textproduct: Boston / Norton

WHAT HAS CHANGED

Issued small craft advisories for the southern waters for Saturday night and Sunday with southeast winds. Rain totals for this weekend were increased as well.

KEY MESSAGES

- Steady light rains develop Saturday evening in western New England, leading to a soggy and cool Sunday with much needed rainfall. Cool daytime highs Sunday in the 40s to mid 50s but warming Sunday night into the upper 50s.

- A damp morning on Memorial Day but improving for the afternoon, followed by summer like warmth for the middle of next week before trending more seasonable with a few showers to end the week.

DISCUSSION

KEY MESSAGE 1...Steady light rains develop Saturday evening in western New England, leading to a soggy and cool Sunday with much needed rainfall. Cool daytime highs Sunday in the 40s to mid 50s but warming Sunday night into the upper 50s.

Most of the daytime hours Saturday are overcast with easterly onshore breezes, but with generally dry weather and highs mid 50s east coast to the low to mid 60s interior. However we're looking a damp and soggy Saturday evening and especially Sunday/Sunday night, as a slow-moving warm front associated with a anomalous burst of moisture moves NE through Southern New England.

Initial burst of warm-frontal rain breaks out in western sections of New England (Berkshires/CT Valley into Tolland Hills) by Saturday night, but will struggle to advance east into central/eastern MA and RI as antecedent sfc ridging maintains itself. Most of the non-NAM- based guidance brings this rain into eastern MA and RI by Sunday morning, while the NAM is considerably slower and waits to bring it in Sunday afternoon. NAM seems too dry so sided towards the non-NAM- based guidance, which brings rain into eastern portions of Southern New England by Sunday morning.

Buoyed by SE 925mb low level jet on the order of 40 kts, increasing moisture advection Sunday allows for PWAT values to rise to around 1.3 to 1.6", in the 1.5 to 2 standard deviation range above late-May climatology. Despite the favorable moisture/theta-e advection, am skeptical about thunder prospects with poor lapse rates. I think it's highly unlikely we'll be able to muster any surface-based instability; but if we do, it's worth noting that low-level hodographs are pretty curved in the warm advection and SE low-level jet Sunday morning, particularly over the southern waters. It's way too conditional to include in the forecast for now. Regardless, it still looks like Sunday into Sunday night are a washout in most of Southern New England with steady light to moderate rain, with some downpours possible especially in southeast MA/RI where moisture convergence appears maximized. Really, a beneficial and much-needed widespread rain looks on tap, with storm total rainfall from Saturday early evening through early Monday morning running upwards of an inch in northern MA north of the Mass Pike, to 1.5-2 inches south of the Mass Pike with the highest totals along the South Coast, Cape and Islands. It also creates a scenario where the Sunday maximum temperature occurs just prior to midnight Monday, with cool Sunday daytime highs (upper 40s terrain to the low-mid 50s elsewhere) then warming up through the night Sunday night (mid 50s to near 60).

KEY MESSAGE 2...A damp morning on Memorial Day but improving for the afternoon, followed by summer like warmth for the middle of next week before trending more seasonable with a few showers to end the week.

Latest model guidance not offering any significant changes in the expected weather pattern next week, and the overall NBM guidance looks pretty good. I'm optimistic that although Memorial Day Monday will start damp, that by later in the day much of southern New England will see better weather for the afternoon. The exception would be the far eastern areas where clouds and light rain could persist until late day. After that, models are in strong agreement for a warmer and dry patter moving in for Tuesday and Wednesday. 925mb temperatures both days look to be in the 16-18C range, which would support high temperatures solidly in the mid 80s. Probabilities for reaching 90F are low, but does have a signal. Currently it's about a 5% chance on Tuesday across the CT River Valley. Wednesday is a higher chance, reaching 30% for Springfield/Hartford area and some 10-15% chances across eastern CT and northeast into the Boston area. That said, the latest GFS deterministic run is a little warmer Tuesday and then a bit cooler on Wednesday, so if that is the start of a model trend, then the current probabilities may flip flop. Either way, it's high confidence for warm weather. Humidity levels won't be too high, so it's not looking like Heat headlines will be needed. As we go later in the week, guidance is suggesting an upper low developing well to our north. Primary "impacts" would be temperatures slightly cooling closer to normal and perhaps a spot shower/t-storm in the afternoons, but generally dry for most of the region.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

18z TAF Update:

This Afternoon through Saturday: High confidence.

VFR; mainly BKN/OVC high clouds thru Sat morning, then lowering to a midlevel cloud deck rest of Sat. Winds through this afternoon are easterly around 8-12 kt (gusts 20 kt SE New England), with seabreezes turning light/variable by 03z. Winds Sat return to ENE to ESE around 10 kt.

Saturday Night: High confidence in trends but moderate on timing.

Ceilings continue to lower in the VFR range, but rain and MVFR ceilings/visbys develop towards BDL by early Saturday evening, spreading east into ORH during the overnight. E to SE winds increasing to around 10-15 kt.

KBOS...High confidence in TAF.

KBDL...High confidence in TAF.

Outlook /Saturday Night through Wednesday/...

Sunday: Mainly MVFR, with areas IFR possible. Windy with local gusts up to 30 kt. RA.

Sunday Night: MVFR/IFR conditions possible. Breezy. Chance SHRA, isolated TSRA.

Memorial Day: Mainly VFR, with local IFR possible. Chance SHRA.

Monday Night: VFR. Slight chance SHRA.

Tuesday: Mainly VFR, with local IFR possible.

Tuesday Night: VFR.

Wednesday: VFR. Breezy. 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.

Sub-SCA conditons continue through Saturday afternoon, with easterly winds around 10-15 kt and seas 4 ft or less.

A frontal system will bring enhanced southeast winds, building seas, and steady rain for the waters Saturday early evening through Sunday. Over the southern waters, SE winds increase to 25-30 kt by Saturday night right through Sunday and seas building to 6 to 10 ft over the through Sunday. For the eastern waters, winds become SE and increase to 15-20 kt by Sunday morning and into the 20-25 kt range thru Sunday, with around 4 to 6 ft seas over the eastern waters. Given the holiday weekend and with stronger confidence, SCAs have been hoisted for the southern waters. SCAs will need to be considered for the eastern waters for Sunday. Rain, some heavy at times Sunday, could reduce visibility as well.

Outlook /Saturday Night through Wednesday/...

Sunday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Rain, isolated thunderstorms. Local visibility 1 to 3 nm.

Sunday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Rain showers, slight chance of thunderstorms.

Memorial Day: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers.

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

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

Tuesday Night: Winds less than 25 kt.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 5 AM Sunday to 2 AM EDT Monday for ANZ231. Small Craft Advisory from 2 AM Sunday to 5 AM EDT Monday for ANZ232>235-237. Small Craft Advisory from 8 PM Saturday to 5 AM EDT Monday for ANZ254>256.