Old Res Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 100740
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
340 AM EDT Wed Aug 10 2022

.SYNOPSIS...
A backdoor cold front brings much cooler temperatures today but
humidity remains elevated. A wave of low pressure may bring 
some showers to mainly Rhode Island and southeast Massachusetts 
tonight into Thursday if it tracks close enough to the coast. 
Prolonged stretch of dry and tranquil weather Friday through Sunday 
with cooler than normal temperatures and low humidity levels. 
Weather pattern turns more unsettled early to mid next week 
with better chances for rains around Tuesday or Wednesday. 
Temperatures remain at seasonable levels with no indications of 
significant heat and humidity returning to Southern New England 
in the foreseeable future.

&&

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

345 AM Update...

* Much cooler today with mostly dry weather and a mix of sun/clouds. 

The back door cold front pushes just south of New England then 
stalls, with weak low pressure traveling along it. Radar 
reflectivity shows a few isolated showers across northern CT and 
just off Nantucket. These are forming right along the frontal 
boundary that is expected to stall just south of the MA/RI south 
coast. SPC mesoanalysis shows 25 kt 0-6km shear across the south 
coast and some MLCAPE just offshore. So there is a low probability 
of a few thundery showers or an isolated thunderstorm, with better 
chances offshore through the early morning hours. In addition, due 
to the weak nature of the cold front and the fact that we are coming 
off PWAT values that are near/at max of SPC sounding climo (2-2.3 
inches), there is plenty of moisture trapped under the low-level 
inversion. So did include slight chance PoPs (mostly in the form of 
drizzle away from the immediate coast) all the way up to the Mass 
Pike, with chance PoPs along the south coast along with mention of 
isolated thunder. Not expecting anything strong or severe but don't 
be surprised to wake up to a rumble of thunder if you live along or 
near the south coast. 

Then for the remainder of the day, we will have a much cooler 
northeast wind flow, and with SSTs northeast of our area only in the 
mid to upper 60s, highs will only in the mid 70s to mid 80s, 
bringing an end to the heat wave. Mid 70s should be found along the 
eastern MA coast, with upper 70s to low 80s across much of interior 
MA, northeast CT and RI. Best shot for mid 80s will be across CT 
valley due to downsloping warming effect on temperatures on a 
northeast flow. It should be a mostly dry day with rather 
comfortable dew points as well as a mix of sun and clouds. Expect 
more clouds than sun earlier in the day trending more sun than 
clouds later in the day. Talk about a nice finish to the work day. 
Enjoy!

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM THURSDAY/...

* A period of showers on Thursday with best chance for appreciable, 
  steady rainfall south of the Mass Pike, and especially along the 
  MA/RI south coast into Cape and the Islands. 

A wave of low pressure approaches our area from the Mid Atlantic 
states. Looks like best chance for appreciable rainfall will be 
south of the Mass Pike, and especially near and along the MA/RI 
south coast into Cape and the Islands. Timing wise, the leading edge 
of the precipitation will be entering Connecticut during the 
overnight hours, spreading into eastern MA around or right after 
daybreak. Forecast sounding cross sections show deeper RH values 
only up to 6-7k ft, so not expecting too much in the way of 
rainfall, i.e. mainly in the form of a few sprinkles or showers. 
PWATs over 1.5 inches (seasonably high, although not record 
territory like the past couple of days) will overspread areas south 
of the Pike and into eastern MA by daybreak. Then during the day, a 
swath of 0.75 to 1 inch PWATs (roughly 25th percentile according to 
SPC sounding climatology for Chatham, MA) overspreads from west to 
east, which should help suppress the best shot for appreciable 
rainfall to areas near and along the south coast into Cape and 
Islands. 

A disclaimer here is that given limited baroclinicity this time of 
year, it is somewhat challenging to pinpoint the northward extent of 
a synoptic QPF field. Nonetheless, 00z CAMs are coming into better 
consensus with the track of the low pressure giving areas north of 
the Mass Pike mostly dry weather. 

Otherwise, the only thing will have to watch is for perhaps some 
scattered showers and isolated thunderstorms trying to enter western 
MA during the evening hours with the cold front approaching. More 
details in the long term discussion section. Dynamics weaken as this 
moves east so may fall part as it tries to enter southern New 
England. Highs on Thu will mainly be in the 80s, but perhaps places 
on the immediate coast may not reach 80.

&&

.LONG TERM /THURSDAY NIGHT THROUGH TUESDAY/...

Highlights: 

* Dry, tranquil weather with pleasant humidity levels and temps a 
  few degrees below normal Fri thru Sun.

* Turning unsettled Mon thru Wed, with increasing chances for 
  showers toward Tue-Wed. Temps seasonable but may see a modest 
  increase in humidity level by midweek but nothing like what was 
  experienced recently.

Details:

Through this portion of the forecast, the governing large-scale 
pattern transitions to one of mid-level troughing, as the 
Intermountain West ridge amplifies and retrogrades towards the NW. 
Longwave troughing digs into western New England Thurs night. It 
then more-or-less settles into New England and the mid-Atlantic 
states through at least midweek, reinforced by additional trough 
energy around early to midweek. This 500 mb configuration, reflected 
in most deterministic models and the ensemble means, should make our 
weather pattern more unsettled as we move into next week. That said, 
lower-than-normal heights and cooler lower-level temps translate to 
no significant heat or humidity surges with temps trending around or 
just below normal. 

Though there may be some spotty rain chances near coastal New 
England on Fri, much of Fri into the upcoming weekend will feature 
dry and tranquil weather with comfortable humidity levels. Dewpoints 
could be as low as the upper 40s in the interior by this weekend! 
So, a much more refreshing air mass with fairly strong diurnal 
ranges. Highs generally in the 70s to lower 80s with lows in the mid 
50s to low 60s should be common through much of this period. Thus 
should be ideal for outdoor activities, though temps will run a few 
degrees below normal. 

By Mon through Wed, shortwave energy emanating from the Gt Lakes 
helps reinforce the longwave trough. A bit more southwest flow looks 
to bring deeper moisture into our area, making our weather pattern 
more unsettled with better opportunities for increased rain chances. 
Timing and location of PoPs and QPF are still uncertain though; 
assessment of ensembles don't really shed much light on the unclear 
pattern either. Looks like Tues and Wed may offer better chances 
regionally, but some opportunity for rain showers could develop as 
early as Monday. Will carry NBM-based Chance-level PoP in this 
period, higher toward Tues-Wed. Significant rains don't look likely 
at this point though. Temps run closer to seasonable levels but may 
also see an uptick in humidity level moving into midweek; at the 
moment, nothing like the sauna-like humidity levels we saw on 
several occasions recently.

&&

.AVIATION /08Z WEDNESDAY THROUGH SUNDAY/...
Forecaster Confidence Levels:

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

07Z TAF Update...

Rest of tonight...High confidence in trends, moderate in exact 
timing. 

A backdoor cold front has brought IFR/LIFR ceilings to much of Cape 
and eastern MA/RI terminals during the overnight hours behind the 
cold front near the southeast New England coast. Elsewhere across 
interior MA/CT, low VFR to MVFR ceilings. Winds shift to the NNE at 
5 to 10 knots behind the cold front, but will briefly gust stronger 
along the immediate coast right behind the front. 

Today...Moderate confidence.

MVFR/IFR ceilings slowly improving to VFR. E/NE winds turning to the 
SE at 5-10 kts. 

Tonight...Moderate confidence.

MVFR to IFR conditions with perhaps some rain showers spreading in 
toward the south coast. Lots of uncertainty with this activity as a 
low develops along the frontal boundary nearby. Light SE/S winds 
perhaps shifting to the SW toward daybreak.

Thursday...Moderate confidence. 

Mainly VFR, with areas MVFR possible during periods of rain. Best 
chance for showers south of the Mass Pike. 

KBOS...Moderate confidence. 

KBDL...Moderate confidence.

Outlook /Thursday Night through Sunday/...

VFR. 

&&

.MARINE...
Forecaster Confidence Levels:

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

340 AM Update...

Today...High confidence. 

NE/E winds at 5-10 kts with seas 2-4 ft.

Wednesday night...Moderate confidence.

Light E/SE winds around 5 kts. Seas 2-4 ft, but some uncertainty 
with regards to the northward extent of the rainfall associated with 
a low pressure system passing to our south. Best chance for showers 
developing late overnight across southern waters, with eastern 
waters likely remaining dry.

Thursday...Moderate confidence. 

Winds and seas below SCA criteria. Chance of rain showers especially 
across the southern waters. 

Outlook /Thursday Night through Sunday/... 

Thursday Night: Winds less than 25 kt. Slight chance of rain
showers. 

Friday through Sunday: Winds less than 25 kt. 

&&

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

&&

$$
SYNOPSIS...Loconto/Chai
NEAR TERM...Chai
SHORT TERM...Chai
LONG TERM...Loconto
AVIATION...Loconto/Chai
MARINE...Loconto/Chai