textproduct: Boston / Norton

WHAT HAS CHANGED

No changes to the forecast at this time.

KEY MESSAGES

- Widespread rain tonight into early Tuesday with periods of heavy rain. Showers likely continue Tuesday. A few embedded storms or downpours possible.

- Dry and warm temperatures Wednesday and Thursday. Shower and storm chances increase for the end of the work week.

DISCUSSION

KEY MESSAGE 1...Widespread rain tonight into early Tuesday with periods of heavy rain. Showers likely continue Tuesday. A few embedded storms or downpours possible.

Widespread rain has overspread southern New England this afternoon. Expect this activity to continue for the remainder of today into tonight as the first wave of low pressure moves across the region. There will likely be just enough instability to support embedded downpours and even a few embedded thunderstorms. The highest risk for this will be tonight and overnight into very early Tuesday morning as an axis of instability shifts across the region. Precipitable water values range 1.2-2.0" and model soundings show sufficient warm cloud depths to support efficient rain processes, so pockets of heavier rain rates are supported. The HREF 3-hour PMM QPF shows 3-hour amounts 0.5 to near 1.2" in 3 hours overnight into early Tuesday morning. Given the instability and moisture amount, 1"/hr rates are possible, but would be fairly isolated and within any embedded storms.

Confidence decreases with regards to the details Tuesday. A second wave will track nearby Tuesday into Wednesday; however, the track is still uncertain. How north or south this tracks will dictate the how widespread the rain/showers will be as well as chances for any embedded storms. It is likely showers continue Tuesday morning into the afternoon slowly clearing from west to east in the late afternoon and evening. HREF means track the main portion of the system south of the region with the north shield of the showers/embedded storms brushing across mainly the south coast of southern New England and southeast MA through the evening. Some hints of instability support a few embedded weak storms or downpours and given the more likely track should keep the highest risk south and east. In terms of totals, 1-2" continues to be most likely for amounts. Given we have had an extended dry period, flash flood guidance is fairly high is 2-3 inches/hour in most areas. Therefore, widespread flash flooding is not a concern. Urban and low drainage flooding is possible, especially in areas that are impacted by the embedded heavier rain rates. We will have to keep a watch on our more flashy areas (Providence).

KEY MESSAGE 2...Dry and warm temperatures Wednesday and Thursday. Shower and storm chances increase for the end of the work week.

Surface high pressure will keep the weather dry through the middle of the week, after the rain comes to an end on Tuesday. High temperatures will be in the low to mid 80s across the area, which is near to a few degrees above seasonal normals, and overnight lows in the 50s and 60s. High temperatures could be tempered a bit under cloud cover and rain for Friday, but rebound over the weekend as the front moves away from the region.

A low pressure system will move into the Great Lakes region Thursday, then into southeastern Canada by the end of the week, while a shortwave trough passes across the northeast. This system will bring the next chances for rain to New England, beginning as early as Thursday night, and continuing into Friday morning. Coverage becomes more scattered by Friday afternoon, with isolated to scattered thunderstorms are possible during those afternoon hours.

Ensemble and some machine learning guidance has low probability for severe storms Friday, but how high that probability is and how much of the region is covered varies fairly significantly among models. Given this spread, and how far out in the forecast it is, confidence on overall severe potential is low, but a couple strong thunderstorms cannot be totally ruled out at this time.

High pressure and dry weather return for the weekend.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

00Z Update

Today: High confidence.

Mostly VFR conditions, with MVFR or lower within heavier embedded rain showers. -SHRA starting to erode from west to east, becoming more scattered in coverage, rather than widespread rain. Ceilings decrease to MVFR from west to east later this evening. SE to E winds at 6-12 kts.

Tonight: Moderate confidence (ceilings/thunder probs)

Ceilings deteriorate to IFR/LIFR overnight. Scattered rain showers that could be heavy at times, with isolated embedded thunder. Location of heavier rain and any thunderstorms uncertain. Patchy fog possible for Cape and Island terminals, potentially down to 1/2 or 1/4SM at ACK early Tuesday morning. Easterly winds 8-12 kts.

Tuesday...Moderate Confidence.

IFR/LIFR at least for the morning. Scattered showers through the day with a few embedded downpours possible. Embedded storms possible for SE MA terminals through mid-morning. Scattered showers continue through much of the day. There is another risk for an isolated storm by the afternoon into early evening; however, confidence is lower on this potential. Wind NW 5-10 kts, shifting NE at BOS in the afternoon. Precipitation ends from west to east gradually by around 18Z, with improving ceilings after 20Z. Sub VFR conditions will linger the longest for Cape and Island terminals.

KBOS Terminal...Moderate Confidence.

Rain. Moderate to heavy at times. Ceilings fall to MVFR after 00Z and to IFR after 03Z. LIFR ceilings are possible. Winds may become steadier east tonight. Potential for embedded thunder overnight mainly between 04 through 12Z. Scattered showers continue Tuesday with NW winds shifting NE in the afternoon 8-12 kts. KBDL Terminal...High confidence in TAF trends. Moderate confidence in timing.

Outlook /Tuesday Night through Saturday/...

Wednesday through Thursday: VFR.

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

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

Friday Night: VFR. Slight chance SHRA.

Saturday: VFR. 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 Tuesday...High confidence.

A Small Craft Advisory continues for the outer coastal waters south of Block Island and east to Nantucket for this afternoon into Tuesday morning. Gusts 22-25 kt possible for brief periods across the Cape and islands, as well as the eastern outer coastal waters.

Rain and a few embedded storms tonight before finally moving off to the east Tuesday evening. Moderate to heavy rainfall at times expected, resulting in poor visibility less than 1 mile at times.

Outlook /Tuesday Night through Saturday/...

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

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

Thursday: Winds less than 25 kt.

Thursday Night: Winds less than 25 kt. Slight chance of rain showers.

Friday: Winds less than 25 kt. Chance of rain showers, slight chance of thunderstorms.

Friday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.

Saturday: Winds less than 25 kt. Chance of rain showers, slight chance of thunderstorms.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 AM EDT Tuesday for ANZ255-256.