Old Res Weather

Lexington, Massachusetts, USA

49°F

4/18/2024 3:08pm

Lexington Conditions: Light rain, Overcast
Temperature: 48.7°F / 9.3°C
Dew Point: 38.7°F
Relative Humidity: 68%
Wind: Calm, 10-min avg: Calm, gust: None
Barometer: 30.19 in Steady
Visibility: 10 miles
Rain Today: 0.00 in
UV Index: $VPuv None

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 161145
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
745 AM EDT Tue Apr 16 2024

.SYNOPSIS...
High pressure over Southern New England will bring dry weather 
through mid week. Mild temperatures are on tap for today, but it 
will be cooler Wednesday along the coast with sea breezes. 
Isolated to scattered showers across the interior on Thursday with 
slight cooler than seasonable temperatures. Dry on Friday with high 
pressure in control. A cold front brings another round of light rain 
showers late Friday through Saturday. Turning drier Sunday and 
Monday.

&&

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

* Plenty of sunshine & beautiful today with highs mainly 65-70

The last of the scattered showers across the Cape/Islands were in 
the process of coming to an end early this morning. This in 
association with a departing shortwave/cold front. Otherwise...dry 
northwest flow behind this front will result in a beautiful day. 
Plenty of sunshine is expected with just a bit of fair weather 
diurnal CU. Given northwest flow in pre-greenup...thinking temps 
overachieve the guidance by a few degrees. Afternoon highs should 
top off between 65 and 70. Enough mixing should yield some NW 20-25 
mph wind gusts this afternoon...but a very nice mid-April day is in 
store for the region.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM WEDNESDAY/...
Key Points...

* Mainly clear tonight with light winds, lows mainly 30s to lower 40s
* Filtered sun Wed with sea breezes...highs 50s coast & 60s inland

Details...

Tonight...

A ridge of high pressure overhead will result in mainly clear skies, 
light/calm winds and a very good night of radiational cooling with 
the dry airmass in place. Overnight low temps will bottom out well 
down into the 30s across the outlying locations...to between 40 and 
45 in some urban centers. 

Wednesday...

Upper level ridge axis approaches from the west on Wednesday. Plenty 
of sunshine to start will be filtered by some increasing mid/high 
cloudiness as the day wears along. The mid level trough axis will 
weaken the pressure gradient sufficiently enough to result in sea 
breeze development along the coast. This should keep highs in the 
lower to middle 50s along much of the immediate coast...while 
further inland across the interior highs will be into the 60s.

&&

.LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
Highlights

* Isolated to scattered showers on Thu, mainly across the interior. 
  Temps slightly cooler than seasonable.

* Dry for much of Fri with temps returning to seasonable levels.

* Cold front brings scattered showers late on Fri through Sat. Mild 
  temps return. 

* The temp roller coaster continues with a return to near normal 
  temps and dry weather for Sun/Mon.

Wednesday Night through Thursday...

Will have an omega block situated over eastern Canada, the Great 
Lakes and Northeast to start the period. The ridge axis will be 
extend from Long Island into western Quebec Wed Night, but a 
shortwave will be riding the ridge into early Thu. At the same time 
a trough will lift into the eastern Great Lakes. The trough lifts 
into Quebec/New England by late Thu. A warm front will lift toward 
our region during this timeframe, but remains shunted to our SW. 

Expect increasing chances of isolated to scattered light rain 
showers across southern New England during this period. Do have some 
uncertainty on the northeastward extent of the precip shield. 
Deterministic guidance shows this discrepancy via the PWAT plume. 
The GFS is much more progressive and pushes the 0.75-1" plume to the 
coastline, whereas the ECMWF/NAM/ICON/UKMET keep these values 
confined to the interior. In combination with the easterly LLJ am 
expecting the best shot for showers from roughly central MA to RI 
westward. Further to the east there could be some isolated hit/miss 
activity. Really not expecting to eek much of the moisture out given 
the upper forcing is well off to the NW. Could see perhaps a few 
hundredths of accumulation.

Given the onshore easterly flow did opt to nudge down our temps from 
the NBM. Appeared to be running just a bit too warm, so went down to 
the 50th percentile of guidance for now. Highs in the low to mid 50s.

Friday through Saturday...

Ridge axis slides offshore on Fri. Will get stuck in cyclonic flow 
later on Fri. A trough will dig across the Great Lakes late Fri and 
into New England by Sat. The trough may be mostly through by late 
Sat, but there is some discrepancy on the timing. High pressure 
builds overhead early on Fri before shifting offshore late in the 
day. A cold front slides in from the west late on Fri through Sat.

Dry and quiet weather expected for much of Fri with high pressure in 
control. There is some uncertainty with how quickly the front slides 
in from the west. Think that the NBM could be a tad to fast with the 
precip onset and may actually remain dry through the day. Though far 
western areas could see showers spread in toward the evening. Main 
reason for this thinking is the lower levels (1000-850 hPa) are 
quite dry and should take a bit to moisten. This will appears more 
likely to happen Fri eve and continue into Sat as the front is 
sliding through. Fortunately the front is progressive and am not 
expecting much precip as it slides through. 

Temperatures will return to near normal levels for this time of year 
on Fri as winds turn southerly. Highs range from the 50s to the low 
60s. Better shot for mild readings on Sat as we get into breezy W to 
WNW flow. The NBM in this case appears a bit too cool, so did bump 
up our temps a bit due to a well mixed boundary layer. Highs range 
from the upper 50s to the mid 60s. 

Sunday and Monday...

Still caught under cyclonic flow through this time period. Will have 
some mid level ridging in place over the Great Lakes and into New 
England. This should nudge high pressure into our region keeping our 
weather dry and quiet. The NBM seems reasonable at this point, so 
haven't deviated for this timeframe. High temps right around 
seasonable levels.

&&

.AVIATION /12Z TUESDAY THROUGH SATURDAY/...
Forecast Confidence Levels:

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

06z TAF Update...

Today...High Confidence. 

A few lingering showers very early this morning across RI/SE MA
with even a rumble of thunder towards Nantucket will be coming
to an end shortly. Otherwise...VFR today with NW winds
increasing to between 8 and 13 knots with a few gusts over 20 
knots developing by early afternoon.

Tonight...High Confidence. 

VFR. Calm/light NNW winds.

Wednesday...High Confidence.

VFR. Light N winds becoming variable and remaining light during
the afternoon inland, while sea breezes develop around 10 knots
along the coast.

KBOS TAF...High confidence in TAF.

KBDL TAF...High confidence in TAF.

Outlook /Wednesday Night through Saturday/... 

Wednesday Night: VFR. Isolated SHRA.

Thursday: VFR. Breezy. Scattered SHRA.

Thursday Night: Mainly VFR, with local MVFR possible. Isolated
SHRA.

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

Friday Night through Saturday: Mainly VFR, with local MVFR
possible. Breezy. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels:

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

Today through Wednesday...High Confidence.

Weak pressure gradient will keep winds & seas below small craft 
advisory thresholds through Wednesday. Good mixing over the land may 
result in some NW 20 knot near shore wind gusts this afternoon. We 
are also not expecting any issues with visibility/fog given the dry 
nature of the airmass.

Outlook /Wednesday Night through Saturday/... 

Wednesday Night: Winds less than 25 kt. Isolated rain showers. 

Thursday through Thursday Night: Winds less than 25 kt. Seas
locally approaching 5 ft. Isolated rain showers. 

Friday: Winds less than 25 kt. 

Friday Night through Saturday: Winds less than 25 kt. Seas
locally approaching 5 ft. Chance of rain showers.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...None.

&&

$$

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