Somerville, Massachusetts 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

383
FXUS61 KBOX 070515
AFDBOX

Area Forecast Discussion
National Weather Service Boston/Norton MA
115 AM EDT Mon Jul 7 2025

.SYNOPSIS...
Higher than normal heat and humidity expected Monday with a
Heat Advisory in place. Unsettled weather makes a return Monday
into Monday night, continuing off and on through much of next
week. Cooler weather expected middle to late next week.

&&

.NEAR TERM /UNTIL 6 AM THIS MORNING/...
Key Messages...

* Mild with low clouds/patchy fog for the south coast and
  Cape/Islands.

Still thinking low clouds and fog push onto the south coast of
New England overnight. Still tough to pin down the timing, as
the stratus and fog is not yet visible via satellite over the
ocean. The best estimate is just before midnight towards
Nantucket, and between to 2-5 AM for the south coast of RI and
MA.

Previous Discussion...

Mild temperatures and dry conditions expected tonight. Deeper
moisture moves in from the south overnight, which may in aid in
some development of lower clouds. Most high- res guidance shows
lower clouds extending from the south mainly south of the Mass
Pike, but there are a few models that show potential for lower
clouds further north. Can`t rule out some patchy fog for the
immediate south coast and Cape/Islands overnight. The warm
temperatures from Sunday and limited radiational cooling will
keep lows warmer in the upper 60s to low 70s.

&&

.SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TUESDAY/...
Key Messages:

* Warmer than normal and humid. Heat Advisory in effect.

* Isolated showers and thunderstorms in afternoon, mainly for
  western CT and MA.

Monday:

Mid-level ridging continues over southern New England on Monday.
Southerly jet should help transport a plume of above normal
moisture (150-180% of normal) into the region. This will keep
more humid air around for Monday. Temperatures will lean above
normal as well with highs in the upper 80s to low 90s, although
a bit cooler for the immediate south coast and Cape/Islands in
the low-mid 80s. With the humidity it will feel more like low to
mid 90s which has lead to a Heat Advisory being in effect
Monday. Breezy SW winds.

A weak shortwave approaches in the flow aloft later in the day.
An approaching wave/cold front combined with instability (MLCAPE
500- 1,000 J/kg) should support isolated to scattered showers
and thunderstorms developing in the afternoon as the front moves
eastward. Highest chances will be in western MA and CT where the
better instability is. 0-6km bulk shear values are low and
mid level lapse rates are weak, so not expecting a severe risk.
Model soundings do exhibit deeper warm cloud layers, skinny
CAPE, and above normal PWATs, so any storm may be capable of
heavy downpours. There is potential for a shower or storm to
move further eastward, although a lower probability. HREF PMMs
show isolated 6 hour QPF amounts up to a half inch while the
ensemble max is closer to an inch. So overall, very isolated
risk for a storm with a heavy downpour.

Monday Night:

Another mild night with temperatures hanging in the upper 60s
and lower 70s. A cold front slowly works across the region into
early Tuesday. Showers are possible overnight with higher
chances of the Cape and Islands and SE MA.

&&

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

* Marginal risk of flash flooding and severe thunderstorms Tuesday

* Unsettled weather continues through the workweek

* Below average temperatures late week

TUESDAY

The region will be in the right entrance region of a weak jet on
Tuesday. At the same time, a cold front will move south, slowing
and weakening as it does so. The remnant circulation of TS
Chantal will likely partially interact with this boundary
resulting in a period of rain Tuesday morning. After a brief
lull in rainfall late Tuesday morning, attention turns to the
possibility for widespread showers and scattered thunderstorms
Tuesday afternoon. The WPC has placed the region in a marginal
risk for excessive rainfall and flash flooding Tuesday. NAEFS
ensemble tables indicate the chance for PWAT values to rise as
high as 1.9-2.1" (+2.5 STD above climatology!) by Tuesday
afternoon. The tropical airmass will also bring deep warm cloud
depths approaching 13K feet and weak steering currents. BUFKIT
model soundings show winds < 30kts all the way up to 300mb!

The other risk Tuesday will be the chance for isolated severe
thunderstorms. Dewpoint values in the 65-70 degree range will
allow for MLCAPE values to easily climb to the 1500-2000 j/kg
range. Despite sufficient instability levels effective shear
values < 20kts will likely limit coverage and intensity of any
severe storms. The SPC has placed areas of western and central
Connecticut and Massachusetts in a marginal risk of severe
storms with the primary risk being damaging winds.

The NBM blend shows temperatures rising into the upper 80s and
lower 90s on Tuesday. Heat index values climb further, with a
few areas rising to as high as 95-100 degrees. Future shifts
will decide on extending the Heat Advisory as the spatial and
temporal extent of the hot conditions Tuesday afternoon comes
into better focus.


WEDNESDAY THROUGH SATURDAY

Clockwise flow around a Bermuda ridge will maintain a steady
stream of moisture into the region Wednesday through Friday.
Guidance shows PWAT values between 200-250% above normal
throughout the middle of the week. A series of disturbances
arrive on near zonal flow starting early Wednesday. The flow
becomes more meridional Thursday in response to a building
ridge across far northern Canada. At the surface, models are
hinting at a weak area of low pressure passing through the
region on Thursday. NBM guidance currently shows low probs of
24-hour rainfall totals exceeding 1" on Thurs but this could
change as model guidance irons things out going forward.
Finally, temperatures will fall quite a bit by Thursday and
Friday with an easterly onshore flow developing. Ensemble
guidance shows surface temperature anomalies falling to between
5 and 10 degrees below climatology Thursday afternoon.

&&

.AVIATION /05Z MONDAY THROUGH FRIDAY/...
Forecaster Confidence Levels...

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

06Z update...

Through 12z...Moderate confidence.

VFR for most terminals. Areas of MVFR/IFR expand mainly south
of I-90 through 10-12z. Patchy fog develops across the south
coast.

Today...Moderate confidence.

MVFR to IFR along the south coast of RI and MA in the morning.
South coast may scatter after 12z. Confidence is moderate in
whether it scatters or stays BKN. Cape/Islands slower to improve
in the AM gradually improving into the early afternoon. SSW to
SW winds 10-15 kts, gusts 20-24 kts by early afternoon. Isolated
showers and few thunderstorms may develop after 16z, but low
confidence on where any storms will form.

Tonight...Moderate confidence.

IFR cigs expand from the south coast into most terminals by
06-10z. Winds light.

Tuesday...Moderate confidence.

VFR. W winds 5-10 kts. Scattered SHRA/TSRA with heavy downpours
likely in the afternoon and evening.

KBOS Terminal...Moderate confidence in TAF.

Low clouds develop to the south early this morning, but are
unlikely to reach the terminal. BKN mid-level ceilings Monday
with SW winds with gusts around 20 kts in the afternoon. Low
chance for an isolated shower/storm makes it east to to BOS
after 18z.

KBDL Terminal...Moderate confidence in TAF.

Forecast confidence is moderate beyond 10z with the potential
for lower ceilings. Isolated -SHRA/-TSRA possible after 16z.

Outlook /Tuesday Night through Friday/...

Tuesday: Mainly VFR, with local MVFR possible. Breezy. Chance
SHRA, chance TSRA.

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

Wednesday: Mainly VFR, with local IFR possible. Slight chance
SHRA.

Wednesday Night: Mainly VFR, with local IFR possible. Chance
SHRA.

Thursday: Mainly VFR, with areas IFR possible. Chance SHRA,
slight chance TSRA.

Thursday Night: MVFR/IFR conditions possible. Chance SHRA,
slight chance TSRA.

Friday: 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 tonight: High confidence.

SW winds this evening, gusting 20-25 kts, as high as 30 kts on
eastern waters. Seas 3-5 ft. Most zones will stay shy of SCA
criteria except the northern outer waters with gusts 25-30 kts
in the afternoon and sea 4-5 ft. SCA will be in effect for that
zone through 06z Monday.

Monday-Monday Night: High confidence.

After a brief lull Monday morning, SW winds increase Monday
afternoon to 10-15 kts with gusts 20-25 kts on southern waters,
25-30 kts on the eastern waters. May need a SCA for the north
outer waters zone. Seas 2-3 ft, increasing to 2-4 ft on the
outer waters late in the day. Seas increase to 5 ft for the
southern outer waters after overnight into Tuesday.

Outlook /Tuesday Night through Friday/...

Tuesday: Low risk for Small Craft Advisory winds with gusts up
to 25 kt. Local rough seas. Chance of rain showers, chance of
thunderstorms.

Tuesday Night: Winds less than 25 kt. Areas of seas approaching
5 ft. Chance of rain showers, slight chance of thunderstorms.

Wednesday: Winds less than 25 kt. Areas of seas approaching
5 ft. Slight chance of rain showers.

Wednesday Night through Thursday: Winds less than 25 kt. Chance
of rain showers.

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

&&

.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...Small Craft Advisory until 2 AM EDT early this morning for
     ANZ250.

&&

$$

SYNOPSIS...Mensch/FT
NEAR TERM...Belk/Mensch
SHORT TERM...Mensch
LONG TERM...FT
AVIATION...BW/FT
MARINE...Mensch/FT