textproduct: Boston / Norton

WHAT HAS CHANGED

A Rip Current Statement has been issued for Plymouth and Barnstable Counties for Saturday.

KEY MESSAGES

- Below normal temperatures and overcast conditions continue through the weekend. Drizzle/misty weather through Saturday then a period of heavier rain possible overnight into Sunday.

- Drier and warmer next week.

DISCUSSION

KEY MESSAGE 1...Below normal temperatures and overcast conditions continue through the weekend. Drizzle/misty weather through Saturday then a period of heavier rain possible overnight into Sunday.

The low pressure system that's brought the misty and overcast weather today has dipped a little further south of Long Island than previously expected. The latest guidance suite is projecting the low slowly moves east through today then swings northeast around Nantucket tonight into Saturday. The interior is more likely to remain dry with a few pockets of mist through the rest of today, but eastern and Southeast MA and RI should see the mist linger with periodic light showers into Saturday. Most of southern New England should see a dry Saturday morning, except the Cape/Islands could see a few lingering showers. As the low weakens and wraps around the Cape Saturday, another round of heavier showers is expected to push into southern New England later Saturday evening into the overnight period. This round has the potential to develop a few heavier, convective bands of rain given the higher PWATs near 2.0" and favorable IVT. Guidance is split a few different ways on QPF totals: Global ensembles show generally a 30 to 40 percent chance of 1.0" in 24 hours over the Cape/Islands by sunrise Sunday, except the GFS ensemble which indicates much less rainfall and also located further offshore. CAM and higher resolution guidance has the same bullseye on the Cape, but also identifies and secondary precip max approaching 1.0" in 24 hours across interior CT and western MA. Given how the guidance is struggling to resolve the exact track of the low due to the unexpected southern drop today, confidence is on the lower end specifically regarding rainfall across the interior, as a little wobbling east or west in the northeastward progression of the low will have a larger impact on precip totals.

More of the same on Sunday as a cold front slowly approaches, sending moisture from the south out ahead of it. NE/E flow early becomes southerly advecting 70+ dewpoints into the region with PWATs 2+ inches. This while the surface low lifts north and east with the best convergence/forcing in the early morning with a lull possible in the late morning/afternoon then potential for some showers and thunderstorms in the afternoon. Given those dewpoints, CAPE values jump to 500-1000 J/kg and depending on how quickly the cold front arrives it could overcome marginal lapse rates to produce a strong to severe storm, especially in western SNE, given 0-6 km bulk shear values of 50+ kts.

Otherwise, temperatures through the first half of the weekend will remain below seasonable under prolonged onshore/northeasterly flow... highs likely remain in the upper 60s to low 70s through Saturday.

KEY MESSAGE 2...Drier and warmer next week.

By Monday the cold front has pushed through and ushers in a much drier and warmer start to the week. Dewpoints fall from near 65-70F Sun to 45-50F Mon. Rising heights and building surface high pressure will help to keep the forecast drier with perhaps some diurnal showers Tue under a weak shortwave. Otherwise, generally zonal flow takes hold through at least Thursday with no significant disturbances on the horizon, and no intrusions of anomalous heat or cold. Temperatures remain comfortable ranging from the mid 70s to low 80s.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

18z TAF Update:

Through 00z Saturday: Moderate confidence.

BKN/OVC VFR ceilings (bases 035-045) generally govern, though MVFR/IFR ceilings more common for southeast MA and RI airports. Intervals of mist/drizzle possible at BOS to PVD, but with off- and-on light showers for the Cape and Islands. NE winds around 5-10 kt, around 10-15 kt for the eastern airports.

Tonight into Saturday: Moderate confidence.

IFR for southeast MA but ceilings should deteriorate down to MVFR-IFR levels tonight and overnight northward to BOS, BED and ORH. Intervals of mist and drizzle at 4-6 SM. BDL should stay BKN VFR most of the night. Conditions should then generally hold steady into Sat daytime hrs. N to NE winds 5-10 kt.

Saturday Night: Moderate confidence.

Conditions to turn to widespread MVFR-IFR with a round of steadier light to moderate rain after approximately 06z Sunday; timing is uncertain and subject to further adjustment. NE to N winds 5-10 kt.

KBOS Terminal...Moderate confidence in TAF. Mainly OVC VFR ceilings today with NE winds around 10 kt, with off-and-on mist and drizzle. Categories more likely to deteriorate to sub-VFR ceilings with 4-6 SM BR/DZ tonight.

KBDL Terminal...High confidence in TAF. Stronger confidence in prevailing VFR and relatively drier weather.

Outlook /Sunday through Wednesday/...

Sunday: Mainly VFR, with local IFR possible. Chance SHRA, slight chance TSRA.

Sunday Night: VFR.

Monday: VFR. Breezy.

Monday Night: VFR.

Tuesday through Wednesday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

Through Saturday Night...High confidence.

Gusty NE winds near 25kts and waves near 5 ft across the southern waters gradually diminish through this evening and into tonight as the low weakens and moves further offshore. Otherwise, winds generally 18-20 kts and seas 3-4 ft through most of Saturday become more variable as the low breaks down Saturday night into Sunday morning.

Despite the lower wave heights, the prolonged northeasterly flow will cause higher swells and longer swell periods Saturday which has prompted a Rip Current Statement for Plymouth and Barnstable Counties. Eastern, ocean-facing beaches will be primarily affected, especially across the northern portion of Cape Cod; however, bay- facing beaches may also experience rip currents.

Outlook /Sunday through Wednesday/...

Sunday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers, slight chance of thunderstorms.

Sunday Night: Winds less than 25 kt. Local rough seas. Chance of rain showers, slight chance of thunderstorms.

Monday through Monday Night: Winds less than 25 kt. Seas up to 5 ft.

Tuesday through Wednesday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...High Risk for Rip Currents from Saturday morning through Saturday afternoon for MAZ019-022. RI...None. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ235- 237-256.