textproduct: Boston / Norton

WHAT HAS CHANGED

Issued a couple of marine and coastal headlines for the holiday weekend. For boaters, a Small Craft Advisory has been issued and is in effect from 2 am to 8 pm Sunday. For beachgoers, a Rip Current Statement is in effect for east-facing beaches and the islands from 7 am to 8 pm through much of the day on Sunday.

KEY MESSAGES

- A mainly dry day on tap except along and east of the I- 495 corridor where there is a chance for afternoon showers and perhaps a thunderstorm or two.

- Fall-like feel for Sunday, then more seasonable for Labor Day. A gradual warm-up throughout the week with continued dry weather through at least Wednesday or Thursday.

- Elevated risk for dangerous rip currents through the Holiday Weekend, especially Sunday into Labor Day.

DISCUSSION

KEY MESSAGE 1... A mainly dry day on tap except along and east of the I-495 corridor where there is a chance for afternoon showers and perhaps a thunderstorm or two.

The main weather maker for the next day or so will be a broad cutoff low pressure over the Canadian Maritimes. As a result, some unsettled weather is possible for the start of the Labor Day Holiday weekend, more details ahead. Should see a rather pleasant start to the day with mainly clear skies and temperatures in the lower to mid 60s. Temps climb into the lower to mid 70s, and when combined with cooling aloft (925 mb temps cooling to 12-14C), will result in steep low level lapse rates. These lapse rates will drive diurnal cumulus which likely builds into areas of showers and a few thunderstorms as SFC CAPE values climb to 300-500 J/kg. High-res guidance features an inverted trough moving across the CWA from NE to SW between 18-22z. This feature serves as a focus for convection and more organized precipitation chances during that timeframe. Believe the latest NBM has a good handle on these changes with hourly POPs increasing to 45- 50 percent across interior areas. Not expecting a washout by any means, but a brief period of heavy rain is possible as these showers move through. Any lingering showers quickly dissipate with the loss of daytime heating this evening. Expect a cooler night as somewhat ideal conditions for radiational cooling are expected with light winds and mostly clear skies. Lows will generally be in the low to mid 50s and even the upper 40s in more favorable locations such as local river valleys.

KEY MESSAGE 2...Fall-like feel for Sunday, then more seasonable for Labor Day. A gradual warm-up throughout the week with continued dry weather through at least Wednesday or Thursday.

Saturday night through the middle of the upcoming week features fairly benign conditions, with little in the way of rainfall chances. The 500mb forecast map shows somewhat of an omega ridge centered across the middle of the country, with a closed mid-level low centered over Nova Scotia Sunday afternoon. The omega ridge flattens out, with semi-zonal flow developing across the coast by Tuesday and then shortwave troughing for late week across the northeastern states, likely leading to the next chance for active weather for southern New England. At the surface, high pressure builds in from the northwest Sunday, with its origins in northern Canada. Surface high pressure remains the dominant weather feature throughout the majority of the forecast period, leading to a stretch of dry weather.

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 should feature decent radiational cooling with high pressure settling across the region, though this will depend on how quickly winds diminish. Did opt for a blend of colder guidance on Sunday night, which brought temperatures down into the upper 40s to low 50s for most of southern New England, with urban centers like Boston remaining in the middle 50s.

Good news if you aren't ready for pumpkin spice weather, as temperatures will trend warmer throughout the week from WAA aloft. 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...Elevated risk for dangerous rip currents through the Holiday Weekend, especially Sunday into 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 /06Z SATURDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

UPDATE: 06Z TAF

Rest of Tonight...Moderate confidence.

VFR for the majority of terminals through daybreak. Slight chance of MVFR across the Cape and Islands. Light northwest winds, with light north- northeast wind for eastern MA.

Today...Moderate confidence.

Forecast guidance suggest there may be two cloud bases today, one being MVFR to low-end VFR (020-040)VFR, then a secondary base between 050-080. Isolated SHRA/TSRA threat 19z-23z. North- northeast winds 10-15 kts.

Saturday night...High confidence.

Lower-end VFR to MVFR ceilings. Winds light and variable.

KBOS Terminal...Moderate confidence in TAF.

Where confidence is moderate is with the development of MVFR ceilings, whether the deck of clouds are SCT or BKN/OVC. Also moderate confidence in the risk for -SHRA between 18-22z this afternoon.

KBDL Terminal...High confidence in TAF.

Outlook /Sunday Night through Wednesday/...

Sunday Night through Tuesday Night: VFR.

Wednesday: VFR. Windy with local gusts up to 30 kt. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Through Sunday...

Winds shift N and NE today sustained to 10-15 kt. Seas 2-3 ft, increasing slightly heading into Sunday. Moderate chance of showers later this afternoon across much of the waters. Slight chance for isolated thunderstorms. Small Craft conditions develop across the eastern outer waters after 06z Sunday lingering through much of the day. Rip Current Statement is in effect from early Sunday morning to the evening.

Outlook /Sunday Night through Wednesday/...

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

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 through Tuesday Night: Winds less than 25 kt.

Wednesday: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Seas locally approaching 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...High Risk for Rip Currents from late tonight through Sunday evening for MAZ007-014>016-019-022>024. RI...None. MARINE...Small Craft Advisory from 2 AM to 8 PM EDT Sunday for ANZ250- 254-255.