Lexington Weather

Area Forecast Discussion
for Lexington, MA

        
000
FXUS61 KBOX 260801
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
401 AM EDT Mon Oct 26 2020

.SYNOPSIS...
Weak low pressure passing southeast of New England will bring areas 
of light rain and drizzle into tonight. A cold front will move 
across the region late tonight followed by high pressure and dry 
weather Tuesday and Wednesday. The remnants of Zeta may bring a 
soaking wind swept rain Thursday into Friday, with rain possibly 
ending as snow Friday across the high terrain of northern 
Massachusetts. Behind this departing system, dry but blustery and 
cold weather follows later Friday/Fri night. High pressure returns 
next weekend with dry but chilly weather Saturday followed by milder 
temperatures Sunday. 


&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Putting it rather frankly...we are looking at a fairly raw and 
cloudy Monday with periods of very light rain or drizzle, and
we'll add some mist or fog for the afternoon.

Early this morning, a ridge/wedge of high pressure extended 
southward through Southern New England into the mid-Atlantic region.
A weak inverted trough/ill-defined surface low is located over the 
southern waters. Periods of mainly light rain, rain which is barely 
resulting in measurable precip, is falling into the ridge in an 
easterly onshore flow. Following trends and the latest short-term 
high res models, these light rains project to continue at least 
through mid to late morning, gradually shifting northward as it does 
so with surface low passing just to our east. 

Noting the low clouds, fog and periods of drizzle or light showers 
prevalent early this AM across much of the I-95 corridor in PA/NJ 
into southern NY. With model soundings showing lots of low-level RH 
left behind across most of Southern New England this afternoon, it's 
anticipated that we'll see similar conditions settle in by the late-
morning/early-afternoon hrs and continue through the rest of the 
day. All told, not looking at a washout with QPF values only a few 
hundreths. 

Modest warm advection does take place today, but abundant cloudiness 
and periods of rain and drizzle will make for a very slow rise to 
temperatures. Looks like today is one of those days where the high 
temperature occurs later tonight (ahead of a cold front, more on 
that below) as opposed to typical diurnal/late-afternoon. Current 
temps in the mid 40s to low 50s may only rise a couple degrees into 
the upper 40s to the mid 50s through the day today, with upper 50s 
across Cape Cod and the Islands.

&&

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

Southeast flow allows for continued warm advection to occur, ahead 
of a cold front which crosses through Southern New England for the 
second half of tonight. Temperatures should continue to undergo a 
slow rise into the low to mid 50s through about midnight, amid 
continued overcast skies with intervals of drizzle and fog/mist. A 
cold front then approaches interior western MA overnight tonight and 
continues to progress eastward toward pre-dawn/early Tues AM. A 
return to cooler and drier conditions on NW flow should allow for 
some greater clearing but appears unlikely to happen any sooner than 
late-overnight/pre-dawn hrs of Tuesday. Lows by Tuesday AM should 
dip back into the 40s, though a few low 50s towards the South Coast 
and Cape Cod. 

Tuesday:  

Surface ridge from the Great Lakes ridges into Southern New England 
for Tuesday, with moderate cold advection occurring as the day 
progresses. 925 mb temps fall from the low teens Celsius to around 
+3 to +5C in that cold advection. Will be somewhat blustery early on 
Tuesday with northwest winds around 10-15 mph, though diminishing by 
afternoon. Partial sun will offset the cold advection to bring highs 
in the mid 40s to lower 50s.   

Some indication late in the day that a weak vort max in fast west-
southwest flow allows for increasing clouds from west to east. A few 
models break out some showers as this feature mostly passes to our 
north. However forecast soundings show some drier mid to low-level 
air that probably results in more virga than anything else. Did 
leave slight chance PoPs for late in the day, but many areas should 
be dry. 

&&

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

* Mainly dry & seasonably cool weather Tue night/Wed/Wed night

* Remnants of Zeta may result in a wind driven soaking rain late Thu 
  into early Fri, possibly ending as snow across the high terrain

* Blustery & cold late Fri into early Sat, then milder Sunday
  
Precipitation...

Northern stream energy drives frontal boundary farther south of New 
England with high pressure advecting into the region Tue 
night/Wed/Wed night. This will promote mainly dry weather Tue and is 
evident as PWATs lower to about a 0.5 inches. Then our attention 
shifts to Tropical Storm Zeta as it emerges out of the Gulf of 
Mexico Wed. Closed low over west TX will eject Zeta northeast. 
Confluent flow across New England will steer remnant Zeta to track 
along or near 40N. Expecting two rounds of precip late this week 
with first round associated with remnants of Zeta late Thu/Thu 
night. Periods of moderate to heavy rain given tropical moisture 
running up and over cooler low level airmass, combined with banding 
Fgen potential from confluent flow aloft. Then second round of 
potential moderate to heavy precip late Thu night into early Fri, as 
closed low over TN Valley ejects northeast and potentially mergers 
with northern stream energy as this features approach New England. 
This northern stream s/wv will drive colder air into northwest 
portion of precip shield, possibly changing rain to snow late Thu 
night into Fri morning across northern MA, especially over the high 
terrain. Will have to watch closely the evolution of this as there 
is a low probability of minor snow accumulation across the high 
terrain. Then drying trend likely follows late Fri into Sat as 
system appears progressive, as trailing northern stream short wave 
serves as a kicker, rather than close system off. Next trough/cold 
front may approach our area Sun/Sun night, but amplitude and 
moisture remain uncertain. 

Temperatures...

1020+ mb high pressure delivers temperatures at or slightly cooler 
than normal with highs in the low to mid 50s Wed, then lows in the 
30s Tue night and 40s Wed night. Seasonably cool Thu with highs in 
the 50s but will feel cooler given rain overspreading the region 
along with increasing ENE winds, as low pres/remnants of Zeta track 
south of New England. Very chilly Friday with highs only in the 40s, 
upper 30s high terrain, becoming blustery and even colder Fri night 
as intensifying coastal low exits and 1030+ mb high over Great Lakes 
advects toward New England. Cold air advection on gusty north winds 
will yield lows in the 20s Fri night and wind chills possibly in the 
teens! NNE winds may gusts up to 45 mph late Fri/Fri night. Given 
trees remain fully to partially leaved across Cape Cod and the 
Islands, potential for some wind impacts here. Chilly but dry 
weather Sat with highs only in the 40s to near 50s, but milder 
Sunday ahead of next short wave/cold front, with highs rebounding 
into the 50s to near 60. 

&&

.AVIATION /08Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

06z TAF Update:

Rest of the Overnight (thru 12z Mon): High confidence in 
trends/flight categories, moderate on timing.

VFR at the start, with a south to north deterioration towards 
MVFR ceilings. Better confidence in MVFR ceilings into the AM
push, but may occur a couple hrs sooner (about 08z) especially 
towards PVD/BDL. Unrestricted-visby light rain spreading 
gradually northward overnight/early AM, but coverage may be 
fairly scattered/spotty. East winds 3-7 kt in the interior, a 
bit stronger to about 6-10 kt near the eastern MA and southern 
coasts.

Today: Moderate confidence. 

MVFR through most of the morning, with periods of light rain 
interspersed with drizzle. Light rain comes to an end around
late-AM/early-PM, but ceilings deteriorate toward IFR/LIFR with
into the afternoon mist/fog, drizzle and stratus. Generally
higher confidence in these trends, but exact timing when 
categories deteriorate below MVFR levels is less clear. East 
winds 6-12 kt (around 15 kt at ACK, gusts lower-20s kt), then 
lighten and become southeast around 4-8 kt.

Tonight: Moderate confidence. 

IFR/LIFR with continued drizzle, mist/fog and low stratus for
the first part of the evening. A cold front arrives late tonight
that should bring about improvement towards VFR- MVFR levels.
This improvement may start in the far west around 05-07z and 
towards early Tue AM towards the eastern coast. Light south 
winds shift to northwest and increase to around 7-12 kt, 
occasional gusts around 20 kt near eastern MA and Cape Cod 
toward early Tue AM. 

Tuesday: High confidence. 

Improvement toward SCT-BKN VFR ceilings. Ceilings may lower
towards VFR-MVFR levels late for western TAFs as a weak 
disturbance aloft approaches but should be predominantly VFR. 
Very light showers possible underneath this deck late in the day
but may be more virga. 

KBOS Terminal...Moderate confidence in TAF. MVFR cigs develop
into the AM push, possibly as soon as 09z. IFR cigs develop in
the aftn. 

KBDL Terminal...Moderate confidence in TAF. MVFR cigs develop
around ~07-09z. IFR cigs develop in the aftn.

Outlook /Tuesday Night through Friday/... 

Tuesday Night: Mainly VFR, with local MVFR possible. Slight
chance SHRA.

Wednesday: Mainly VFR, with areas MVFR possible. 

Wednesday Night: Mainly VFR, with local MVFR possible. Breezy. 

Thursday: Mainly MVFR, with areas VFR possible. RA.

Thursday Night: Mainly MVFR, with areas IFR possible. Strong
winds with local gusts up to 40 kt. RA.

Friday: Mainly MVFR, with local IFR possible. Strong winds with
gusts up to 40 kt. Chance RA, SN likely.

&&

.MARINE...
SCAs continue on most southern waters through today, though will 
continue into early tonight on the southern outer waters. On the 
eastern waters, long-period seas have been running around 4 ft and 
opted to drop the SCA for these waters. 

A weak surface low will bring light rains with periods of fog and 
some enhancement to east winds early today. East winds may bring 
about a period of gusts to SCA levels on the southern waters through 
the morning, with seas in the 4-6 ft range on the outer waters. 
Winds to decrease a bit and shift to SE by afternoon, with gusts to 
around 15 kt. Seas will still be in the SCA range until early 
tonight. Periods of mist, drizzle and fog (visbys 1 to 3 SM) this 
afternoon into a good part of tonight.

Late-overnight tonight into early Tuesday, a cold front will cross 
the waters allowing for a period of NW wind gusts. It's possible 
that gusts may briefly approach SCA levels on the eastern waters but 
speeds decrease around mid to late AM. Seas mainly in the 3-4 ft 
range for Tuesday.

Outlook /Tuesday Night through Friday/...

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

Wednesday: Winds less than 25 kt. Slight chance of rain
showers. 

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

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

Thursday Night: Low risk for gale force winds with gusts up to
40 kt. Rough seas up to 10 ft. Rain. 

Friday: gale force winds with gusts up to 45 kt. Rough seas up
to 11 ft. Rain likely. 

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...None.
MA...None.
RI...None.
MARINE...Small Craft Advisory until 10 PM EDT this evening for 
     ANZ254>256.
     Small Craft Advisory until 5 PM EDT this afternoon for ANZ235-
     237.

&&

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