Somerville, Massachusetts 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

779
FXUS61 KBOX 251929
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
329 PM EDT Fri Jul 25 2025

.SYNOPSIS...
Showers and areas of severe thunderstorms continue this
afternoon with a cold front. Cooler and mainly dry Saturday
with showers and thunderstorms returning for Sunday. Outlook for
early next week shows summerlike warmth and humidity, with
generally dry weather for the majority of the time. Showers and
thunderstorms return for Sunday. Outlook for early next week
shows summerlike warmth and humidity, with generally dry weather
interrupted by a few shots at scattered showers and
thunderstorms, mainly Tuesday and late Wednesday into Thursday.
Trending drier and cooler Friday into the weekend.

&&

.NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
** Severe Thunderstorm Watch for scattered damaging wind gusts in
  effect for much of the forecast area through 9pm this evening.

* Dangerous heat and humidity through early evening

* Drier and calmer conditions Saturday as high pressure builds in
  overhead.


THIS AFTERNOON:

Convection has begun to blossom mainly south of the Mass Pike as a
prefrontal trough pushes southeast. Storms have thus far taken on
multicellular characteristics but will begin to consolidate into more
of a linear mode as they push south and east. Current mesoanalysis
shows that the storms will be moving into a somewhat robust
environment for maintenance and even growth. Instability-wise, RAP
mesoanalysis shows a band of MLCAPE values between 1500 and 2000
J/kg across much of central and eastern CT and MA. Lower values
exist SE of I-84 where a seabreeze has made some decent headway. Mid
level lapse rates are meager, but low level lapse rates have
increased to between 8.5 and 9 C/km ahead of convection. The steep
lapse rates and high temp dewpoint spreads will help storms produce
damaging winds as updrafts collapse. Enhanced outflow from initial
convection and 25-30kts of effective 0-6 km shear will help storms
organize into more of a linear mode with isolated bowing segments
and pockets of damaging winds becoming more likely as the complex
moves to the southeast.

Outside of damaging winds, there is plenty of moisture available for
heavy rain and isolated of flash/poor drainage flooding with any
storm activity. Precipitable water values have risen to between 1.9
and 2.1 inches ahead of the trough. Model soundings show sufficient
warm cloud depths as well for efficient rain processes. This
together will support thunderstorms capable of locally heavy rain
fall rates, and thus an isolated flash flood risk. The 12z runs have
backed off some from previous runs with regards to HREF
probabilities for 6-hour precipitation exceeding 5 or 10 year ARIs.
However, there is a 5-15% probability for 6 hr precip exceeding the
2 year ARI across northern RI and east/southeast MA. The HREF PMM 3-
hr QPF highlights similar areas with higher probabilities for > 1".
This provides context that a few storms may be capable of causing
localized flash flood impacts to areas especially flood prone ones
(low lying, poor drainage, urban). However, a widespread flash flood
risk is not likely. Additionally, winds aloft should keep storms
moving which will prevent a storm from sitting over an area dropping
heavy rain.

Finally, high heat and humidity values will continue through the
remainder of the afternoon. A current look at dewpoints shows
widespread high humidity with dewpoint values ranging from 70 to 75
degrees! Actual air temperatures in the 90s have resulted in heat
index values in the 95-103 degree range, especially in the interior.
The good news is that improvement will follow quickly behind storm
activity as it pushes offshore early this evening.

TONIGHT:

Any lingering shower or thunderstorm activity will quickly wane with
the loss of daytime heating. Otherwise, the surface cold front
pushes through from northwest to southeast overnight resulting in
slowly improving temperature and dewpoint values. High pressure
builds in from the northwest as the night progresses.

.SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/...
Key Messages:

* Drier and cooler Saturday

Saturday and Saturday Night:

A much drier airmass follows on Saturday behind the cold front.
Temperatures will be considerably cooler as 850 temps fall to + 12-
15C. Low level easterly flow will keep the coolest conditions across
eastern MA and the Islands while areas in the interior may still see
temperatures rise into the middle and upper 80s. Seasonably cool
lows and clear conditions for the first part of Saturday night
before an approaching warm front brings an increasing chance for
showers and elevated thunderstorms by daybreak Sunday.


&&

.LONG TERM /SUNDAY THROUGH FRIDAY/...
Key Messages:

Key Messages...

* Showers and thunderstorms return on Sunday. Severe weather is not
  expected at this time.

* Temps warm up into the 90s through mid week but cooler weather
  arrives late week into the weekend.

* Mostly dry this week with a chance of showers and t-storms around
  Tuesday and late Wed/Thu.

Sunday...

Sunday unsettled weather returns to the region thanks to a weak mid
level shortwave sliding through the quasi-zonal flow with a weak
surface trough replacing Saturday`s high pressure. This brings with
it increasing moisture in the form of cloudcover and humidity,
adding fuel for showers and garden variety thunderstorms. Limited
lift and marginal lapse rates/instability should preclude any severe
weather. Arrival of shower activity may be as early as the overnight
hours Saturday night into Sunday morning. Increased cloudcover as
well as lingering cooler air in the low/mid levels keep highs in the
upper 70s to low 80s.

Next week...

500 mb heights will be on the rise to start next week keeping things
dry and kicking off some warm advection which pushes 850 mb temps
closer to 18-20 C resulting in highs in the upper 80s and 90s Mon -
Wed. Then, a cooler mid level airmass pushes in from the north as
850 mb temps drop to 8-9C by Friday! This should bring high
temperatures back down to the 70s to low 80s and lows back into the
50s.

Mostly dry next week save for a few disturbances that move through;
a weaker one on Tuesday and a potentially more robust one around mid
week. Timing on these features, though is less certain; can expect
scattered showers and potential for thunderstorms with each of
these.

&&

.AVIATION /20Z FRIDAY THROUGH WEDNESDAY/...
Forecaster Confidence Levels...

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

18Z update...

Today: Moderate in timing of storms, but high confidence in
trends.

VFR. SSW/SW winds at 8-14 kts with occasional gusts up to 22
kts in the afternoon. Isolated to scattered TSRA likely. Best
timeframe between 18z through 02z as storms develop in northwest
MA and move southeast. Due to low coverage of storms, kept the
PROB30 for TSRA at most terminals per latest CAMS. Within storms
can expect brief MVFR conditions, gusty winds, torrential rain,
and frequent lightning.

Tonight: High Confidence.

Any lingering storms exit the coastal waters/islands by 06z.
Cold front drops from NW to SE early evening, shifting winds
from SW to NW speeds at 8-12 kts. Ceilings are generally VFR
with lingering MVFR possible for the outer Cape and Islands.
There is potential for a period of FG/BR for the Cape and
Islands after 00-02z after the cold front moves through.

Saturday: High Confidence.

VFR. Northeast winds 5-8 kts for the interior and 6-12 kts
closer to the coast.

Saturday Night: High Confidence

VFR. NE winds turning SE 5-8 kts.

KBOS terminal...High confidence trends, moderate confidence in
timing for KBOS TAF.

Exact timing of line of storms lower confidence. Storms are
expected to be scattered in coverage making it more difficult to
pin point exact timing. Kept as a PROB30 group.

KBDL terminal...High confidence trends, moderate confidence in
timing for KBDL TAF.

Outlook /Sunday through Wednesday/...

Sunday: Mainly VFR, with local IFR possible. Chance SHRA,
slight chance TSRA.

Sunday Night: VFR. Slight chance SHRA.

Monday through Monday Night: VFR.

Tuesday: VFR. Breezy. Slight chance SHRA, slight chance TSRA.

Tuesday Night: VFR.

Wednesday: Slight chance SHRA, slight chance TSRA.

&&

.MARINE...
Forecaster Confidence Levels...

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


Through Saturday Night...High Confidence.

SW winds 10-15 kts, closer to 20 kts for the southern waters
with gusts 20-25 kts. Borderline criteria for SCAs for southern
waters, Cape Cod Bay, Nantucket Sound and Buzzards Bay. Storms
develop late afternoon into early evening as a cold front slides
from the northwest to southeast, then pushing south of the
waters by early Saturday morning and shifting wind to the NNW.
Winds veer SSW Saturday evening.

Outlook /Sunday through Wednesday/...

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

Monday through Wednesday: Winds less than 25 kt.

&&

.BOX WATCHES/WARNINGS/ADVISORIES...
CT...Heat Advisory until 8 PM EDT this evening for CTZ002>004.
MA...Heat Advisory until 8 PM EDT this evening for MAZ003>007-
     010>019-026.
RI...Heat Advisory until 8 PM EDT this evening for RIZ001>004.
MARINE...None.

&&

$$

SYNOPSIS...BW/FT
NEAR TERM...McMinn/FT
SHORT TERM...McMinn/FT
LONG TERM...BW
AVIATION...Dooley/McMinn
MARINE...McMinn