textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Rain showers with brief downpours ending early tonight, then decreasing cloudiness, falling temperatures and increasing westerly winds through the rest of tonight.

- Mostly sunny, cool and blustery Monday. Then increasing cloudiness into the afternoon and perhaps isolated rain or snow showers late in the day into Monday night.

- Mostly dry and cool to start the week with some lingering showers not ruled out entirely for Tuesday.

- Temperatures increase through the second half of next week and conditions remain dry.

DISCUSSION

KEY MESSAGE 1...Rain showers with brief downpours ending early tonight, then decreasing cloudiness, falling temperatures and increasing westerly winds through the rest of tonight.

After a cloudy, cool and dreary Sunday with mist/fog around, light to at times moderate rain showers are developing in an elevated-PWAT environment (around 1.2"). This is in association with a cold front, which as of early this afternoon was just approaching the Berkshires and Litchfield Hills. Rain showers should be rather widespread through late this afternoon as the frontal boundary lurches eastward toward the eastern coast; though some showers have produced some brief (< 5 min) downpours, that should be the extent of it with scant instability to work with. The front could be slower to exit Cape Cod and the Islands until later this evening, but in most areas, rain should be coming to an end between 4-8 PM. A few areas could see rain totals up to a half-inch, though a quarter to third of an inch of rain should be more common - not too impactful overall.

Frontal passage will be marked with a westerly windshift around 10 mph, falling dewpoints through the 20s and 30s and a general decrease in cloudiness, although sky conditions could be more partly cloudy than fully clear. Lows tonight cool off into the 30s, with mid/upper 30s Cape and Islands and temps around freezing in the interior higher terrain.

KEY MESSAGE 2...Mostly sunny, cool and blustery Monday. Then increasing cloudiness into the afternoon and perhaps isolated rain or snow showers late in the day into Monday night.

We then become entrenched in general longwave troughiness starting Monday, with a prominent cold pool aloft (e.g. 500 mb temps -32C!). While the first part of the day is mostly sunny, it will end up being chilly and blustery with WNW gusts 25-35 mph with mixing heights up to 800 mb. Sunshine offset by cold advection (925 mb temps dip to -4C), so offered highs closer to the 40s for most, with spot 50 degree readings southeast MA. Will feel cooler than that though with the breezes.

Later in the day, the first of a couple fast-moving 500 mb shortwave troughs rippling through the broader longwave trough allows for increasing cloud cover toward a partly to mostly cloudy look. Most models show at least an increase in cloud cover into the afternoon and carrying over into the evening - though with a dry/rather mixed sub-cloud layer, guidance gives mixed signals if we'd be able to wring out any rain or snow showers with some solutions offering cloudiness but dry weather while others show some precip and possible snow coatings overnight. Current thinking in looking at the 12z guidance is that the potential is enough such that chance PoPs seem warranted for the evening into early Tuesday morning, but rain/snow showers probably are isolated enough such that any impact would be minimal at worst. With easing winds into the evening, lows will be quite chilly with most areas in the upper 20s to around freezing, except mid 30s Cape and Islands.

KEY MESSAGE 3...Mostly dry and cool to start the week with some lingering showers not ruled out entirely for Tuesday.

Generally colder and drier conditions take hold after Monday night as surface high pressure starts to take hold and an upper level trough settles overhead. A shortwave moving through the region may have some lingering showers from Tuesday morning stick around through part of the day. Aside from that, drier conditions can be expected as dewpoints fall into the 20s across the region (30s over the Cape and Islands), and even into the teens for Tuesday night into Wednesday. Tuesday night will be noticeably cooler as the trough sits overhead and 925 mb temperatures could approach -10C (particularly in northern MA, but elsewhere may settle to around -8C to -6C) after being just at or below 0C Monday/Monday night. Surface lows may dip into the upper teens over the interior and the 20s to low 30s closer to the coasts. Winds remain mostly W and NW Tuesday into early Wednesday in the post-frontal airmass.

KEY MESSAGE 4...Temperatures increase through the second half of next week and conditions remain dry.

The general trends from the previous forecast remain consistent. High pressure moves into the Mid-Atlantic region Wednesday then shifts more offshore, which will aid in bringing back SW flow over southern New England and keep the region dry. Temperatures will improve as the week goes on as the upper level trough moves off to the east during the second half of the week. Highs will likely end up back in the 50s and 60s. Some uncertainty remains towards the end of the week as some ensemble guidance hints at another backdoor front moving in Saturday night into Sunday. High pressure moving east from just to our north could encourage onshore flow early Sunday morning and possibly continuing through the day before it shifts further offshore and winds return to SW. We should get more clarity on details as we get closer in time.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

Forecaster Confidence Levels...

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

18z TAF Update:

Today: Moderate confidence.

Still IFR/LIFR due to stratus, mist and areas of fog until cold frontal passage. Cold front has moved into Southern New England and is bringing widespread rains, with some brief downpours possible. Expect rains to come to an end from 21-23z west to east, though could linger until 02z for the Cape and Islands. Post-frontal, expect lifting of ceilings into the SCT- BKN VFR range and winds becoming NW and increasing to around 10 kt.

Tonight: High confidence.

Leftover MVFR ceilings should scatter out to VFR all areas early. NW winds increase to 10-15 kt with developing gusts to 25 kt after midnight.

Monday: High confidence.

Mainly VFR; for the interior higher terrain, wouldn't rule out some MVFR bases interior high terrain in the aftn as disturbance aloft approaches and there could be some hit-or-mostly-miss sprinkles or flurries. Main concern for aviation is gusty NW winds, around 12-17 kt with gusts 25-35 kt, highest at ORH.

Monday Night: High confidence overall, though moderate on possible precip chances.

Disturbance aloft moves through Southern New England Mon night, which will bring at least SCT-OVC mainly VFR ceilings. Less clear if we can wring out any precip; if we do, potential for brief periods of MVFR visby -SHSN. NW winds decrease to 8-12 kt with gusts in low 20s kt range.

KBOS Terminal...Moderate confidence. IFR, widespread rain at MVFR visbys continue thru 23z with arrival of cold front. Clearing to VFR likely into the early evening with NW winds increasing to around 10-13 kt before midnight, with gusts to 25 kt toward daybreak Mon.

KBDL Terminal...Moderate confidence. IFR/LIFR, widespread rain at MVFR visbys continue thru 22z with arrival of cold front. Clearing to VFR likely by sundown, with NW winds increasing to around 10-15 kt late evening, with gusts to 25 kt toward daybreak Mon.

Outlook /Monday Night through Friday/...

Tuesday: VFR. Breezy. Chance RA.

Tuesday Night through Wednesday: VFR. Breezy.

Wednesday Night:

Thursday through Thursday Night: Breezy.

Friday:

MARINE

Forecaster Confidence Levels...

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

High confidence.

Due to combo of SW winds of 25-30 kt and building wave heights to around 5-10 ft (lower 1-2 ft near bays), SCAs continue on all waters. We'll gradually be able to peel away at the nearshore SCA for tonight - but it seems likely that we'll need to re-hoist SCAs for the nearshore waters again on Monday as NW winds increase to around 25 kt. Seas will also be slow to decrease into Monday, with SCAs on the outer waters continuing into Monday evening. Conditions to trend below SCA by Monday evening with NW winds around 15-20 kt and seas 4 ft or less.

Foggy conditions still prevail through early tonight with visibilities as low as one-half mile, although widespread rains should develop with brief downpours this afternoon into early tonight. Expect better visibilities as a cold front moves east of the waters as winds turn northwesterly.

Outlook /Monday Night through Friday/...

Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain.

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

Wednesday through Thursday Night: Winds less than 25 kt.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ230>234-236-251. Small Craft Advisory until 2 AM EDT Monday for ANZ235-237. Small Craft Advisory until 2 PM EDT Monday for ANZ250. Small Craft Advisory until 8 PM EDT Monday for ANZ254>256.