textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- Seasonable conditions continue through tonight.

- A storm system will bring a prolonged period of rain to much of southern New England Thursday through Saturday with periods of snow in the higher elevations. Significant accumulation is not expected.

- High pressure brings cool and dry conditions back to southern New England for the start of the next work week.

DISCUSSION

KEY MESSAGE 1...Seasonable conditions continue through tonight.

Persistent WNW flow continues through this evening, bringing seasonable temperatures and dry conditions ahead of the next storm. High temperatures today remain similar to yesterday... in the mid 50s. A dry shortwave pushing through before sunrise will allow for some wind gusts 20 to 25 mph in the higher elevations and coastal plain through mid-morning before conditions slowly calm through the afternoon.

KEY MESSAGE 2...A storm system will bring a prolonged period of rain to much of southern New England Thursday through Saturday with periods of snow in the higher elevations. Significant accumulation is not expected.

A vertically stacked trough of low pressure over the Ohio Valley will pass over the Mid-Atlantic on Thursday, strengthening as is moves into the waters south of New England Thursday night and lifts into the Gulf of Maine Friday night. This leads to a prolonged period of unsettled weather, even continuing into Saturday thanks to the slow progression/trailing behind of the upper trough/cold pool aloft. Light to moderate warm advection rain will expand over southern New England on Thursday as the low approaches. Eventually a cooler airmass is pulled down as flow around the low backs to the north and northwest while the mid/upper levels cool with the arrival of the trough. This, together with some diabatic cooling will allow for places in the high terrain of the Berkshires and Worcester Hills to flip to snow by Thursday night. However, given the lack of antecedent cold air in the boundary layer those outside of the higher elevations will more likely experience a cold rain for most if not all of the period. The decidedly mild airmass in place over the last week will not bode well for much in the way of accumulation. Model soundings show a lack of omega in the snow growth zone as well as a dry slot which may move in overnight Thursday cutting into potential snowfall amounts. Ensemble guidance is fairly steady in showing only a few outlier members with substantial snowfall across MA/CT/RI; probabilities of AOA 3" in the Worcester Hills range from 10-30% (both EPS and GEFS) but keeping in mind these are using 10:1 SLR while in reality they would be less. In early season situations like this it is often useful to utilize the positive snow depth change guidance as a more realistic expectation; thus, continuing to expect a low impact event with only minor accumulations in the highest terrain. That being said, as we get in range of the higher resolution guidance we will continue to evaluate and update the forecast based on the newest information.

KEY MESSAGE 3...High pressure brings cool and dry conditions back to southern New England for the start of the next work week.

As the low slowly pushes further into Atlantic Canada, high pressure begins to build over the Great Lakes Sunday into Monday. The tighter pressure gradient will allow blustery conditions to linger through Sunday, but the strengthening high will mark the return of a dry period through the start of the next work week. High temps slowly climb through the early week... in the upper 40s Sunday to the mid 50s Tuesday/Wednesday.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

12z TAF Update...

Wednesday...High confidence.

VFR conditions. SCT to BKN mid to high level clouds. Winds WNW at 8-10 kts.

Wednesday night...High confidence.

VFR. Ceilings lowering toward 12z. Winds calm to light and variable.

Thursday...High confidence.

VFR to start, lowering to MVFR after 18Z in incoming -RA with IFR possible at ORH. E winds 10-15 kts after 18z gusting 15-20 kts.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday Night through Sunday/...

Thursday Night: Mainly VFR, with areas IFR possible. Windy with local gusts up to 30 kt. RA, FZRA.

Friday: Mainly VFR, with areas IFR possible. Windy with areas of gusts up to 30 kt. RA.

Friday Night: MVFR/IFR conditions possible. Windy with local gusts up to 30 kt. Chance RA, chance SN, chance FZRA.

Saturday: Mainly VFR, with local IFR possible. Breezy. Slight chance RA.

Saturday Night: Mainly VFR, with local IFR possible. Breezy.

Sunday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

Through Thursday...High confidence.

Surface high pressure across the coastal waters Wednesday. Winds decrease early Wednesday morning, although seas may remain near 5 ft across portions of the southern outer waters through the afternoon Wednesday. Seas 2-3 ft. Low pressure moves over the waters on Thursday leading to winds 20-25 kt gusting to 30 kt. Seas becoming 3- 5 ft.

Outlook /Thursday Night through Sunday/...

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

Friday: Strong winds with gusts up to 30 kt. Rough seas up to 9 ft. Rain.

Friday Night: Strong winds with areas of gusts up to 30 kt. Rough seas up to 10 ft. Rain likely.

Saturday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 10 ft. Rain likely.

Saturday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 12 ft. Chance of rain.

Sunday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 10 ft. Chance of rain.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 10 AM EST this morning for ANZ250- 254>256.