textproduct: Boston / Norton

WHAT HAS CHANGED

Wind Advisory posted for the higher terrain of the Worcester Hills and East Slopes of the Berkshires. Gale Warnings for the southern coastal waters of MA and RI.

KEY MESSAGES

- Strong westerly wind gusts of 35-50 mph Saturday.

- A period of heavy rainfall, strong winds, and unseasonably mild temps Mon into Mon night. Some river and small stream flooding expected.

- Trending colder with mainly dry weather Tue through Thu.

DISCUSSION

KEY MESSAGE 1...Strong westerly wind gusts of 35-50 mph Saturday.

After a brief period of light rain and snow showers late this evening into the early morning hours, attention turns to the more significant impact of gusty winds. Little to no snow accumulation expected, except perhaps across the highest elevations towards NW MA, where 1-2 inches is possible.

Increasing south to southwest winds late tonight into Saturday. Based on model sounding, thinking much of southern New England will have wind gusts of 30-40 mph. Some locations across the higher terrain, namely the Worcester Hills and the east slopes of the Berkshires, are expected more in the 45-50 mph range. This was more in line with the NBM 90th percentile gusts, which were used for this forecast. Stronger wind gusts are possible, but would require near perfect mixing and momentum transfer. Posted a Wind Advisory for the higher terrain areas, but it is marginal.

Otherwise, dry weather expected for Saturday as winds become west by mid morning.

KEY MESSAGE 2...A period of heavy rainfall, strong winds and unseasonably mild temps Mon into Mon night. Some river and small stream flooding expected.

Monday and Monday night are looking like the most impactful weather period of the forecast bringing heavy rain and gusty winds. This, as a deep mid level trough digs into the Ohio Valley Monday into Tuesday dragging a surface frontal system through Southern New England Monday into Monday night. A warm front lifts north during the day on Monday as a deep plume of moisture begins to move overhead. This will lead to widespread warm advection showers as well as temperatures 10 to 15 degrees warmer than Sunday, in the upper 50s and low 60s. This is an anomolous system both in the magnitude of moisture and wind/dynamics. Dewpoints surge into the mid to upper 50s in the warm sector on Monday while PWATs reach nearly 1.5 inches which is outside of the climatology for mid March. There's a very strong LLJ present as well, 60-70kt at 925 mb. Additionally, given the anomalous warmth and and moisture in the warm sector, we can't rule out some convective elements with elevated instability, even potential for a fine line along the cold front. This could serve to contribute to localized downpours and to help bring those strong winds to the surface. Added together, there is a signal for a potentially significant event if things come together. An addition of 1 to 2 inches of rain (locally even higher) together with the rapid snow melt will lead to flooding concerns on local rivers and streams. MMEFS ensemble guidance continues to highlight a 60-80% chance of minor flooding and 20-30% chance for moderate flooding. The greatest risk looks to be the Pawtuxet, Pawcatuck, and wood Rivers in RI with lesser concerns on the Assabet River, Deerfield River, and the lower reaches of the CT River.

The southerly wind trajectory will make it difficult to mix down the LLJ, limiting wind damage potential much of the time thanks to a decent inversion. If there was a window for the best chance of some of these strong winds mixing down it would be overnight Monday as the cold front passes through. Precip comes to an end by sunrise, potentially as late as mid morning for far eastern MA.

KEY MESSAGE 3...Trending colder with mainly dry weather Tue through Thu.

Cooler and drier weather Tuesday behind a front. Cyclonic flow remains overhead, but things remain dry through at least Thursday. The peak of the cold airmass overhead is Wednesday, so that will be the coolest day of the week with highs in the 30s to near 40. 40s return late week.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

Tonight...High confidence.

VFR dominates, but brief MVFR conditions possible for a few hours around midnight EDT in brief passing rain/snow showers. Greatest risk for this will be across northern MA. Southerly wind gusts increasing to between 20 and 30 knot for a time overnight.

Saturday...High confidence.

Mainly VFR conditions expected outside a few brief passing rain/snow showers possible mainly in northwest MA. Westerly wind gusts of 30-40 knots with a few gusts up to 45 knots possible across the higher terrain.

Saturday Night...High Confidence.

VFR with a diminishing west wind.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Sunday through Wednesday/...

Sunday: VFR. Breezy.

Sunday Night: Mainly VFR, with local IFR possible. Windy with local gusts up to 30 kt. Chance RA, chance FZRA.

Monday: Mainly IFR, with areas MVFR possible. Strong winds with local gusts up to 40 kt. RA, isolated TSRA.

Monday Night: Mainly MVFR, with areas IFR possible. Strong winds with gusts up to 45 kt. RA, slight chance TSRA.

Tuesday: VFR. Windy with gusts up to 30 kt. Chance RA, slight chance SN.

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

Wednesday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

Rough seas linger across the outer coastal waters into Saturday night. Winds expected to increase from the south to southwest tonight, then become west by mid morning Saturday. Frequent gale-force gusts, mainly across the southern coastal waters. There is a risk for gale-force gusts across the Stellwagen Bank NMS during Saturday afternoon into the evening. However, do not yet have enough confidence in this outcome, so opted for a Gale Watch instead. Diminishing winds and seas Saturday night.

Outlook /Sunday through Wednesday/...

Sunday: Winds less than 25 kt.

Sunday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Slight chance of rain.

Monday: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 15 ft. Rain, isolated thunderstorms.

Monday Night: gale force winds with gusts up to 45 kt. Rough seas up to 15 ft. Rain, slight chance of thunderstorms.

Tuesday: Strong winds with gusts up to 35 kt. Rough seas up to 13 ft. Chance of rain, slight chance of snow.

Tuesday Night: Strong winds with gusts up to 35 kt. Rough seas up to 12 ft.

Wednesday: Winds less than 25 kt. Local rough seas.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...Wind Advisory from 10 AM to 7 PM EDT Saturday for MAZ002-004- 008-009. RI...None. MARINE...Small Craft Advisory from 10 AM Saturday to 1 AM EDT Sunday for ANZ230. Small Craft Advisory from 1 AM Saturday to 1 AM EDT Sunday for ANZ231. Gale Warning from 2 AM to 5 PM EDT Saturday for ANZ232>235-237. Small Craft Advisory from 1 AM to 7 PM EDT Saturday for ANZ236. Gale Watch from Saturday afternoon through Saturday evening for ANZ250. Small Craft Advisory from 10 PM this evening to 1 AM EDT Sunday for ANZ251. Gale Warning from 5 AM to 7 PM EDT Saturday for ANZ254. Gale Warning from midnight tonight to 7 PM EDT Saturday for ANZ255-256.