textproduct: Boston / Norton

WHAT HAS CHANGED

Bumped up today/s highs well into the 80s to near 90 with the later arrival of smoke.

KEY MESSAGES

- Smoky conditions to reduce air quality but highs still warm well into the 80s to near 90.

- Cold front brings passing showers to northern and northeast Massachusetts later today.

- Showers and thunderstorms bring beneficial rains late this weekend, then cooling off into early next week.

DISCUSSION

KEY MESSAGE 1...Smoky conditions to reduce air quality but highs still warm well into the 80s to near 90.

Main story for today revolves around the continued plume of smoke emanating from the ongoing wildfires burning in far western Ontario and northeast Minnesota. Air quality alerts continue in effect today for fine particulate matter (PM2.5) owing to the smoke at the request of MA, CT and RI state environmental agencies.

Enhanced northwesterly steering flow aloft is allowing a conduit for the transport of this smoke into New England and the mid-Atlantic. This is leading to hazy, smoky, brownish-yellow skies and reduced solar insolation owing to the smoke limiting temperature warming. We should again see more of the same today. Latest near-surface smoke guidance from the HRRR-Smoke and RRFS shows a significant influx of near-surface smoke arriving into our western counties by late morning, spreading ESE today through the afternoon and continue into early tonight. Surface visibilities could be reduced as well, especially into western/central portions of Southern New England, by late this afternoon. Those who are sensitive to fine particulates should take the appropriate precautions to limit exposure outside today, but that could be sensible advice for anyone with outdoor plans today. Given the sunny start and the later arrival of smoke have bumped up highs back into the 80s to near 90....but relative humidity not too bad for this time of year.

KEY MESSAGE 2...Cold front brings passing showers to northern and northeast Massachusetts later today.

Pretty potent cold front analyzed near central Quebec is expected to cross through northern New England this afternoon, and into northern MA/North Shore and offshore late this afternoon into early tonight. Westerly winds pick up ahead of the front today, and could turn gusty this afternoon with models showing potential for gusts upwards of 30 mph, though I'm skeptical since mixing could be reduced with the persistent smoky haze. Guidance seems more bullish on strong t- storms well to our north where more insolation leads to stronger instability and better wind fields there as well. Still left open a mention of scattered showers later today moving southeastward from NH as the front crosses our area, but most of the area end up dry. Windshift to NW occurs behind the front and dewpoints crash into the 40s to mid 50s. The passage of the this front should also help orient the smoke plume more to our south and west by Friday.

KEY MESSAGE 3...Showers and thunderstorms bring beneficial rains late this weekend, then cooling off into early next week.

Turns warmer and more humid again by Saturday. Seasonably- strong frontal system and parent shortwave disturbance aloft approaches New England Saturday, with increasing chances for showers and thunderstorms late in the day Saturday, but especially Saturday night into early on Sunday. PWATs off the 21z/15th run of the SREF show values increasing to nearly 2 inches toward the south coast, which could favor downpours at times. Global ensemble QPF probs show moderate to high (40-60%) probs of 24-hr rains of at least one- half inch, and low (< 30%) probs of 24-hr rains of at least 1 inch. Instability profiles look tall and skinny, but low-level flow fields are pretty strong for mid-July (30-40 kt SW flow at 950 mb is notable Saturday night), with machine learning progs showing low probs for strong/severe storms.

This front clears on Sunday, ushering in a somewhat cooler, drier and much less humid airmass for Monday. 850 mb temps around +9 to +11C Monday, leading to highs in the upper 70s to lower 80s.

AVIATION /13Z THURSDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

Today and Tonight: High confidence in TAF trends, but moderate confidence in wind gusts and visibilities in smoke.

Mainly VFR, although smoke should begin to reduce visibility into the 3 to 6 SM range by this afternoon to early tonight, with lowest visibilities toward BDL and ORH. A passing cold front could bring scattered SHRA to northern MA after 21z, but should stay away from TAFs. Less-smoky conditions overnight tonight.

West winds increase to around 10-15 kt, with gusts to 25 kt, but potential for lower gusts if daytime smoke limits mixing. Passage of the cold front brings a NW wind shift to around 10 kt mainly northern MA before 00z, and across remaining TAFs thru late tonight/overnight.

Friday: High confidence.

VFR. Smoke/haze looks to remain to our west and south Friday. NW to W winds around 10 kt.

KBOS Terminal...Moderate confidence. VFR, hazy/smoky conditions continue this morning. Better chance of visbys in smoke dropping to 4-6 SM this afternoon to early tonight, then improving after 01z. W gusts to 25-28 kt, but gusts could be lower if smoke reduces mixing; windshift to NW early tonight.

KBDL Terminal...Moderate confidence. VFR, hazy/smoky conditions continue this morning. Visbys then drop into the 3-5 SM range (low prob of IFR visby) by afternoon into early evening with a thick layer of near-surface smoke. W gusts to 20-25 kt, but gusts could be lower if smoke reduces mixing. Windshift to NW after 03z with improving visbys.

Outlook /Friday Night through Monday/...

Friday Night: VFR.

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

Saturday Night: MVFR/IFR conditions possible. Breezy. SHRA, chance TSRA.

Sunday: VFR. Breezy. Slight chance SHRA, slight chance TSRA.

Sunday Night through Monday: VFR.

MARINE

Forecaster Confidence Levels...

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

Through Thursday Night: High confidence.

Issued Small Craft Advisories for the waters this afternoon and evening. Westerly gusts increase to around 25 kt with gusts 25-30 kt possible near the Cape and Islands. There is less certainty on the gusts than usual for an SCA as persistent smoky conditions could reduce mixing. Windshift to NW occurs tonight with winds around 15-20 kt. NW winds continue into Friday at sub-SCA levels. Seas 4 ft or less all waters.

Smoky conditions today and especially by this afternoon, locally reducing visibilities to 3-6 miles. More improvement likely tonight, with good visibility anticipated Friday.

Outlook /Friday Night through Monday/...

Friday Night: Winds less than 25 kt.

Saturday: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Seas locally approaching 5 ft. Slight chance of rain showers.

Saturday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Seas up to 5 ft. Rain showers, chance of thunderstorms.

Sunday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Slight chance of rain showers, slight chance of thunderstorms.

Sunday Night: Winds less than 25 kt. Areas of rough seas.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...Air Quality Alert until midnight EDT tonight for CTZ002>004. MA...Air Quality Alert until midnight EDT tonight for MAZ002>024- 026. RI...Air Quality Alert until midnight EDT tonight for RIZ001>008. MARINE...Small Craft Advisory until 2 AM EDT Friday for ANZ230>237-250- 251-254>256.