Old Res Weather

Area Forecast Discussion
for Boston / Norton, MA

        
000
FXUS61 KBOX 141121
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
721 AM EDT Mon Jul 14 2025

.SYNOPSIS...
Mainly dry with seasonably warm and humid conditions continue 
through most of Monday. A frontal system could bring showers
and thunderstorms Monday afternoon and evening. Increasing heat and  
humidity around the middle of next week with increasing
confidence in the need for Heat Advisories for at least
Wednesday and Thursday. Trending cooler and drier for the
weekend.

&&

.NEAR TERM /UNTIL 6 PM THIS EVENING/...
Key Points:

 * Slow-moving Thunderstorms will bring heavy rain, scattered flash 
   flooding, and isolated severe wind gusts to the western interior

 * Seasonably warm and humid conditions again today


Today starts off very similar to the last few days with low stratus 
and light fog this morning, burning off within a few hours after 
sunrise.  High temperatures stay seasonal in the mid-80s today with 
partly sunny skies.  Dewpoints rise into the low to mid 70s today, 
making it feel very muggy.

Flash Flood Threat:

A flood watch is in effect from noon to midnight today for the CT 
river valley and west into the Berkshires.  A weak shortwave trough 
and frontal system will be the focus for slow-moving thunderstorms 
today across the western interior.  The environment is primed for 
very heavy rain and scattered flash flooding as PWATS jump to 2 
inches with dewpoints in the 70s. There will be very efficient rain 
processes with warm cloud depths around 13-14kft with long skinny 
cape profiles.  Steering winds aloft are very weak, on the order of 
20-30 knots from the WSW.  What that means is that storms will be 
very slow-moving and may train over the same spots for extended 
periods of time.  Although the highest probabilities lie southwest 
of SNE, the HREF highlights far western MA and CT for 3 inches of 
rain in 3 hours.  The href also highlights the far western interior 
with moderate probs (15-30%) for rainfall totals to exceed 5-year 
ARIs.  The flash flood threat drops quickly to the southeast of the 
flood watch as storms will run out of instability and diurnal 
heating by the time they exit the CT river valley.  


Severe Threat:

The best axis of instability lines along a SW to NE line in the far 
western interior with roughly 1000-1500 J/kg.  Even with little to 
no shear, there is a chance for wet microbursts, mainly in western 
MA.  Thunderstorm updrafts will become very hydro-loaded and will 
likely drop their cores on top of the updrafts.  Steep low-level 
lapse rates near 10 C km mean the momentum of the precip cores will 
easily continue to the surface.  With freezing levels around 14-15 
kft, hail is unlikely as any frozen precip will melt before reaching 
the surface.  While the environment is not supportive of rotating 
updrafts, the one wild card would be if any thunderstorms can hook 
onto outflow boundaries. 0-3km CAPE values are around 130 J/kg, 
which just might be enough to spawn a brief landspout should an 
outflow boundary be able to create enough low-level spin.  The 
severe threat will remain confined to the northwestern interior as 
Cape values drop off quickly to the southeast.  

Timing of thunderstorms:

Guidance is still somewhat mixed regarding convective initiation 
placement and timing, but the general consensus seems to be that a 
line of thunderstorms will form near the high terrain in eastern NY 
or western MA around 2-4 pm.  Storms then slowly move east through 
about 8-10 pm, weakening as they move southeast past the CT River 
Valley.

&&

.SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/...
Key Points:

 * Warm and muggy conditions continue tonight

 * Hot and humid conditions begin Tuesday

Tonight:

The frontal system will not bring any relief to the humid 
conditions, with lows bound by dewpoints remaining in the low 70s. 
Low stratus and fog will form once again, especially in areas that 
receive rainfall during the afternoon. 

Tuesday:

Hot and humid conditions are expected to return starting Tuesday, 
with high temperatures rising into the upper 80s to low 90s and 
dewpoints in the low 70s.  The heat index values currently look like 
they will fall just short of 95, but with heat indices likely above 
95 for Wednesday, heat advisories may be needed starting Tuesday. 
Most model guidance sources keep the region dry as a weak mid-level 
ridge builds in.  However, the NSSL WRF does have some convection 
breaking the mid-level CAP.

&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
Key Messages: 

* Hot and humid during the middle of next week, with elevated
  heat indices around 95-100F. Heat Advisories likely for at
  least Wed & Thur
 
* Becoming more unsettled late Thursday-Friday with increasing
  chances for showers/storms. 

Wednesday-Thursday: 

Heat and Humidity...

Weak mid-level ridging persists over the region Wednesday with
more zonal flow arriving Thursday. Temperatures aloft increase 
with 850mb temperatures peaking at around 20C in the Weds- Thurs
timeframe. Ensemble guidance shows a plume of above normal 
moisture in the flow which will add increased humidity to the 
mix. Temperatures Wednesday through at least Thursday will range
in the upper 80s to mid 90s with the exception of the immediate
coast. With the the added element of higher humidity, it will 
feel more like mid 90s to near 100 Wednesday and Thursday. This 
combo provides a good signal for potential heat impacts. NWS 
Heat Risk reflects this potential well with Heat Risk in the 
Major Category Wednesday and Thursday. There is a high 
probability that we will need Heat Advisories for Wednesday and 
Thursday. We'll need to keep an eye on cloud cover for Thursday 
as this may limit highs a bit. Friday may also end up being a 
hot day as well with ensembles showing little change in the 
temperatures aloft with again a similar risk of clouds limiting 
high temperatures. 

Precipitation...

Wednesday stay mainly quiet when it comes to the passage of any
substantial system. Despite a weakly forced atmosphere, above 
normal moisture, hot temps, and marginal daytime instability 
will support isolated shower activity. Ensemble members are 
still spread across the board with timing and given the low 
coverage nature of the showers and lack of definitive forcing. 
This has made it it bit more difficult to message in the 
forecast. Overall, expect a tropical-like atmosphere with 
periods of higher cloud cover and perhaps a spot shower. 

There will be a better signal for more organized forcing later 
Thursday and a weak trough shifts in from the west. This will bring 
higher chances for more widespread showers/storms. Weak winds aloft 
will support slower storm motions and given the high amounts of 
moisture signal a threat for flash flooding. We'll have to keep eyes 
on that as we go through the week. 

Friday-Weekend: 

Ensemble guidance shows the main axis of the trough pushing across 
the region by early Saturday. Similar story to Thursday with 
increased chances for showers/storms later Friday ahead of an 
approaching cold front. Winds aloft are slightly higher than 
Thursday, but slower moving storms still look to bring a potential 
threat for flash flooding. Friday may be another potentially hot 
day. Ensemble members show more of a wider envelope of solutions for 
temperatures Friday. However, there are still plenty of very warm 
members that would support another Heat Advisory criteria given the 
humidity. We'll have to watch cloud cover as this could keep it cool 
enough to not meet Advisory criteria. 

Behind the trough, conditions dry out through the day on Saturday. 
Ensembles hint at potential for another system later Sunday, 
although confidence is low this far out.

&&

.AVIATION /11Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

12z Update:

Monday: Moderate Confidence 

Low stratus and fog burn of gradually 13z-15z. VFR by mid to 
late morning. A line of slow moving showers and thunderstorms 
forms or moves into western MA and CT in the mid to late 
afternoon, continue to move east through about 10pm to midnight.
How far east convection gets is still uncertain, with terminals
inside the I-95 corridor possibly being spared.

Monday Night: Moderate Confidence

After remaining showers and thunderstorms dissipate, winds turn
SSW brining in yet another round of low stratus and fog. Highest
confidence near the south coast and CT river valley. Less
certain in and around Boston. 

Tuesday: Moderate Confidence

VFR outside the Cape and Islands where IFR stratus may hang on
much of the day. Low chance for a weak shower or thunderstorm.

KBOS Terminal...Moderate confidence in TAF.

Stratus lifting 13z-14z, then VFR. Thunderstorms will struggle 
to reach the terminal this evening, likely just left over 
showers, thus continued with the PROB30 -SHRA.

KBDL Terminal...Moderate confidence in TAF. 

MVFR stratus deck becoming IFR before sunrise. The stratus deck
took longer then anticipated to burn off yesterday, however, 
winds turn more SSW today which should allow it to lift mid 
morning. VFR this afternoon with slow moving heavy showers and 
thunderstorms. 

Outlook /Tuesday Night through Friday/... 

Tuesday Night: VFR. 

Wednesday: VFR. Slight chance SHRA.

Wednesday Night: VFR. Slight chance SHRA, slight chance TSRA.

Thursday: VFR. Breezy. Chance TSRA, slight chance SHRA.

Thursday Night: VFR. Breezy. Slight chance SHRA, slight chance
TSRA.

Friday: VFR. Chance SHRA, chance TSRA.

&&

.MARINE...
Forecaster Confidence Levels...

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

Today through Tuesday...High confidence.

Weak pressure gradient will keep winds/seas below Small Craft  
Advisory thresholds through Sunday: seas 2-3 ft with E winds 
over the southern waters and SE winds over the eastern waters up
to 15 kts during the afternoon hours, remaining light in the 
overnight hours. Main concern for mariners will be areas of fog 
tonight that may redevelop again tonight. Inland Thunderstorms
are unlikely to affect the waters this evening. Winds turn more
SW on Tuesday between 10-15 knots. 

Outlook /Tuesday Night through Friday/...

Tuesday Night through Wednesday Night: Winds less than 25 kt. 

Thursday: Winds less than 25 kt. Seas locally approaching 5 ft.
Slight chance of rain showers, slight chance of thunderstorms. 

Thursday Night through Friday: Winds less than 25 kt. Areas of
seas approaching 5 ft. Slight chance of rain showers, slight
chance of thunderstorms.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Flood Watch from noon EDT today through this evening for 
     CTZ002.
MA...Flood Watch from noon EDT today through this evening for 
     MAZ002-003-008>011.
RI...None.
MARINE...None.

&&

$$

SYNOPSIS...Mensch/KP
NEAR TERM...KP
SHORT TERM...KP
LONG TERM...Mensch
AVIATION...McMinn/KP
MARINE...KP