textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes were made to the forecast during this update.

KEY MESSAGES

- A warm and rather windy Tuesday is on tap, with the exception of areas along the immediate south coast of RI and MA where onshore flow off the cooler ocean will limit temperatures.

- Cold front brings the wettest period of the week Wednesday afternoon into Thursday with scattered showers, a few embedded thunderstorms, and a turn to cooler temperatures.

- Late week into the weekend trends cooler, Friday is looking drier but increasing uncertainty for Saturday/Sunday.

DISCUSSION

KEY MESSAGE 1... A warm and rather windy Tuesday is on tap, with the exception of areas along the immediate south coast of RI and MA where onshore flow off the cooler ocean will limit temperatures.

Overall, the synoptic setup remains largely unchanged, with high pressure offshore and a slow-moving cold front approaching from the west. This configuration supports a tightening pressure gradient and a period of strong southwest winds.

A robust 925mb low-level jet of 35-45 kt is expected along and east of I-95 from Boston to Providence. BUFKIT soundings indicate a shallow inversion early in the day, which should erode with daytime heating and allow stronger winds to mix toward the surface. That said, southwest wind events are typically more uncertain that northwest flow event, so some uncertainty remains regarding the extent to which 40-45 kt winds aloft will mix down. Those winds come most likely between 3-7 PM. Notably, the strongest core of the low- level jet increases to 50-65 kt shortly after sunset. However, as boundary layer decoupling increases with the loss of daytime heating, redevelopment of a nocturnal inversion should limit the ability of these stronger winds to reach the surface. A Wind Advisory remains in effect for southern RI and most of eastern MA from noon through 10 PM.

In addition to the wind threat, it will be quiet warm for early May. Southwest flow will advect anomalously warm air into the region, with 925mb temperatures peaking between +17C and +20C. This supports highs in the upper 70s to lower 80s, well above normal, though still well below daily record values in the lower 90s.

Given ongoing dry conditions combined with gusty winds and minimum RH values dropping to around 30-35 percent, there is an elevated fire weather concern. Coordination with state partners has led to issuance of a Special Weather Statement for much of southern New England.

Precipitation chances remain minimal today. A slow-moving cold front approaching from the west may trigger an isolated shower or thunderstorm, primarily across far northwest MA. The better convective potential remains well to our north across northern New York and northern New England.

KEY MESSAGE 2...Cold front brings the wettest period of the week Wednesday afternoon into Thursday with scattered showers, a few embedded thunderstorms, and a turn to cooler temperatures.

A slow-moving cold front moves across southern New England starting late Wednesday afternoon as it approaches western New England and should exit the coastal waters by Thursday morning. This will likely be the wettest stretch of the week as a plume of higher PWATs, with values ~1.3" (1.5-2 standard deviations above normal) advect into the region with modest 850mb shortwave energy. Temperatures are going to be noticeably cooler, in the upper 60s to lower 70s. With the high PWATs, dew points are 53-57F, should support 100-200 units of CAPE and should promote embedded thunder. The front moves offshore and while previous model runs have indicated a secondary surface low moving near or south of the coastal waters, tonight's runs do not favor this outcome. A shift of winds occur Thursday to the northwest and this will lead to PWATs falling below 0.3". Feeling a bit more confident in drier conditions into Thursday afternoon, though it will be seasonable in the mid 60s.

KEY MESSAGE 3...Late week into the weekend trends cooler, Friday is looking drier but increasing uncertainty for Saturday/Sunday.

Late week into the weekend will be a noticeable change from the warm start to the week, with cooler temperatures settling in. Highs generally run slightly below normal for early to mid-May, mainly in the lower 60s, though temperatures may approach the 70 degree mark by Mother's Day (do not forget kiddos).

Friday currently looks drier as the system departs, but uncertainty increases heading into the weekend. Guidance continues to suggest another area of low pressure may approach sometime Saturday, though timing and evolution remain low confidence at this range. Whether conditions improve in time for Sunday is still uncertain and will be monitored in subsequent forecasts.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

12z TAF Update....High confidence

VFR today but main issue will be strengthening southwest wind gusts later this morning and especially this afternoon. SW wind gusts of 30-40 knots are expected with potentially some 40-45 knot gusts after 17z/18z with the greatest risk across the coastal plain. Low risk for a spot shower into mid morning across the distant interior. There also will be a low risk for a brief spot shower/t-storm across northwest MA late today into this evening.

Strong gusts will be slow to diminish this evening and remain in the 25 to 35 knot range well into the overnight hours. LLWS will also become an issue. Lastly...we also will need to watch some MVFR-IFR stratus developing overnight towards the south coast, Cape and Islands.

Otherwise...Low end VFR to MVFR conditions dominate Wednesday. Numerous showers will overspread the region from west to east...mainly during the afternoon hours. SW winds will gust between 25 and 35 knots...strongest near the coastal plain where a few brief gusts near 40 knots will be possible.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Wednesday Night through Saturday/...

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

Thursday: VFR. Chance SHRA.

Thursday Night: VFR.

Friday: VFR. Breezy.

Friday Night: VFR.

Saturday: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Today through Wednesday...High confidence.

After a brief lull, another round of near shore SW Gales are on tap for this afternoon and evening with strong small crafts persisting across the outer-waters. Agitated seas 5-9 ft across the souther waters and 3-7 ft for the eastern waters Tuesday night, with areas of low stratus and fog develop across the southern waters. SW wind becomes S overnight, 25-30 kt, areas under a Gale Warning will need to be converted to a Small Craft Advisory, which could linger into the day on Wednesday. Wednesday features unsettled conditions with showers and embedded thunderstorms during the afternoon.

Outlook /Wednesday Night through Saturday/...

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

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

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

Friday through Friday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...Wind Advisory from noon today to 10 PM EDT this evening for MAZ005>007-013>022. RI...Wind Advisory from noon today to 10 PM EDT this evening for RIZ002>007. MARINE...Gale Warning from 11 AM this morning to 11 PM EDT this evening for ANZ230>237-251. Small Craft Advisory until 8 PM EDT Wednesday for ANZ250- 254>256.