textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast. Noted potential for minor coastal flooding at Nantucket Friday afternoon. Gale Watches were converted to Gale Warnings.

KEY MESSAGES

- 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 a majority of the weekend and into next week.

DISCUSSION

KEY MESSAGE 1...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.

Light radar returns are visible across central SNE early this morning as the first taste of the rain to come later today overspreads the region. This, as a strengthening low pressure center and lagging mid level trough will track over the Mid-Atlantic today and move off the coast (south of New England) tonight. Eventually it lifts into the Gulf of Maine Friday night into the weekend taking its associated moisture with it. Thus, the next 36-42 hours are expected to be wet before we dry out for the weekend. Low/mid level warm advection ahead of the low will bring rather widespread rain today, mainly confined to the interior/NW SNE under favorable E/upslope flow off the water with a moderate LLJ. Rain then overspreads the rest of the region this evening as the low moves south of Long Island. As this low moves further east flow becomes N then NW pulling in cooler air into the previously relatively mild boundary layer. This cold advection combined with potential diabatic cooling in any heavier bands of precipitation will be able to flip precipitation over to a wet snow for the higher elevations in the Berkshires and to a lesser extent the Worcester Hills. Outside of these areas, a cold rain is expected. Fortunately precipitation should be exiting/sinking south by late Friday so as the colder overnight temps arrive precipitation should be coming to an end. For this reason, while snow is expected to be confided to the high elevations, can't rule out a period of light snow further south into CT or the RI hills late in the day Friday though it is a low probability scenario. Overall, this is expected to be a non-event for most of the region, and a very low impact event in the high elevations with accumulations of a coating (Worcester Hills) to a few inches (Berkshires) most likely on grassy surfaces. Given the trajectory of the wind on Friday, temperatures will struggle to get out of the upper 30s in the high elevations and the mid to upper 40s toward the south coast.

One more thing to note, with regard to coastal flooding potential. While tides are not astronomically high, guidance does indicate potential for ~1-1.5 ft of surge. While not an issue for most of the coast, this would put Nantucket Harbor within reach of minor flood levels during Friday afternoon's high tide. If this signal persists coastal flood headlines may be needed.

KEY MESSAGE 2...High pressure brings cool and dry conditions back to southern New England for a majority of the weekend and into next week.

Latest round of guidance has trended the low pushing offshore into Atlantic Canada earlier than previously anticipated... likely sometime Saturday instead of Sunday. High pressure then builds over the Great Lakes this weekend. 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 Saturday to the mid 50s Tuesday/Wednesday. The high pressure will also bring back nights of radiational cooling, potentially dropping low temperatures into the 20s through mid week as well.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

12z TAF Update...

Thursday...High confidence.

VFR to start for most terminals, lowering to MVFR after 18Z with -RA overspreading the region. IFR possible at ORH after 18z. NE winds 10-15 kts, then gusting 20-25 kts at times after 18z. Periods of 25-30 kt gusts possible across Cape and Island terminals after 18z.

Thursday night...Moderate confidence.

MVFR/IFR in -RA, with -SN possible at ORH toward 12z. NE winds 10-15 kt gusting 20-30 kt.

Friday...Moderate confidence.

MVFR/IFR in -RA and -SN (for ORH). Precipitation exiting south by 00z Sat.

KBOS Terminal...High confidence in TAF through 18z, then some uncertainty on exacting timing arrival of MVFR and rain in the afternoon.

KBDL Terminal...High confidence in TAF through 18z, then some uncertainty on exacting timing arrival of MVFR and rain.

Outlook /Friday Night through Monday/...

Friday Night: Mainly VFR, with local IFR possible. Windy with local gusts up to 30 kt. Slight chance SHRA.

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

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

Sunday: VFR. Breezy.

Sunday Night through Monday: VFR.

MARINE

Forecaster Confidence Levels...

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

Through Friday night...

* Gale Watch for the open waters Thu night through Friday night

Low pressure will move off the mid-Atlantic coast over the waters Thursday evening through Friday night. In response...the pressure gradient will increase and Gale Watches are in effect for our open waters Thu night through Fri night for the potential of N-NE wind gusts up to 35 knots. Seas will also become quite rough. Small craft advisories are also in effect for Boston Harbor/Narragansett Bay during this time.

Outlook /Friday Night through Monday/...

Saturday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 8 ft. Chance of rain.

Saturday Night: Winds less than 25 kt. Rough seas up to 8 ft. Chance of rain.

Sunday: Winds less than 25 kt. Areas of rough seas. Slight chance of rain.

Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 6 PM this evening to 7 PM EST Friday for ANZ230-236. Gale Warning from 1 AM to 7 PM EST Friday for ANZ231>235-237- 255-256-282-283. Gale Warning from 6 PM this evening to 7 PM EST Friday for ANZ250-251-254-280-281.