textproduct: Boston / Norton

WHAT HAS CHANGED

Flood Watch continues for today and tonight across RI and southeast MA. Guidance trended slightly farther north with axis of heaviest rainfall.

Otherwise, overall forecast remains in good shape.

KEY MESSAGES

- Widespread rain arrives today and continues tonight before tapering off early Saturday. Rain will be heavy at times across RI and southeast MA, including Cape Cod and the Islands.

- Unsettled weather continues into this weekend, then cooler and drier conditions arrive next week.

DISCUSSION

KEY MESSAGE 1...Widespread rain arrives today and continues tonight before tapering off early Saturday. Rain will be heavy at times across RI and southeast MA, including Cape Cod and the Islands.

Still trying to pinpoint the axis of heaviest rainfall. Some of the latest guidance have shifted this axis slightly farther north, owing to a slightly slower timing of a cold front. Still have the greatest confidence in the heavier rainfall across RI and southeast MA.

Temperatures remained well above normal for early November. Expecting low temperatures this morning to be higher than our normal high temperatures. A few records See the climate section below for more details.

Still strong signals for a significant rainfall across our region into Saturday. Thus, not much change to the overall forecast. There was some lightning around midnight south of Long Island, as well as a few flashes south of Cape Ann more recently. A few thunderstorms remain a possibility. Thus far, it has not been particularly widespread, but will keep a broader mention of thunderstorms in the forecast due to the supporting dynamics.

Rainfall totals were not changed substantially. Continue to have high confidence for 1-3", with lower probabilities for isolated 4-5". This might result in urban/poor drainage flooding, including the typical flood prone areas of New Bedford, Fall River, Providence, Cranston, etc. Given the time of year, leaf clogged drains will only exacerbate the urban/poor drainage flood potential. Regarding small rivers and streams in RI and southeast MA, 4+ inches would be required for minor flooding. Hence, looking more like a poor drainage/urban flood potential. Elsewhere across CT into northern MA, less rainfall is expected. Thus, the flood threat is limited to RI and southeast MA. Given the flood potential and uncertainty in the exact location of heaviest rainfall, a Flood Watch continues to message the threat for flooding.

Rainfall chances initially diminish Saturday morning with a lull in the precipitation. Will see a resurgence in rainfall chances Saturday afternoon into Saturday night as the colder core of an upper level low moves overhead. The anomalously cold air aloft paired with partial clearing at the surface likely results in steep lapse rates and widespread showers. A few showers may be capable of producing heavy rainfall and small hail as strong cold air advection cools the mid levels of the atmosphere.

KEY MESSAGE 2...Unsettled weather continues into this weekend, then cooler and drier conditions arrive next week.

In the wake of today's system, surface low pressure develops in the Gulf of Maine Saturday night into Sunday morning. This low shifts off to the north and east through Sunday morning while the core of an upper level trough steadily follows it from the west. This core is expected to move over southern New England over the same time period, and with it, much cooler temperatures aloft. Temperatures at 500 mb dip to around -20C, with some guidance falling to -25C. Closer to the surface, temperatures at 925 mb fall to around 2-4C and temperatures at 850 mb fall to around 0C by early Sunday morning. Once the upper level trough clears off to the north and east, 850 mb temperatures improve slightly to just around 2C. This colder air aloft will be more supportive of highs Sunday into the start of next week falling back to the 50s with cool nights in the 30s and 40s.

NAEFS guidance indicates no significant deviations from the climatological percentiles for temperatures or moisture for the next week, though did note 90th percentile zonal winds aloft Monday into Wednesday across much of the region. Persistent westerly flow with notably breezy conditions Monday and Tuesday is expected. Winds generally stay westerly through much of the week, given the series of fronts expected to move through the region. With the drier conditions (PWATS to around 0.5" and less and dew points back in the 30s and 40s) at the surface, not much in the way of precipitation is expected with these frontal passages; just cooler air. Occasional cloudiness is expected at most with passing moist air aloft.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

Today and Tonight...High confidence on trends, lower confidence on exact timing and details.

Widespread LIFR/IFR in periods of rain, heavy at times across RI and southeast MA terminals. Low risk of -TSRA, especially off the south coast of RI/SE MA.

More of the same tonight. IFR conditions in periods of rain, locally heavy at times across RI and southeast MA. As wave of low pressure tracks along the south coast and then exits the canal, winds will shift to the N-NE. Low risk of marginal LLWS as low level southwest jet of 40-45 kt moves across RI and southeast MA.

Saturday...High confidence on trends, lower confidence on exact timing and details.

Slow improvement from W to E from IFR to mainly MVFR. Areas towards SW New England could be VFR during the afternoon.

KBOS Terminal...High confidence in trends, moderate confidence in exact timing and exact details. Brief lull this morning, but SHRA returns towards 14Z. Visibilities may fall to IFR before 20z in any periods of heavier rainfall, but uncertainty remains on exact timing.

KBDL Terminal...High confidence in trends, moderate confidence in timing and exact details. Visibilities may fall lower than 2SM in any periods of heavier rainfall during the day. Ceilings could flirt with LIFR, but confidence is just too low to include in TAF for now.

Outlook /Saturday Night through Tuesday/...

Saturday Night: Mainly VFR, with areas IFR possible. Breezy. Chance RA.

Sunday: Mainly VFR, with local MVFR possible. Breezy. Chance RA.

Sunday Night through Tuesday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

Through Saturday...High confidence on trends, lower confidence on exact timing and details.

A cold front is still expected to stall across eastern New England this afternoon. A low pressure traverses this front, reaching eastern MA tonight, then moving east across the waters Saturday. Main impacts will be from areas of moderate to heavy rainfall with poor visibility at times. A few thunderstorms are possible as well.

Rough seas expected across the southern coastal waters. Posted a Small Craft Advisory for those waters. Seas subside some tonight as winds diminish.

Outlook /Saturday Night through Tuesday/...

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

Sunday: Strong winds with gusts up to 30 kt. Rough seas up to 10 ft. Chance of rain.

Sunday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 9 ft.

Monday: Strong winds with areas of gusts up to 30 kt. Rough seas up to 9 ft. Slight chance of rain.

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

Tuesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas.

CLIMATE

Persistent unseasonable warmth will challenge calendar-day record highs and record high minimums across southern New England climate sites.

Daily Record Lows to Watch:

Boston (BOS): Today 65F (2022)

Hartford/Bradley (BDL): Today 64F (2022)

Providence (PVD): Today 64F (2022)

Worcester (ORH): Today 62F (2024)

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...Flood Watch through Saturday morning for MAZ017>023. RI...Flood Watch through Saturday morning for RIZ001>008. MARINE...Small Craft Advisory until 1 AM EST Saturday for ANZ255. Small Craft Advisory until 4 AM EST Saturday for ANZ256.