textproduct: Boston / Norton

WHAT HAS CHANGED

The Small Craft Advisory has been extended until 8pm Monday.

KEY MESSAGES

- Lingering showers this morning give way to a slow clearing trend this afternoon and tonight.

- 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... Lingering showers this morning give way to a slow clearing trend this afternoon and tonight.

Expect a few lingering wrap-around showers mainly across eastern Massachusetts this morning with continued cyclonic flow. Shower activity wanes by the mid morning as a layer of drier air filters in at 925 mb. After a brief period of clearing, lingering cyclonic flow aloft and low-level instability will help form widespread diurnal CU and stratus clouds. Temperature-wise, not much change in the mid levels and we're looking at near persistence if not a few degrees warmer in valley locations where highs may break into the lower 60s. Breezy day on tap with model soundings showing a well mixed boundary layer extending to around 850 millibars paired with a low level jet that increases to around 25-30 kt.

KEY MESSAGE 2...Turning significantly drier Monday into Tuesday with warmer temperatures and breezy southwest winds.

The week starts with increasingly zonal flow aloft stemming from the breakdown of a broad trough over the Eastern CONUS. Further west, building heights help to develop a Rex block over the Pacific Northwest serving to re-amplify the upper air pattern. Closer to the surface, low pressure deepens over the Canadian Maritimes Monday while high pressure builds to our south over the southwestern Atlantic resulting in an increasing pressure gradient. In terms of sensible weather, expect mainly dry conditions with increasing sunshine and a marked 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. One final note, dew points fall into the 20s and 30s Monday and 30s and 40s Tuesday. These values in combination with much warmer temperatures will result in relative humidity values falling to 25-35% Monday afternoon and 30-40% Tuesday afternoon. This combination will mean 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 suggests some instability with up to 1000 J/kg of CAPE, mainly across NW Mass, which may support scattered convective showers and thunderstorms. Latest CSU-ML guidance still paints the northern border of our CWA with low-end (~5%) severe probabilities. This will need to be monitored give a strengthening low- level jet in the vicinity. The limiting factor will be moisture with dewpoints in the lower to mid 50s Tuesday afternoon. 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 /07Z SUNDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

06z Update:

Rest of Tonight: Moderate confidence on timing.

Continued MVFR to IFR conditions and SHRA across the Cape and Islands. Cannot rule out a passing shower for KBOS to KPVD, but chances fall significantly after 12z. Winds come around to NW 5-10 kts, easing across the interior to a light NW less than 5kts.

Today: Moderate confidence in the extent of cloudcover.

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 this morning 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.

Tonight: High confidence. VFR. W wind 5-10 kt

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 Night through Thursday/...

Monday Night through Tuesday: VFR. Breezy.

Tuesday Night: VFR. Breezy. Slight chance SHRA.

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

Wednesday Night: Mainly VFR, with local IFR possible. Breezy. SHRA likely.

Thursday: Mainly MVFR, with local VFR possible. Breezy. SHRA likely.

MARINE

Forecaster Confidence Levels...

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

Overall high confidence.

NW winds increase this afternoon with some gusts to 25kts thru Monday evening. Will also see seas build to 4-6 feet across the outer waters this afternoon thru Monday. Given these conditions, the Small Craft Advisory goes into effect at 11am this morning and has been extended until 8pm Monday. Further extensions to the SCA will likely be needed with future forecast updates.

Outlook /Monday Night through Thursday/...

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

Tuesday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas.

Tuesday Night: Strong winds with gusts up to 30 kt. Areas of rough seas.

Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Chance of rain showers.

Wednesday Night: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Rain showers likely.

Thursday: Winds less than 25 kt. Local rough seas. Rain showers likely.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 11 AM this morning to 8 PM EDT Monday for ANZ250-254>256.