Lexington Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 231135
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
635 AM EST Thu Jan 23 2020

.SYNOPSIS...
High pressure will remain in control through Friday with dry and 
mild days and a cold night tonight. A storm is expected to 
impact the region Saturday into Saturday night with mostly rain
and gusty coastal winds, but some snow is possible over the 
higher elevations in northern MA. Mainly dry and seasonable 
conditions return Sunday lasting into the middle of next week.

&&

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

630 AM update...

No major changes with this morning's update. Mesoanalysis shows
the high pressure moving overhead, with a few high clouds
visible on IR satellite. Overall a very nice day to spend 
outside, with sunny skies, mild temperatures, and light 
southwest winds.

Previous Discussion...

Mid level ridge SE of New Eng with anticyclonic
flow and very dry air in the column will continue to support 
mostly sunny skies today. Pronounced low level warming today 
although subsidence inversion will limit mixing depth. However, 
sunshine and SW flow with 950 mb temps 3-5C support highs in the
mid/upper 40s.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/...
Tonight... 

A weak mid level shortwave approaching from the SW will bring some 
increase in high clouds. Still decent radiational cooling with light 
winds yielding lows in the teens in the colder locations and mostly 
20s elsewhere. Weak frontal boundary will slip south across SNE 
after midnight with a wind shift to light north. 

Friday... 

Frontal boundary south of New Eng with high pres building to the 
north will result in low level easterly winds developing. Cross 
sections show increasing low level moisture from the north with 
lower clouds developing in the afternoon across northern MA. 
Otherwise, partly sunny skies. Temps will be a bit cooler due to 
E/NE winds with highs upper 30s to mid 40s.

&&

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

* Dry weather Friday night with above normal temperatures.

* Coastal storm this weekend initially bringing a cold rain for much 
  of southern New England. Best opportunity for snowfall is across 
  the highest elevations of the interior where things begin as a 
  wintry mix before transitioning to rain. 

* Scattered snow showers across the region late on Sunday into early 
  Monday, then dry through mid week. 

* Slightly cooler temperatures after the weekend.

Details...

Friday night into Saturday morning...

Large surface high remains overhead though on its way out, with a 
mid level ridge axis crossing New England during this period. This 
keeps things dry and about 10-15 degrees above normal overnight on 
S/SE flow in the low levels (+2 to 3 C at 850 mb). Most locations 
dip into the mid/upper 30s or upper 20s (inland). Average low temps 
for late Jan are in the teens and low 20s. Winds are light but high 
clouds should keep us from radiating too well. 

Saturday and Sunday...

Again with the trend, unfortunate for snow lovers, toward the north 
and west with the track of this weekend's storm system. Signs point 
more and more to a cold rain for the majority of southern New 
England on Saturday. Confidence is very high that a soaking storm 
system arrives over the weekend, while chances of snow outside of 
the highest elevations are decreasing. A 500 mb trough and surface 
low will dig into the mid Atlantic on Saturday. A secondary low 
along the frontal boundary strengthens as it crosses over southern 
New England (or even potentially northern New England if some of the 
newest guidance has anything to say about it). Further up at 700 mb 
where yesterday the low center looked to cross directly over 
southern New England it now has trended northward, crossing northern 
New England. As a result, the bulk of the cold air we would need to 
see more snow is too far north. At the moment the most likely 
solution on the front end of the event looks to be a cold rain for 
most, with a rain/snow mix in interior lower elevations, and snow in 
the highest elevations of the Berkshires and Worcester Hills. Things 
will then change to rain as the low pulls in warmer low level air 
and this will continue into the overnight hours. By early overnight 
hours the dry slot moves into the region and erodes the heaviest 
rain from the west through the overnight hours so by sunrise most of 
the precip will have fallen. There is potential for a significant 
rainfall (QPF values from 1 PM Sat to 7 am Sunday approach 1.25 or 
1.5 inches in spots). A few inches of snow in the highest elevations 
of the Berkshires is possible but totals continue to be lowered. 

Sunday the low lifts into the Gulf of Maine and colder air will wrap 
back around the low, but the bulk of the moisture is gone by then so 
most will stay dry. Some scattered light snow showers are possible; 
best chance will be the orographically favored western MA/CT. No 
real accumulation is expected except up to an inch in the Berkshires 
perhaps. Winds with this system will be gusty, picking up on 
Saturday afternoon/evening with gusts 25 to 30 mph possible, closer 
to 40 mph along the southeast coast. Gale headlines may be necessary 
over the waters where gusts will be even greater. 

Monday through Wednesday...

Drying out Monday and into midweek. The low is slow it exit thanks 
in part to an area of high pressure off the coast of eastern Canada. 
However, it eventually moves off and is replaced by high pressure 
with drier air moving in. We're looking at partly sunny skies for 
the first half of the work week with cooler temperatures, but still 
warmer than normal. Monday is the warmest in the low 40s before 
highs cool a few degrees Tues/Wed.

&&

.AVIATION /12Z THURSDAY THROUGH MONDAY/...
Forecaster Confidence Levels...

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

Short Term /through Friday/...High confidence. 

Through tonight...
VFR. SW wind 10 kt or less today becoming light N after 
midnight.

Friday...
VFR, but areas of MVFR cigs developing across northern MA in 
the afternoon. NE wind 10 kt or less. 

KBOS Terminal...High confidence in TAF. 

KBDL Terminal...High confidence in TAF. 

Outlook /Friday Night through Monday/ ...

Friday Night: Mainly VFR, with local IFR possible. Breezy.
Slight chance FZRA.

Saturday: Mainly VFR, with areas IFR possible. Windy with local
gusts up to 30 kt. RA, chance SN, slight chance FZRA.

Saturday Night: Mainly VFR, with areas IFR possible. Windy with
gusts up to 35 kt. Chance RA, chance FZRA.

Sunday: Mainly VFR, with local MVFR possible. Breezy. Chance
SN, slight chance RA.

Sunday Night: Mainly VFR, with local MVFR possible. Breezy.
Slight chance SN.

Monday: Mainly VFR, with local MVFR possible. Breezy.

&&

.MARINE...
Short Term /through Friday/...High confidence. 

SW flow today with winds turning N late tonight behind a cold front. 
E/NE flow Fri. Flat seas today then slowly building late tonight 
into Fri, especially NE MA waters as winds turn NE, but remaining 
below 5 ft. 

Outlook /Friday Night through Monday/...

Friday Night: Winds less than 25 kt. Seas up to 5 ft. 

Saturday: Low risk for Small Craft Advisory winds with local
gusts up to 30 kt. Rough seas up to 10 ft. Chance of rain. 

Saturday Night: Low risk for gale force winds with gusts up to
40 kt. Rough seas up to 13 ft. Rain. 

Sunday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Rough seas up to 13 ft. Slight chance of rain. 

Sunday Night: Low risk for Small Craft Advisory winds with
gusts up to 25 kt. Rough seas up to 10 ft. 

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

&&

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

&&

$$
SYNOPSIS...KJC/BW
NEAR TERM...KJC/BW
SHORT TERM...KJC
LONG TERM...BW
AVIATION...KJC/BW
MARINE...KJC/BW