textproduct: Boston / Norton

WHAT HAS CHANGED

Small Craft Advisories extended through tonight (northern waters) and through Thursday (southern waters).

KEY MESSAGES

- Warmer and drier for the most part today with the chance for isolated showers and thunderstorms in the afternoon.

- Mainly dry with seasonable temperatures Thursday through the weekend.

DISCUSSION

KEY MESSAGE 1...Warmer and drier for the most part today with the chance for isolated showers and thunderstorms in the afternoon.

The high coverage showers and thunderstorms have cleared southern New England early this morning. However, a second batch will push into the south coast, far southeast MA/Cape & Islands after 4 AM continuing through the early morning hours. Other areas will remain dry; however, residual high dewpoints and recent rainfall have supported patchy fog this morning. Expect conditions to improve through the morning with breaks of sun developing from west to east. Temperatures rise into the low to mid 80s in most spots.

There is still the risk for showers and thunderstorms this afternoon. A cold front approaches from the west bringing a push of higher dewpoint air out ahead of it. With the added heating, instability should likely build through the afternoon with SBCAPE values 1000-1800 J/kg. Model guidance has been more consistent with showing clearing early enough to support the building instability. The moisture and instability are sufficient to support development of showers and thunderstorms as the cold front progresses eastward. With 0-6 km shear 30-40 kts, the environment is supportive of organized convection with potential for an isolated strong to severe storm or two. Profiles will not be nearly as saturated as last night with model soundings showing plentiful moisture at the surface, but also dry air in the mid-levels. In some cases this can limit convection. The high-res CAMs have generally exhibited isolated coverage of showers and thunderstorms this afternoon, so most places will stay dry. Despite this, it is still possible for a strong to severe storm in the mix given the supportive environment. Main threat would be locally damaging gusts. Showers and thunderstorms likely develop mid to late afternoon from west to east with any lingering showers/storms exiting offshore early tonight.

A cold front sweeps through tonight with winds shifting to the northwest ushering in drier air and cooler temperatures.

KEY MESSAGE 2...Mainly dry with seasonable temperatures Thursday through the weekend.

The cold front pushes offshore by Thursday while an upper trough tracks across the northeast. High pressure gradually builds in from the west supporting a period of dry conditions. 925mb temperatures generally range 16-20C support seasonable temperatures in the low to mid 80s through the weekend. Ensembles lean toward keeping the region dry through the weekend with a transition to a more unsettled pattern with rain chances early next week.

AVIATION /12Z WEDNESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

12Z Update...

Today... Moderate confidence.

Tricky ceilings today with most areas MVFR, but pockets of VFR sporadically across southern New England. IFR/MVFR ceilings lingering over the Cape/Islands terminals into the afternoon. Confidence moderate on exact timing of improvements to VFR. Showers and thunderstorms possible after 18Z, though isolated in coverage. Due to low coverage and uncertainty in intensity of showers/storms, kept as PROB30s for TSRA. SW winds 10-15 knots with gusts 20-25 kts.

Tonight...High Confidence.

Any afternoon SHRA/TSRA wanes after 00Z. VFR conditions tonight. Winds shift to WNW/NW at 5-10 knots behind a passing cold front between 22-03Z.

KBOS Terminal...Moderate confidence in TAF.

Lower confidence with the potential for showers/thunderstorms this afternoon, mainly due to the isolated nature of showers/storms. Included a PROB30 for now to TSRA with the most likely timeframe being between 21-01Z.

KBDL Terminal...Moderate confidence in TAF.

Highest chances for TSRA between 21-00Z.

Outlook /Thursday through Sunday/...

Wednesday Night: VFR. Breezy.

Thursday through Sunday: VFR.

MARINE

Forecaster Confidence Levels...

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

Tonight through Thursday

Small Craft Advisories remain in effect for SW winds 10-20 kts with gusts 25-30 kts and 6-10 foot seas for the outer coastal waters and southern waters. Highest waves are expected over the south coastal waters. Isolated showers and thunderstorms possible early tonight.

A cold front crosses the waters tonight resulting in a wind shift to the NW. Winds and seas will slowly decrease overnight across the northern waters. Seas will be the slower to decrease, especially across the southern waters. Extended SCAs through Thursday for south and east coastal waters. They may need to be extended further (through Fri AM) for southern outer waters because of 5 ft seas.

Outlook /Thursday through Sunday/...

Wednesday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 10 ft. Rain showers likely, patchy fog.

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

Thursday Night: Winds less than 25 kt. Seas up to 5 ft.

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

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

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...High Surf Advisory until 8 PM EDT Thursday for MAZ020>024. RI...High Surf Advisory until 8 PM EDT Thursday for RIZ006>008. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ231. Small Craft Advisory until 2 AM EDT Thursday for ANZ232>234- 250. Small Craft Advisory until 2 PM EDT Thursday for ANZ235-237. Small Craft Advisory until 8 PM EDT Thursday for ANZ254>256.