Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 232005
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
405 PM EDT Fri Oct 23 2020

.SYNOPSIS...

High pressure will maintain dry and mild weather tonight and 
Saturday. A dry cold front will move across southern New 
England Saturday afternoon and evening. In wake of the front
much colder is expected as a Canadian high builds in. The dry
weather continues but it will be much cooler on Sunday. A 
couple waves of low pressure and a frontal boundary will result 
in several chances of showers next week. Not a washout as there 
will be many hours of dry weather especially around Wednesday. 
Seasonably cool temperatures expected much of next week, with 
highs in the 50s to near 60 and night time lows in the 30s and 
40s. 

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...

Highlights...

* Cloudy with areas of fog. Could have some drizzle across the 
  eastern slopes of the Berkshires. 

Subtropical ridge axis building east of Cape Cod while a shortwave 
trough lifts from Upper Michigan into southern Quebec by Saturday 
morning. At the surface high pressure nudges in from the Carolinas 
while a cold front slides across the eastern Great Lakes. 

Will see east to southeast flow across eastern areas that will 
advect in ocean stratus per RAP RH from the SFC to 925 hPa. Central 
and western areas will remain cloudy due to southerly flow advecting 
in moisture. This will result in a cloudy night across much of 
southern New England. It will be mild as southwesterly warm air 
advection of 10 to 12 degree Celsius 850 hPa moves in. Low 
temperatures falling into the 50s. 

The additional influx of moisture in combination with light winds 
will result in areas of fog. Expect the lowest visibilities to be 
concentrated across the CT River Valley. Could also see some spotty 
drizzle as indicated by the NAM/ARW/NMM/CMC and ECMWF across the CT 
River Valley and eastern slopes of the Berkshires. 

&&

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...

Highlights...

* Few light showers possible across the west, but generally a dry 
  cold frontal passage on Saturday. Skies clearing out during the 
  afternoon.

* Much cooler Saturday night into Sunday morning.

Shortwave trough lifts into northern Quebec on Saturday. A ridge 
builds from the Northern Plains into Ontario/the central Great Lakes 
late on Saturday into early Sunday. The cold front is well removed 
from the upper forcing, so am anticipating a dry frontal passage on 
Saturday. There may be a few light spotty showers across the far 
west. Should see clearing skies during the afternoon from northwest 
to southeast as high pressure builds in from the northwest. The high 
will remain in place through the overnight hours.

Saturday...

A somewhat tricky temperature forecast on Saturday due to the front 
sliding through in combination with colder air advecting in from 
westerly flow aloft. Despite this, am expecting another above normal 
temperature day across southern New England. The westerly flow will 
result in some downsloping, so should see most areas getting well 
into the 60s and there may even be a few readings in the low 70s 
across the typical warm spots. 

The cold front may bring a few spotty rain showers across western 
portions of the CWA, but the front is far removed from the upper 
forcing. This is backed up by the latest deterministic guidance, so 
have only kept slight chances of precipitation.  

Skies will clear in wake of the front. Winds will shift to the 
northwest and it could be a bit breezy at times with gusts getting 
up to 20-25 mph during the afternoon with the highest speeds over 
the eastern slopes of the Berkshires.

Saturday Night...

Gusty winds diminishing across the interior as high pressure relaxes 
the pressure gradient. However, it still may be a bit breezy along 
the coastal plain. 

Skies will generally be mostly clear across much of southern New 
England with relatively light winds. Have nudged down the low 
temperatures in the latest update toward the 20th percentile of 
guidance. May need to go lower in future updates, but have held off 
as there may be enough mechanical mixing to keep temperatures from 
plummeting further. Low temperatures generally in the 30s across 
the interior with patchy frost. Coastal areas will range from the 
upper 30s to the mid 40s. 

&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...

Highlights...

* Fall weather returns Sunday

* Not a washout next week but multiple chances for showers 

* Driest day next week may be Wednesday

Precipitation...

Confluent flow pattern sets up over or near New England much of next 
week. This results in a storm track and associated frontal boundary 
remaining close to our region much of the time. Thus low confidence 
forecast on exact placement of this boundary and timing of low 
amplitude waves traversing the front along with individual precip 
shields. Although confidence is high early in the period with dry 
weather expected Sunday as 1025+ mb high pressure builds into 
southern Quebec and northern New England. Then the next wavy frontal 
boundary impacts the region Sun ngt into Tue night. Ensembles 
suggest northern stream trough may be sufficient to drive frontal 
boundary south of New England midweek, offering a period of dry 
weather around Wed. Then ensembles trending more bullish on trailing 
frontal wave to move across the Northeast Thu/Fri, as closed low 
over the dessert southwest ejects northeast. So to summarize, 
multiple chances for showers next week, although not a washout with 
many hours of dry weather likely, especially mid week around 
Wednesday. 

Temperatures...

Much cooler Sunday with highs only in the low to mid 50s with upper 
40s high terrain! Big cool down from our recent warmth. In fact 
these temps are cooler than normal for late Oct, with normal highs 
55-60. Although sunshine especially morning and early afternoon 
Sunday combined with light winds will help take the edge off the 
cooler temps. For next week, low confidence on temps given 
uncertainty in exact frontal position, cool side of boundary vs warm 
sector. Although given clouds, showers and proximity of frontal 
boundary, temps near normal appear most likely. 

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...

Forecaster Confidence Levels...

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

Through 00Z...High confidence

VFR conditions across eastern MA and northern RI, but will see
MVFR ceilings spreading in as stratus advects in from the ocean.
Central and western areas will see a mix of MVFR/IFR ceilings.
SE to S winds around 5-10 kts. 

Tonight...Moderate confidence. 

Onshore flow brings MVFR to LIFR stratus, which will move in
from west to east. Areas of fog developing. Expect lowest vsbys
along the CT River Valley, ORH and BED. Could be some fog at 
BOS, but once winds shift to the SW expect vsby to improve. 
Light SE/S winds shift to the SW. Also think that there may be 
some light drizzle across the eastern slopes of the Berkshires 
into the CT River Valley. 

Saturday...High confidence. 

Starting off with MVFR to LIFR stratus, but will see
improvement to MVFR/VFR from west to east as a mainly dry cold
front slides through. SW winds shifting to the W and eventually
the NW as the front moves through. Speeds generally 5-10 kts.
Could see some 15-20 kt gusts during the afternoon.

Saturday night...High confidence.

Borderline MVFR/VFR ceilings across Cape Cod and the Islands.
Elsewhere will be VFR with clear skies and relatively light
winds.  

KBOS Terminal...High confidence in trends, but moderate in exact
timing of IFR conditions. Possibility of LIFR ceilings between
04-12Z. 

KBDL Terminal...High confidence in trends, but moderate in exact
timing of return to IFR conditions.

Outlook /Sunday through Wednesday/... 

Sunday: VFR. Breezy. 

Sunday Night: Mainly VFR, with areas MVFR possible. Breezy.
Slight chance SHRA.

Monday: Mainly MVFR, with areas IFR possible. Breezy. Chance
SHRA.

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

Tuesday: Mainly MVFR, with local VFR possible. Breezy. SHRA
likely.

Tuesday Night: Mainly MVFR, with local IFR possible. Chance
SHRA.

Wednesday: Mainly MVFR, with areas VFR possible. Slight chance
SHRA.

&&

.MARINE...

Extended all Small Craft Advisories into Sunday morning and expanded
Small Craft Advisories to Ipswich/MA Bay, Rhode Island and 
Block Island Sound due to building seas. The building seas is
due to southeasterly swell from distant Hurricane Epsilon through
Saturday. Peak long-period seas occur on Saturday with wave 
heights around 9 ft across the outer waters. These long period 
seas will bring building surf and an increasing risk of rip 
currents to southern/eastern exposed beaches through Saturday.
 
While seas serve are the main focus for the small craft 
advisory, northwest winds increase later Saturday into Saturday
night behind a cold front. This will reach into solid SCA 
criteria on the majority of waters. Borderline Gale Force Gusts
are possible Saturday night into early Sunday across the outer
eastern waters.

Another period of low clouds and fog is expected across the
waters tonight.

Outlook /Sunday through Wednesday/...

Sunday: Winds less than 25 kt. Areas of rough seas. 

Sunday Night through Monday: Winds less than 25 kt. Seas up to
5 ft. Slight chance of rain showers. 

Monday Night through Tuesday: Winds less than 25 kt. Seas up to
5 ft. Rain showers likely. 

Tuesday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers. 

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

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 8 AM EDT Sunday for ANZ235-237-250-
     251-254>256.

&&

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