LexMAWeather

Area Forecast Discussion
for Lexington MA

        
000
FXUS61 KBOX 110301
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
1001 PM EST Mon Dec 10 2018

.SYNOPSIS...
Mainly dry and cold weather prevails into Thursday, except for some 
scattered ocean effect snow showers possible late Tuesday night into
Wednesday night mainly across the outer-Cape. Milder 
temperatures arrive Friday and continue into early next week 
with the best chance for rain Friday night into Saturday in 
association with low pressure.

&&

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

No major changes with this update. Brought the forecast back in
line with observed trends, particularly temperatures. Ocean
effect clouds continue to linger around the outer Cape and
portions of Nantucket. Adjusted sky cover a bit using the latest
high resolution guidance. Still expecting more clouds to work
farther west across the Cape later tonight.

640 pm update...

Previous forecast on track with a ridge of high pressure in
control. Light winds/mainly clear skies will result in an ideal
night of radiational cooling. Low temps by daybreak should be 
well down into the teens in many locales with perhaps even a 
few high single digit readings in the normally coldest outlying
locations. 

The only exception to the mainly clear skies will be some ocean
effect clouds mainly impacting the Cape/ACK at times
overnight...but can not rule out a few across Cape Ann/Plymouth
county. While they have temporarily dissipated...we may see 
them reform as flow just off the deck turns a bit more easterly
albeit very light.

&&

.SHORT TERM /6 AM TUESDAY MORNING THROUGH TUESDAY NIGHT/...
Tuesday...

Dry conditions prevail during the day, with high pressure over our 
area. A clipper type system approaches our area from the west, 
moving thru the Great Lakes Region as the day progresses. This 
allows the flow to shift from N/NNE to W/SW over the course of the 
day. 

If some ocean stratocumulus redevelop, could have partly cloudy
skies over mid and outer Cape/Nantucket to start. Then 
increasing sunshine expected as the winds turn to the W/SW. 
Otherwise another sunny/mostly sunny and cold day is forecast 
for southern New England. Highs will range from the upper 20s to
mid 30s across the interior, to the 30s along the coastal 
plain. 

Tuesday night...

The surface low pressure and associated northern stream short 
wave/mid level trough push eastward thru our area during Tue night. 
There is not much moisture with this feature as it moves thru our 
area, expecting mainly some clouds. Slight chance of snow showers 
during the overnight, mainly near/across the Cape and Islands as 
winds turn to the NNW, enabling an ocean effect component. Little or 
no accumulation is expected.

&&

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

* Mainly dry/cold Wed into Thu but some ocean effect snow showers 
  possible mainly across the outer-Cape Wed into Wed night

* Milder weather arrives Friday into early next week, but some wet 
  weather possible at times w/greatest risk Fri night into Sat

Details...

Wednesday and Wednesday night...

Vigorous northern stream energy swings across the region early 
Wednesday. This upper level energy will be associated with a distant 
ocean storm...so will have to watch for an inverted trough.  At this 
point...guidance indicates that the bulk of the moisture/instability 
and convergence remains offshore and is also rather progressive. 
While these things are difficult to forecast even in the very short 
term...odds favor this being too progressive/offshore for much 
impact. Therefore...most of the region probably remains dry except 
for mainly portions of the Cape, which will discuss in the next 
paragraph. It will be rather cold with highs on Wed mainly in the 
lower to middle 30s. Low temps Wed night should be well down into 
teens in most locations...but some high single digit readings are 
possible across the normally coldest outlying locations.

With that said...there may be enough convergence and moisture with 
the inverted trough for a brief period of snow showers into part of 
Wednesday morning across the Cape and and perhaps even 
Nantucket/Plymouth county. Then later Wed into Wed night...strong 
cold air advection will allow 850T to drop to between 
-13C and -15C across far eastern New England. This will result in 
the SST differential around 20C and ocean induced capes near 400 
J/KG. This modest instability and favorable northerly wind 
trajectories will probably bring a period of ocean effect snow 
showers to the outer-Cape Wed afternoon/night. Depending on exact 
wind direction may see this activity get briefly into Plymouth 
county and Nantucket. Snow accumulations of a coating to 1 inch are 
possible mainly across the outer-Cape with perhaps very localized 2 
inch amounts.

Thursday...

Large high pressure will be centered over our region.  Given the 
very cold start/limited mixing and low December sun angle it will be 
a rather cold day.  Despite lots of sunshine...many locations will 
only see high temperatures in the lower to middle 30s.

Friday through Monday...

A significant pattern change will be occurring with an active 
Pacific jet taking control.  The cold weather we have been dealing 
with the last month will be flushed out with the active Pacific jet. 
Given the pattern in transition...the models are going to struggle 
with northern and southern stream energy, timing and their 
interactions. The long range guidance and ensembles show quite the 
spread in solutions.  We will say that the best chance for 
precipitation looks to be Friday night into Saturday...but 
additional chances will be possible into early next week. Ptype will 
strongly favor rain given milder Pacific air invading the region.

&&

.AVIATION /03Z TUESDAY THROUGH SATURDAY/...
Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...High confidence.

Tonight and Tuesday... Mainly VFR. Exception is possible SCT-BKN 
VFR/MVFR cigs tonight into Tuesday across the mid to outer 
Cape/Nantucket. Low risk for some of these clouds to briefly
impact Cape Ann/Plymouth county too. Light N/NNE winds tonight 
becoming light S/SW Tue.

Tuesday night... VFR, except MVFR cigs possible Cape/Islands. Slight 
chance -SHSN, mainly Cape/Islands. 

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Wednesday through Saturday/... 

Wednesday: VFR. Breezy. 

Wednesday Night: Breezy. 

Thursday through Thursday Night: 

Friday: Breezy. 

Friday Night: Windy with local gusts to 30 kt. Chance RA.

Saturday: Windy with gusts to 35 kt. Chance RA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...High confidence. 

Tonight...

Winds slowly diminish but remain N-NE. Gusts up to 20 kt possible 
across the outer waters this evening. Seas around 2 to 4 feet away 
from the coast. 

Tuesday...High pressure moves across the waters as another weak low 
approaches from the W. light NE winds become variable to SW. Seas 
continue at 4 ft or less.

Tuesday night...Weak low pressure moves across the waters. Light 
west winds becoming NW and increasing to 10 to 15 kts, gusts to 20 
kts possible towards daybreak. Slight chance of snow showers. 

Outlook /Wednesday through Saturday/...

Wednesday: Moderate risk for Small Craft Advisory winds with
gusts up to 25 kt. Local rough seas. Chance of snow showers. 

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

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

Thursday Night: Winds less than 25 kt. 

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

Friday Night: Moderate risk for Small Craft Advisory winds with
gusts up to 30 kt. Chance of rain. 

Saturday: Low risk for gale force winds with gusts up to 40 kt.
Local rough seas. Chance of rain.

&&

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

&&

$$
SYNOPSIS...Frank/NMB
NEAR TERM...Belk/Frank
SHORT TERM...NMB
LONG TERM...Frank
AVIATION...Frank/NMB 
MARINE...Frank/NMB