textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Much cooler with periods of rain tonight into Thursday.

- Temperature roller coaster continues through next week with continued rain chances through at least Sunday. Drier and cool next week.

DISCUSSION

KEY MESSAGE 1...Much cooler with periods of rain tonight into Thursday.

Backdoor front has moved into NE MA with wind shift to N-NE and a sharp temp drop into the 50s. This front will push south and west across SNE through late afternoon with sharply falling temps. Scattered showers will be focused south of the MA Pike this afternoon and there is a brief window for an isolated t-storm across eastern CT-RI and SE MA where marginal instability will develop.

The front will set up south of New Eng tonight as strong high pres builds over the Maritimes. Low level E-NE flow will bring much cooler temps tonight into Thu with temps dropping into the 30s late tonight with minimal recovery on Thu with highs upper 30s to lower 40s. Meanwhile SW flow aloft overriding the cool air near the surface with deepening moisture in the column and weak surface wave tracking along the boundary will bring periods of rain tonight into Thu. It looks like the bulk of the rain will be later tonight through Thu morning, with some improvement in the afternoon as the deeper moisture plume lifts to the north. But still dreary in the afternoon with low clouds and patchy drizzle. 925 mb temps drop to 0 to -2C across northern MA late tonight into Thu so the rain may mix with sleet here at times but no impact expected. Rainfall amounts of 0.25 to 0.50" expected with localized amounts up to an inch.

Cold front will begin to lift back north as a warm front Thu night but remain to the south. Stratus and patchy drizzle and fog will continue with temps remaining steady in the 30s. There is a low risk for localized pockets of freezing drizzle over higher elevations near the VT/NH borders where temps may drop close to 32F.

KEY MESSAGE 2...Temperature roller coaster continues through next week with continued rain chances through at least Sunday. Drier and cool next week.

Friday the pattern flips again as high pressure exits to the northeast replaced by low pressure crossing northern New England Friday and Friday night. This brings the return of warm, moist south westerly flow pumping temperatures back up into the 60s (low 50s along the south coast thanks to cool onshore flow). A few showers are possible on Friday but most will be dry. It's a brief warm up as the trailing cold front arrives sometime early Saturday bringing the return of colder temperatures and a renewed chance of scattered showers as the front stalls. This all then repeats once again on Sunday with a brief warm frontal passage followed by a more robust cold front accompanying a deeper mid level trough. Still some uncertainty on the timing of the heaviest precip, but a later Sunday/Sunday night period looks most likely. Moisture parameters are better with this round (PWATS over 1.25") and EPS/GEFS ensemble guidance indicate a 20-40% chance of rainfall totals AOA 0.5". Looking into next week a cooler airmass moves overhead and so while we should dry out, a seasonable to cooler than normal stretch looks on tap with highs in the 40s and low 50s.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

18z TAF Update...Moderate confidence.

Backdoor front across NE MA will push south across SNE from NE to SW through 00z. Lowering cigs to MVFR behind the boundary and eventually to IFR tonight. Scattered showers and possibly a t-storm will develop across RI and SE MA this afternoon, transitioning to periods of rain developing across the region tonight into Thu morning. IFR-MVFR persists through Thu night with rain tapering to patchy drizzle by Thu afternoon. Wind shift to NE behind the front through this afternoon with gusts to 20-25 kt developing along the coast tonight into Thu.

KBOS Terminal...Moderate confidence in TAF. Uncertainty revolves around timing of lowering cigs to MVFR then IFR.

KBDL Terminal...Moderate confidence in TAF. Uncertainty revolves around timing of lowering cigs to MVFR then IFR.

Outlook /Friday through Monday/...

Friday: Mainly VFR, with local IFR possible. Breezy.

Friday Night: VFR. Breezy.

Saturday: Mainly VFR, with areas MVFR possible. Breezy. Chance SHRA.

Saturday Night: Mainly MVFR, with areas IFR possible. Breezy. Chance SHRA.

Sunday: Mainly MVFR, with areas IFR possible. Windy with gusts up to 30 kt. SHRA likely.

Sunday Night: Mainly VFR, with areas MVFR possible. Breezy. Chance SHRA.

Monday: Breezy.

MARINE

Forecaster Confidence Levels...

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

High confidence through Thu night.

SCAs expanded across all waters except Boston Harbor and Narragansett Bay tonight into Thu for NE gusts to 25 kt. Diminishing E winds Thu night.

Outlook /Friday through Monday/...

Friday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Local visibility 1 to 3 nm.

Friday Night: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft.

Saturday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers.

Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of seas approaching 5 ft. Chance of rain showers.

Sunday: Strong winds with gusts up to 35 kt. Areas of rough seas. Chance of rain showers.

Sunday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Chance of rain showers.

Monday: Winds less than 25 kt. Local rough seas. Slight chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 2 AM to 8 PM EDT Thursday for ANZ231- 250-251. Small Craft Advisory from 8 PM this evening to 8 PM EDT Thursday for ANZ232>234. Small Craft Advisory until 8 PM EDT Thursday for ANZ235-237. Small Craft Advisory until 2 AM EDT Friday for ANZ254>256.