textproduct: Boston / Norton

WHAT HAS CHANGED

Gale Watches have been upgraded to Gale Warnings Monday for Cape Cod/Buzzards Bays and Nantucket/Vineyard Sounds.

KEY MESSAGES

- Dry weather through this afternoon with highs in the 50s. A few showers tonight, mainly across northern MA. Gusty southerly winds develop for Monday, especially across the Cape and Islands.

- Unseasonably warm, summer-like conditions are expected next week with highs mainly in the 70s to low 80s, though confidence is tempered by uncertainty in a possible backdoor cold front; otherwise, mainly dry with only isolated showers and a period of gusty winds Wednesday afternoon.

DISCUSSION

KEY MESSAGE 1...Dry weather through this afternoon with highs in the 50s. A few showers tonight, mainly across northern MA. Gusty southerly winds develop for Monday, especially across the Cape and Islands.

A large high pressure moves further offshore this afternoon, leaving southern New England dry through the rest of the evening with increasing cloudiness and high temperatures in the low to mid 50s.

Later tonight, a shortwave associated with a warm front pushes through the region, bringing increased chances for a few rain showers (mainly across northern MA). As the warm front approaches the region by daybreak Monday, a 45-55 knot southwesterly LLJ develops over the South Shore and Cape. This will bring a surge of warm air and gusty winds, leading to high temperatures ranging from the mid 50s over the Cape/Islands to upper 60s/low 70s further inland. Wind gusts increase to 30-40 mph over the Cape/Islands... 25- 30 mph elsewhere.

KEY MESSAGE 2...Unseasonably warm, summer-like conditions are expected next week with highs mainly in the 70s to low 80s, though confidence is tempered by uncertainty in a possible backdoor cold front; otherwise, mainly dry with only isolated showers and a period of gusty winds Wednesday afternoon.

Bottom line up front: a period of summer-like warmth is expected away from the immediate coast beginning Tuesday and lasting through the end of the workweek, as a strong subtropical ridge develops over the Gulf. This will support southwest flow, advecting higher moisture and temperatures into the Northeast. That said, there are forecast challenges that could lead to notable temperature busts, primarily tied to a potential backdoor cold front. Uncertainty remains regarding the placement of the backdoor cold front. On Tuesday, it appears to be displaced north of southern New England. However, localized sea breezes may develop, resulting in onshore flow and keeping coastal communities noticeably cooler (upper 50s), while areas just inland warm into the 70s. Few spots in the Connecticut River Valley may approach 80F. By Wednesday, NAM12km places the backdoor cold front across northeastern Massachusetts. While not taken as gospel, it highlights the potential for a sharp temperatures gradient across southern New England. Upper 40s to lower 50s at the tip of Cape Ann and Cape Cod versus lower 80s in the Connecticut River Valley. Ensembles guidance supports this uncertainty, with temperature spreads of 20-25 degrees, reflecting sensitivity to frontal placement and potential for forecast busts. Confidence should improve as higher-resolution guidance resolves this feature. For now, expect highs generally in the 70s through the week (and possible into the upcoming weekend) with a few days potentially reaching the lower 80s. Western areas will likely be the warmest, while eastern areas remain most susceptible to cooler marine air. Overnight lows will be mild, in the mid-50s to lower 60s.

In terms of sensible weather, no significant synoptic systems are on the horizon for the coming week. However, with elevated PWATs, even weak forcing may be enough to generate a few isolated showers or a rumble of thunder at times, mainly Tuesday night and again Wednesday afternoon into the evening, as weak surface lows and mid-level shortwaves traverse the periphery of the Gulf-centered ridge. No widespread or washout rainfall is expected. Additionally, Wednesday afternoon could become gusty from a low-level jet passage. Opt'd to increase wind/gusts with a blend of the NMB 90th percentile which bumped wind gusts across interior southern New England to 20-30 mph.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

High confidence.

Mainly VFR conditions continue through Monday. A few showers tonight mainly across northern MA may result in briefly lower conditions in some areas. Possible MVFR-IFR conditions in low clouds and fog patches developing near the south coast Monday afternoon as high dewpoint air begins to work over the relatively cold ocean.

Southerly winds 6-12 kt this afternoon, but with localized sea breezes developing along parts of the immediate coast. SW winds will increase overnight tonight into Monday with gusts of 20 to 30 kts expected in most areas, except up to 35 kts possible over the Cape/Island terminals

KBOS Terminal... High confidence in TAF. Sea breeze should kick out 23z-00z.

KBDL Terminal... High confidence in TAF.

Outlook /Tuesday through Friday/...

Tuesday through Tuesday Night: VFR. Slight chance SHRA.

Wednesday: VFR. Breezy. Slight chance SHRA.

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

Thursday through Friday: VFR. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Through Monday Night...High confidence.

Winds/seas increase to Small Craft Advisory thresholds tonight as a strengthening LLJ brings southwesterly wind gusts of 25 to 30+ kt over all the waters. Buzzards/Cape Cod Bays and Nantucket/Vineyard Sounds could see some nearshore 35 kt gusts, which prompted upgrading Gale Watches to Warning for Monday. Will also likely see the development of fog across the southern waters on Monday as high dewpoint air advects northward over the relatively cold ocean.

Outlook /Tuesday through Friday/...

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

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

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

Wednesday Night through Thursday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 2 AM to 8 PM EDT Monday for ANZ230- 236. Gale Warning from 6 AM to 6 PM EDT Monday for ANZ231>234. Small Craft Advisory from 2 AM Monday to 5 AM EDT Tuesday for ANZ235-237. Small Craft Advisory from 10 PM this evening to 2 AM EDT Tuesday for ANZ250-251. Small Craft Advisory from 2 AM Monday to 8 AM EDT Tuesday for ANZ254>256.