textproduct: Boston / Norton

WHAT HAS CHANGED

Issued small craft advisories for all waters and extended them through Saturday early evening, as west winds will remain breezy. Increased wind gusts with a risk for scattered afternoon showers on Saturday.

KEY MESSAGES

- Cooler with westerly breezes this weekend. Risk of scattered afternoon showers thru sundown, then scattered showers and a rumble of thunder on Sunday afternoon, but risk for severe weather is very low.

- Periods of heavy rain possible Monday into early Tuesday. Drier air with seasonable temperatures expected midweek.

DISCUSSION

KEY MESSAGE 1...Cooler with westerly breezes this weekend. Risk of scattered afternoon showers thru sundown, then scattered showers and a rumble of thunder on Sunday afternoon, but risk for severe weather is very low.

Cyclonic mid-level flow governs our weather in Southern New England this weekend. In that broader cyclonic flow aloft, a stronger closed low over Quebec is expected to dig south-southeast into Maine and the Gulf of Maine Saturday afternoon. Another weaker disturbance moves through the flow on Sunday. Each of these disturbances will be responsible for diurnally-driven scattered shower activity, with a little more (if still weak) instability leading to scattered diurnal showers with a risk for a thunderstorm or two. Highs should be in the 70s to lower 80s on Saturday, and in the low 80s on Sunday, but both days feature comfortable humidities.

Westerly winds have been gusting to 25-35 mph this afternoon with the cold pool of air aloft helping to drive good mixing. Most models show the low-level jet increasing post-sundown, but by that point, more limited mixing as temperatures fall should temper the gusts to around 20-25 mph. Gust speeds are expected to be similar by mid- morning Saturday too - around 25 to 30 mph - but the directions are more from the NW than today.

Shallow, weak instability is forecast for Saturday, and with a litle better dynamics coming down from the upper trough on Saturday, best chance for afternoon scattered showers is from Springfield to Providence north and east. Not everyone sees these showers, but there will be some to dodge during the afternoon to early evening hours. With temps running a few degrees warmer on Sunday, there's a better risk for pop-up showers with a garden-variety thunderstorm or two possible during the daytime hours.

KEY MESSAGE 2...Periods of heavy rain possible Monday into early Tuesday. Drier air with seasonable temperatures expected midweek.

A 500mb closed off low will slowly rotate through the upper Great Lakes region with a weak shortwave trough moving into the Northeast on Monday. At the surface, a low pressure system will track across Southern New England, bringing significant moisture to the region. Models continue to show precipitable water values of 1.50 to 2.00 inches, which would be well above climatological normals for mid June. Widespread precipitation is likely mainly Monday into Monday night with pockets of heavy rainfall possible. The latest National Blend of Models run continues to show high probabilities (around 80% chance) of greater than 1 inch of rainfall areawide and around 50% chance of greater than 2 inches.

Behind the system, high pressure and northwest flow will bring rapidly drying conditions during the day on Tuesday. Temperatures are then expected to be pleasant midweek with seasonable highs in the upper 70s to low 80s and only isolated rain chances possible at the end of the period on Thursday.

AVIATION /19Z FRIDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

18z TAF Update:

Through Tonight: High confidence.

VFR. A spot shower possible toward BDL around 23-01z but confidence is too low for a mention in TAF. W wind gusts 25-30 kt, and though they should begin to ease some after sundown, still could see gusts in the 20-25 kt range overnight as the low-level jet increases.

Saturday: High confidence.

VFR; some risk for diurnal SHRA with brief MVFR-VFR visbys after 17z mainly from BDL to PVD north and east through sundown and indicated with PROB30s. WNW winds again gusting 25-28 kt by mid-morning Saturday, then easing into sundown.

Saturday Night: High confidence.

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

KBOS Terminal...High confidence in TAF. Westerly gusts 25-30 kt continue through sundown, but will still be clocking in around 20-25 kt overnight. KBDL Terminal...High confidence in TAF.

Outlook /Saturday Night through Wednesday/...

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

Sunday Night: VFR.

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

Monday Night: Mainly MVFR, with local IFR possible. Breezy. SHRA, slight chance TSRA.

Tuesday: VFR. Breezy. Chance SHRA.

Tuesday Night through Wednesday: VFR.

MARINE

Forecaster Confidence Levels...

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

Have issued SCAs on all waters and extended them through Saturday early evening, as westerly winds will be gusting to around 25-30 kt through Saturday. There may be some lull in the gusts overnight but would be short-lived and/or resume early Saturday morning. Seas in the 4-6 ft range, with 3-5 ft nearshore through Saturday. Risk for scattered showers during Saturday afternoon.

Winds and seas should trend below SCA criterion Saturday night through Sunday, with gusts to 20 kt.

Outlook /Saturday Night through Wednesday/...

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

Sunday Night: Winds less than 25 kt.

Monday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Seas locally approaching 5 ft. Chance of rain showers.

Monday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft. Rain showers, chance of thunderstorms.

Tuesday: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Chance of rain showers.

Tuesday Night: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 9 PM EDT Saturday for ANZ230>235- 237-251. Small Craft Advisory until 1 AM EDT Sunday for ANZ250-254>256.