textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the current forecast.

KEY MESSAGES

- A cluster of showers & thunderstorms works across the region between 5 and 11 pm this evening. A few storms may become severe and produce damaging wind gusts, dangerous cloud to ground lightning and brief torrential rainfall. - Scattered showers and perhaps a few embedded t-storms develop Sunday afternoon/early evening with the focus across eastern New England Drier and much cooler weather follows Sunday night.

- Cooler Monday with onshore breezes, but drier weather prevails.

- Potential multi-day stretch of 90+ degree temperatures mid to late next week, with some potential for showers and thunderstorms later in the week.

DISCUSSION

KEY MESSAGE 1...A cluster of showers & thunderstorms works across the region between 5 and 11 pm this evening. A few storms may become severe and produce damaging wind gusts, dangerous cloud to ground lightning, and brief torrential rainfall.

Breaks in the mid-high level cloudiness has allowed for partial sunshine to develop. This will continue to push highs well into the 80s to near 90 in many locations by late afternoon. Low level moisture is limited and will probably keep surface Capes on the order 1000 to 1500 J/KG. This is on the marginal side...But bulk effective shear increasing to between 30 and 40 knots will try to offset that.

Given the above parameters...we expect a cluster of showers and thunderstorms to develop and enter western MA and CT after 5-6 pm. This potential will likely not reach the BOS-PVD corridor until after 7-8 pm. A few of the storms may become severe and produce damaging wind gusts. While this potential exists across most of our region...the greatest risk will be across interior MA & CT given better instability/more favorable timing.

We will have to see if the bulk effective shear is enough to overcome the limited instability...but mid level lapse rates are decent for our standards on the order of 6/6.5 C/KM. Main severe weather risk will be localized damaging wind gusts given decent T/Td spread. Much of the machine learning guidance supports this as well indicating localized damaging wind gusts the main severe weather threat. They also indicating this potential across most of our region...But show the greatest threat across interior MA & CT.

So in a nutshell...a few severe thunderstorms possible between 5 and 11 pm this evening. Greatest risk will be after 5-6 pm across interior southern New England...But can not rule out the risk approaching the I-95 corridor after 7-8 pm this evening. In addition...brief heavy rain and dangerous cloud to ground lightning are possible too. Bulk of any activity will probably exit the region by midnight followed by mainly dry weather. It will remain mild and a bit muggy compared to what we have experienced lately...low temps will only drop into the 60s.

KEY MESSAGE 2...Scattered showers and perhaps a few embedded t- storms develop Sunday afternoon/early evening with the focus across eastern New England.

Dry weather is on tap Sunday morning...but a strong shortwave/cold pool aloft and associated cold front will be dropping south Sunday afternoon. This will combined with diurnal heating and trigger the development of afternoon scattered showers and a perhaps a few embedded thunderstorms. While a few showers will be possible across the entire region...areal coverage should be the greatest in central/eastern MA and RI given better instability. Not expecting severe weather...But a few thunderstorms possible especially towards the I-95 corridor. Given 500T dropping to between -14C to -16C we can not rule out some small hail if a thunderstorm two is able to develop. Highs will mainly be in the upper 70s to the lower 80s.

Showers may linger into the evening across parts of eastern MA/RI into the evening. Otherwise...drier and much cooler air works into the region overnight. Lows by daybreak Monday will be in the middle to upper 40s in the outlying locations and lower to middle 50s in the urban centers.

KEY MESSAGE 3...Cooler Monday with onshore breezes, but drier weather prevails.

An enhanced NE onshore flow develops into Monday in the wake of the upper low/cold front Sunday night, with 925 mb temps running around 8-10C. Although mostly sunny conditions are expected, expect a cooler and breezy day for most of central and eastern portions of Southern New England, with highs only in the 60s to lower 70s. NE gusts could punch as high as 30 mph out over the Cape, but should clock in around 20-25 mph further inland to central MA and RI. Highs should reach well into the 70s to low 80s in western MA and most of CT away from the onshore breezes.

KEY MESSAGE 4...Potential multi-day stretch of 90+ degree temperatures mid to late next week, with some potential for showers and thunderstorms later in the week.

The main story in the medium-range is a steady warming trend to temperatures, which begins on Tuesday with temps running around or slightly above mid-June normals. However we are looking at a potential multi-day stretch of 90+ degree temperatures Wed into early next weekend, as 850 mb temps are in the mid to upper teens C range as a pronounced upper level ridge over the Gt Lakes flattens and advects east. Humidity levels could also be on the rise and could drive higher heat indices. There is time to assess this in forthcoming guidance but potential for heat headlines could be needed in portions of this period.

Shower/t-storm chances are more uncertain, but the potential could stand to increase late in the week as the upper ridge axis flattens and introduces a stronger belt of westerlies into Southern New England. Too early at this time to determine if storms develop if they'll be strong/severe or not, but the degree of heat and humidity could certainly provide fuel for at least some thunderstorms.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

18z TAF Update...

Through tonight...Moderate confidence.

The main issue will be for scattered showers and thunderstorms that will likely enter western MA/CT after 21z/22z and approach the coastal plain after 00z/01z. Brief MVFR/IFR conditions are possible with this activity along with localized strong wind gusts. Greatest risk for this is across interior southern New England...But there is the risk for this right to the I-95 corridor. The bulk of this activity should exit the southeast New England coast near 05z-06z. Outside this activity...VFR conditions will dominate tonight. The exception might be towards the Cape/Islands...where low clouds and fog patches may develop overnight with the best chance across Nantucket.

Sunday and Sunday night...High confidence.

Any lower clouds/fog patches that form towards the Cape/Islands should burn off Sunday morning. Otherwise...VFR conditions dominate outside of scattered showers that are expected to develop Sunday afternoon. A few embedded t-storms are possible too...but areal coverage and intensity is expected to be significantly less than this evening. Winds shift to the NW on Sun and gust to between 20 and 25 knots. Winds then turn N Sun night at speeds of 5 to 15 knots but may temporarily decouple for a few hours in the typically prone locations late Sun night.

KBOS Terminal...Moderate confidence in TAF. The main concern for thunderstorms crossing the terminal will be between 00z and 04z.

KBDL Terminal...Moderate confidence in TAF. The main concern for thunderstorms crossing the terminal will be between 23z and 03z.

Outlook /Monday through Thursday/...

Monday: VFR. Breezy.

Monday Night: VFR.

Tuesday: VFR. Breezy.

Tuesday Night: VFR.

Wednesday: VFR. Breezy. Slight chance SHRA.

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

Thursday: VFR. Chance SHRA, slight chance TSRA.

MARINE

Forecaster Confidence Levels...

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

Tonight through Sunday night...High confidence.

We will continue marginal near shore small craft advisories into early-mid evening for marginal SW wind gusts near 25 knots. Otherwise...marginal 5 foot seas will flirt with the southern waters into Sunday while the rest of the region will be below small craft advisory criteria. However...a surge of northerly small craft wind gusts is expected Sunday night behind the cold front especially in our eastern waters. New small craft headlines will eventually be needed once most of current headlines expire.

Lastly...a cluster of strong t-storms may approach our waters after 7-8 pm this evening. They eventually should weaken and clear the southeast waters after 6z-7z or so.

Outlook /Monday through Thursday/...

Monday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft.

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

Tuesday through Wednesday: Winds less than 25 kt.

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

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...Air Quality Alert until 11 PM EDT this evening for MAZ013- 016>024. RI...Air Quality Alert until 11 PM EDT this evening for RIZ001>008. MARINE...Small Craft Advisory until 9 PM EDT this evening for ANZ231>235-237. Small Craft Advisory until 11 PM EDT this evening for ANZ250. Small Craft Advisory until 8 AM EDT Monday for ANZ254>256.