textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Showers fill back in this morning with brief downpours and a thunderstorm possible, transitions to drier weather in the mid to late afternoon from west to east. Warmer and more humid today with partial sunshine late.

- Above normal temperatures for the middle of next week before trending closer to normal late next week. A couple periods of showers possible, but no washouts expected.

DISCUSSION

KEY MESSAGE 1...Showers fill back in this morning with brief downpours and a thunderstorm possible, transitions to drier weather in the mid to late afternoon from west to east. Warmer and more humid today with partial sunshine late.

Warm front continues to approach from the south and will bring a brief surge of especially warm and moist air with dewpoints into the upper 50s to low 60s over southeastern SNE as the low lifts north directly overhead. Plenty of moisture in the warm sector when eventually the cold front drops through later this morning leading to another surge of rain showers and even some thunderstorms over the south coast where a few hundred J/kg of CAPE will briefly move overhead. This may lead to localized higher amounts of rain under any brief convection. Quickly, though, winds turn out of the west then northwest pulling in much drier air as PWATs drop quickly behind the frontal passage generally 18-00z. Given slowly clearing skies and potential for lingering high clouds, as mentioned yesterday, some locations could see a good sunset tonight. While most parts of SNE will see showers continuing through around noon (west) to mid afternoon (east) we will have a respite from the cold of yesterday as warm advection leads to temperatures around 15 degrees warmer than yesterday, in the low to mid 70s. Warmest spots will be the CT valley where skies clear soonest and west flow provides a downslope component.

KEY MESSAGE 2...Above normal temperatures for the middle of next week before trending closer to normal late next week. A couple periods of showers possible, but no washouts expected.

Not much change to the expected overall mid level synoptic pattern from yesterday. However, considerable differences remain between the deterministic models after Wednesday. Thus, have low confidence in the details late next week into next weekend. Will be relying more on ensembles and focusing more on the trends until greater clarity develops.

Expecting well above normal temperatures to be in place Tuesday into Wednesday. While we should be on the backside of a cold front for Thursday, there are signals in the NAEFS and NationalBlend that the lower temperatures for Thursday could still turn out to be slightly above normal for late May, with the near to slightly below normal temperatures hold off until Friday into next weekend. Given the uncertainty at this time range, anticipating this timing part of the forecast is likely to change over the coming week.

Rainfall-wise, it is very difficult to pin down specific windows of time when the risk for showers is greatest. We can't seem to get sufficient moisture aligned with lift. The synoptic pattern suggests that Wednesday still has potential to be one of those periods as a cold front should be crossing our region. However, the ensembles started to dry out the atmosphere a little more, meaning that shower coverage could be less than previously anticipated. For Thursday, the cooler conditions means increased relative humidity, but there is not much organized lift to focus it. Perhaps colder air aloft could trigger diurnal showers, but the timing of this colder air is questionable. These issues continue right into next weekend with the potential approach of a low pressure. Again, anticipating this aspect of the forecast is likely to undergo changes as this week progresses.

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...Moderate confidence.

LIFR conditions were widespread early this morning along with fog which was locally dense. In addition...another round of showers will cross the region this morning. Slow improvement from west to east to MVFR during the afternoon...But IFR conditions may persist into this evening towards the Cape and Islands. Light- calm winds early this morning gradually become WNW at 5-10 knots as the day wears along.

Tonight...Moderate confidence.

Areas of IFR conditions in lower clouds/fog patches may linger near the Cape and Islands for much of the night. Meanwhile...many areas northwest of that region will improve to VFR by early evening at least temporarily. However...lingering low level moisture/light-calm winds tonight may result in areas of ground fog developing especially in the typically prone locations. So a wide variety in conditions is possible overnight from VFR to localized IFR- LIFR conditions.

Tuesday...High confidence.

VFR once any lingering fog patches burn off early Tuesday morning. Light and variable winds becoming SW at 7-13 knots as the day wears along. We may also have a period of localized sea breezes along parts of the very immediate coast.

KBOS...Moderate confidence in TAF.

KBDL...Moderate confidence in TAF.

Outlook /Tuesday Night through Friday/...

Tuesday Night: VFR.

Wednesday: VFR. Breezy. Slight chance SHRA.

Wednesday Night: VFR.

Thursday: VFR. Slight chance SHRA.

Thursday Night: VFR.

Friday: VFR. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Showers with embedded heavy rain, areas of dense fog and low risk of an isolated thunderstorm this morning, lingering into the early/mid afternoon for the southern waters. This is followed by drier/improving weather in the afternoon/evening from northwest to southeast (later south of the islands). Wind shift from SSW in the morning, to west in the afternoon and evening, then NNW overnight. Tuesday light winds become S/SW 10-15 kts.

Outlook /Tuesday Night through Friday/...

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

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

Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers.

Wednesday Night: Winds less than 25 kt.

Thursday: Winds less than 25 kt. Slight chance of rain showers.

Thursday Night: Winds less than 25 kt.

Friday: Winds less than 25 kt. Slight chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 2 AM EDT Tuesday for ANZ250-254>256.