textproduct: Boston / Norton

WHAT HAS CHANGED

The Small Craft Advisory for the outer waters has been extended until 8 pm this evening.

KEY MESSAGES

- Dry and warm today with sea breezes possible along the east coast.

- Becoming warmer with increasing humidity Thursday and Friday. Chance for showers and thunderstorms, mainly on Friday.

- Much drier and cooler this upcoming weekend as a cooler airmass settles in.

DISCUSSION

KEY MESSAGE 1... Dry and warm today with sea breezes possible along the east coast.

High pressure settles in for Wednesday with dry and clear conditions building in for the entire CWA by the afternoon. Could see some lingering patches of fog along the Cape and Islands with some patchy low level moisture. Expecting any fog to quickly mix out this morning with mid level RH values falling to 5-10%. Expect a dry and clear day with seasonable temperatures in the upper 70s and low 80s. Winds will be light out of the N/NW with sea breezes possible along the east coast.

KEY MESSAGE 2...Becoming warmer with increasing humidity Thursday and Friday. Chance for showers and thunderstorms, mainly on Friday.

Broad WSW flow brings warmer and increasingly humid conditions Thursday and Friday. The warm and humid airmass pairs with a weak disturbance arriving from the Ohio Valley to bring a risk for scattered showers and thunderstorms mainly to portions of Southern New England later Thursday into Thursday night. CSU machine learning probs still highlight the greatest chance for severe weather over the Mid Atlantic

Ensemble guidance continues to show a better potential for thunderstorms on Friday with a cold front moving into southern New England later in the day. the front moves into a moist unstable airmass marked by dew points in the upper 60s to low 70s. In terms of instability, the NBM shows a 40-60% chance for CAPE values >1000J/kg across the interior. That said, the risk of severe weather is still quite low with poor middle-tropospheric lapse rates leading to tall-skinny CAPE profiles and deep layer shear in the 30 kt range.

Higher confidence in warm, humid weather both days with highs in the mid 80s to lower 90s, supporting heat indices in the mid 90s to mid/upper 90s, more likely falling short of heat headlines.

KEY MESSAGE 3...Much drier and cooler this upcoming weekend as a cooler airmass settles in.

For the weekend the 500 mb pattern transitions to one of cyclonic flow/troughing in the mean, which favors cooler temperatures (low to mid 80s) and lower humidity levels. Weekend appears favorable for outdoor plans with nice summer weather. We'll be on the western periphery of a pretty impressive upper level ridge of nearly 600 dm building over the northern/central Plains and upper Midwest. We could have to keep an eye on possible storminess pivoting around the ridge but it looks as though the weekend ends up drier than not.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

12Z TAF Update:

Wednesday...High confidence in trends but moderate on timing.

Lingering sub-VFR SCT to BKN decks around BOS, PVD this morning. IFR/LIFR ceilings linger on the Cape and Islands this morning slowly improving through the morning and VFR 16-18Z. May see SCT lower decks through early afternoon 030-040. Northerly winds 5-10 kts. Possible seabreeze at BOS, which could develop 16-18Z if it develops.

Wednesday night...High confidence.

VFR. SW winds 5-10 kts.

Thursday...High confidence.

VFR. SW winds 8-12 kts with gusts 20-25 kts. Isolated shower or thunderstorm possible after 20Z.

KBOS Terminal...High confidence.

KBDL Terminal...High confidence in TAF.

Outlook /Thursday Night through Sunday/...

Thursday Night: VFR. Breezy. Slight chance SHRA.

Friday: VFR. Chance SHRA, chance TSRA.

Friday Night: VFR. Slight chance SHRA.

Saturday through Sunday: VFR.

MARINE

Forecaster Confidence Levels...

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

Through Thursday Night...High confidence.

SCA conditions continue in the the coastal waters through the day today with NE wind gusts around 25 kts. Conditions improve overnight into Thursday as high pressure builds over the region. A weak front approaches the region later Thursday with showers and thunderstorms possible over the southern waters.

Outlook /Thursday Night through Sunday/...

Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, slight chance of thunderstorms.

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

Friday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.

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

Saturday Night through Sunday: Winds less than 25 kt.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ250- 254-255.