textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Scattered showers Wed and Thu. Some wet snow possible Wed morning in the higher elevations, then a thunderstorm with small hail possible Thu.

- Mainly dry and seasonable Fri through the weekend, then pattern looks to turn more unsettled next week.

DISCUSSION

KEY MESSAGE 1...Scattered showers Wed and Thu. Some wet snow possible Wed morning in the higher elevations, then a thunderstorm with small hail possible Thu.

You know it's April in southern New England when you have to refer to your winter weather and convective forecast procedures on the same day.

Broad NW flow aloft dominates as upper low over Maritimes drops southward toward Gulf of Maine Wed and Thu. This will help suppress a weak short wave and surface low approaching from the lower Great Lakes which eventually passes off NJ coast and south of New England Wed. There is enough low level moisture convergence to bring scattered showers to southern New England late tonight into Wed morning, especially for western MA and much of CT which are closer to the better lift and moisture convergence. We also can't rule out some wet snow across the higher elevations at onset due to marginal temperature profiles but at most there should only be a coating on the grass.

Kind of an interesting setup for Thu and guidance may be underplaying convective potential a bit, something typical in these situations with cold air aloft and closed low lurking nearby. There's enough cyclonic flow coupled with daytime heating and ample moisture to at least generate diurnally driven clouds and perhaps a few showers. Certainly seeing some signals in the high-res models for a few low-topped showers or thunderstorms, especially in eastern MA where there should be additional support from potent mid level short wave rotating through along with minimal lower level instability. Small hail or graupel is possible should cores grow tall enough given presence of cold air aloft.

KEY MESSAGE 2...Mainly dry and seasonable Fri through the weekend, then pattern looks to turn more unsettled next week.

Broad cyclonic flow dominates later this week and through the weekend as upper low meanders around Atlantic Canada. This essentially blocks any systems approaching our area from the Plains and Great Lakes and maintains dry weather, although it's certainly possible that we see diurnal clouds and perhaps a brief shower from combination of daytime heating and cold air aloft. Temperatures should end up near or just below average highs for late April which are in the upper 50s to lower 60s.

There are some signals in longer range guidance that blocky pattern breaks down early next week which allows a series of closed upper lows to track through region, each bringing rounds of steadier rainfall, so it's possible we see a return to a wetter pattern toward the middle of next week.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

00z TAF Update: High confidence.

VFR through early tonight before MVFR ceilings arrive after midnight with scattered showers. Most locations will have a few hours of showers Wed morning with MVFR ceilings and visibilities. It's possible some terminals lower to IFR ceilings during the day but confidence wasn't high enough to include that yet. Showers come to and end by Wed afternoon but MVFR (or perhaps IFR) ceilings should persist all day.

Light winds with coastal sea breezes become S/SW tonight and Wed. May see a few 20-25kt gusts Wed afternoon, especially closer to South Coast.

Outlook /Thursday through Sunday/...

Thursday: VFR. Breezy. Slight chance SHRA, slight chance TSRA.

Thursday Night through Friday Night: VFR.

Saturday through Saturday Night: VFR. Slight chance SHRA.

Sunday: Mainly VFR, with local MVFR possible.

MARINE

Forecaster Confidence Levels...

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

High confidence through the weekend.

Expecting winds and seas to remain below SCA through the weekend. Weak low pressure passes south of New England Wed. We may see some southerly 20kt gusts ahead of it on south coastal waters Wed morning along with 3-4 ft seas, before winds shift to N/NE and subside later Wed and Wed night.

Overall, light winds and calm seas will prevail into the weekend as high pressure remains near Maritimes and a series of low pressure systems track west and south of New England.

Outlook /Thursday through Sunday/...

Thursday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers, slight chance of thunderstorms.

Thursday Night through Saturday: Winds less than 25 kt.

Saturday Night through Sunday: Winds less than 25 kt. Slight chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

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