Lexington Weather

Lexington, Massachusetts, USA

34°F

4/25/2024 3:35am

Lexington Conditions: Clear
Temperature: 34.3°F / 1.3°C
Dew Point: 20.7°F
Relative Humidity: 57%
Wind: Calm, 10-min avg: Calm, gust: None
Barometer: 30.17 in Steady
Visibility: 10 miles
Snow Today: 0.0 in

Southeast Middlesex County, MA - Freeze Warning - Freeze Watch
- SEE ALL NEARBY ALERTS -

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 220724
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
324 AM EDT Mon Apr 22 2024

.SYNOPSIS...

A ridge of high pressure will result in dry weather today 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 /UNTIL 6 PM THIS EVENING/...

325 AM Update...

* Sunny & pleasant today with highs between 55 and 60

A ridge of high pressure building over the region will result in 
very pleasant late April weather across the region. After a chilly 
start with areas of frost...the increasing sun angle coupled with a 
very dry airmass will allow for a nice recovery in temperatures. 
Afternoon high temperatures should reach between 55 and 60 degrees. 
These readings are about 5 degrees below normal of this time of 
year. But with lots of sunshine it will feel quite a bit milder than 
yesterday did with all the mid level cloudiness.

&&

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

Key Points...

* Mainly clear tonight & chilly with frost/freeze conditions
* Sunny & milder Tue, highs in the low-middle 60s away from the coast

Details...

Tonight...

A ridge of high pressure will remain in control of our weather 
tonight. This will result in mainly clear skies/light-calm winds 
with a dry cool airmass in place for this time of year. Overnight 
low temps should bottom out in the middle to upper 20s in the 
normally coldest outlying locations with mainly 30s 
elsewhere...except lower 40s in the urban Heat Island of Boston. We 
did issue Frost Advisories again tonight for CT/RI/SE MA where we 
are passed the median date of the last freeze. Temps will probably 
be a few degrees lower than early this morning...so perhaps a few 
areas may need to be considered for upgrades to freeze warnings.

Tuesday...

The high pressure system will move off the southeast coast on 
Tuesday. We still expect plenty of sunshine and with a milder 
southerly flow of air across the region...temps will rebound to 
fairly seasonable levels. After a chilly/frosty early morning 
start...high temperatures should reach the lower to middle 60s away 
from the cooling marine influences along parts of the immediate 
coast where highs will be held in the middle to upper 50s. Southerly 
winds may gust up to 20 mph or so during the afternoon.

&&

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

Long Term:

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. 

Tuesday Night through Wednesday...

Caught under cyclonic flow through this timeframe. A trough will 
initially be over the central Great Lakes Tue Night. This 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 /08Z MONDAY THROUGH FRIDAY/...

Forecast Confidence Levels:

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

06z TAF Update...

Today...High Confidence.

VFR. NW winds 5 to 15 knots. There might be a brief sea breeze
along portions of the immediate coast during the late 
afternoon/early evening hours.

Tonight...High Confidence.

VFR. Light/Calm winds.

Tuesday...High Confidence. 

VFR. S winds of 10 to 15 knots with some afternoon 20+ knot 
possible.

KBOS TAF...High Confidence in TAF. 

KBDL TAF...High Confidence in TAF. 

Outlook /Tuesday Night through Friday/... 

Tuesday Night: VFR. Breezy. Chance SHRA.

Wednesday: Mainly VFR, with local IFR possible. Breezy. SHRA
likely, isolated TSRA.

Wednesday Night: VFR. Windy with gusts up to 30 kt. 

Thursday: VFR. Breezy. 

Thursday Night through Friday: VFR. 

&&

.MARINE...

Forecaster Confidence Levels:

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

Today through Tuesday...High Confidence.

A ridge of high pressure to our south today and tonight will be in 
control of our weather. NW winds may gust to between 15 and 20 knots 
nearshore this afternoon...but this ridge of high pressure will keep 
winds/seas below small craft advisory thresholds. This high shifts 
east of the region Tue allowing a return southerly flow of air. 
Southerly winds will gust to between 15 and 20 knots...but again 
expect winds/seas to remain below small craft advisory thresholds.

Outlook /Tuesday Night through Friday/... 

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

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

Wednesday Night: Moderate risk for Small Craft Advisory winds
with gusts up to 30 kt. Seas up to 5 ft. 

Thursday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Local rough seas. 

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

Friday: Winds less than 25 kt. 

&&

.FIRE WEATHER...

Today and Tuesday...

There will be elevated fire weather concerns today and Tuesday. 
Given that we are in a pre-greenup and a very dry atmosphere is in 
control...expect minimum afternoon relative humidities to drop to 
between 15 and 25 percent today and between 20 and 30 percent on 
Tuesday. Winds will be NW today with some gusts of 15 to 20 mph, but 
will shift to the south on Tuesday with some gusts again of 15 to 20 
mph. This will all result in some elevated fire weather concerns 
today and Tuesday. 

&&

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

&&

$$

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