textproduct: Boston / Norton

WHAT HAS CHANGED

In addition to the risk for dangerous rip currents this Holiday Weekend there will be a risk for Small Craft Advisory conditions on Sunday.

KEY MESSAGES

- Rounds of showers and thunderstorms impact the region today. The first arrives this morning and the second arrives later in the afternoon.

- Mainly dry & very pleasant Fri into early next week except for some diurnally scattered showers mainly on Sat. Pleasant temps too with highs in the 70s...but lower-middle 80s Fri.

- Elevated risk for dangerous rip currents for the Holiday Weekend especially by Sun into Mon.

DISCUSSION

KEY MESSAGE 1... Rounds of showers and thunderstorms impact the region today. The first arrives this morning and the second arrives later in the afternoon.

Impacts from a frontal wave continue through this morning with scattered showers and thunderstorms possible. Activity overspreads western parts of our CWA between 2 and 3 AM before it overspreads the entire region by daybreak. Heavy downpours are likely with rich moisture in place. There is a marginal risk for flash flooding across western MA/CT in the Springfield/Hartford areas, but there is no strong signal for anything overly impactful at this time. Elevated instability will support some rumbles of thunder as showers move across the region, but deep layer shear and low/mid-level lapse rates do not appear to be favorable for deep moist convection capable of producing strong to severe storms.

The passage of the frontal wave brings significant mid-level drying with 700-500 mb RH values falling below 35 percent. The drier airmass aloft will result in clearing and strong diurnal heating. High temperatures will be warmer than they've been over the last several days with widespread readings in the lower to mid 80s likely. Warmer temps and dew points in the upper 60s to low 70s result in CAPE values climbing to between 1500 and 2000 J/kg around the region. Still, expecting any convection to be isolated to scattered in nature with low mid-level RH values. High-Res guidance has generally trended towards this solution with the NAM showing isolated convection. The HRRR and RRFS are a bit more aggressive and depict clusters of storms developing after 2 pm. Think the NBM has a good handle on POPs with widespread values between 35 and 45 percent throughout the CWA. Greatest chance for any storm activity will be along and S of a frontal boundary at it makes its way SE. Guidance generally shows this boundary S of the Mass Pike by 18z tomorrow thus, the greatest chance of storms will likely be S of the Mass Pike.

KEY MESSAGE 2...Mainly dry & very pleasant Fri into early next week except for some diurnally scattered showers mainly on Sat. Pleasant temps too with highs in the 70s...but lower-middle 80s Fri.

Upper level shortwave energy will close off over the Canadian Maritimes over the Holiday Weekend. This will carve out an upper trough over the northeast resulting in pleasant weather. Mainly dry weather expected over the majority of this time. However...some northern stream shortwave energy will probably result in diurnally driven scattered showers mainly on Sat...but can not rule out a few on Fri. High pressure building southward from eastern Canada Sun into Mon should bring an end to this risk for the latter half of the Holiday Weekend. Highs on Fri will mainly be in the lower to middle 80s...but generally 70s to near 80 this weekend into early next week. In fact...coolest days will be Sat and Sun as the eastern MA coast/Cape and Islands probably only see highs in the upper 60s to the lower 70s with a stiff northeast afternoon breeze. Overnight lows mainly in the 50s to the lower 60s...but there might be some 40s in the normally coolest outlying locations by Sun night/Mon AM as high pressure builds across the region.

KEY MESSAGE 3...Elevated risk for dangerous rip currents for the Holiday Weekend especially by Sun into Mon.

Given persistent NE low level flow and swell...we do expect an elevated risk for dangerous rip currents for the Holiday Weekend. This is especially true by Sun into Mon on east facing ocean exposed beaches.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

12z TAF Update:

Today: Moderate confidence, especially on timing.

Mix of MVFR-IFR for most with -SHRA and stratus and mist, except BKN/OVC VFR over the Cape and Islands. General deterioration in most areas widespread MVFR-IFR levels thru late-morning/noontime as rain pulls offshore. S winds 5-10 kt.

By around ~17-21z, some indication that ceilings could begin to scatter to VFR-ish range (SCT025/035 at best) in interior MA/CT but could hold onto sub-VFR decks longer for PVD, BOS/BED and the Cape. Potential for BOS to seabreeze during this 17-20z timeframe but the exact timing is uncertain. Risk for widely SCT SHRA/TS between 20-02z from central MA to the eastern MA coast, which was left as VCSH for now and will reassess with incoming guidance. Other than BOS, SW/W winds 5-10 kt this afternoon for most.

Tonight: Moderate confidence.

SHRA/TS moves offshore, with brief period of VFR except MVFR-IFR holding on for Cape and Islands. Winds turn N/NE after 03z in NE MA, which could bring return of MVFR stratus from the waters/coastal ME/NH. Uncertain on the timing and how far west the low clouds could make it, but seems ORH eastward has the best shot.

Friday: Moderate confidence.

VFR west of ORH, MVFR-IFR for ORH south and east with stratus to start. Should see SCT-BKN VFR/MVFR decks with MVFR more likely for the Cape and Islands rest of the day. N/NE winds 5-10 kt, decreasing to light and could be variable directions by afternoon.

KBOS Terminal...Moderate confidence in TAF. MVFR-IFR with -SHRA, mist and fog thru at least 14z. SHRA then ends but MVFR ceilings hold on after 14z, with possible seabreeze ~18-21z. May have to watch for possible afternoon widely scattered SHRA/TS but uncertain if it develops.

KBDL Terminal...Moderate confidence in TAF. IFR in fog and stratus; some indication by 14-16z for MVFR and then VFR by mid-afternoon. S winds 5-10 kt, which shift to light northerly overnight.

Outlook /Friday through Monday/...

Friday: VFR. Slight chance SHRA.

Friday Night: VFR.

Saturday: VFR. Breezy. Chance SHRA.

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

Sunday: VFR. Breezy.

Sunday Night through Labor Day: VFR.

MARINE

Forecaster Confidence Levels...

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

Today through Friday Night

A frontal wave moves over the coastal waters early this morning. This will be accompanied by heavy downpours and possibly some thunder/lightning. Some locally stronger wind gusts to 20 knots are possible, but otherwise expect modest but steady southeast flow around 10 knots with gusts from 15 to 20 knots possible. Seas stay at sub SCY levels. Winds shift to the west/northwest tomorrow afternoon and carry into Friday with generally tranquil conditions. Tranquil conditions continue overnight Friday as high pressure builds in.

Outlook /Friday through Monday/...

Friday: Winds less than 25 kt. Slight chance of rain showers, patchy fog.

Friday Night: Winds less than 25 kt.

Saturday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of seas approaching 5 ft.

Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas.

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. Local rough seas.

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

BOX WATCHES/WARNINGS/ADVISORIES

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