LexMAWeather

Area Forecast Discussion
for Boston, MA

        
112 
FXUS61 KBOX 212320
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
720 PM EDT Mon May 21 2018

.SYNOPSIS...
Dry and tranquil weather continues tonight. Rather cloudy skies
are anticipated Tuesday along with cooler temperatures. A warm 
front will bring some showers to the region...generally Tuesday
afternoon and evening. Mainly dry weather Wednesday through 
Saturday. Moisture increases through the weekend with the best 
chance of showers on Sunday. Much warmer Friday into the 
weekend.

&&

.NEAR TERM /UNTIL 6 AM TUESDAY MORNING/...
7PM update...
Overall, forecast remains on track. Both cloud cover and rain
activity is going to be very slow as the column is quite dry
even at this time. With light flow developing early, some
radiational cooling should allow temps to fall into the low 50s
before the cloud shield prevents further outgoing radiation.
Lowered mins a bit.

&&

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

A rather cloudy day is on tap for Tuesday ahead of a warm 
front. There appears to be enough forcing/moisture along with a 
modest low level jet for some showers Tuesday afternoon/evening.
Not expecting a complete washout...but most locations should 
see a period of wet weather during this time. There is even a 
low risk for a rumble or two of thunder...mainly near the south 
coast with some marginal elevated instability. High temperatures
will be held in the upper 60s to around 70 in most locations 
given the clouds along with the afternoon/evening showers. 

The bulk of the showers should come to an end Tuesday
evening...but a few will remain possible after midnight as a
weak cold front crosses the region. Clouds will probably hang
tough for most of the night and may see some fog develop given 
ample low level moisture. This should hold overnight low 
temperatures in the lower to middle 50s.

&&

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

* A spot shower lingers Wednesday
* Cool Thursday but much warmer into the weekend
* Risk of showers increases by Sunday

Overview...
Through the mid term, the N stream dominates, mainly in the 
form of a longwave trof settling across the Maritimes which is 
linked to a Baffin Sea vortex. However, with the mean trof axis 
to the W, central CONUS ridging will lead to rising heights and 
generally cyclonic flow through the latter half of the week. It 
is not until the tropical disturbance in the Gulf of Mexico gets
caught up with shortwave energy moving out of the Pacific that 
there is a transition for New England. These impacts, 
particularly with a plume of tropical moisture, could yield a 
wet latter half of Memorial Day weekend. Overall, enough 
agreement between guidance to use a consensus blend for this 
forecast update.

Wed...
Cold front slows as it begins to parallel mid lvl flow. 
However, soundings support rapid influx of drier air through the
column, reducing PWATs to below 1.00in by mid day. Although 
this does steepen lapse rates, the overall lack of moisture may 
limit convective potential. Near NIL QPF supports this thinking.
Still enough to warrant at least slight chance POPs. Delayed 
cold advection suggests highs should reach the mid 70s to around
80, especially as some clearing is observed.

Thu through Sat...
Mainly dry thanks to implied ridging through mid and upper lvl 
height rises and sfc high pres as a response. Thu looks to be 
the coolest day, but with H85 temps avg around +8C, it still 
should yield low 70s across much of the region. Milder Fri and 
Sat with temps in the upper 70s and low 80s thanks to a gradual 
increase in mid lvl temps. These are best observed inland 
however, as weak pres gradient suggests local sea breezes at 
area coastlines.

Sun into early next week...
Echo previous forecasters concern and lack of overall 
confidence as guidance widely diverges during this period. This 
is not surprising, as models often struggle with complex 
tropical interactions. At odds for New England, is a resurgence 
in N stream forcing trof out of the Arctic with its sfc 
response, a N-S moving cold front front which makes temperatures
rather uncertain. From the S stream, is tropical moisture plume
with PWATs potentially reaching near 2.00 inches just to the S.
If this dominates a period of wet and very unsettled conditions
are possible, keeping the front to the N. For now, will lean 
most heavily on ensemble means for this period as it takes into 
account the potential solutions. This will come into focus 
better as the feature players, particularly the tropical wave 
become better sampled.

&&

.AVIATION /00Z 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/...

Tonight...High confidence.
VFR.  Winds becoming light and variable.

Tuesday and Tuesday night...Moderate to high confidence. Mainly
VFR conditions into Tuesday afternoon. It probably will take 
until evening especially along the coast for MVFR to localized 
IFR ceilings and visibilities to arrive. These lower cigs/vsbys 
will likely persist Tuesday night. Some showers expected 
especially Tuesday afternoon and evening. A low risk for a 
rumble or two of thunder mainly near the south coast Tue 
evening.

KBOS Terminal...High confidence in TAF. Still uncertainty though
in wind direction through 22z. BOS sea breeze kicked offshore as
of 19z...but still close enough where it needs to be watched for
another few hours.

KBDL Terminal...High confidence in TAF.

Outlook /Wednesday through Saturday/...Moderate confidence.

Wednesday: Mainly VFR. 

Wednesday Night: VFR. Breezy. 

Thursday through Thursday Night: VFR. 

Friday through Friday Night: VFR. Breezy. 

Saturday: Mainly VFR, with areas MVFR possible. Chance SHRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Short Term /through Tuesday Night/...

Tonight through Tuesday night...High confidence. Weak pressure
gradient will keep winds and seas below small craft advisory
thresholds through Tuesday night. Biggest concern for mariners
will be the potential for some fog developing Tuesday night
along with the low risk for a rumble or two of thunder across
our southern waters.

Outlook /Wednesday through Saturday/...Moderate confidence.

Wednesday: Winds less than 25 kt. Slight chance of rain
showers, patchy fog. Local visibility 1 to 3 nm.

Wednesday Night: Winds less than 25 kt. Seas locally
approaching 5 ft. Patchy fog. Local visibility 1 to 3 nm.

Thursday through Thursday Night: Winds less than 25 kt.

Friday: Winds less than 25 kt. Local rough seas. 

Friday Night: Winds less than 25 kt. Areas of rough seas. 

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

&&

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

&&

$$
SYNOPSIS...Frank/Doody
NEAR TERM...Frank/Doody
SHORT TERM...Frank
LONG TERM...Doody
AVIATION...Frank/Doody
MARINE...Frank/Doody