textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the overall forecast, though minor refinements were made to weekend timing and temperature confidence.

KEY MESSAGES

- Quiet and dry stretch of weather through the end of the work week, with increasingly warm temperatures.

- Potentially unsettled and cooler conditions late this weekend into early next week.

DISCUSSION

KEY MESSAGE 1...Quiet and dry stretch of weather through the end of the work week, with increasingly warm temperatures.

Confidence remains fairly high in dry weather through Friday as surface high pressure shifts from the Great Lakes toward the southeastern CONUS, while mid-level ridging develops across the Northeast in the wake of a departing trough. Guidance remains in good agreement on this overall pattern, supporting continued quiet and pleasant conditions.

Today, a well-mixed boundary layer and 850 mb temperatures rising to around +10C to +12C should support highs in the upper 70s to lower 80s inland. A rather strong sea breeze will keep immediate south and east coastal areas cooler, with highs likely occurring earlier in the afternoon. Expect periods of fair weather cumulus clouds amid abundant sunshine. Dewpoints generally below 50 degrees will contribute to very comfortable conditions.

Mid-level ridging strengthens Thursday into Friday as 850 mb temperatures climb to around +13C to +15C. Combined with deep mixing and west-northwest flow aloft promoting compressional warming/downsloping off the higher terrain of western Massachusetts, temperatures should climb into the middle to upper 80s Thursday. The greatest potential for 90 degree temperatures on Thursday will be across the Connecticut River Valley, where downsloping and deeper mixing will be maximized.

Friday is expected to be the warmer of the two days, with highs in the upper 80s to potentially lower 90s, becoming more widespread across the coastal plain away from the immediate shoreline, where onshore flow will still provide some moderation along the coast. NBM probabilities continue to indicate a 70 to 75 percent chance of exceeding 90 degrees across the Connecticut River Valley Friday afternoon, while much of the coastal plain away from the immediate shoreline has a 40 to 60 percent chance. Immediate coastal locations should remain cooler due to local sea breezes.

KEY MESSAGE 2...Potentially unsettled and cooler conditions late this weekend into early next week.

There remains moderate confidence early Saturday, but confidence decreases quickly by late Saturday afternoon as timing differences in the approaching frontal boundary increase.

Saturday trends toward a somewhat more favorable window for dry and warm conditions during the daytime, though timing of an approaching frontal boundary remains uncertain. This may allow much of the day to remain dry, with a continued anomalous warmth ahead of the front. 850 mb temperatures increase to +17C to +19C, and despite increasing cloud cover, this may still support a warm to hot day. Highs in the upper 80s to lower 90s remain possible, with dewpoints in the 60s resulting in a more humid feel. The greatest potential for 90+ temperatures remains across the interior river valleys. NBM guidance indicates a 25 to 40 percent chance of exceeding 95 degrees across portions of the Springfield to Hartford corridor Saturday afternoon, though confidence in reaching these values is low to moderate given timing uncertainty and cloud cover trends.

By Sunday, a more defined mid-level trough and associated shortwave energy become established over southern New England. This supports a better signal for scattered showers as weak surface low pressure develops along a weakening frontal boundary. Temperatures trend notably cooler, generally 10 to 15 degrees lower than Saturday, though exact values will depend on frontal timing and cloud cover.

Unsettled and cooler conditions may persist into Monday as the mid- level trough may close off into a weak low, maintaining additional shower chances. Gradual improvement is possible by Tuesday as the system lifts out of the region.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

12z TAF Update:

No significant changes from 06z update.

Today through Thursday...High confidence.

VFR conditions expected through the TAF period. High pressure will provide dry weather and mainly clear skies, with some fair weather mid-level clouds possible today and Thursday. Light northwest winds early this morning will give way to sea breeze development along both the south and east coasts between 14-16Z due to land-sea temperature differences. Terminals across Cape Cod and the Islands (including KACK) may experience variable wind directions through the day as multiple sea breeze circulations influence the area. Winds may shift from N-NW early, becoming NE to SE, and eventually SW by late afternoon. Confidence in the exact timing and sequence of these shifts is lower. Winds become light to calm overnight. SW to WSW winds develop Thursday at 6 to 12 kt.

KBOS...High confidence in TAF. Sea breeze between 14-16Z with speeds of 8 to 10 kt. Winds then turn south shortly after sunset, becoming S-SW overnight and continuing into Thursday.

KBDL...High confidence in TAF.

Outlook /Thursday Night through Sunday/...

Thursday Night: VFR.

Friday: VFR. Breezy.

Friday Night: VFR.

Saturday: VFR. Breezy. Slight chance SHRA.

Saturday Night: VFR. Chance SHRA, slight chance TSRA.

Sunday: MVFR/IFR conditions possible. Breezy. SHRA likely, chance TSRA.

MARINE

Forecaster Confidence Levels...

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

Today through Thursday...High confidence.

In general, conditions today through Thursday will support tranquil boating conditions as surface high pressure remains the dominant feature. Winds will be somewhat variable early today as high pressure settles over the region, becoming southerly this afternoon with speeds generally less than 15 kt. Colder sea surface temperatures relative to warmer land temperatures will support localized onshore flow near the immediate coast. On Thursday, southerly to southwesterly winds increase to 15 to 20 kt, with the strongest winds expected across the southeast waters. Seas generally 1 to 3 feet today and Thursday.

Outlook /Thursday Night through Sunday/...

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

Friday: Winds less than 25 kt. Seas locally approaching 5 ft.

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

Saturday Night through Sunday: 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.