textproduct: Boston / Norton

WHAT HAS CHANGED

Forecast remains on track. Heat Advisories remain in effect from 11 AM today through 8 PM Friday for most of southern New England (excluding the eastern slopes, Cape, and Islands).

KEY MESSAGES

- Heat and humidity climb to Advisory level today and lingers through Friday, possibly into the weekend.

- Diurnal pop-up thunderstorms remain a daily threat, but are most likely Saturday, with a lower chance on Sunday. Unsettled weather may return early next week, as well as continuing high humidity.

DISCUSSION

KEY MESSAGE 1...Heat and humidity climb to Advisory level today and lingers through Friday, possibly into the weekend.

A Bermuda high begins to build in across the western Atlantic Ocean and southerly flow continues today. Temperatures and dew points have already begun to rise: T of 73 (up from 69 just before midnight) and Td of 71 (up from 67). They'll only continue to surge throughout the day and again on Friday, with temperatures likely topping out near 90 and oppressive dew points near 75, leading to "feels like" temperatures climbing into the mid to upper 90s... possibly even near 100 at times. Greatest risk of heat indicies reaching triple digits remains in the CT and Merrimack River Valleys where localized downslope winds could help boost temperatures. Some uncertainty remains regarding the magnitude of heat elsewhere due to the chance for increasing cloud cover from any thunderstorms that develop today and Friday afternoons. Expecting poor overnight relief heading into Friday with nighttime temperatures hovering 71-73 as well as dewpoints struggling to drop to 70... tonight's heat indicies are likely to hover 77-80. The warm overnight temperatures will be dangerous for those without adequate access to cooling, especially in urban areas.

A Heat Advisory remains in effect from 11 AM today through 8 PM Friday, and future shifts may need to extend the Advisory into Saturday if the heat persists.

KEY MESSAGE 2...Diurnal pop-up thunderstorms remain a daily threat, but are most likely Saturday, with a lower chance on Sunday. Unsettled weather may return early next week, as well as continuing high humidity.

A few weak, upper level disturbances passing through New England combining with the high heat/humidity and just enough instability will likely be enough to pop a few diurnal showers/thunderstorms each day through the weekend, with greatest chances Saturday. While the potential for storms to be severe is on the lower end, any thunderstorms that do pop have the potential to produce frequent lightning, gusty winds, and torrential downpours as PWATs will likely be around 2.0". Model soundings also indicate the mid-level steering flow could be rather week, leading to slow moving storms or even training. Given the amount of rain southern New England has seen over the last week or so, any heavy downpours could lead to localized flooding.

Expecting a few more shortwaves to move through the upper-level flow as well as a trailing cold front early next week, bringing additional chances for showers to southern New England Monday night into Tuesday. The FROPA could bring a small amount of relief from the heat for the start of the next work week, but humidity levels likely will remain elevated through mid-week.

AVIATION /08Z THURSDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

06z Update:

Today...High confidence.

MVFR/IFR CIGS this morning slowly improves to VFR by 12-14z wtih SW to WSW winds 8-12 kts, gusting up to 20 kts this afternoon, especially across eastern southern terminals. Low chances for an isolated afternoon SHRA or TSRA across western areas of southern New England. Have opted to include a PROB30 for TSRA at KBDL after 20z today.

Tonight into Friday...Moderate confidence.

VFR conditions drop to MVFR south of the Mass Pike, IFR across the Cape/Island terminals. Gustier winds 15-20 kts remain a possibility overnight and into Friday for the Cape and Islands as well. Afternoon SHRA/TSRA chances return Friday, but uncertain how far east impacts could reach at this time.

KBOS Terminal...High confidence.

IFR CIGS linger through 12-14z and gusty southwest winds are expected this afternoon.

KBDL Terminal...High confidence.

IFR CIGS/MVFR Visby's improve to VFR 12-14z then drop to MVFR again tonight. Low chance remains for an isolated afternoon SHRA or TSRA across western areas of southern New England, with PROB30 for TSRA after 20z today.

Outlook /Friday Night through Monday/...

Friday Night: VFR. Chance SHRA, slight chance TSRA.

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

Saturday Night: VFR. Breezy. Slight chance SHRA.

Sunday: VFR. Breezy.

Sunday Night: VFR.

Monday: VFR. Breezy. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Through Friday... High Confidence.

A few periods of gusty SW winds near 20 kts are possible today across the southern waters. Winds calm Friday as high pressure builds over the region. Waters and winds will be below SCA for the foreseeable future.

Outlook /Friday Night through Monday/...

Friday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers.

Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft.

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

Sunday through Sunday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

Monday: Winds less than 25 kt. Seas locally approaching 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES

CT...Heat Advisory from 11 AM this morning to 8 PM EDT Friday for CTZ002>004. MA...Heat Advisory from 11 AM this morning to 8 PM EDT Friday for MAZ003>007-010>021-026. RI...Heat Advisory from 11 AM this morning to 8 PM EDT Friday for RIZ001>007. MARINE...None.