Lexington Weather

Lexington, Massachusetts, USA

45°F

4/26/2024 8:50am

Lexington Conditions: Clear
Temperature: 45.3°F / 7.4°C
Dew Point: 26.8°F
Relative Humidity: 48%
Wind: Calm, 10-min avg: Calm, gust: 3 mph
Barometer: 30.46 in Steady
Visibility: 10 miles
Rain Today: 0.00 in

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 221830
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
230 PM EDT Mon Apr 22 2024

.SYNOPSIS...
A ridge of high pressure will result in dry weather through
Tuesday with pleasant days and chilly frosty nights, along 
with elevated fire weather potential. Unsettled with showers and
scattered thunderstorms on Wed. Winds will be gusty at times. 
Cool on Thu, but temperatures rebound late in the week and 
heading into the weekend with dry weather.

&&

.NEAR TERM /THROUGH TONIGHT/...
High pressure over the central Appalachians will move closer to
our region overnight. A lingering front should move back north
as a warm front late this afternoon and evening. Most of the
near term guidance, such as the LAMP and HRRR, have been
persistent and consistent with a brief seabreeze developing early
this evening before being pushed out by the overall southerly
synoptic flow.

Mainly clear skies and diminishing wind will set the stage for
very good radiational cooling. Expecting dew points to rise from
the teens overnight, but it will take a while to do so. Thinking
patchy frost will remain a concern, so the Frost Advisory
continues. Can see a scenario where some of our usual effective
radiators could get below freezing where the frost/freeze
program has begun. However, also thinking these freezing
temperatures will not be widespread enough to warrant an upgrade
to a Freeze Warning. That possibility will need to be watched
this evening.

&&

.SHORT TERM /TUESDAY THROUGH TUESDAY NIGHT/...
High pressure moves off the Eastern Seaboard for Tuesday and
Tuesday night. Dry weather continues Tuesday with a persistent 
southerly wind. This should result in near normal temperatures 
for late April through Tuesday night.

Our next chance for showers is anticipated to be late Tuesday
night as a front approaches from the west. It is more likely
these showers will impact the western half of southern New
England by the Wednesday morning commute.

&&

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

* Showers spreading in late Tue night through Wed as a cold front 
  slides through. Scattered thunderstorms along with gusty winds and 
  could perhaps see some graupel as well.

* Dry, breezy and cool on Thu. 

* Trending milder late in the week into the weekend. Generally dry, 
  but we could see some showers pushing in late in the weekend. 

Wednesday...

Caught under cyclonic flow through this timeframe. A trough will 
dig into the eastern Great Lakes/Mid Atlantic by early Wed. There
is a northern stream trough digging toward northern New England
on Wed, which may interact with that previous trough as it is 
lifting through our area on Wed. This will swing a cold front 
through out region.

Main concern in the latest update is the thunderstorm risk along 
with gusty winds. Appears that there is some interaction going on 
between the two troughs on Wed, which given the cold pool aloft will 
steepen mid level lapse rates. At this point guidance showing values 
ranging from 6-8 degrees Celsius. We may even have low level lapse 
rates of a similar range, but there is some discrepancy amongst 
guidance. Do have some question on the instability at the NAM/GEM 
show a few hundred J/kg of MUCAPE along with the GEPS. The ECMWF/GFS 
along with their ensemble counterparts (EPS/GEFS respectively) are 
much more muted. Despite the discrepancy we've got a fairly dynamic 
system working its way in and a ribbon of 40-60 kts of deep layer 
shear moving in. Have added more thunder to the forecast as all 
guidance has good mid level lapse rates in place. Added a gusty wind 
mention given the setup and also think it is not out of the question 
there is a stronger storm or two. Though this may be limited by the 
moisture available (0.7-0.8 inches) along with the best instability 
and shear only briefly overlapping. Stay tuned for future updates. 

Regardless of the thunder potential do think we will have breezy 
conditions throughout the day Wed, especially during the afternoon 
as flow shifts from the SW to the NW. Still some uncertainty on the 
strength of the jet, but could range from 20-40 kts at 850 hPa. The 
default NBM appears fine at this juncture. High temps range from the 
mid 50s to the low 60s.

Thursday through Sunday...

Will initially be in cyclonic flow on Thu, but will have a ridge axis 
over the Plains. The ridge will build into the Mississippi River 
Valley by late Thu. The ridge builds into the TN Valley to central 
Great Lakes by late Fri and the East Coast by late Sat. Confidence 
high through this period. By Sun confidence lowers as the ridge may 
be reinforced over the region or a shortwave may ride/shunt the 
ridge offshore. High pressure nudges in from the Great Lakes Region 
on Thu and overhead on Fri/Sat. The high shifts offshore on Sun.

Dry and quiet weather anticipated through the vast majority of this 
timeframe. Could be a bit breezy due to a tightened pressure 
gradient on Thu, but some uncertainty here as the high could build 
over the region a bit quicker than the latest NBM indicates. This 
would relax the gradient much fast and result in lighter winds. For 
now have stuck with the higher NBM. The other risk heading into Thu 
and Fri is there could be cold enough air in place where widespread 
frost develops. More confident in heading into Fri with the high 
overhead. For heading into Thu we may be a bit too windy for 
widespread frost development. Frost/freeze headlines may be needed 
in future updates.

Coldest temps of the week on Thu with a -2 to -4 degree Celsius 
airmass overhead at 850 hPa. Will warm up Fri through the weekend as 
flow turns W on Fri and S/SW through the weekend. High temps ranging 
from the mid 50s to the mid 60s. Could be a bit warmer on Sun with 
us generally being in the 60s. There is uncertainty here given 
guidance is all over the place with our next shortwave lifting in. 
Some still have the high dominating, so for now have stuck with the 
NBM. This brings chances of showers.

&&

.AVIATION /18Z MONDAY THROUGH SATURDAY/...
Forecast Confidence Levels:

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

Through Tuesday...High confidence. 

VFR. Gusty NW winds diminish this evening, permitting a brief
seabreeze along the coasts before light S winds develop
overnight into Tuesday.

Tuesday Night...High confidence.

Mainly VFR through the night. MVFR/IFR cigs should develop from
west to east across the western half of southern New England
after midnight. -SHRA increasing from west to east as well.

KBOS TAF...High confidence in TAF.

KBDL TAF...High Confidence in TAF. 

Outlook /Wednesday through Saturday/... 

Wednesday: Mainly MVFR, with local IFR possible. Breezy. SHRA
likely.

Wednesday Night through Thursday: VFR. Breezy. 

Thursday Night through Friday Night: VFR. 

Saturday: VFR. Breezy. 

&&

.MARINE...
Forecaster Confidence Levels:

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

Through Tuesday Night...High Confidence.

High pressure moving off the Eastern Seaboard tonight into
Tuesday will result in rather light winds and seas across the
waters. Good visibility. Increasing risk for showers late
Tuesday night. Increasing south winds may lead to rough seas
across the outer coastal waters late Tuesday night. However, do
not have enough confidence in the timing for a Small Craft
Advisory at this time.

Outlook /Wednesday through Saturday/... 

Wednesday: Winds less than 25 kt. Seas up to 5 ft. Chance of
rain showers. 

Wednesday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Areas of rough seas. 

Thursday: Winds less than 25 kt. Areas of seas approaching
5 ft. 

Thursday Night through Saturday: Winds less than 25 kt. 

&&

.FIRE WEATHER...
Tuesday...

There will be elevated fire weather concerns Tuesday. Given 
that we are in a pre-greenup and a very dry atmosphere is in 
control, expecting minimum afternoon relative humidities to 
drop to between 20 and 30 percent. Winds will be from the south
with some gusts again of 15 to 20 mph.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Frost Advisory from 11 PM this evening to 7 AM EDT Tuesday for 
     CTZ002>004.
MA...Frost Advisory from 11 PM this evening to 7 AM EDT Tuesday for 
     MAZ013-016>023.
RI...Frost Advisory from 11 PM this evening to 7 AM EDT Tuesday for 
     RIZ001>008.
MARINE...None.

&&

$$

SYNOPSIS...Belk/KJC
NEAR TERM...Belk
SHORT TERM...Belk
LONG TERM...BL
AVIATION...Belk/KJC
MARINE...Belk/KJC
FIRE WEATHER...Belk