textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Dry and seasonable weather prevails through the weekend, although some light rain is possible in western New England Saturday.

- Pattern turns more unsettled next week with several chances for beneficial rainfall.

DISCUSSION

KEY MESSAGE 1...Dry and seasonable weather prevails through the weekend, although some light rain is possible in western New England Saturday.

Winds diminish tonight as high pressure builds into New England. Even though low level moisture will recover as deep mixing subsides this evening, it's still a dry airmass in place and that means we'll see radiational cooling outside of urban areas and away from the immediate coast, especially in RI and eastern MA.

Farther to the west, strong upper jet may provide enough convergence aloft to produce clouds and perhaps a few sprinkles across CT later tonight, though most of the forcing appears to be farther to the SW. Several of the high-res models show narrow bands of reflectivity but note it's too dry in lower levels to support precipitation. That will also keep temperatures from bottoming out too low there.

Blocky pattern continues into weekend as closed low remains over Maritimes and upper ridge stays in place across Great Lakes. Between the two, confluent NW flow will dominate which should keep southern New England dry overall as surface high pressure remains in control. However, upper low may shift just far enough to east to allow weak short wave and surface low to pass just south of New England, producing a NW-SE oriented band of clouds and showers that could reach western MA and much of CT, while areas farther east remain dry. Thermal profiles also support some wet snow in the hills, especially Saturday night, but probably no more than a coating on the grass.

Ensemble probabilities show about a 50/50 chance for measurable rainfall (0.01" or more) along a line from Stockbridge, MA to Hartford and New London, CT with higher chances to the west (60-70%) and a sharp cutoff (<30%) to the east. Since these are based on coarser global models, in reality there will probably be a sharp cutoff as to how far into MA/CT any showers can get; it's certainly possible that we end up more with cloudy skies in western New England with little or no rain at all. We're not quite into window for high-res models but 12km NAM does show a similar pattern.

KEY MESSAGE 2...Pattern turns more unsettled next week with several chances for beneficial rainfall.

Closed upper low moves farther out to sea over North Atlantic early next week and from there we see fairly significant differences among longer range guidance as to how the pattern will unfold, although each guidance cluster shows trough moving through eastern U.S. and either ridging to its north or back across Great Lakes.

No matter which solution ends up being more correct, this setup favors a series of low pressure systems heading across northern tier of states potentially bringing showers in Tue-Wed timeframe and perhaps again Thu. This certainly doesn't look like a setup for excessive rainfall but one that should bring needed rainfall to region. Temperatures look to average near or just above late April normals which are in the upper 50s to mid 60s.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

18z TAF Update: High confidence.

VFR. NW winds gusting to 25-30kt inland will diminish toward sunset followed by lighter N winds Fri. Expect winds to turn NE along E MA coast Fri afternoon with sea breezes possible after 18z.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Saturday through Tuesday/...

Saturday: VFR.

Saturday Night through Monday Night: VFR. Slight chance SHRA.

Tuesday: Mainly VFR, with local MVFR possible. Chance SHRA.

MARINE

Forecaster Confidence Levels...

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

High confidence through this weekend.

High pressure builds into region through tonight and remains in place through early next week, keeping winds and seas below SCA.

Outlook /Saturday through Tuesday/...

Saturday: Winds less than 25 kt.

Saturday Night through Monday: Winds less than 25 kt. Chance of rain showers.

Monday Night through Tuesday: Winds less than 25 kt. Slight chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...None.