textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast with this update.

KEY MESSAGES

- Pleasant/cool weather tonight and Fri. Lows tonight in the 30s & 40s with highs Fri mainly in the upper 50s-lower 60s. Dry weather prevails outside a few brief spot showers possible.

- Wet weekend ahead with beneficial rain expected Saturday then again Sunday night into Monday.

DISCUSSION

KEY MESSAGE 1...Pleasant but cool weather tonight and Fri. Lows tonight in the 30s & 40s with highs Fri mainly in the upper 50s-lower 60s. Dry weather prevails outside a few brief spot showers possible.

Upper trough over the northeast will result in pleasant early May weather tonight and Friday...albeit a bit on the cool side. Winds diminish some tonight and will likely decouple in the typically prone low-lying locations. A period of mid level cloudiness will impact areas overnight especially near and south of I-90 with a mid level shortwave. A few brief spot showers are also possible across CT/RI...but any precipitation will be very brief/light given dry boundary layer. The mid level clouds do make overnight lows a bit tricky...but still think enough of a window for many areas to drop into the 30s with lower to middle 40s in the urban heat islands of Boston and Providence. There may even be some patchy frost in the typically coolest outlying locations...especially in northwest MA.

The upper level trough remains in place on Friday. There is an impressive piece of shortwave energy and an associated cold pool aloft that crosses the region too. This should result in a scattered to broken deck of strato-cu developing and perhaps a few brief spot showers too. However...the vast majority of the day will be dry in a given location. Highs will be on the cool side for early May standards...mainly in the upper 50s to the lower 60s.

A mid level ridge axis crosses the region Friday night. This should result in dry/tranquil weather...But we do expect to see some mid- high cloudiness increase overnight ahead of the next shortwave. Low temps will bottom out in the 30s and 40s.

KEY MESSAGE 2...Wet weekend ahead with beneficial rain expected Saturday then again Sunday night into Monday.

Increasing confidence in a widespread light rain event Saturday ahead of an approaching trough and weak low pressure system. Guidance has come into better agreement with rain arriving Saturday afternoon. Temperature wise, Saturday appears raw and cool with highs mainly in the lower 60s. Rainfall amounts will likely be mostly beneficial with ensemble guidance indicating greater than a 60 percent probability of at least 0.25 inches of rainfall. There is also a lower, but non-negligible, 10-20 percent chance of totals exceeding 0.50 inches. The ECMWF remains the most aggressive with these probs with the GFS showing the lower end of possibilities as it resolves a weaker upper level disturbance.

Fortunately, it still looks like there will be a well-timed lull in gloomy conditions in time for Mother's Day (Sunday) as the northern edge of high pressure moves over Southern New England. Dry weather and somewhat milder temperatures are expected, with highs in the upper 60s to lower 70s.

Attention then turns to late Sunday into early next week as another mid-level trough and embedded shortwave energy move through the Northeast. This will likely support the development of weak surface low pressure and a return to unsettled weather with another round of rain late Sunday night into Monday. Brief drying Tuesday as high pressure attempts to build south of the region. Temperatures trend back below normal early next week, with highs generally in the upper 50s to lower 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 conditions continue tonight through Friday night. Just some mid level cloudiness expected at times with perhaps a brief spot shower or two...mainly on Friday. Westerly winds may gust into the lower 20 knots again by Friday afternoon.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Saturday through Tuesday/...

Saturday through Saturday Night: Mainly VFR, with local IFR possible. Breezy. Chance RA.

Sunday: VFR. Breezy. Slight chance RA.

Sunday Night: Mainly VFR, with local MVFR possible. Chance RA.

Monday: Mainly VFR, with local MVFR possible. RA likely.

Monday Night through Tuesday: VFR. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Tonight through Friday night...High confidence.

The pressure gradient will remain weak enough to keep winds/seas below small craft advisory thresholds through Friday night. However...some lower 20 knot wind gusts are expected again on Friday particularly nearshore. This may result in some choppy seas.

Outlook /Saturday through Tuesday/...

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

Saturday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Rain.

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

Sunday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain.

Monday: Winds less than 25 kt. Seas locally approaching 5 ft. Rain likely.

Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers.

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

BOX WATCHES/WARNINGS/ADVISORIES

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