textproduct: Boston / Norton

WHAT HAS CHANGED

Increased probability for 1-2" of rainfall possible Thu into Fri.

KEY MESSAGES

- Widespread rainfall Thu into Fri, with 1-2" possible in spots.

- Cool weather Friday, gives way to a pattern change this weekend into next week, accompanied by unseasonable warmth.

DISCUSSION

KEY MESSAGE 1...Appreciable rainfall Thursday, lingering into Fri.

High amplitude pattern Thu and Fri, yields roughly a 48 hr period of wet weather. This high amplitude pattern contributes to a slower arrival time of the rainfall, with much of this afternoon and evening dry across MA/RI/CT. Just expecting some warm frontal showers this morning and mainly confined to CT and northern MA. It will become breezy this afternoon and continuing into early this evening, with south winds gusting up to 20-30 mph at times. Cloud cover and southerly winds off the cool ocean will cap highs this afternoon to the low to mid 60s, about 5 degs cooler than normal.

Potent short wave streaming across the Great Lakes Tue night, digs southeast and evolves into a high amplitude vertically closed cool season low Thu, that slowly tracks just south of New England Fri. This yields deep layer Atlantic moisture advection into SNE, with PWATs greater than 1 inch Thu and Thu evening, along with strong synoptic scale forcing for ascent. This will result in widespread rain Thu and Thu night, then transitioning to lighter rain/drizzle Fri, as dry slot overspreads the region. Rain will be moderate to heavy at times, given strength and persistence of low level S-SE jet (possible upslope enhancement), combined with some elevated instability. Widespread rainfall of 0.5-1.0 inches, however up to 2 inches possible per hi res guid, ensembles and AI models. However, given rainfall will be spread out over 2 days, not expecting any flooding, more of a beneficial rainfall, with typical nuisance street/highway flooding possible.

KEY MESSAGE 2...Cool weather Friday, gives way to a pattern change this weekend into next week, accompanied by unseasonable warmth.

Departing vertically closed low and associated cloud cover, spotty light rain/drizzle (especially Fri AM) and cool NE flow (only +6C at 925 mb), likely keeps highs in the 50s across the area Fri, with coolest temps in eastern MA. Normal high this time of year is 65-70. Then over the weekend and into next week, a pattern change evolves with the northern stream jet deamplifying and giving way to the subtropical ridge emerging and building up along the east coast.

Ensembles indicate high probabilities for temps well into the mid/upper 70s Saturday and continuing to warm into the low and mid 80s Sunday! Possibly not quite as warm Monday, especially in eastern MA, if a backdoor cold front makes it this far south. Otherwise, the unseasonably warm weather continues early next week and likely peaks Tue, with highs possibly as warm as 85-90, as some guidance streams +23C/+24C airmass at 925 mb across SNE! It will be relatively dry airmass/low humidity, with dew pts in the 50s, possibly rising into the low 60s briefly Tue.

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:

Today...High confidence.

VFR. Light rain showers possible through 16z. Otherwise dry weather prevails. Light S/SSE winds this morning at 6-12 kts becoming S/SSW this afternoon at 10-20 kts with gusts up to 30 kt possible at times.

Tonight...high confidence.

VFR ceilings to start then becoming MVFR/IFR after 04z from west to east. Few showers are possible in west/central southern new england after 06Z. As surface winds slacken after 00Z, marginal LLWS possible given modest low level SW jet of 35-40 kt.

Thursday...high confidence on trends but some uncertainty on exact timing of details.

MVFR/IFR with periods of rain, moderate to heavy at times. 20-25% probability of -TSRA in embedded heavier showers. ESE winds at 8-12 kts with a occasional gust up to 20 kts.

KBOS...High confidence.

KBDL...High confidence.

Outlook /Thursday Night through Sunday/...

Thursday Night: MVFR/IFR conditions possible. SHRA likely, slight chance TSRA.

Friday: Mainly VFR, with areas IFR possible. SHRA likely.

Friday Night: VFR.

Saturday through Sunday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

2 AM update...

Today through Thursday...High confidence.

Strengthening low level SW jet moves across SNE today, with light SW early this morning, becoming south and increasing to 20-25 kt this afternoon, except 25-30 kt in gusts near shore. Hence, SCA remains posted. Other than a spot morning shower across northern MA waters, dry weather and good vsby prevail today. South winds slacken tonight with mainly dry weather. Rough conditions Thu, with S-SE winds 20-25 kt in the morning, then slacken in the afternoon and become east as low pressure tracks south of New England. This low will bring widespread rain to region Thu, moderate to heavy at times with reduced vsby.

Outlook /Thursday Night through Sunday/...

Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Rain showers likely, slight chance of thunderstorms.

Friday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers.

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

Saturday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft.

Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 11 AM this morning to 11 PM EDT this evening for ANZ230>237-250-251-254>256.