Lexington, Massachusetts, USA

3/20/2019 5:29pm 
  • Lexington Conditions: Partly cloudy
  • Temperature: 48.9°F / 9.4°CColder 0.7°F than last hour.
  • Dew Point: 31.1°FIncreased 4.9°Fsince last hour.
  • Relative Humidity: 50%Increased 10.0% since last hour.
  • Wind: S 4 mph, 10-min avg: 5 mph, gust: 18 mph
  • Barometer: 30.22 in Steady
  • Visibility: 10 miles
  • Rain Today: 0.00 in

Area Forecast Discussion
for Lexington MA

FXUS61 KBOX 201957

Area Forecast Discussion
National Weather Service Boston/Norton MA
357 PM EDT Wed Mar 20 2019

High pressure remains in control of our weather tonight. A 
coastal storm impacts the region late Thursday into Friday with 
periods of rain, heavy at times, and stronger winds. Low 
pressure departs through the Maritimes Friday, bringing gusty 
winds to Southern New England. High pressure then builds drier 
air in for the weekend. A cold front sweeps south from Canada 
Sunday night and Monday bringing showers. High pressure buidls 
colder air in from Canada early next week.


The center of a high pressure will move off to the east
overnight. That said, there will be enough of a ridge where an
approaching low pressure will be held off from reaching our
region for a time. Will keep the forecast dry tonight.
Temperatures should not be as low, due to a combination of light
south winds and increasing clouds, especially after midnight.


Dry weather to start Thursday, and most of the eastern half of
southern New England may be dry through the day. There will be
an increasing risk for precipitation from west to east,
especially during the afternoon. Any precipitation will likely
falls as rain, and will be most likely west of the CT River by
late Thursday afternoon. With some sunshine to start, and a S to
SE wind, should see temperatures near to slightly above normal
away from the immediate coastline.

Surface low pressure from the Mid Atlantic should move over the
eastern half of southern New England Thursday night. Track of
the closed low at both 925 mb and 850 mb suggests this will be
mainly a rain event, with some wet snow possible towards the
higher terrain of the Berkshires. Precipitable water remains
about 1-2 standard deviations above normal. Expecting rainfall
of 0.5-1.00 inches, with locally higher amounts should any
convection develop. Any instability would be elevated, and 
should only enhance rainfall rates.



Big Picture...

On the longwave scale, Hudson's Bay upper low maintains cyclonic 
flow over the Northeast USA through the weekend. The flow then 
becomes more zonal next week. At shorter scales, closed upper low 
sweeps from Northern Ontario over New England Friday with heights 
that are 2-3 std deviations below normal. The low then moves off 
through the Maritimes on Saturday. Heights then return to near 
normal or a little above during the weekend. 

Expect that temperatures will trend to seasonably mild levels over 
the weekend. Differences in timing a cold front coming south from 
Canada early next week, but agreement that a cold front moves 
through, followed by colder temperatures the first half of the week.

Confidence is moderate over the weekend and low-moderate early next 



The coastal weather system moves north of our area, allowing drier 
air to move in. Expect any lingering rain to taper off, although 
scattered showers possible through the afternoon. Breaks of sun late 
in the day. Winds to 25 knots aloft will be available to mix to the 
surface in gusts.

The central pressure of the weather system will also be deepening, 
which should tighten the pressure gradient and lead to increasing 
wind. The strongest pressure rises are expected Saturday, with 1-2 
mb/hour rates. Adding to that, the upper low and its cold pool sweep 
overhead Friday night and Saturday morning. The strong vertical 
temperature lapse rates should mix strong northwest winds to the 
surface in gusts. Cross-sections show 35-40 knot winds aloft in the 
mixed layer Saturday. As usual, guidance underplays these 
values...we will nudge wind gust guidance up about 5 knots. Moisture 
cross sections show deep moisture the first half of Saturday, 
especially during the time of strong lapse rates. Expect at least 
partly cloudy skies Saturday with periods of mostly cloudy possible. 

Sunday through Wednesday...

High pressure builds for Sunday. Temps in the mixed layer suggest 
max temps in the 50s

Consensus on a cold frontal passage Monday.  The ECMWF shows fropa 
early Monday morning, while the GFS shows passage Monday 
afternoon/evening and the GGEM aims for early Monday night. Some 
models keep the supporting upper jet up on the Canadian border, 
while others show the right entrance region of the northern jet 
reaching down over Southern New England. We will maintain chance 
pops for showers Monday afternoon/evening.

That right entrance region may generate a wave on the front, 
delaying the departure of the showers Monday night. Otherwise, high 
pressure builds south from Canada with cooler, drier air for Tuesday 
and Wednesday.


Forecaster Confidence Levels...

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

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

Through 00Z...VFR with light south winds. Seabreezes along the
coast should diminish as the southerly winds become more 
dominant towards sunset. Dry weather prevails.

Tonight...VFR, dry weather and light SSW winds.

Thursday...VFR and dry to start the day with MVFR arriving in 
the afternoon across western MA/CT along with increasing chances
of light rain. Increasing ESE winds. 

Thursday Night...Mainly IFR, with local MVFR possible. Breezy. 
Widespread -RA/RA with patchy FG.

KBOS Terminal...High confidence in TAF. Timing for the end of
the seabreeze may be off by an hour.

KBDL Terminal...High confidence in TAF. 

Outlook /Friday through Monday/...

Friday: Mainly MVFR, with areas IFR possible. Windy with gusts
up to 30 kt. Chance SHRA, patchy FG.

Friday Night: MVFR/IFR conditions possible. Strong winds with
local gusts up to 40 kt. Chance SHSN, chance SHRA.

Saturday: VFR. Strong winds with gusts up to 40 kt. 

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

Sunday: VFR. Breezy. 

Sunday Night: VFR. 

Monday: Mainly VFR. Slight chance SHRA.


Forecaster Confidence Levels...

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

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

Rather light winds and seas will continue through Thursday
morning. An approaching low pressure Thursday afternoon will
pass through our region Thursday night. Winds increase Thursday
afternoon into Thursday night. Small Craft Advisories will be
needed. Depending upon timing for the strengthening of this low
pressure, might see some gusts to gale force. Have much greater
confidence in gusts 25-30 kt at this time.

Widespread rain develops Thursday afternoon into Thursday 
night, resulting in poor visibility at times. 

Outlook /Friday through Monday/...

Friday: Low risk for Small Craft Advisory winds with gusts up
to 30 kt. Rough seas up to 11 ft. Chance of rain showers. Local
visibility 1 nm or less.

Friday Night: Moderate risk for gale force winds with gusts up
to 40 kt. Rough seas up to 13 ft. Chance of rain showers,
chance of snow showers. Local visibility 1 to 3 nm.

Saturday: Moderate risk for gale force winds with local gusts
up to 45 kt. Rough seas up to 13 ft. 

Saturday Night: Low risk for gale force winds with gusts up to
35 kt. Areas of rough seas. 

Sunday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Areas of seas approaching 5 ft. 

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

Monday: Winds less than 25 kt. Seas locally approaching 5 ft.
Slight chance of rain showers. 


Seeing a decent signal for onshore winds overnight Thursday into
Friday. Peak surge looks to occur just after the timing of low 
tide early Fri morning per latest ensembles. However, lingering
surge or a slower timing could lead to create coastal impacts.
At this time, thinking pockets of minor coastal flooding are 
most likely. Astronomical tides are rather high, about 11.7 ft 
MLLW in Boston. The Friday morning/early afternoon high tide 
looks to be the high tide of greatest concern along the east 
coast, with the Friday morning high tide the concern for the 
south coast.


MARINE...Small Craft Advisory from 9 PM Thursday to 6 PM EDT Friday for 
     Small Craft Advisory from midnight Thursday night to 6 PM EDT 
     Friday for ANZ231-251.
     Small Craft Advisory from 6 PM Thursday to 6 PM EDT Friday for 
     Small Craft Advisory from 8 PM Thursday to 6 PM EDT Friday for 
     Small Craft Advisory from 1 PM Thursday to 6 PM EDT Friday for