textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Light rain continues this afternoon. More widespread rain arrives for the Cape and Islands tonight into the early morning hours Sunday.

- Drying trend Monday into Tuesday with warmer temperatures and breezy to gusty southwest winds.

- Cold front brings a chance of showers and thunderstorms late Tuesday, followed by an unsettled and cooler pattern mid to late week.

DISCUSSION

KEY MESSAGE 1...Light rain continues this afternoon. More widespread rain arrives for the Cape and Islands tonight into the early morning hours Sunday.

A mid level trough digging into the Mid Atlantic this evening and overnight continues to send a plume of moisture ahead of it on SW flow. This moisture together with a surface boundary and favorable placement beneath a 120kt upper jet will continue to produce light to moderate rain showers over much of the region, though it will be exiting east through the afternoon and evening. Attention then turns to the more widespread soaking expected to accompany a sub 1000mb coastal low lifting north but remaining offshore overnight. This will bring a soaking rain, mainly confined to Cape Cod and the islands. That being said, wrap around moisture will likely bring widely scattered showers to much of eastern MA on Sunday morning. By mid to late morning Sunday drier air will have moved in the at the surface and upper levels for most of SNE; however, a layer of moisture at 850 mb together with lingering cyclonic flow aloft will lead to widespread diurnal clouds so don't expect skies to clear fully even as the mid/high clouds from the overnight system exit. Temperature-wise, not much change in the mid levels and we're looking at near persistence if not a few degrees warmer than Saturday owing to the breaks of sun. Finally, better mixing behind the system will lead to some breezy winds Sunday afternoon with a weak LLJ overhead, but damaging winds are not expected.

KEY MESSAGE 2...Drying trend Monday into Tuesday with warmer temperatures and breezy to gusty southwest winds.

Low pressure lifts into the Canadian Maritimes Monday while high pressure builds to our south over the southwestern Atlantic. Aloft, quasi-zonal flow dominates much of the CONUS, though a developing Rex block over the Pacific Northwest may influence the pattern later in the forecast period. For sensible weather, expect mainly dry conditions with increasing sunshine and a warming trend. Southwest flow will advect milder air into the region, with 850mb temperatures rising from around +4C to +6C Monday to +12C to +14C Tuesday. Forecast soundings support a well-mixed boundary layer, expecting highs in the mid 60s to lower 70s Monday and upper 70s to low 80s Tuesday. The pressure gradient tightens through the period, resulting in breezy conditions Monday with southwest gusts 20-30 mph, increasing to 25-35 mph Tuesday. Given recent dry conditions, gusty winds, and relatively low humidity (min RH 25-35% Monday and 30-40% Tuesday away from marine influence), elevated fire weather concerns are possible. Coordination with state fire weather partners is ongoing, and headlines may be needed early next week.

KEY MESSAGE 3...Cold front brings a chance of showers and thunderstorms late Tuesday, followed by an unsettled and cooler pattern mid to late week.

Cold front approaches late Tuesday, though timing remains uncertain. With highs climbing well above normal, guidance suggest a few hundred J/kg of CAPE, which may support scattered convective showers and thunderstorms. Current CSU-ML guidance indicates low-end (~5%) severe probabilities But this will need to be monitored give a strengthening low-level jet in the vicinity. The front may be slow to clear the region, sagging south of southern New England Wednesday with lingering showers and possible thunderstorms.

Looking ahead, the pattern becomes more active as mid-level ridge develops across western CONUS, replacing the Rex blocking, and a trough across the eastern CONUS. This will support multiple shortwaves and surface lows moving through the flow, resulting in periodic chances for showers Thursday into Friday. Timing details remain uncertain at this range. Late week bears watching, as guidance suggests a stronger system could impact the region Thursday night into Friday, accompanied by a robust southerly low-level jet. This may bring a period of heavier rainfall and gusty winds. While details remain uncertain this far out, the potential exists for impactful conditions including hazardous marine weather. Astronomical tides appear relatively low late week, which should limit coastal flood potential unless a stronger system materializes.

Behind the front, cooler temperatures return with highs generally in the upper 50s to lower 60s Wednesday and beyond.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

00z Update:

Tonight: Moderate confidence.

VFR for western terminals, along the I-95 corridor between KBOS and KPVD will have low-end VFR conditions with low chance for a shower or two, as for the Cape and island terminals as a system offshore brings low-end MVFR to IFR conditions and SHRA. Cannot rule out a passing shower for KBOS to KPVD, but more likely mid Sunday morning. Winds come around to NW 5-10 kts, easing across the interior to a light NW less than 5kts.

Sunday: Moderate confidence.

VFR and dry for western terminals. Eastern terminals for Sunday AM is MVFR-IFF, with improvements through the late morning to VFR, the Cape and island terminals improve by early afternoon. Will have gusty NW winds 8-12 kts with a gusts to 20-25 kts.

IFR-MVFR, at least for east terminals early Sunday AM. For BOS this is likely a short window of lowered ceilings and scattered showers. Improving to VFR mid to late morning and closer to early afternoon for Cape/Island terminals. VFR for west/central terminals. NW winds 8-12 kts with a few gusts to 20 kts.

Sunday night: High confidence.

VFR. W winds 5-10 kts become lighter SW through the night.

KBOS Terminal...Moderate to high confidence in TAF. Likely a short window of lowered ceilings between 10z-15z and scattered showers. Improvements after 15z to VFR with NW gusts 20-25 kts.

KBDL Terminal...High confidence in TAF.

Outlook /Monday through Thursday/...

Monday through Tuesday: VFR. Breezy.

Tuesday Night: VFR. Windy with gusts up to 30 kt. Slight chance SHRA.

Wednesday: VFR. Windy with gusts up to 30 kt. Chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Overall high confidence.

S winds become NW tonight, turning NW and becoming 10-20 kts with some gusts to 25kts Sunday. Rain begins to increase on the southern waters later tonight into Sunday.

Seas also increase Sunday morning, and a small craft advisory is in effect for the outer waters for seas of 4-6 ft.

Outlook /Sunday Night through Thursday/...

Sunday Night: Winds less than 25 kt. Local rough seas.

Monday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft.

Monday Night: Winds less than 25 kt. Seas up to 5 ft.

Tuesday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas.

Tuesday Night: Strong winds with gusts up to 35 kt. Local rough seas.

Wednesday: Strong winds with gusts up to 35 kt. Seas up to 5 ft. Chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 11 AM Sunday to 2 PM EDT Monday for ANZ250-254>256.