, along with rain chances. Areas of fog is possible 
with reduced visibilities. Seas remain below 4 foot. 


Outlook /Saturday through Tuesday/...  

Saturday: Winds less than 25 kt. Chance of rain showers. Local
visibility 1 to 3 nm.

Saturday Night: Winds less than 25 kt. Seas locally approaching
5 ft. 

Sunday through Tuesday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 7 PM EDT Friday for ANZ255-256.

&&

$$

SYNOPSIS...Dooley/Nash
NEAR TERM...Dooley/Nash
SHORT TERM...Dooley
LONG TERM...Nash
AVIATION...Dooley/Nash
MARINE...Dooley/Nash