textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Showers mainly across far southeastern areas of southern New England this morning, followed by drier conditions this afternoon through Tuesday night and cooler temperatures.

- Unsettled period with increasing chances for widespread soaking rain and continued cooler temperatures.

- Warmer weekend, lower confidence in sensible weather details.

DISCUSSION

KEY MESSAGE 1...Showers mainly across far southeastern areas of southern New England this morning, followed by drier conditions this afternoon through Tuesday night and cooler temperatures.

Rain showers early this Monday morning are associated with a surface wave of low pressure moving along a departing cold front that extends from northern Maine south through the Seacoast of New Hampshire, then southwest toward the Jersey Shore. This cold front slowly moves southeast over the waters, while there remains a risk for light rain this morning mainly from southeast Connecticut through Providence to the southern Boston suburbs. The rest of the region should remain dry. Showers are most prevalent across coastal Rhode Island, the south coast of Massachusetts, Cape Cod, and the Islands, coming to an end by 8 AM to 10 AM, though clouds and showers may persist over Nantucket into the afternoon given its proximity to the front. Rainfall amounts are light, generally a few hundredths of an inch to as much as a tenth or two across Cape Cod and the Islands.

Behind the cold front, winds aloft shift from west to northwest, advecting lower humidity into the region. PWATs fall below one-third of an inch. Low stratus clears behind the front from northwest to southeast, giving way to a blend of sunshine and fair weather cu during the afternoon. That said, given the slow movement of the front, far southeast Massachusetts, Cape Cod, and the Islands may remain overcast into the afternoon. Associated with the drier airmass are cooler temperatures. 850 mb temperatures fall sharply from +7 to +10C Sunday afternoon to 0 to +3C Monday afternoon. BUFKIT soundings show deep mixing with strong cold air advection, supporting high temperatures in the upper 50s to mid 60s. Along with dew points lowering into the lower to mid 20s. Winds from the northwest around 10 mph with gusts up to 20 mph are expected mainly across central and western Massachusetts and northern Connecticut.

Late Monday night into Tuesday morning, a fairly amplified mid-level trough and robust shortwave moves through southern New England. As mentioned, PWATs remain low, and outside of an isolated and brief shower, the night should be dry with intermittent low to mid-level cloud cover. Tuesday morning begins with low temperatures in the upper 30s to low 40s across most of southern New England, with the Cape and Islands in the mid to upper 40s. This trough shifts east and offshore, leading to increasing mid-level heights from the west. Overall, Tuesday looks pleasant albeit cool given abundant sunshine. With 850 mb temperatures not rebounding, expect another day of highs in the upper 50s to mid 60s.

KEY MESSAGE 2...Unsettled period with increasing chances for widespread soaking rain and continued cooler temperatures.

High pressure exits east of the region on Wednesday ahead of the next opportunity for active weather. Shortwave ridging provides drier conditions for the first half of Wednesday, but as the flow turns from northwest to southwest, this directional shift advects higher humidity and PWATs between 0.8 and 1.0 inches back into southern New England by late Wednesday afternoon. Exact timing remains uncertain, but the general idea is that morning hours are dry, with rain chances increasing during the afternoon from west to east as a mid-level warm front approaches from the west-southwest. The longwave trough becomes cutoff over northern New England and southern Quebec on Thursday, then slowly shifts southeast toward the Gulf of Maine on Friday. As the mid-level low and surface low become vertically stacked, unsettled conditions are likely to persist into Thursday, with gradual improvement by Friday as surface high pressure builds in from the southwest and ridging develops from the west.

This system could bring beneficial rainfall. Global ensembles indicate moderate probabilities for 0.5"+ of rainfall, with ECMWF and Canadian ensembles between 60 and 80 percent, while the GEFS is slightly lower at 40 to 60 percent. Another way to view this: the 25th percentile across these ensembles suggests 0.20 to 0.40 inches of total rainfall, while the 75th percentile ranges from 0.50 to 1.00 inches. Still, there is plenty of time to refine details. Temperatures mid to late week remain below normal, with afternoon highs in the lower to middle 60s Wednesday and Thursday, and mid to upper 60s by Friday, assuming the cutoff low shifts east of the region and ridging develops. If the cutoff low lingers, another cooler day is possible.

KEY MESSAGE 3...Warmer weekend, lower confidence in sensible weather details.

Upper trough exits and heights rise heading into next weekend, supporting above-normal temperatures with highs into the 70s. Confidence remains lower regarding precipitation timing due to potential embedded shortwaves, but overall trends favor mainly dry conditions with only low-probability scattered showers.

AVIATION /12Z MONDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

12z TAF Update:

Today...High confidence.

VFR. -RA exits Cape Cod and the Islands by 15z. WNW winds less than 10 kts, except a few gusts around 20 kts along the leading edge of the rain.

Tonight...High confidence.

VFR. Light NW to NNW winds 5 to 8 kt, with locally calm conditions possible in sheltered interior locations.

Tuesday...High confidence.

VFR. Light NW flow. Sea breeze development possible after 15Z along eastern MA coastal terminals.

KBOS Terminal...High confidence in TAF.

VFR prevailing outside of any brief early morning -RA potential. Sea breeze development possible after 15Z on Tuesday.

KBDL Terminal...High confidence in TAF.

VFR.

Outlook /Tuesday Night through Friday/...

Tuesday Night: VFR.

Wednesday: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA.

Wednesday Night through Thursday: Mainly MVFR, with local IFR possible. Breezy. SHRA, slight chance TSRA, patchy BR.

Thursday Night: Mainly VFR, with local IFR possible. Chance SHRA, patchy BR.

Friday: VFR. Chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Today through Tuesday...High confidence.

Residual elevated seas across the southern outer waters, generally 4 to 6 ft, supporting continued Small Craft Advisories into late morning to early afternoon. A cold front moves offshore today with isolated showers possible over the southern outer waters. Winds shift from SW to NW this morning with brief gusts 20 to 25 kt possible. Winds and seas diminish tonight into Tuesday. Seas subside to 2 to 4 ft with light N winds generally less than 10 kt. Sea breeze development is possible Tuesday late morning into afternoon along nearshore waters.

Outlook /Tuesday Night through Friday/...

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

Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers.

Wednesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. Chance of rain showers, patchy fog.

Thursday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Rain showers, patchy fog.

Thursday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, patchy fog.

Friday: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain showers, patchy fog.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 PM EDT this afternoon for ANZ254>256.