textproduct: Boston / Norton

WHAT HAS CHANGED

No changes to the forecast at this time.

KEY MESSAGES

- While the risk for severe weather remains low, diurnal thunderstorms are a possibility through the end of the weekend. Otherwise, cooler with westerly breezes.

- Periods of heavy rain possible Monday into early Tuesday.

- Drier air with seasonable temperatures expected midweek. Chances for rain return for the end of next week.

DISCUSSION

KEY MESSAGE 1...Scattered diurnal thunderstorms linger through this evening.

Already seeing some thunderstorms fire across NH, VT, and upstate NY. These will likely push south into southern New England, especially across the north coast and eastern MA. CAPE values 350- 550 J/kg through sunset will provide enough instability for thunderstorms to linger into the evening hours; however, not expecting storms to become severe in nature.

KEY MESSAGE 2...Periods of heavy, beneficial rain possible Monday into Tuesday.

A much needed widespread, soaking rain is expected with the passage of a low pressure system Monday into Tuesday. The probability for 1+ inch of storm total rainfall remains between 70 to 80 percent across most of southern New England, with 80+ percent probs across the interior. The probability for 2+ inches of rainfall remains about 30 to 50 percent. Latest flash flood guidance from NERFC is showing we need at least 2.5" in 1 hour (3.5"+ in 3 hours), so while these rains will be beneficial, flooding is not expected across the region. We should dry out from west to east as a low pressure along the south coast of New England moves offshore Tuesday.

KEY MESSAGE 3...Drier air with seasonable temperatures expected midweek. Chances for rain return for the end of next 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, possibly creeping towards the upper 80s across CT, RI, and parts of southern and eastern MA by the weekend. A low pressure system will move into the Great Lakes region by Thursday, then tracking into southeastern Canada by the end of the week, with a weak shortwave trough tracking across the northeast. This system will bring the next chances for rain to New England, and to much of the Mid Atlantic as well, beginning by Friday morning. Isolated to scattered thunderstorms are possible Friday afternoon, with the highest chances over western MA. The GEFS has low, but non- zero, probability for severe storms Friday, as well as some of the other ensemble and machine learning guidance, but how high that probability is varies fairly significantly among guidance. Given this spread, and how far out in the forecast it is, confidence on overall severe potential is low. 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.

AVIATION /00Z MONDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

00z TAF Update:

Tonight: High confidence.

Residual SHRA near BED and west of BOS which could bring brief showers thru 02z, but should be trending dry in all areas thereafter. Increasing canopy of high clouds toward daybreak from the west. NW winds interior/south winds coastal areas to turn W overnight. ESE winds at BOS to turn SW by 02z then become W after 05z.

Monday: High confidence overall, though trending moderate for the afternoon.

VFR most of the day, though clouds thicken up and lower through the day. Sub-VFR ceilings and arrival of light -SHRA unlikely to be sooner than 20z in western New England, and not until 22-00z at earliest for central/eastern TAFs. Any -SHRA during this period should be light. W winds under 10 kt, then shift to S/SE then E late under 10 kt.

Monday Night: Moderate confidence.

Conditions deteriorate to widespread MVFR-IFR. Steadier, eventually becoming moderate to heavy rain arrives Monday night, but the timing is still unclear; earliest reasonable start time as soon as 01-03z in western New England, and after 03-05z for the eastern TAFs. While the exact timing is uncertain, there is high confidence that rain turns steady/heavy at times overnight, with visbys 2-4 SM. Thunder also possible. ESE to E winds 5-10 kt.

KBOS Terminal...High confidence in TAF. KBDL Terminal...High confidence in TAF.

Outlook /Tuesday through Friday/...

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

Tuesday Night through Thursday: VFR.

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

Friday: Mainly VFR, with local IFR possible. Chance SHRA, chance TSRA.

MARINE

Forecaster Confidence Levels...

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

Through Monday Night...High confidence.

The risk for scattered showers and isolated thunderstorms continues for this afternoon and evening, especially along the eastern coast of MA. This activity should wane after sunset.

A Small Craft Advisory has been issued for the southern waters south of Block Island and east to Nantucket for Monday afternoon into Tuesday morning. Gusts up to 25 knots are possible, along with wave heights between 4 to 6 ft. Rain showers with a chance for storms Monday through Tuesday.

Outlook /Tuesday through Friday/...

Tuesday: Winds less than 25 kt. Seas up to 5 ft. Rain showers, chance of thunderstorms. Local visibility 1 to 3 nm.

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

Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft.

Wednesday Night through Thursday Night: Winds less than 25 kt.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 4 PM Monday to 8 AM EDT Tuesday for ANZ255-256.