textproduct: Boston / Norton

WHAT HAS CHANGED

Showers and storms may return Wednesday evening as a warm front approaches the region. No major changes otherwise.

KEY MESSAGES

- Dry through the rest of today and tonight before the risk for showers and thunderstorms returns Wednesday afternoon/evening.

- Diurnal showers and thunderstorms possible Wednesday through Friday. Above normal temperatures peaking Thursday into Friday.

- Warm conditions with lower humidity throughout this weekend. Uncertainty remains high regarding potential rain showers for Saturday, and again early next week.

DISCUSSION

KEY MESSAGE 1...Dry through the rest of today and tonight before the risk for showers and thunderstorms returns Wednesday afternoon/evening.

High pressure south of Long Island continues moving off to the south and east as the ridge aloft starts receding from the northeast US. Some shortwave disturbances will then start to make their way across the region as its influence wanes, which will aid in the return of some showers and storms. Lows tonight will generally be in the upper 50s and low 60s as light SW winds continue for most; winds to 15 kt will be possible through tonight across the Cape and Islands.

A warm front will push through southern New England Wednesday evening/night and showers and thunderstorms will likely accompany it. With regards to severity, not seeing much that would scream a severe weather threat with these possible storms. CSU ML guidance has about a 5-15 percent chance for severe winds in western MA and CT, along with part of central MA for Wednesday. Winds also shift more southerly going into Wednesday afternoon/evening, helping bring in more moisture from the south. PWATs may approach 2.0", and NAEFS guidance indicates that values Wednesday into Thursday morning may be around 2-3 standard deviations above normal. Details regarding the coverage of these showers and storms still need to be ironed out, but the latest guidance is favoring the heavier rainfall remaining to our north and south. With the moist airmass overhead, some spots with locally heavier rainfall can't be ruled out, but much can still change between now and when this front comes through. Rainfall amounts at this time may only reach around 0.10-0.20". Hot and humid conditions will be left in the wake of this warm frontal passage.

KEY MESSAGE 2...Diurnal showers and thunderstorms possible Wednesday through Friday. Above normal temperatures peaking Thursday into Friday.

High pressure towards the southeast USA will push heat and humidity into southern New England later this week. Will likely need to consider heat headlines with later forecasts. Uncertainty remains for how quickly and how far west a backdoor cold front can make it Friday. This would have implications for heat headlines across eastern MA as well as RI. Should this front be delayed from its current timing, then more of southern New England would be at risk for headlines using the lower 2-day threshold.

Portions of the CT River Valley in MA and CT could see heat index values around 100F, while more of our region should be well into the 90s both Thursday and Friday. Coastal areas of MA and RI are expected to be cooler Friday, but the timing still needs to be ironed out.

The increased heat and humidity will also set the stage for possible showers and thunderstorms later this week. There is not much concern for the threat of widespread severe thunderstorms at this time due to the lack of wind shear and weak forcing mechanisms. The western half of southern New England would have the higher risk, which is not unusual for this time of year.

KEY MESSAGE 3...Warm conditions with lower humidity throughout this weekend. Uncertainty remains high regarding potential rain showers for Saturday, and again early next week.

Anticipating the passage of a couple fronts Saturday and Sunday. The main impact will be lower humidity, with Sunday anticipated the drier of the two. Lingering showers possible Saturday, but plenty of dry hours too. Some guidance members indicated a weak low pressure passing by towards the south coast of New England sometime Monday into Tuesday. Kept a mention of showers in the forecast, but confidence in these details is low.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

Through Wednesday Night...High confidence.

VFR conditions continue through much of Wednesday. Some MVFR to localized IFR conditions may overspread parts of the region from southwest to northeast by early evening Wednesday along with a few showers. Showers become more likely Wednesday night, but coverage is still relatively uncertain.

Gusts will diminish this evening, but may linger a bit longer near the upper Cape/Buzzards Bay area. For Wednesday, gusts to around 20 kt may make a return by the mid/late morning hours. SW winds will persist through tonight and into Wednesday before shifting more S Wednesday night in the wake of a passing warm front.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday through Sunday/...

Thursday through Thursday Night: Mainly VFR, with local MVFR possible. Chance SHRA, slight chance TSRA.

Friday: Mainly VFR, with local MVFR possible. Chance SHRA, chance TSRA.

Friday Night: VFR. Chance SHRA, slight chance TSRA.

Saturday: VFR. Slight chance SHRA.

Saturday Night through Sunday: VFR.

MARINE

Forecaster Confidence Levels...

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

Through Wednesday Night...High confidence.

Small Craft Advisories continue over the nearshore southern waters with the elevated SW winds continuing into this evening. After that, winds will be sustained at or below 15 kt with only occasional gusts to 25 kt expected more towards Nantucket and the outer waters near it. Winds shift more SW then SSW Wednesday afternoon, sustained at around 15-20 kt with gusts remaining just below Small Craft criteria. Seas generally 2-4 ft through Wednesday night, though the southern outer waters may start to creep to 5 ft heading into Thursday morning.

Outlook /Thursday through Sunday/...

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

Thursday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers, isolated thunderstorms.

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

Friday Night through Saturday: Winds less than 25 kt. Slight chance of rain showers.

Saturday Night through Sunday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...None.