textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Showers linger across southern New England today. Friday will still see some showers, though more scattered and accompanied by increasing breaks of sun.

- Mix of clouds and sun with seasonable temperatures and some humidity this weekend. Next chance for showers and t-storms return with a frontal boundary moving in late Sunday into Sunday evening, possibly lingering into Monday along the southeast coast.

DISCUSSION

KEY MESSAGE 1...Showers linger across southern New England today. Friday will still see some showers, though more scattered and accompanied by increasing breaks of sun.

A more manageable amount of rain expected today compared to Wednesday as the upper low continues to spin overhead. The surface low shifts east over the Gulf of Maine today. This will back low level flow to the north, eliminating the bulk of the orographic enhancement while the low level jet pivots and lifts out as well. Even so, given the cold pool aloft (-10 to -12C at 500mb) and mid level PVA combined with elevated PWATs and a saturated atmospheric column we're in for another day of low clouds, accompanied by light to moderate rain showers. By Friday we finally get some mid level height rises as the trough lifts into the maritimes and this allows for some drier air filter in reducing shower coverage and increasing the breaks of sun on Friday. Friday's building ridge will also mean a warmer airmass nudging into the region bringing us upper 70s/low 80s for the first time in several days.

KEY MESSAGE 2...Mix of clouds and sun with seasonable temperatures and some humidity this weekend. Next chance for showers and t-storms return with a frontal boundary moving in late Sunday into Sunday evening, possibly lingering into Monday along the southeast coast.

Weekend on the whole looks favorable with high pressure to our south allowing for modest warming and an increase in humidity level too, with a mix of clouds and sun. Seasonable highs in the low to mid 80s.

Things turn more unsettled as we move into late Sunday into Sunday evening, and in some global model ensemble solutions possibly lingering into part of Monday. Another seasonably-strong upper level trough moving across Ontario and into Quebec drags a slow-moving surface cold front through the northern-central Appalachians and the Northeast. This frontal boundary will draw upon some deeper moisture with precipitable water values increasing to 1.5-1.7", about 1 standard deviation above early August climatology. This front looks to offer our next chance for rain/thunderstorms, with most of the ensemble means offering a timing around late in the day Sunday into Sunday night. AI-based severe weather progs show very limited chances for severe weather, which seems reasonable as flow aloft is not particularly strong and the evening time-of-day putting a limit to how much destabilization can occur. While nothing like the lingering slow-moving rainstorm, this front could still produce some decent rainfall with EPS/GEFS probabilities showing moderately high (40-70%) probs 24-hr rains over a half inch but low (< 30%) probs of 24-hr rains over an inch. Some spots in interior Southern New England have seen higher rain totals in the last 24-48 hrs, so these areas could need to be monitored for heavy rain/flooding but it's still viewed as a low risk at the moment. Where there is still some uncertainty is if a lobe of mid-level energy on the southern end of the mid-level trough axis can close off until a closed low over the lower Ohio Valley; if this happens, we'd still clear out sufficiently enough by early Monday, but there may be some lingering clouds/showers Monday near the southern waters and perhaps into southeast New England. That'll need to be monitored in subsequent model runs.

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.

LIFR/IFR cigs with MVFR vsbys in areas of lingering light rain/drizzle and fog, only slowly improve to IFR/MVFR cigs and MVFR/VFR vsbys. Low risk for a few heavy showers and isolated TSRA across RI and southeast MA terminals this PM. Light surface winds with broad area of low pressure over the region.

Thursday Night...Moderate confidence.

Widespread IFR and lower end MVFR in lingering spotty light showers/drizzle and areas of fog. N winds remaining generally below 10 kt.

Friday...High confidence.

VFR. Light N winds with coastal sea breezes. Slight chance of some scattered showers.

KBOS Terminal...Moderate confidence in TAF.

KBDL Terminal...Moderate confidence in TAF.

Outlook /Friday through Monday/...

Thursday Night: Mainly VFR, with local IFR possible. Patchy BR.

Friday: VFR. Slight chance SHRA, slight chance TSRA.

Friday Night: VFR.

Saturday: VFR. Breezy.

Saturday Night: Mainly VFR, with local MVFR possible.

Sunday: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA, slight chance TSRA.

Sunday Night: Mainly VFR, with local MVFR possible. Chance SHRA, slight chance TSRA.

Monday: VFR. Chance SHRA, slight chance TSRA.

MARINE

Forecaster Confidence Levels...

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

As the low shifts overhead and begins to move into the maritimes winds will become N/NE on Thursday then N Thursday night. Seas will remain rough, 3-5 ft, diminishing to 2-4 ft by Friday. Rain showers will limit vsby at times. Vsby 1-3NM at times in areas of fog and showers much of Thursday, improving Thursday night into Friday.

Outlook /Friday through Monday/...

Thursday Night: Winds less than 25 kt. Seas up to 5 ft. Patchy fog. Local visibility 1 to 3 nm.

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

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

Saturday through Sunday: Winds less than 25 kt. Seas locally approaching 5 ft.

Sunday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.

Monday: Winds less than 25 kt. Areas of rough seas. Chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ250. Small Craft Advisory until 2 PM EDT this afternoon for ANZ254>256.