textproduct: Boston / Norton

WHAT HAS CHANGED

No major changes to the forecast. Trends remain relatively consistent.

DISCUSSION

KEY MESSAGE 1...Spot showers towards the south coast today.

Generally dry across the region today aside from some spot showers towards the south coast. Guidance has continued to keep these showers there, reaching somewhat into RI and SE MA. Any showers that pop up are not expected to be very impactful, let along severe. Highs today in the midst of light winds with some sunshine will reach the low 80s and upper 70s. Given localized seabreezes, spots along the immediate coastlines may be cooler than surrounding areas.

KEY MESSAGE 2...Scattered showers possible Sunday, then the start of a warming trend.

Ahead of the ridge building in from the west, we find ourselves under some troughing Sunday with surface high pressure extending into New England and a somewhat stationary front just to the south of southern New England. With this messier setup, the chance for some afternoon showers returns; the latest CAMs all seem to have a signal for these showers popping up across southern New England. Some of the latest global guidance plus the NAM does also hint at the chance of these showers extending into the nighttime hours. No specific area within our region seems to be more likely than the others at this time. As for the risk of any of these becoming thunderstorms, the chance is quite low at this time given the lack of forcing and MLCAPE generally only maxing out around 500 J/kg.

Drier weather is expected to return (at least briefly) as high pressure associated with an amplified upper level ridge moves into southern New England. This ridge will be a key feature to monitor for next week, as it is the anticipated heat dome that will impact much of the eastern US. A warming trend also kicks off, continuing and intensifying into midweek.

KEY MESSAGE 3...Warm and humid midweek, along with a risk of showers towards the second half of next week.

The increased warmth looks to peak sometime mid- to late-week as we sit just on the edge of the anticipated heat dome building over much of the eastern US. Ensembles have indicated mean high temperatures Wednesday and Thursday climbing into the 90s with even a shot at 100F, supported by 850 mb temperatures at 20-22C and 925 mb temperatures in the deterministic guidance approaching 30C. Probabilities for temperatures at 100F or higher are around 20-40 percent across a number of the ensembles, with the GEFS more bullish with probabilities to 60 percent Thursday afternoon. For Wednesday afternoon, probabilities are mostly between 20-40 percent. The highest probabilities both days lie mostly in eastern MA but do reach into CT both days. It's worth noting, too, that this is before factoring in any humidity, which will also be increasing in this pattern. A shortwave or two may "roll" along the eastern edge of the upper level ridge, which may bring some unsettled weather for midweek. Location-specific and refined timing details are not yet known, though latest guidance is pointing towards sometime between Tuesday evening and Thursday.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

12z TAF Update...

Today...High confidence except low confidence on portions of the eastern MA coast.

Most locations will remain VFR today with light winds. However...along parts of the immediate coast things were more uncertain. One area of low clouds/fog was attempting to back onto the north shore and remains to be seen if it gets into Boston or is offset by developing diurnal heating. Another area of low clouds and fog should burn off across the Cape/Islands this morning...but may return later this afternoon or by evening. Light N-NE winds become light S-SE with sea breezes developing on portions of the immediate coast.

Tonight...Moderate confidence.

Areas of IFR-LIFR may expand westward off the ocean with light/calm winds coupled with cooling boundary layer and lingering low level moisture. However...it is uncertain as to how far west these low cloud/fog will get. Greatest risk for low clouds and fog will be across eastern MA.

Sunday...Moderate confidence.

Mostly VFR with the chance for scattered showers mostly in the afternoon. Onshore flow prevails with light winds.

KBOS Terminal...Low confidence in TAF. Main concern is if a low cloud/fog bank covering the north shore continues to push southwest and impacts the terminal for a few hours today. Or if diurnal heating breaks it up before entering the terminal.

KBDL Terminal...High confidence in TAF.

Outlook /Sunday Night through Wednesday/...

Sunday Night through Monday Night: VFR.

Tuesday: VFR. Breezy. Chance SHRA, chance TSRA.

Tuesday Night: VFR. Breezy. Slight chance SHRA, slight chance TSRA.

Wednesday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

Through Sunday..High confidence.

A weak pressure gradient will keep winds/seas below small craft advisory thresholds through tonight. With earlier showers and storms having long since moved out of our waters, areas of fog may impact the waters at times through early this morning.

Some fog may linger through today and even tonight in the eastern waters while showers may impact the southern outer and ocean waters today. Fog may also redevelop tonight in areas over the southern waters that see some clearing today. However, winds remain very light (below 10 kt!) into Sunday and seas also remain generally between 2-3 ft. Fog should diminish greatly for Sunday.

Outlook /Sunday Night through Wednesday/...

Sunday Night through Monday Night: Winds less than 25 kt.

Tuesday: Winds less than 25 kt. Slight chance of rain showers.

Tuesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Chance of rain showers, slight chance of thunderstorms.

Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

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