Lexington, Massachusetts, USA

4/20/2019 4:44am 
  • Lexington Conditions: Overcast
  • Temperature: 67.3°F / 19.6°CWarmer 0.7°F than last hour.
  • Dew Point: 64.9°FIncreased 0.1°Fsince last hour.
  • Relative Humidity: 92%Decreased 2.0% since last hour.
  • Wind: WSW 9 mph, 10-min avg: 5 mph, gust: 15 mph
  • Barometer: 29.73 in Steady
  • Visibility: 9 miles
  • Rain Today: 0.05 in

Area Forecast Discussion
for Boston, MA

FXUS61 KBOX 200753

Area Forecast Discussion
National Weather Service Boston/Norton MA
353 AM EDT Sat Apr 20 2019

A slow moving low pressure system moving slowly northeast from
the Ohio valley will bring showers with locally heavy rainfall 
into this evening. The low pressure will linger across New 
England into early next week. Off and on rain chances through 
Wednesday, perhaps a drying trend for late week.



High amplitude trough to the west with mid level low drifting 
to the Ohio Valley today. Downstream meridional flow into New 
Eng will set up an anomalous 3-4SD PWAT and low level wind axis
which which will support numerous showers with locally heavy 
rainfall today. Models are showing some elevated CAPE today so
isold t-storms also possible. 

Numerous showers are lifting north across western/central MA and
northern CT early this morning with additional convection
extending south along the mid Atlc coast. This process will
continue today with convection firing over the ocean to the
south and lifting north into SNE. The axis of heavier rain is
currently fairly well aligned with the low level jet which 
slowly shifts east during today. As a result, the focus for 
showers and heavy rainfall should slowly shift east to eastern 
New Eng during the afternoon while the showers become more 
scattered in the west. 

Low level jet across SNE will result in more gusty winds today.
However, temps will be a bit cooler today with BL mixing not as
robust so gusts should not be as strong as yesterday. Expecting
occasional gusts 30-40 mph. Highs will reach upper 60s to lower
70s, except 60-65 along the immediate south coast where areas 
of fog may persist.

Flood watches will continue for western half of SNE where
heaviest rainfall expected. Total rainfall of 1-2 inches
expected in the flood watch area with locally up to 3 inches 



Low level jet and moisture axis is focused across eastern New 
Eng where numerous showers will continue through the evening 
before becoming more scattered overnight. But rainfall 
intensity will diminish as the low level jet weakens. In 
western New Eng, the threat of scattered showers will continue 
but some mid level drying moves in from the west which will 
lead to less coverage of showers. 

Diminishing winds expected during the night with temps falling
into the low/mid 50s by daybreak. 


Mid level low remains west of New Eng with deep southerly flow
continuing. However, somewhat drier air wraps around the low 
and moves into New Eng while main PWAT axis moves offshore. The
risk of showers will continue, especially eastern New Eng 
although there will be dry periods as well and some breaks of 
sunshine will be possible in the interior. Highs will reach
mid/upper 60s, cooler south coast.  


Highlights ...

* Showers and cooler conditions continue Monday into Tuesday
* Brief break possible Tuesday before rain chances return overnight 
  into Wednesday
* Cooler with shower chances late week

Monday and Tuesday...

Once again we see the slowing exit of an amplified cutoff low over 
delmarva Sunday night. The upper low languishes over over the 
region, struggling to re-enter the steering flow, and approaches 
southern New England Monday night. It finally exits to the east 
around morning/mid day Tuesday. During the Monday morning to early-
mid Tuesday period we'll see the return of widespread rain chances 
with some convection possible on Monday afternoon/evening. We see a 
secondary surface low form along the frontal boundary to our south 
Monday morning which proceeds to meander northward over the region 
during the day. At the same time we have a good source of moisutre as 
the plume of high PWATs wraps back around the upper low and over 
SNE. We could get some good rain out of this system with 0.5-1" of 
rain possible from Monday morning to Tuesday morning. Under the 
500mb cold pool lapse rates steepen as well and could allow for some 
convection as well. Temperatures are a bit cooler than we saw over 
the weekend under said cold pool, reaching into the 60s. Tuesday we 
may be able to get into the upper 60 or 70s in spots if we can get 
enough breaks of sun during peak heating hours. 

Wednesday through Friday... 

A very progressive pattern sets up mid-late week with several 
shortwaves dipping through a broad eastern US trough. This comes 
with below average confidence in timing of the individual waves as 
models have struggled the last several runs to come to any sort of 
consensus. As these shortwaves move through, at the surface we see a 
couple of distinct low centers crossing SNE bringing rain chances 
through the entire forecast period. As is to be expected, highest 
confidence comes with the earliest of these systems which moves 
through around late Tuesday night/Wednesday. Moving from the Great 
Lakes region a low crosses Northern New England dragging a warm 
front through late Tuesday night followed by a cold front later 
Wednesday. With this, rain returns much of Wednesday with slightly 
cooler temperatures. Beyond Wednesday timing is uncertain but 
periodic rain chances continue with noticeably cooler temperatures.


Forecaster Confidence Levels...

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

Short Term /through Sunday/...Moderate confidence.

Through Today...
Widespread IFR/MVFR conditions with numerous SHRA/+SHRA and 
isold thunder in western New Eng gradually shifting to RI and 
eastern MA this afternoon. Areas of LIFR fog along the immediate
south coast. Continued LLWS south coast. S/SW gusts to 30-35 

IFR/MVFR conditions with numerous showers, mainly across 
eastern New Eng. Patchy fog near the coast. Slow improvement 
in the west. Diminishing winds.

VFR/MVFR cigs with sct showers, especially eastern New Eng. 

KBOS terminal...Moderate confidence in TAF

KBDL terminal...Moderate confidence in TAF.  

Outlook /Sunday Night through Wednesday/...

Sunday Night: Mainly VFR, with areas MVFR possible. Chance

Monday: Mainly VFR, with areas MVFR possible. Chance SHRA,
isolated TSRA.

Monday Night: Mainly VFR, with areas MVFR possible. Chance

Tuesday: Mainly VFR, with areas MVFR possible. Slight chance

Tuesday Night: Mainly VFR, with areas MVFR possible. Chance

Wednesday: Mainly VFR, with local MVFR possible. Slight chance


Forecaster Confidence Levels...

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

Short Term /through Sunday/...High confidence.

Gusty south winds today as low level jet remains across the 
waters. Gusts to 30-35 kt expected and have issued gale warnings
today for the south coastal nearshore waters. Reduced vsbys in
fog over south coastal waters. Numerous showers moving into the
waters reaching eastern MA waters this afternoon.  

Up to 30 kt gusts in the evening, then winds slowly diminish 
during the night. Showers continue along with patchy fog. 

Southerly winds below 15 kt but rough seas persist over southern

Outlook /Sunday Night through Wednesday/...

Sunday Night: Winds less than 25 kt. Rough seas up to 10 ft.
Chance of rain showers. 

Monday: Winds less than 25 kt. Rough seas up to 9 ft. Chance of
rain showers. 

Monday Night: Winds less than 25 kt. Areas of rough seas.
Chance of rain showers. 

Tuesday through Tuesday Night: Winds less than 25 kt. Seas up
to 5 ft. Chance of rain showers. 

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


Only minimal tidal departures were noted during last evenings
high tide along the south coast. Tidal departures for Saturday
nights high tide should remain less than 1 ft. Given that
astronomical tides are a bit less than last evening, not
expecting much if any inundation issues. 


CT...Flood Watch through this evening for CTZ002>004.
MA...Flood Watch through this evening for MAZ002>004-008>012.
MARINE...Gale Warning until 6 PM EDT this evening for ANZ232>237.
     Small Craft Advisory until 10 PM EDT this evening for ANZ230-
     Small Craft Advisory until 6 AM EDT Sunday for ANZ231-250-