textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes. Monitoring the potential for early morning strong thunderstorms slipping into northern MA.

KEY MESSAGES

- Strong thunderstorms possible early this morning in northern MA, then generally dry today.

- Very warm to hot today, but tempered by hazy/smoky conditions.

- Dangerous rip currents expected on south-facing beaches today.

- Seasonable temperatures with less humidity for the second half of the week, though unsettled conditions with chances for showers and thunderstorms remain possible into this weekend.

DISCUSSION

KEY MESSAGE 1...Strong thunderstorms possible early this morning in northern MA, then generally dry today.

Continuing to monitor developments regarding a cluster of rather potent storms working their way into the Northern Adirondacks and central VT as of 215 AM. Due to the presence of mid- level lapse rates on the order of 8 C/km atop warm and increasingly humid air, instability values remain sizable for New England standards with CAPEs up to 3000 J/kg using a parcel of air lifted from the lowest 100-mb of atmosphere. Strong WNWly mid/upper level flow is contributing to straight hodographs, and this hodograph shape is favoring more messy splitting-cell structures vs a larger line of storms. These storms have had a history of producing hailstones up to baseball size in central St. Lawrence County in upstate NY, so they do mean business. Severe Thunderstorm Watches are in place for adjacent southern VT and southwestern NH until 7 AM, with this cluster of storms expected to trek southeastward through the pre-dawn hours. High- res guidance has really struggled to handle this activity, with most depictions weakening these intense storms upon arrival. But given its current track, some threat for strong thunderstorms could exist during the 3 to 7 AM timeframe across northern Worcester County eastward into the Merrimack Valley/North Shore area and potentially into northern sections of Metrowest Boston. Frequent lightning and hail (some possibly large in the most intense of storms) are the main threats with these. Although the better potential for severe weather exists just to our north and west, remember that severe thunderstorm watches mean that severe weather is possible in and near the watch area.

These storms as they move offshore will then drape a frontal boundary thru northern MA, with a considerable drop in dewpoint temperatures and a WNW wind shift with it. This then slowly sags southward toward the south coast by the afternoon. The atmosphere becomes more strongly capped the further south and west one goes, and its debatable if we can muster a triggering source for possible afternoon storms into CT/western RI later today. This aspect of the forecast is more uncertain as it won't take much of an impulse to get storms to fire, but this seems unlikely at this time. Will offer generally dry weather the rest of the day.

KEY MESSAGE 2...Very warm to hot today, but tempered by hazy/smoky conditions.

Very warm and muggy conditions across Southern New England open the morning, with some areas early this morning still not having dropped below 80 degrees, with dewpoints in the upper 60s to low 70s to boot. After coordination with NWS Albany and NWS Upton, we opted to retain the Heat Advisory given the poor overnight recovery, but during the day it probably ends up being borderline, with peak heat indices in the mid to upper 90s. This is partly due to the sagging cold front bringing a drop in humidity levels, but more because we are again looking at an influx of smoky/hazy conditions from the ongoing wildfires burning in northern MN and western Ontario. Highs were adjusted well below NBM values, with forecasts in the mid 80s to around 90.

We saw yesterday the influence of the hazy, milky-looking skies: being a significant reduction in temperatures. Latest guidance from the 00z HRRR-Smoke and 00z RRFS vertically-integrated smoke progs show another considerable concentration of smoke aloft today and also into Thursday too. But unlike yesterday, there are now some notable concentrations of near-surface smoke developing this afternoon across the southern half of Southern New England and the northern mid-Atlantic. Think it's overdone but there's some solutions offering reductions in visibility, too, in the smoke layer. Ended up adding haze or smoke in the zone forecast for today. I think based on the near-surface smoke progs that you could smell this smoke today. Remains to be seen if air quality alerts would be needed, and recall that those are issued by state environmental agency partners, with our role being to relay those. Also added haze in for Thursday based on output in the longer forecast range in the 00z RRFS smoke progs. Expect rather milky looking skies with red/orange sunrises/sunsets today and again on Thursday, likely to temper stronger heating both days.

KEY MESSAGE 3...Dangerous rip currents expected on south-facing beaches today.

WSWly breezes over the southern waters combined with lowering wave heights of 4-6 ft still will support a high risk for rip currents for those beaches exposed to the south and southwest. Swim near vicinity of lifeguards and stay off jetties today.

KEY MESSAGE 4...Seasonable temperatures with less humidity for the second half of the week, though unsettled conditions with chances for showers and thunderstorms remain possible into this weekend.

The upper level ridge that has been dominating the pattern for much of this week will start to slide more SE of the region for the second half of the week as an upper level trough with broad cyclonic flow to our north takes hold. A cold front passes through the region late Wednesday into early Thursday morning, which will help usher in more seasonable temperatures for the back half of the week. 925 mb temperatures fall to generally around 18-20C, which will be more supportive of high temperatures in the 80s. Thursday may be slightly warmer compared to later days due to breezy westerly winds and resultant downsloping, but drier air overall and lower temperatures aloft (as mentioned above) may only push highs into the low 90s. After that, expect 80s to persist into the start of next week.

Latest guidance is hinting at the possibility for a ripple in the NW flow aloft later in the week that could lead to more unsettled conditions. Guidance is also indicating a shift to more southerly flow for the weekend and a surge in PWAT values as a result. A surface low approaches from the west Saturday and with more of a NE track as currently indicated, its fronts would likely drag through the region and increase the risk for showers and thunderstorms through the weekend. Exact timing is still quite uncertain this far out, but ensembles and deterministic guidance suites remain favorable for a wetter end to the week, both on Saturday and Sunday.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

06z TAF Update:

Through 12z Wednesday: High confidence in trends but moderate on TSRA coverage.

Monitoring strong/severe TSRA moving through central VT, which are moving quickly southeastward. These storms could approach ORH, BED and BOS between 08-11z but messaged as PROB30s for now. Lightning and hail are the main risks in these storms. Will proactively AMD if it looks like a direct hit is imminent. VFR otherwise, with SW winds around 10-15 kt, with gusts to 25-28 kt Cape and Islands.

Today: High confidence in trends, but moderate on reduced visbys.

Mainly VFR, though hazy/smoky skies are expected. Haze/smoke could reduce visibility to MVFR levels, mainly at BDL and PVD this afternoon. Winds shift from SW to WNW around 10-15 kt today.

Tonight and Thursday: High confidence.

VFR, though hazy skies continue tonight into Thursday. WNW winds around 5-10 kt tonight, then increasing to around 8-12 kt with gusts to 20 kt Thurs.

KBOS Terminal...Moderate confidence. Possible TS near or north of terminal 08-11z Wed. Otherwise mainly VFR but hazy/smoky conditions may reduce visibility. Windshift to WNW around 13z Wed.

KBDL Terminal...Moderate confidence. MVFR visibility restrictions are possible today due to surface smoke from Canadian wildfires.

Outlook /Thursday through Sunday/...

Thursday through Thursday Night: VFR. Breezy.

Friday through Friday Night: VFR.

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

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

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

MARINE

Forecaster Confidence Levels...

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

Through Thursday: High confidence.

SCAs continue on the southern waters through today, with WSW winds gusting to around 25-30 kt with seas in the 4 to 6 ft range, shifting to W/WNW late today. Into Thursday, westerly to west/northwest winds should be around 15-20 kt, falling below SCA criterion.

Monitoring the risk for strong thunderstorms on the northeastern waters early this morning, which could become strong and produce lightning, erratic winds and hail. Otherwise, hazy/smoky sky conditions are expected today and Thursday. Some areas of reduced visibility could be possible due to this smoke.

Outlook /Thursday through Sunday/...

Thursday through Thursday Night: Winds less than 25 kt. Seas locally approaching 5 ft.

Friday through Friday Night: Winds less than 25 kt.

Saturday: Winds less than 25 kt. Chance of rain showers.

Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Rain showers likely, slight chance of thunderstorms.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...Heat Advisory until 8 PM EDT this evening for CTZ002>004. MA...Heat Advisory until 8 PM EDT this evening for MAZ017>021. High Risk for Rip Currents through this evening for MAZ020>024. RI...Heat Advisory until 8 PM EDT this evening for RIZ001>007. High Risk for Rip Currents through this evening for RIZ006>008. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ232>235-237-254>256.