textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes made to the forecast.

KEY MESSAGES

- Quiet weather continues through Tue night with highs mainly in the 60s to 70+ in the CT Valley...But only 50s along the immediate coast. Lows in the 30s to the lower 40s.

- Unsettled weather around Wednesday night and Thursday with a welcomed soaking rain looking likely.

- Remains unsettled Friday into the weekend with partly to mostly cloudy weather, cooler than normal temperatures and pop-up showers.

DISCUSSION

KEY MESSAGE 1...Quiet weather continues through Tue night with highs mainly in the 60s to 70+ in the CT Valley...But only 50s along the immediate coast. Lows in the 30s to the lower 40s.

A ridge of high pressure will remain in control of our weather through Tue night. This high pressure system will result in mainly clear skies tonight with another excellent night of radiational cooling. Low temps will drop well down into the 30s across the many of our locations...to the lower 40s in some of the urban centers. Airmass is still quite dry...But can not rule out some patches of fog/low clouds developing overnight near the coast. Low confidence on whether or not this happens...but greatest risk towards the Cape and Islands.

Plenty of sunshine is expected on Tue...Although do expect some mid- high level cloudiness to overspread the region during the day. Onshore flow a bit stronger than today...so high temps probably a few degrees lower than today on the coastal plain. Nonetheless...still expect highs to reach into the 60s in most locations away from the immediate coast. The mild spots will again be the CT Valley where high temps of 70+ seem likely. Meanwhile...onshore flow will hold high temps mainly in the lower to middle 50s along the immediate coast, Cape and Islands.

Mainly dry and cool again Tue night with another good night of radiational cooling. Lows will be in the 30s in many locations with lower 40s in most urban centers. We will need to watch for some stratus and perhaps some fog patches working in off the ocean into eastern MA/Cape overnight. Perhaps even a touch of spotty drizzle/very light showers working in off the ocean too.

KEY MESSAGE 2...Unsettled weather around Wednesday night and Thursday with a welcomed soaking rain looking likely.

The more active period of weather takes shape late Wednesday night and especially into Thursday. Overcast skies but mainly dry weather holds on for Wed, but by later Wednesday night into Thursday, a frontal occlusion with possible secondary low pressure development along it sweeps NNE through Southern New England. Pretty robust dynamics acting on a 1" PWAT airmass should bring a welcomed soaking rain. Some of the details are still uncertain this far out, including if and how strong might a secondary low pressure developing on the front might be. That would affect rain amounts and also enhanced ESE winds. Did look briefly at coastal flooding as astro tides start to come up Thursday too, but it would take about a 2 ft surge to get most areas to minor coastal flooding for the evening high tides and an early look suggests values around 1-1.3 ft, thus likely falling short. Still, a good soaking rain with moderate to high probs of 24 hour rain of at least a half inch, and lower to moderate probs of 24 hour rains of at least an inch.

KEY MESSAGE 3...Remains unsettled Friday into the weekend with partly to mostly cloudy weather, cooler than normal temperatures and pop-up showers.

Beyond Thursday...weather pattern remains unsettled with cyclonic flow aloft governing the area, bringing a return to cooler than normal temperatures and at least some partial cloudiness to open the first couple days of May. The question is if we can generate any instability showers for Friday into the weekend underneath the trough. Earlier 12z guidance was hinting at this more bullishly, but the recent 00z guidance has backed off and shunts most of the moisture off towards northern New England. If showers were to develop, they wouldn't necessarily be washouts but could produce some graupel given the anomalously cold airmass for early May (850 mb temps -1 to -4C). Highs in the mid to upper 50s with a modest WNW wind.

AVIATION /15Z MONDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

18z TAF Update...High confidence.

Mainly VFR conditions continue through Tue night. We will need to watch for some spotty low clouds/fog patches towards the Cape/Islands overnight...But not completely sold on it given the airmass is quite dry. We are more concerned about stratus and perhaps some fog patches approaching the eastern MA coast, Cape and Islands very late Tue night. An easterly component to the winds continue on the order of 5 to 15 knots during the daylight hours with the strongest near the coast. NE winds gust to between 20 and 25 knots across the Cape and especially Nantucket during the daylight hours.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Wednesday through Friday/...

Wednesday: VFR. Slight chance SHRA.

Wednesday Night: Mainly VFR, with local IFR possible. Chance SHRA.

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

Thursday Night: Mainly VFR, with local MVFR possible. Windy with gusts up to 30 kt. Chance SHRA.

Friday: Mainly VFR, with local MVFR possible. Windy with local gusts up to 30 kt. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Tonight through Tuesday night...High confidence.

High pressure centered over the Canadian Maritimes with distant low pressure well southeast of the Benchmark will result in persistent NE winds tonight through Tue night. This long fetch will generate 3 to 6 foot seas across the outer-waters...so current small craft headlines will persist. Some marginal NE 20-25 knot wind gusts possible for Nantucket sound again on Tue...so another small craft headline may need to be posted for Tue once the current once expires this evening for that region.

Outlook /Wednesday through Friday/...

Tuesday Night through Wednesday: Winds less than 25 kt. Areas of rough seas. Slight chance of rain showers.

Wednesday Night: Winds less than 25 kt. Local rough seas. Chance of rain showers.

Thursday: Winds less than 25 kt. Local rough seas. Rain showers, slight chance of thunderstorms.

Thursday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers.

Friday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ232. Small Craft Advisory from 2 AM Tuesday to 2 AM EDT Wednesday for ANZ250. Small Craft Advisory until 2 AM EDT Wednesday for ANZ254>256.