textproduct: Boston / Norton

WHAT HAS CHANGED

Ended Small Craft Advisories early as wind gusts and seas continue to diminish early this morning.

KEY MESSAGES

- Early morning clouds give way to some sunshine today, while a cold front sparks widely scattered showers or a weak thunderstorm this afternoon into early evening.

- Widespread rainfall is becoming less likely for late Sunday night through Monday.

- Briefly dry Tuesday, perhaps turning unsettled Wednesday into Thursday, with uncertainty increasing beyond.

DISCUSSION

KEY MESSAGE 1...Early morning clouds give way to some sunshine today, while a cold front sparks widely scattered showers or a weak thunderstorm this afternoon into early evening.

Good morning and Happy Mothers Day to all the mothers and mom figures! We are kicking off this morning with somewhat humid and mild conditions, with temperatures between the upper 40s and lower 50s along with low clouds and areas of fog. While it is a gloomy start, conditions are expected to improve through the morning. Model guidance remains in good agreement that subtle mid-level height rises will support a quieter and milder day ahead. While southwest to west-southwest flow persists, a notably drier airmass is not expected to move into southern New England. In fact, dewpoints climb into the lower to mid 50s, making it feel somewhat more humid compared to the much drier conditions observed late this week.

Given lingering moisture, embedded shortwave energy within the flow, and an approaching cold front, cannot completely rule out a passing afternoon shower or thunderstorm as a few hundred J/kg of CAPE may develop. That said, Sunday does not appear to be a washout. CAMs indicate a fragmented line of showers and perhaps a few weak thunderstorms moving through southern New England from northwest to southeast between 2 PM and 8 PM. Despite the cloud cover this afternoon, highs remain comfortable in the lower to mid 70s across much of the region, though slightly cooler along the immediate coast and across the higher terrain of northern and western MA, where highs remain in the upper 60s.

KEY MESSAGE 2...Widespread rainfall is becoming less likely for late Sunday night through Monday.

In general, forecast trends continue to show the bulk of any precipitation Sunday night into Monday remaining to our south. While a mid-level trough and shortwave move through the Northeast, the greatest forcing is displaced southward near the Mid-Atlantic coastline. Here, a weak surface wave develops and moves northeast into the North Atlantic.

What has changed? Over the past two nights, model guidance has consistently shifted this feature farther south. Earlier guidance tracked the surface wave across the nearshore waters south of New England, with the axis of heaviest rainfall extending across portions of the CWA. More recent guidance now keeps the heaviest rainfall farther offshore.

That all being said, there remains potential for light showers mainly across the south coast of RI and MA, as well as Cape Cod and the Islands. A washout is not expected. In fact, probabilities for greater than 0.10 inches of rainfall over the 24-hour period ending Monday evening, based on the 00z HREF, are only around 10 to 20 percent for areas southeast of a Norwich to Providence to Brockton line. Across interior southern New England, any precipitation would more likely take the form of isolated diurnally driven showers rather than a widespread stratiform rain event. Temperatures Monday afternoon trend 8 to 12 degrees cooler than Sunday, resulting in a noticeably cooler feel.

KEY MESSAGE 3...Briefly dry Tuesday, perhaps turning unsettled Wednesday into Thursday, with uncertainty increasing beyond.

The mid-level trough shifts offshore Tuesday, with mid-level ridging developing in its wake. Flow aloft turns north-northwest, advecting lower humidity and cooler temperatures into the region, leading to a cool but sunny day.

This is short-lived, as unsettled conditions may return by late Wednesday and linger into Thursday as another mid-level trough and embedded shortwave move through the Northeast, though confidence in timing and impacts remains low given the longer forecast range. Beyond Thursday, the forecast becomes increasingly uncertain, though mid-level troughing across the Northeast may keep at least some risk for unsettled weather in place. High temperatures remain near to slightly below climatological normals for mid-May, moderating into the upper 50s to lower 60s Tuesday through Friday.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

12z TAF Update:

Today: High confidence in trends, but moderate confidence in timing.

Lowest categories (LIFR-IFR) mainly PVD south and east due to stratus and fog, with MVFR-IFR stratus conditions elsewhere. General improvement toward SCT- BKN VFR between 13-16z from west to east, though lingering/patchy MVFR-IFR decks could still hang tough across the Cape and Islands. SW winds should then generally prevail around 7-10 kt.

Couple things we're monitoring...one is the potential for a seabreeze to develop in E MA if SW winds are lighter than forecast, which could happen as soon as 16z. The other is a potential for widely SCT SHRA and brief MVFR visbys along a frontal boundary between 17-23z mainly BDL to BOS north and west, which is conditional on developing enough daytime heating. These aren't currently indicated in TAFs, but a mention could be added later in AMDs.

Tonight: High confidence.

Frontal boundary links up with coastal moisture and brings MVFR ceilings and off-and-on periods of -RA to PVD/UUU and southeast MA. -RA could be possible as far north and west as BED to ORH but is viewed as unlikely, with mainly VFR ceilings for these and the rest of the interior airports. Rain should continue into most of the evening. SW/W winds around 5-10 kt to turn to NW winds around 10 kt late tonight/overnight.

Monday...High confidence.

VFR. Cannot rule out SHRA mainly across southern RI, the south coast of MA, Cape Cod, and the Islands. WNW winds less than 10 kt.

KBOS Terminal...Moderate confidence in TAF.

Mainly MVFR (brief/tempo IFR) thru 14z, then should see improvement to SCT-BKN VFR levels. Though SW winds around 7-10 kt should prevail, if winds turn lighter then the risk for a potential seabreeze could develop by 16z. Also monitoring risk for a late-day (after 20z) -SHRA but this is not certain. Could need to include one/both of these in TAF AMDs. Otherwise VFR for tonight with W to NW winds around 10 kt.

KBDL Terminal...Moderate confidence in TAF.

MVFR/IFR thru 14-15z, then should see improvement to VFR. Possible risk for -SHRA and MVFR visby after 18z thru 22z. Then conditions trend dry but with VFR cloudiness tonight, as winds become NW around 10 kt.

Outlook /Monday Night through Thursday/...

Monday Night: VFR.

Tuesday: VFR. Breezy.

Tuesday Night: VFR.

Wednesday: VFR. Breezy. Chance SHRA.

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

Thursday: Mainly MVFR, with local IFR possible. Breezy. SHRA, isolated TSRA.

MARINE

Forecaster Confidence Levels...

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

Today through Monday...Moderate confidence.

Areas of marine fog remain possible this morning, with gradual improvement through the day. SW winds 8-15 kt and seas subsiding to 2-4 ft. Winds shift to the N-NW tonight and continue into Monday, with wind speeds less than 15 kt and seas below 4 ft. Showers are possible late Sunday night into Monday across the southern waters from Block Island to Nantucket.

Outlook /Monday Night through Thursday/...

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

Wednesday through Wednesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.

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

BOX WATCHES/WARNINGS/ADVISORIES

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