textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

- Mainly dry conditions expected through the weekend with seasonable temperatures.

- Unsettled weather returns with periodic chances of scattered showers and thunderstorms early to mid week next week, potentially lingering into Thursday.

DISCUSSION

KEY MESSAGE 1...Mainly dry conditions expected through the weekend with seasonable temperatures.

The center of the surface high pushes offshore today shifting winds to the east. With weak high pressure still in place, expect another dry day with mainly sunny skies. Temperatures will be in seasonable ranges with highs in the low to mid 80s for the interior while onshore flow will keep the immediate coastal areas a little cooler (mid-upper 70s).

By Sunday, mid-level troughing arrives from west. Most guidance also indicates a low pressure system passing well offshore. There is still a signal across guidance low level moisture to advect in from offshore within the easterly flow. Model soundings indicate a shallow layer of moisture at the surface with dry air above. It is more likely that this layer will be too shallow to support any showers/drizzle. A worst case would be some patchy drizzle for the outer Cape/Islands. There is some question on if the moisture makes it far enough west to impact our eastern-most CWA, so this is still moderate confidence for now. Aside from the clouds in some areas, it will be a mainly dry day with a northeasterly breeze for the eastern coastal areas. Temperatures likely range in the low to mid 80s for the interior and mid to upper 70s in the eastern and coastal areas.

There will be an increased risk for rip currents Sunday due to the prolonged period of easterly component flow. The risk spans the south and east coastline with the greatest risk for the east-facing beaches along the Cape and Islands and portions of the east coast of MA.

KEY MESSAGE 2...Periodic chances for showers and thunderstorms late Monday into Wednesday, potentially lingering into Thursday. Risk for localized heavy rainfall and flash flooding possible.

A mid-level trough positions across the region through late-week. A series of shortwaves embedded in the flow are expected to progress across the region through the week supporting periodic chances for showers and thunderstorms mainly in the late Mon-Wed timeframe. Model guidance is struggling to come into agreement with the details of the pattern mainly with regard to the speed/position of the main trough and the potential for development of a closed low that tracks across the northeast. If this low develops, there are solutions that indicate an anomalously strong low for late-July. There is a strong signal for PWATs 120-170 percent of normal to advect into the region by Tuesday. If a low pressure develops, this would likely provide additional forcing and increase the risk for convection with localized heavy downpours thus bring in a risk for localized flash flooding. This all comes down to the tracking of the features which will dictate where the threat for the heavy showers/thunderstorms will be the highest. It is possible the threat ends up west or south of the region or confined to western portions of southern New England. This is something we will need to keep watching as model guidance comes into better agreement over the next day or two. This would likely fall in the late Monday through early Thursday timeframe with most guidance favoring development of showers and thunderstorms in a more diurnal cadence (afternoon/evening) with the support of daytime heating/instability.

High temperatures will likely hover between normal and slightly below normal for the week.

AVIATION /08Z SATURDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

06z TAF Update...

Saturday...High confidence.

VFR. Light and variable winds this morning become ESE. Less than 10 kts for interior terminals. 8-13 kts for coastal terminals.

Saturday night...Moderate confidence.

VFR for most. MVFR cigs/vsbys may impact parts of east and southeast MA as a bank of lower clouds may push in overnight into Sunday. Confidence is lower in the coverage and how far west the low clouds extend. Greatest risk would be for far southeast MA, especially the Cape and Nantucket. Calm/light NE winds.

Sunday...High confidence overall (Moderate for cigs in far east).

VFR for most. Uncertainty in the potential for low clouds in eastern MA and how far west they extend will be the main challenge. Greatest risk for Cape and Nantucket with MVFR ceilings possible. E winds for the interior 5-10 kts. NE winds for east coast terminals 8-12 kts.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Monday through Wednesday/...

Monday: VFR.

Monday Night: VFR. Chance SHRA.

Tuesday: Mainly VFR, with areas MVFR possible. Breezy. Chance SHRA, slight chance TSRA.

Tuesday Night: Mainly MVFR, with local IFR possible. Breezy. SHRA likely, chance TSRA.

Wednesday: Mainly VFR, with areas MVFR possible. Breezy. SHRA likely, slight chance TSRA.

MARINE

Forecaster Confidence Levels...

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

Through Monday...High confidence.

Light winds and seas 1-4 ft today. Increasing winds and seas for Sunday; however, likely below SCA. NE winds 8-12 kts with gusts to 20 kts and seas 2-4 ft with 5 ft for the outermost southern waters.

Increased risk for rip currents Sunday with the greatest risk for the east-facing beaches/coastline.

Outlook /Monday through Wednesday/...

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

Monday Night: Winds less than 25 kt.

Tuesday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers.

Tuesday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers, chance of thunderstorms.

Wednesday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers, slight chance of thunderstorms.

BOX WATCHES/WARNINGS/ADVISORIES

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