textproduct: Boston / Norton

WHAT HAS CHANGED

Timing of steadier rain into eastern MA and RI now looks more focused into early afternoon, with downpours developing by mid to late this afternoon.

KEY MESSAGES

- Increasing clouds with rain showers, with downpours by this afternoon. Overcast, cool and with more intermittent rain or drizzle tonight into Friday.

- Warmer temperatures for the weekend into next week, with mostly dry weather.

DISCUSSION

KEY MESSAGE 1...Increasing clouds with rain showers, with downpours by this afternoon. Overcast, cool and with more intermittent rain or drizzle tonight into Friday.

500 mb height falls continue to spread across Southern New England early this morning, associated with a pronounced upper level low in vicinity of Toronto, ON. This upper level feature will be the primary driver of our weather through at least Friday night, with a pretty dreary, gray couple days ahead, to go along with periods of much-needed rain, which end up being steady and at times falling at a moderate to heavy clip later today.

Current radar already showing some spotty rain showers in interior Southern New England ahead of an occluded sfc front. In eastern MA and RI, conditions are partly to mostly cloudy but generally dry. At least through mid to late morning, the greatest risk for rain will be mainly in interior Southern New England in a moist southeast- convergent flow. The exact timing of showers into eastern MA and RI is still uncertain but the risk increases by this afternoon and especially from mid-afternoon on, as a ribbon of subtropical moisture advection from a distant coastal low passing well southeast of 40N/70W is drawn back westward. PWATs rise to an inch by that point, with widespread rains and some brief downpours moving in by later today. It is worth noting that recent HRRR runs have tried to show showers moving into eastern MA and RI a few hours earlier, which also helps spell out the uncertainty in the timing. I'd still anticipate a not-so-great PM commute as these rains move in. Although there is some shallow instability around with some dynamic support could favor a few embedded rumbles of thunder, the risk for thunderstorms overall looks quite low. With onshore flow and lots of clouds/rain around, kept highs in the mid 50s to low 60s.

Although steadier rain tapers off by mid to late evening, we're left with a moist, cool overcast as the upper low settles overhead tonight. Wouldn't rule out there being drizzle or mist, but better chances for light rain is in northern and northeast MA. Unfortunately Friday also looks pretty dreary too, essentially a continuation of anticipated conditions for this evening. Low temperatures tonight only fall into the mid to upper 40s, but highs on Friday seem primed to not go very far with hardly any insolation and onshore flow/cool advection with readings in the 50s, coolest eastern/coastal MA. Total rains range from a half inch to inch for CT-RI-southeast MA, but are around 1 to 1.5 inches north of the Pike. Really, rainfall that's much needed.

KEY MESSAGE 2...Warmer temperatures for the weekend into next week, with mostly dry weather.

Substantial pattern change then takes hold for the weekend and into next week toward milder, summerlike temperatures. Weekend starts off with a fast, quasi-zonal flow which will allow for advection of a warm airmass from the center of the country into Southern New England. NBM guidance offering highs well into the 70s to even some low-mid 80s; it still looks quite mild regardless, though multi- model guidance consensus shows some embedded, difficult-to-time ripples in the westerly zonal flow, perhaps stemming from an active convective pattern in the Midwest. Will have to monitor those for possible cloud cover or showers; too low confidence to hit any shower/t-storm threat in the grids but the risk is not zero either.

Even warmer temperatures then arrive for early to mid next week. Monday looks to feature a potential backdoor front/cooler onshore flow with eastern MA in the upper 60s to low 70s but with mid 80s CT Valley. 500 mb heights then rise by Tuesday and brings anomalously warm 850 mb temps in the mid teens C range, which would support highs potentially well into the 80s, with 70s south coast.

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.

Through at least 18z, lowest categories for BDL and ORH with rain with MVFR ceilings and MVFR visby. Mainly VFR should govern the rest of the TAFs thru that timeframe, outside of a brief/passing -SHRA. The exact timing of rain into eastern MA and RI is uncertain, but the risk increases for MVFR/IFR cigs/visby SHRA/+SHRA in the 17-20z timeframe for eastern MA and RI, moving gradually to the N/NE. Locally heavy downpours could be possible, with a low/outside chc at TS.

SE winds around 8-12 kt to start, then slowly back to E thru the aftn, and could become light NE/N in the interior.

Tonight: Moderate confidence.

Steadier SHRA tapers off to an intermittent -SHRA or even -DZ by 00-03z. MVFR/IFR ceilings then deteriorate to IFR to LIFR for most TAFs. Mist/fog possible too with IFR visbys. Coastal NE winds 5-10 kt, interior winds N/NW 5 kt or less.

Friday: Moderate confidence.

IFR generally prevails, though some optimism for MVFR ceilings toward BDL late in the day. Periods of light -SHRA or -DZ, with better chance for steadier light rain for eastern/coastal MA. NE winds become N/NW around 5-10 kt, though around 10-12 kt for eastern MA.

KBOS...Moderate confidence. VFR to start, SE winds developing by 10z. OVC VFR (MVFR decks lurking around?) as soon as 15z, but think MVFR ceilings steadier rain more likely after 17z, with IFR- visby moderate to heavy SHRA by 20z with winds becoming easterly around 10 kt. SHRA ends around 02-03z to more of a -DZ but ceilings then go to IFR/LIFR levels as winds become NE.

KBDL...Moderate confidence. VFR becoming MVFR in SHRA by 07-08z. SHRA continues thru most of the day with MVFR ceilings; rain tapers off to intermittent SHRA/DZ by 00z, but ceilings then go to IFR/LIFR levels.

Outlook /Friday through Monday/...

Friday: Mainly VFR, with areas IFR possible. Slight chance SHRA.

Friday Night: VFR.

Saturday through Saturday Night: VFR. Breezy.

Sunday: VFR. Breezy. Slight chance SHRA.

Sunday Night through Monday: VFR.

MARINE

Forecaster Confidence Levels...

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

SE to E winds around 10-15 kt through today, but easterly swell increases wave heights to around 4-7 ft tonight and continue into Friday. SCAs seem likely to be needed for tonight into Friday as seas increase. Although the morning is mostly dry for the waters, rain with embedded downpours develop this afternoon, with more intermittent showers, drizzle and fog for tonight into Friday.

Outlook /Friday through Monday/...

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

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

Sunday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers.

Sunday Night through Monday: Winds less than 25 kt. Areas of seas approaching 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES

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