textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- Mainly dry and pleasant today and Saturday with a chance for some isolated showers Saturday afternoon.

- Cooler weather this weekend into early next week gives way to a warming trend and the chance for unsettled weather by mid week.

- Dangerous conditions at the beach for the holiday weekend with as the rip current risk increases Sunday and Labor Day.

DISCUSSION

KEY MESSAGE 1. Mainly dry and pleasant today and Saturday with a chance for some isolated showers Saturday afternoon.

Looking drier and mild over the next couple of days as broad NW flow around a closed low advects a lower PWAT airmass into the region. PWAT values fall below 1.00" by this afternoon into Saturday. Despite the overall drier airmass, a broad cutoff low over the Canadian Maritimes will maintain a non-zero chance of isolated showers today and Saturday. The greatest chance for shower activity falls on Saturday as an embedded shortwave moves S from Canada. Each day will see diurnal cumulus as low level lapse rates steepen during the afternoon. In terms of temperatures, today will be the warmest day of the whole forecast as a slightly warmer airmass pushes in; 850 mb temps briefly reach ~15C this afternoon before dropping to ~8C Saturday resulting in high temperatures in the low to mid 80s and low to mid 70s respectively.

KEY MESSAGE 2... Cooler weather this weekend into early next week gives way to a warming trend and the chance for unsettled weather by mid week.

The upper air pattern later this weekend into next week evolves from an amplified omega block into a more zonal configuration. The changes will come as the persistent closed mid-level low over Nova Scotia finally pushes away from the eastern CONUS. In its place, 500 mb heights rise as a broad southeast ridge amplifies poleward. What this translates to at the surface is a benign weather pattern with somewhat persistent high pressure over the northeast. The next chance for disturbed weather arrives midweek as a strong shortwave passes to the N of the region. Guidance shows a somewhat compact and seasonably strong surface low forming in response to the aforementioned upper low. Details are still somewhat TBD given the time to the event but there is a chance for unsettled weather with this feature around midweek.

Temperatures aloft are cooler Sunday, associated with that mid-level low east of New England. 925mb temperatures are only around +8C to +10C, which with boundary layer mixing supports highs in the upper 60s to low 70s. Thus, Sunday will feel very much like autumn, with a blend of sun and clouds, northerly winds and dew points in the low 50s. While winds won't be overly strong, the combination of cooler temperatures and lower dew points will make for a rather crisp day. Sunday night could feature some decent radiational cooling as high pressure settles across the region, though this will depend on how quickly winds diminish. It appears as though the latest NBM has picked up on this trend for both Saturday night and Sunday night. The latest run shows widespread 50-55 degree readings with even a few upper 40s in the higher terrain of northern Massachusetts. Should see a rebound in temperature readings by early next week as 925mb temperatures climb +14C to +18C, supporting near-seasonable highs in the upper 70s for Labor Day, then upper 70s to lower 80s Tuesday into the middle part of next week. Humidity remains tolerable as well, with dew points generally in the upper 50s to around 60F. Labor Day itself looks quiet and dry, though there will be a high risk for rip currents along the ocean beaches.

KEY MESSAGE 3...Dangerous conditions at the beach for the holiday weekend with as the rip current risk increases Sunday and Labor Day.

Persistent northeast flow, long-period swell, and offshore seas of 4- 7 feet will continue to support an elevated risk for dangerous rip currents through the Holiday Weekend, especially Sunday into Labor Day for east-facing ocean beaches. With otherwise quiet weather expected, those heading to the beach should be mindful that ocean conditions may still be hazardous. Be sure to check with local beach staff or lifeguards regarding ocean conditions before entering the water.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

12z Update...

Today...Moderate confidence in trends, lower confidence in timing.

Between 12-15z, conditions improve to VFR for most, with the exception of the outer Cape and KACK. There, it may take well into the early afternoon for conditions to improve to VFR. Light north- northwest winds for most, though a sea breeze develops across eastern coastal Massachusetts, including KBOS.

Friday Night...High confidence.

VFR. Light northwest winds.

Saturday...High confidence.

VFR. N/NE winds 10-15 kts. Isolated SHRA/TSRA.

KBOS Terminal...Low confidence.

Areas of stratus and fog continue IFR with MVFR visibilities roughly through 12z. Some improvement to MVFR is possible during the morning push, otherwise trending to VFR after 14/15z. An onshore wind is also anticipated for much of the day today.

KBDL Terminal...Moderate confidence.

Areas of MVFR/IFR conditions contingent upon the development of low stratus/fog. Any reduced flight categories resolve shortly after 12z.

Outlook /Saturday Night through Tuesday/...

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

Sunday: VFR. Breezy.

Sunday Night through Tuesday: VFR.

MARINE

Forecaster Confidence Levels...

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

Today through Saturday Night...

W/NW winds this morning gradually shift the S/SW this evening A few showers and t-storms may move over the southern waters this evening then tranquil weather persists. Seas 2-3 ft. Winds shift to the NE and increase to 10-15 kt Saturday. Seas generally remain below Small Craft Advisory criteria during the daytime with an increasing chance later Saturday night.

Outlook /Saturday Night through Tuesday/...

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

Sunday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas.

Sunday Night: Winds less than 25 kt. Areas of rough seas.

Labor Day: Winds less than 25 kt. Areas of seas approaching 5 ft.

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

Tuesday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...None.