textproduct: Boston / Norton

WHAT HAS CHANGED

Risk for showers with brief heavy rain and an isolated thunderstorm possible Monday morning, lingering into early afternoon across RI and eastern MA.

KEY MESSAGES

- Steady rain Sunday afternoon transitions to drizzle and fog overnight.

- Showers Monday 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 Monday 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...Steady rain Sunday afternoon transitions to drizzle and fog overnight.

Large warm frontal rain shield over SNE this afternoon, being driven by a modest 35-45 kt low level SE jet off the Atlantic. This jet is resulting in breezy conditions along the coast, with ESE winds gusting to 20-25 mph at times. Winds will slacken later this evening and overnight, as this jet exits offshore overnight. Thus, steady rains this afternoon and evening will transition to more of a spotty light rain/drizzle overnight. As a warm front approaches from the south, could see some areas of dense fog develop tonight.

KEY MESSAGE 2...Showers Monday 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 Monday with partial sunshine late.

Warm front lifts north through the region Monday morning. Warm sector airmass will be accompanied by dew pts in the 60s, so it will feel warmer and more humid Monday. Short wave trough and accompanying cold front move through the region later in the morning and into the afternoon, from west to east. Modest synoptic and frontal scale forcing, coupled with copious deep layer moisture (dew pts in the 60s and PWATs 1.75-2.0 inches) along with some instability, will yield showers with embedded heavier rain/downpours and a low risk of an isolated thunderstorm. Not expecting any flooding (other than nuisance, minor urban/street) but more beneficial rains, with an additional 0.35 to 0.75 inches of rainfall tonight into Monday. Isolated higher amounts possible if any thunderstorms develop. Good column drying behind the FROPA 18z-00z from west to east, with PWATs crashing and yielding clouds giving way to breaks of sunshine from west to east mid to late afternoon. This should support highs of 70-75 and with dew pts in the 60s, it will feel considerably warmer than previous days.

KEY MESSAGE 3...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 /00Z MONDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

Tonight: High confidence.

MVFR/IFR in steady light rain continues to lower to widespread IFR this evening and tonight, with marginal IFR/LIFR at times in drizzle/spotty light rain and areas of dense fog. Marginal LLWS this evening from low level SE jet of 35-45 kt, ends after 00z-03z west to east as low level jet moves offshore. This jet will result in ENE surface winds gusting up to 20-30 kt at times at coastal terminals until 00z-03z, then slackening thereafter.

Monday: High confidence in trends. Moderate confidence in exact timing.

LIFR/LIFR at 12z Monday in drizzle/areas of rain and fog. As cold front approaches from the west, showers become widespread along with embedded heavier rain and low prob of -TSRA. After 15z LIFR/IFR begin to lift to IFR/MVFR and eventually VFR 18z-00z from west to east. SSW winds in the morning become west in the afternoon with the FROPA.

Monday night: High confidence.

Light west wind becoming NNW late. Any lingering IFR/MVFR over Cape Cod and Islands at 00z, will improve to VFR with the wind shift from SW to west and eventually NNW overnight. Low prob of MVFR in patchy fog overnight.

KBOS...High confidence in TAF. Marginal LLWS (WS020 15040KT) 00z-03z Monday.

KBDL...High confidence in TAF. Marginal LLWS (WS020 14040KT) 00z-03z Monday.

Outlook /Tuesday through Friday/...

Tuesday through 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.

130 PM update...

Sunday afternoon and night...

SCAs remain in effect for most waters, with east winds gusting up to 20-30 kt at times Sunday afternoon and evening, then diminishing 8 pm to 1 am from west to east Sunday night. Rain and fog lowering vsby 1 to 3 miles this afternoon, then less than 1 mile at times tonight in areas of fog and drizzle/light rain. The long easterly fetch of winds will build seas 5-8 ft across the ocean waters of RI/MA.

Monday and Mon night...

Showers with embedded heavy rain, areas of dense fog and low risk of an isolated thunderstorm in the morning, lingering into the early/mid afternoon for the southern waters. Then followed by drier/improving weather 2-5 pm 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.

Outlook /Tuesday 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 Monday for ANZ231. Small Craft Advisory until 5 AM EDT Monday for ANZ232>235-237. Small Craft Advisory until 8 PM EDT Monday for ANZ250-254>256.