textproduct: Boston / Norton

WHAT HAS CHANGED

Flood Watch has been issued for Fri/Fri night across RI and southeast MA.

Increased precipitation chances Saturday and Sunday, otherwise, the long term forecast remains in good shape.

KEY MESSAGES

- Widespread rain arrives Friday and continues Fri night before tapering off early Sat. Rain will be heavy at times Fri/Fri night across RI, southeast MA including Cape Cod and the Islands.

- Unsettled weather continues under an upper level Iow it rotates over the region Saturday and Sunday. Cooler but drier conditions arrive next week.

DISCUSSION

KEY MESSAGE 1...Widespread rain arrives Friday and continues Fri night before tapering off early Sat. Rain will be heavy at times Fri/Fri night across RI, southeast MA including Cape Cod and the Islands.

Warm advection (WAA) pattern has resulted in overcast conditions across the region this afternoon, along with an impressive warm sector airmass for early Nov, with dew pts in the low 60s across the area. The combination of clouds and high dew pts will result in a very mild night ahead by early Nov standards, with min temps only in the low 60s. This will likely result in record warm min temps tonight. See the climate section below for details.

Rain becomes more widespread Friday, especially during the afternoon, along with rain heavy at times across RI and southeast MA, continuing into Fri night. RRQ of 100+ kt upper level jet streak over SNE helps spin up a frontal wave that tracks along or near the south coast Fri night. Copious deep layer moisture available with dew pts in the low to mid 60s, PWATs up to +3 sigma and some weak instability (MU Capes 500-750 j/kg) to enhance the rainfall. In addition, surface wave will be accompanied by a 40-45 kt low level SSW jet, enhancing the low level convergence. Still some uncertainty on the exact axis of heaviest rainfall, but all guidance suggest somewhere over RI and southeast MA, including Cape Cod and the Islands. The development of the surface wave will result in a nearly stationary frontal boundary, increasing the risk for flooding from training cells.

New 12z Hi Res guid simulating 3-5" rainfall across RI and southeast MA, along with support from the 00z global ens offering low probs of 4+ inches. Thus, high confidence for 1-3" with lower probs for isolated 4-5". This would result in potential 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, we will hoist a flood watch to message the threat for flooding.

Rainfall probs initially fall off Saturday morning with a lull in the precipitation. Will see a resurgence in precipitation probabilities Saturday afternoon as the cold core of an upper level low moves overhead lowering 500mb temps to around -20C. 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. The strong cold advection will be most evident at 850 mb as temperatures fall from +9-10C Saturday morning to +1-4C by Saturday night. Guidance depicts surface low pressure developing in the Gulf of Maine Saturday night into Sunday. Currently have the highest POPs along and N of the Mass Pike for Sunday as cool cyclonic flow enhances rainfall chances further to the N. Overall it looks to be a raw weekend between the scattered to widespread showers and high temperatures in the mid 50s to upper 60s.

A series of fronts then move across southern New England next week. However, limited moisture should only mean periods of clouds at times and mainly dry weather.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

18z update...

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

This evening and tonight...Moderate confidence.

VFR/MVFR cigs with VFR vsbys through this evening, then lowering to MVFR/IFR after midnight. Other than a few bands of showers, many hours of dry weather. Despite modest low level jet, overcast conditions will limit SW wind gusts to 20-25 kt at times. Winds drop off with sunset, but with low level SW jet aloft, may have marginal LLWS from 00z Fri to 06z.

Friday/Fri night...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 prob of -TSRA off the south coast of RI/SE MA. Lighter south winds than Today/Thursday, 5-10 kt Fri except gusting up 20 kt along the south coast, ahead of approaching frontal wave.

Friday night more of the same, 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 prob of marginal LLWS as low level southwest jet of 40-45 kt moves across RI and southeast MA.

KBOS Terminal...High confidence in TAF through this evening, then some uncertainty on exact timing and details thereafter.

KBDL Terminal...High confidence in TAF through this evening, then some uncertainty on exact timing and details thereafter.

Outlook /Saturday through Tuesday/...

Saturday: MVFR/IFR conditions possible. Breezy. Chance SHRA.

Saturday Night: Mainly VFR, with areas IFR possible. Breezy. SHRA likely.

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

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.

1 PM update...

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

High pressure offshore will combine with a cold front to the west to generate a modest SW wind 10-15 kt with gusts up to 25 kt at times across the RI and MA waters Thu. Winds slacken Fri as the front stalls over the RI/MA waters, in response to low pressure forming on the boundary south of Long Island Fri night, then tracking northeast along the south coast of RI/MA. South of the low, a few thunderstorms are possible Fri night.

Outlook /Friday Night through Tuesday/...

Saturday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers.

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

Sunday: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Rough seas up to 9 ft. Chance of rain showers.

Sunday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 8 ft.

Monday: Strong winds with gusts up to 30 kt. Rough seas up to 8 ft. Slight chance of rain.

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

Tuesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Seas up to 5 ft.

CLIMATE

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

Daily Record Highs to Watch:

Boston (BOS): Thursday 79F (1994)

Hartford/Bradley (BDL): Thursday 75F (2022)

Providence (PVD): Thursday 75F (1994)

Worcester (ORH): Thursday 73F (1994)

Daily Record Lows to Watch:

Boston (BOS): Thursday 56F (1994)|Friday 57F (2020)

Hartford/Bradley (BDL): Thursday 55F (1994)|Friday 56F (2020)

Providence (PVD): Thursday 56F (1994)|Friday 58F (2020)

Worcester (ORH): Thursday 55F (1994)| 55F (2020)

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...Flood Watch from late tonight through Saturday morning for MAZ017>023. RI...Flood Watch from late tonight through Saturday morning for RIZ001>008. MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ230>237-251.