textproduct: Boston / Norton

WHAT HAS CHANGED

Forecast remains on track.

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

DISCUSSION

KEY MESSAGE 1...While the risk for severe weather remains low, diurnal thunderstorms are a possibility through the end of the weekend. Otherwise, cooler with westerly breezes.

A couple of weak shortwaves embedded within broader cyclonic flow aloft over the next day or so will provide enough fuel to fire a few diurnal thunderstorms through the end of the weekend. CAPE values today in the 500-750 J/kg range primarily over eastern MA will provide enough instability for a few thunderstorms to pop this afternoon and evening, and we're already seeing a few pop-ups in VT and NH. Sunday's CAPE values look to be 200-300 J/kg higher and a little more widespread, leading to more widespread shower chances than today.

Gusty westerly winds are expected to continue through this evening, with peak gust speeds up to 40 MPH. All thing considered, not much different from yesterday. Winds subside with sunset, and should not be as gusty Sunday. Otherwise, high temperatures remain seasonable through the weekend... in the upper 70s to low 80s.

KEY MESSAGE 2... Periods of heavy rain possible Monday into early Tuesday. Drier air with seasonable temperatures expected midweek. Chances for rain return for the end of the week.

A low pressure system will move towards the northeast during the beginning of the work week, pulling ample moisture northward, with forecast PWATs above 1.5", which falls in the 90th percentile relative to the 30 year climatology. That said, this looks to be a widespread rainfall event, with the probability of 1 inch or more of storm total rainfall between 70 to 80 percent across southern New England, and probability for 2+ inches of rainfall were about 30 to 50 percent, greatest across western MA and CT. Timing of the rain looks fairly consistent from the previous forecast, with most of the rain falling from Monday afternoon through Tuesday morning.

High pressure builds into the region behind this system, providing drier with and seasonable temperatures for the middle of the week. Chances for rain begin to increase once again by the end of the work week.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

Today: High confidence.

VFR. WNW winds gusting up to 30 kts through sunset. Some risk for diurnal SHRA with brief MVFR- VFR visibilities after 18Z, mainly across eastern coastal terminals, including BOS. Not impossible for a few TSRA also.

Tonight: High confidence.

VFR, any showers diminish post-sundown. WNW winds decrease to 5-10 kt.

Sunday...High confidence.

VFR. Relatively light west winds could lead to afternoon seabreezes. Another risk for afternoon showers and TSRA.

KBOS Terminal...High confidence in shower activity and moderate confidence in the exact timing. Westerly gusts 25-30 kt continue through sundown. KBDL Terminal...High confidence in TAF. Some diurnal showers are possible, but there is lower confidence on how far west they may reach. So, excluded these showers from the TAF.

Outlook /Monday through Thursday/...

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

Monday Night: MVFR/IFR conditions possible. Breezy. SHRA, slight chance TSRA.

Tuesday: VFR. Breezy. Slight chance SHRA.

Tuesday Night through Wednesday Night: VFR.

Thursday: VFR. Slight chance SHRA, slight chance TSRA.

MARINE

Forecaster Confidence Levels...

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

Small Craft Advisories remain in effect for MA and RI coastal waters today. Could see a few gale force gusts as well, but not thinking it will be prevalent enough to warrant an upgrade to Gale Warnings. Risk for scattered showers and isolated thunderstorms this evening, and again Sunday afternoon. Any showers and thunderstorms should diminish after sunset.

Winds and seas should trend below SCA criteria tonight.

Outlook /Monday through Thursday/...

Monday: Low risk for Small Craft Advisory winds with local gusts up to 30 kt. Chance of rain showers.

Monday Night: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Areas of rough seas. Rain showers, chance of thunderstorms.

Tuesday: Winds less than 25 kt. Areas of rough seas. Chance of rain showers, slight chance of thunderstorms.

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

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

Wednesday Night through Thursday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 7 PM EDT this evening for ANZ230- 232>235-237. Small Craft Advisory until 4 PM EDT this afternoon for ANZ231- 236-250-251. Small Craft Advisory until 1 AM EDT Sunday for ANZ254-256. Small Craft Advisory until 4 AM EDT Sunday for ANZ255.