NWS Forecast Discussion

FXUS61 KBOX 191047

Area Forecast Discussion
National Weather Service Boston/Norton MA
647 AM EDT Fri Jul 19 2024

A broad area of high pressure will build into Southern New England
through this evening. This will bring significantly lower humidity
levels compared to the past several days, along with dry weather and
seasonable temperatures. Dry and pleasant weather this weekend.
Pattern turns more active again next week with increasing


A pleasant day is on tap to end the week thanks to high pressure
overhead which will result in clear skies and no rain, all while
beneath a more comfortable (read: less humid) post frontal airmass.
As of this writing at 3AM dewpoints are in the 50s and low 60s
across the region including the islands. In Worcester, for example,
their dewpoint of 55F is 15 degrees lower than 24 hours ago! This
has made and will continue to make it feel much less humid outside
as high temperatures reach the upper 70s and low to mid 80s.


Given clear skies (at least initially) overnight and a decoupling
boundary layer we may see some valley fog forming in western MA/CT
Friday night. Blended in MOS guidance given the likelihood of
radiational cooling as well, giving lows down into the mid to upper
50s in the typically cool spots. As for Saturday, the forecast
remains dry but with increasing mid and high clouds ahead of a warm
front which lifts through late in the day associated with a trough
of low pressure to our north. Thus humidity will begin to increase
during the latter half of the day especially along the south coast
where a plume of 1+inch PWATs first arrives. Can`t rule out an
isolated shower after sundown with the cold frontal passage. High
temperatures will be a few degrees warmer thanks to a marginally
warmer airmass being advected overhead (850 mb temps rising to 14-
15C). Expect highs in the mid to upper 80s.


High pressure over the Great Lakes continues to spread eastward into
SNE. This will leave the region with dry, sunny, and pleasant
conditions on Sunday. High temperatures climb into the upper 80s on
Sunday with dewpoints in the mid to upper 60s.

A more active pattern looks to set in again next week as deep SW
flow aloft kicks back in bringing increased moisture and humidity.
Temperatures this time wont be nearly as hot with highs peaking in
the upper 80s Monday, then falling into the upper 70s to low 80s by
Wednesday and Thursday. Dewpoints on the other hand will rise into
the upper 60s to low 70s again Monday and stay there through the
week. As for rain chances this week, exact timing of features
remains messy with several weak shortwaves traversing through the SW
flow. Monday at this time appears the driest day with only isolated
thunderstorms possible. Not expecting any severe thunderstorms with
less then 500 J/kg of MLCAPE.

A stronger shortwave and associated surface low looks to exit the
Ohio River valley mid week. Guidance is in good agreement on timing
of this feature bringing it through late Tuesday into early
Wednesday, but disagreement on exact track of the low. PWATS ahead
of this low increase upwards of 2.0-2.2 inches which could spell
issues for excessive rain somewhere in New England depending on the
track of the low. Ensemble mean QPF at this time is showing a wide
spread 1/2 inch of rain, with 99th percentile showing localized
areas of 2 - 3 inches. Will also need to watch for severe weather in
this time period with CSU machine learning guidance showing 5% probs
for severe thunderstorms on Wednesday and Thursday.


Forecast Confidence Levels:

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

12Z update...

Today and tonight...High confidence.

VFR. Easing NW winds during the day. Localized sea breezes
developing 15-17Z. Winds light and variable overnight.

Saturday...High confidence.

VFR. SW winds 5-10 kts.

KBOS TAF...High confidence in TAF.

VFR through the period. Seabreeze Fri starting 15-17Z.

KBDL TAF...High confidence in TAF.

VFR through the period.

Outlook /Saturday Night through Tuesday/...

Saturday Night through Monday: VFR.

Monday Night: VFR. Slight chance SHRA, isolated TSRA.

Tuesday: VFR. Chance SHRA, isolated TSRA.


Forecaster Confidence Levels:

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

Today through Saturday: High confidence.

Winds 5-10 kts. Seas 2-4 feet.

Outlook /Saturday Night through Tuesday/...

Saturday Night through Monday: Winds less than 25 kt.

Monday Night: Winds less than 25 kt. Slight chance of rain
showers, isolated thunderstorms.

Tuesday: Winds less than 25 kt. Chance of rain showers.


MARINE...Small Craft Advisory until 2 PM EDT this afternoon for




NWS BOX Office Area Forecast Discussion