textproduct: Boston / Norton

WHAT HAS CHANGED

The slight risk (level 2 of 5) of severe weather today remains in effect for far western CT and MA. The chance of severe weather also remains low, but not zero, for eastern MA/RI.

KEY MESSAGES

- Heat Advisories advisories remain in effect for northern CT, central and northern RI, and most of MA through 8pm this evening.

- A few scattered strong to severe thunderstorms are possible this afternoon and evening.

- Above normal temperatures continue into early next week, but humidity will be on the decrease. The weekend looks mostly dry with the next round of showers and thunderstorms Sunday night, some of which could be strong.

- Cooldown to more seasonable temperatures with drier weather for early next week.

DISCUSSION

KEY MESSAGE 1...Heat Advisories advisories remain in effect for northern CT and much of interior MA from noon today to 8pm Friday.

The worst of the heat and humidity peaks today away from the coastline. Temperatures soar into the mid 90s inland (low to mid 80s across the eastern coastal communities with onshore flow). Dewpoints near 70 combined with the high heat and sunny skies will lead to "feel like" temperatures in the upper 90s to near 100 (in the CT River Valley) this afternoon. Therefore, the Heat Advisory remains in effect through this evening.

KEY MESSAGE 2...A few scattered strong to severe thunderstorms are possible this afternoon and evening.

The lingering hot and humid airmass clashing with a mid-level shortwave over southern Quebec and northern New England will provide enough lift to produce a few rounds of thunderstorms today. Earliest storms are likely to pop over eastern MA and RI along a stagnating sea breeze boundary this afternoon. A secondary round of thunderstorms, with the highest change of becoming severe, likely fires later in the evening over western MA and CT as a cold front approaches. Some uncertainty remains this morning in exactly how far east storms could push, as the latest suite of guidance is indicating CAPE values upwards of 1200 J/kg quickly decaying around sunset. Model soundings continue to show DCAPE values near or above 1000 as well as PWATs 1.5-2.0", which lean confidence to the greatest risks with any storms that do form to be heavy to torrential rainfall as well as severe wind gusts.

KEY MESSAGE 3...Above normal temperatures continue into early next week, but humidity will be on the decrease. The weekend looks mostly dry with the next round of showers and thunderstorms Sunday night, some of which could be strong.

While temperatures remain well into the 80s through the weekend, dewpoints will drop to the mid to upper 50s Saturday, leading to some much needed relief from the sticky airmass we've been seeing. A ridging pattern will also move into New England, bringing generally dry conditions through the weekend.

Expecting the next round of potential showers and thunderstorms Sunday night into Monday with another approaching cold front. Despite the return of southwesterly flow, and thus higher dewpoints, guidance is indicating instability remains on the lower side, potentially limiting the chances for storms to become severe in nature. Regardless, quite confident in at least showers with some embedded rumbles of thunder.

KEY MESSAGE 4...Early next week could feature a brief cooldown to more seasonable temperatures.

Once the cold front from Sunday pushed offshore, 850mb temperatures cool to near single digits (C) compared to the upper teens we've been seeing. This will help moderate temperatures down to the upper 70s or low 80s with lower humidity Monday and Tuesday.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

12Z TAF Update:

Friday: Moderate confidence.

VFR. Light onshore winds developing, with light W winds away from the coastal TAFs. A few rounds of TSRA could develop, first in the 18-00Z time period over eastern MA and RI terminals along the seabreeze boundary, but confidence in coverage and placement is low. Then again a broken line of storms is possible in the 23z-06z period, diminishing as it moves east.

Friday night...High confidence.

SHRA/TSRA exiting by 06z. VFR except near the Cape/Islands where MVFR visbys under BR may creep in off the waters. NW winds 5-10 kts.

Saturday....High confidence.

VFR. Generally northwesterly winds around 10 kts.

KBOS Terminal...Moderate confidence in TAF. VFR. Could see a few TS develop 16-23z Fri along the seabreeze boundary, but confidence remains to low to include in TAF.

KBDL Terminal...Moderate Confidence in TAF. VFR. Light W winds turn southerly with a round of late-day TS possible.

Outlook /Saturday Night through Tuesday/...

Saturday Night: VFR.

Sunday: VFR. Breezy.

Sunday Night: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA, slight chance TSRA.

Monday: VFR. Breezy.

Monday Night through Tuesday: VFR.

MARINE

Forecaster Confidence Levels...

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

Through Saturday Morning...High confidence.

Seas generally 1-3 ft, except 3-4 ft across the far outer water through Saturday morning. Isolated to scattered showers possible again Friday night. Otherwise, winds remain below SCA levels.

Outlook /Saturday Night through Tuesday/...

Saturday Night through Sunday: Winds less than 25 kt.

Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Rain showers, slight chance of thunderstorms.

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

Monday Night: Winds less than 25 kt.

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

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 MAZ002>006- 008>014-017-018-026. Air Quality Alert from 11 AM this morning to 11 PM EDT this evening for MAZ017>024. RI...Heat Advisory until 8 PM EDT this evening for RIZ001>004. Air Quality Alert from 11 AM this morning to 11 PM EDT this evening for RIZ001>008. MARINE...None.