textproduct: Boston / Norton

WHAT HAS CHANGED

No changes to the forecast for this update cycle. Isolated showers and thunderstorms across Southern Massachusetts continue to move southward offshore and over Martha's Vineyard and Nantucket. Rain chances will quickly diminish this evening and overnight.

KEY MESSAGES

- A few showers and thunderstorms are possible through this evening.

- Dry and seasonable weather with low humidity levels this weekend into Monday.

- Heat and humidity return by midweek.

DISCUSSION

KEY MESSAGE 1...A few showers and thunderstorms are possible through this evening. A cold front will slowly sag south across southern New England through this evening. A warm and humid airmass resides across the region resulting in heat indices in the upper 80s to low 90s. Regional radar shows a line of widely scattered showers from the Hudson Valley to the NH seacoast, with another area of showers on the Upper Cape this afternoon. Instability has increased to 500-1000 J/Kg with weak shear across the forecast area. The showers are expected to slowly sag southward across MA before dissipating this evening. An isolated thunderstorm is possible, mainly across the sea breeze near the Cape where higher dewpoints and low-level convergence are located.

The cold front will move south of the region tonight with patchy fog possible in valleys. Dry weather is expected across the region.

KEY MESSAGE 2...Dry and seasonable weather with low humidity levels this weekend into Monday.

In the wake of a cold front, surface high pressure will build across the region this weekend and become centered over New England Sunday into Monday. This will bring comfortable temperatures in the mid 80s and low humidity with dew points in the upper 50s/low 60s. A much drier air mass will keep rain chances to near zero before moisture returns later in the week.

KEY MESSAGE 3...Heat and humidity return by midweek.

Mid-level high pressure ridging will remain over the Central U.S., stretching across into the Mid Atlantic through much of next week, bringing mostly hot and dry weather across the Northeast. Hot temperatures in the low to mid 90s will return mid week with 850mb temperatures ranging from +18 to +22C. We may need to consider a period of heat headlines with dew points rising into the mid to upper 60s again.

Rain chances through the period will generally remain low with a better chance on Tuesday into Wednesday with a possible shortwave trough moving through Northern New England. Southerly return flow at the surface will be short lived prior to this perturbation moving through, so moisture depth will remain shallow. Models are showing possible deeper upper-level troughing toward the end of the week, so we may start to see increasing rain chances and slightly cooler temperatures if that trend continues.

AVIATION /00Z SATURDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

Through Friday Night: Moderate confidence.

Showers and a few thunderstorms are expected to dissipate this evening from north to south, with a low chance of MVFR visibilities with ongoing convection moving southward near ACK. Winds may become calm overnight, with patchy fog and low ceilings developing at some locations in the early morning hours.

Saturday: High confidence.

MVFR/IFR at ACK will improve to VFR Saturday morning.

Elsewhere VFR. Light E to NE winds.

KBOS Terminal...Moderate confidence. Light southerly winds should reestablish out of the northeast and become light overnight. Lighter winds expected on Saturday with possibly an isolated shower with the seabreeze, but have decided to keep any mention out of the TAF at this time.

KBDL Terminal...High confidence. VFR with light winds.

Outlook /Sunday through Wednesday/...

Sunday through Sunday Night: VFR.

Monday through Monday Night: VFR. Breezy.

Tuesday: VFR. Windy with local gusts up to 30 kt.

Tuesday Night through Wednesday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

Through Saturday Night...High confidence.

Mostly tranquil boating conditions continue into next weak. A weak cold front should cross the waters tonight. A risk for scattered showers or thunderstorms tonight, especially the waters around the Cape and islands. Mainly dry weather Sat into next Wed.

Outlook /Sunday through Wednesday/...

Sunday through Monday: Winds less than 25 kt.

Monday Night: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Seas locally approaching 5 ft.

Tuesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Seas up to 5 ft.

Tuesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas.

Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...None.