textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to the forecast with this update.

KEY MESSAGES

- Cold front shifts offshore this morning with lingering rain ending west to east, followed by drier, cooler, and seasonable conditions through Friday.

- An unsettled weekend is expected with periods of showers Saturday and again late Sunday into Monday.

DISCUSSION

KEY MESSAGE 1...Cold front shifts offshore this morning with lingering rain ending west to east, followed by drier, cooler, and seasonable conditions through Friday.

A cold front continues shifting offshore this morning while a secondary area of light to moderate rain lifts east toward the I-95 corridor for the morning commute. Rain exits from west to east roughly between 6-10 AM, although Nantucket may see lingering showers into early afternoon as the front remains nearby offshore.

In the wake of the front, drier and cooler conditions overspread southern New England through Friday. CAA ushers in a more seasonable airmass characterized by lower PWAT values generally below 0.3 inches. Despite steep low-level lapse rates and a well-mixed boundary layer this afternoon, limited moisture should confine any cloud development to scattered fair weather cu. High temperatures today reach the lower to mid 60s, near climatological normals for early/mid-May.

WNW winds remain breezy today with gusts generally below 20 kt before diminishing overnight, though winds should remain elevated enough to limit strong radiational cooling despite increasingly clear skies. Even so, overnight lows fall into the lower to mid 40s in urban locations and the upper 30s across rural areas. Portions of the eastern Berkshires may briefly dip into the mid 30s.

Heading into Friday, a strong mid-level shortwave may trigger an isolated shower, though most locations should remain dry given limited moisture availability with PWATs only around 0.3-0.4 inches. Slightly cooler temperatures aloft support highs mainly in the upper 50s to lower 60s.

KEY MESSAGE 2...An unsettled weekend is expected with periods of showers Saturday and again late Sunday into Monday.

The next opportunity for rainfall arrives Saturday as a mid-level trough and weak surface low pressure system moves through the Northeast. While some uncertainty remains regarding exact timing, guidance has trended toward showers arriving late Saturday morning into the afternoon. Additional adjustments in timing are still possible. Saturday appears raw and cool with highs mainly in the lower 60s. A period of wetting rainfall is increasing, with ensemble guidance indicating great 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.

Conditions improve for Mother's Day (Sunday) as SNE briefly resides within a relative lull in the active pattern. 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 /06Z THURSDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

06z TAF Update:

Today...High confidence.

IFR conditions and intermittent SHRA until 12z for much of SNE, will persist at Cape Cod and Island terminals through 15z-17z. Otherwise, drying and VFR conditions develop from west to east mid morning into the early afternoon. W to WNW wind 8-12 kt, gusting up to 20 kt.

Tonight...High confidence.

VFR. SCT to BKN 070-100 ceilings. Light W WNW wind 5-10 kt.

Friday...High confidence.

VFR. SCT to BKN 040-070 ceilings. Very low chance of a spot shower, otherwise a dry day. WNW wind 10-14 kt, gusting 20-25kt.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Friday Night through Monday/...

Friday Night: VFR.

Saturday: Mainly VFR, with local MVFR possible. Breezy. SHRA likely.

Saturday Night: Mainly VFR, with areas MVFR possible. Breezy. Chance SHRA.

Sunday: Mainly VFR, with areas MVFR possible. Breezy. Slight chance SHRA.

Sunday Night: Mainly VFR, with areas MVFR possible. SHRA likely.

Monday: Mainly VFR, with local IFR possible. Breezy. SHRA likely.

MARINE

Forecaster Confidence Levels...

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

Through Friday...High confidence.

A cold front will exit S-SE of the coastal waters this morning. A wind shift occurs, SSW to the WNW by late morning. Lower wind speeds and gusts today, 10-15 kt. Seas remain elevated across the outermost waters, 4-6 ft. A Small Craft Advisory will remain in effect through early afternoon due to those conditions. Seas fall by the early to mid-afternoon with high pressure building from the SW. On Friday, a weak frontal passage may produce wind gusts 20-25 kt and seas of 3-5 ft, sub-advisory, but will need to be monitored.

Outlook /Friday Night through Monday/...

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

Saturday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Rain showers likely.

Saturday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Rain showers likely.

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

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

Monday: Winds less than 25 kt. Areas of seas approaching 5 ft. Rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 4 AM EDT early this morning for ANZ250. Small Craft Advisory until 8 AM EDT this morning for ANZ254. Small Craft Advisory until 2 PM EDT this afternoon for ANZ255- 256.