textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- A few showers and possibly a thunderstorm through early evening, mainly south of the MA Pike to the south coast.

- Cooler Thursday with scattered showers developing in the afternoon, especially across eastern MA.

- Broad cyclonic flow over northeastern North America will support unsettled weather in southern New England Friday through the middle of next week

DISCUSSION

KEY MESSAGE 1...A few showers and possibly a thunderstorm through early evening, mainly south of the MA Pike to the south coast.

Cold front will be moving south across SNE this afternoon reaching the south coast this evening. Weak instability develops ahead of the front with MLCAPES 250-500 J/Kg. Instability is weak but low level convergence with the front may be enough for isolated low topped convection to develop later this afternoon and evening, mainly south of the MA Pike. The 3km NAM and NSSL- WRF are most aggressive with scattered storms developing while HRRR, WRF-ARW and RRFS show little to no convection. One of the main limiting factors is dry air in the mid levels which will serve to suppress stronger updrafts from developing, especially given just weak instability. So while we can't rule out a few showers or a t-storm developing, coverage should be limited. Any convection will end this evening as the front pushes south of the coast. This will also clear out any stratus and fog that develops over the Islands through this evening.

KEY MESSAGE 2...Cooler Thursday with scattered showers developing in the afternoon, especially across eastern MA. Cooler temps Thu in the post-frontal airmass as 925 mb temps drop to 12-13C. Expect highs in the low-mid 70s, but likely holding in the upper 60s along the eastern MA coast due to a NE wind. A mid level shortwave rotates southward across the region with an accompanying increase in moisture. Guidance is bullish on scattered showers developing in the afternoon, especially across eastern MA into RI as a coastal front sets up across eastern MA along with a weak wave on the front which will enhance convergence. The showwers will wind down Thu evening as the shortwave moves to the east followed by subsidence.

KEY MESSAGE 3...Broad cyclonic flow over northeastern North America will support unsettled weather in southern New England Friday through the middle of next week

A broad upper-level trough roughly centered over eastern North America/western North Atlantic Ocean will dominate the weather pattern in southern New England between Friday and the middle of next week. Several pulses of short-wave energy embedded in this broad clyclonic flow will bring a pro-longed period of largely unsettled weather.

AThe first pulse of short-wave energy digs through The Northeast late Friday into Saturday bringing rounds of scattered precipitation mailny to eastern MA and NH/ME. As this system exits southeast by Saturday evening, we'll be left with somewhat seasonable conditions for Sunday with a mix of sun and clouds.

Beyond Sunday we begin to see more spread in the global model guidance. The consensus is for broad cyclonic flow to persist over The Northeast with additional precpitation chances on Monday and Tuesday. How long the cylonic upper-level flow meanders over The Northeast is uncertain with some ensemble solutions supporting more significant height rises by Wedensday and others supporting a later departure by late next week. Temperature will be slightly below normal during this stretch with daily highs/lows in the upper 60s/low 70s and 40s/50s between Saturday and Wednesday.

AVIATION /00Z THURSDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

00Z TAF Update:

Tonight...High Confidence.

IFR stratus and fog over the Islands clearing out and becoming VFR toward 06z. VFR elsewhere. NW wind 5-10 kt becoming N.

Thursday...High Confidence.

VFR. Scattered showers developing in the afternoon, especially eastern MA/RI with mainly VFR cigs. NW wind 10-20 kt interior and N-NE around 10 kt near the eastern MA coast.

Thursday night...High confidence.

VFR. Light N-NW wind.

KBOS...High confidence in TAF.

KBDL...High confidence in TAF. Low risk for a brief shower after 20z.

Outlook /Friday through Monday/...

Friday: VFR. Chance SHRA.

Friday Night through Saturday: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA.

Saturday Night: VFR. Breezy. Slight chance SHRA.

Sunday: VFR. Breezy.

Sunday Night: VFR. Slight chance SHRA.

Monday: VFR. Slight chance SHRA, slight chance TSRA.

MARINE

Forecaster Confidence Levels...

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

Through Thursday night...

Winds and seas below SCA thresholds. SW-W winds up to 20 kt will shift to NW then N tonight. N-NE wind 5-15 kt Thu becoming N-NW Thu night. A few showers or a t-storm may develop over the south coastal waters through early evening. Scattered showers developing Thu afternoon.

Outlook /Friday through Monday/...

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

Friday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers.

Saturday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers.

Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Slight chance of rain showers.

Sunday: Winds less than 25 kt. Seas up to 5 ft.

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

BOX WATCHES/WARNINGS/ADVISORIES

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