textproduct: Boston / Norton

WHAT HAS CHANGED

Confidence in light accumulating snow continues to grow for Sunday afternoon. Worst-case accumulations would be 2-4 inches in the high terrain, with the most likely accumulation of a coating to an inch. Continue to watch for a more active pattern heading into the middle to end of next week, which could feature mixed precipitation types.

KEY MESSAGES

- Seasonable mild today and even warmer Saturday.

- Cold front may bring light accumulating snow Sunday, then Arctic outbreak brings well below normal temperatures to start the work week

- Unsettled and warmer weather remains possible through much of next week, but uncertainty remains high.

DISCUSSION

Key Message 1...Seasonable mild today and even warmer Saturday.

Weak impulses of shortwave energy traverse the region today, but with dry air in the mid and upper levels, skies will be mostly sunny again today. 850mb temps rise a couple degrees today from -6C to - 3C, which should help temps warm into the low to mid 40s again today, even after the cold start. Rising heights and warm air advection on Friday night will help keep lows from bottoming out in the low teens again, staying in the upper teens to low 20s. The WAA will also begin to advect in some higher dewpoints which could lead to localized fog overnight especially in low lying areas. Saturday will be the pick of the weekend with high temperatures expected to rise into the low to mid 50s with sunny skies. The warm weather doesnt last long as the first cold front associated with an arctic airmass arrives late Saturday afternoon. The initial cold front lacks significant moisture and forcing, but may be enough to trigger a few isolated showers Saturday evening.

Key Message 2...Cold front may bring light accumulating snow Sunday, then Arctic outbreak brings well below normal temperatures to start the work week

The secondary, stronger cold front and shortwave pass through the region on Sunday. Guidance remains split on the amount of moisture and QPF the secondary cold front will carry, ranging from only a trace to a quarter inch. With rapidly dropping temperatures behind the cold front, any precipitation that falls Sunday will fall as snow, with most likely snow totals of a coating to an inch, and worst-case totals of 2-4 inches if the higher QPF is realized. Higher-end snow totals should remain confined to higher terrain as temperatures become more marginal closer to the coast. High temperatures on Sunday will likely top out in the low to mid-30s early in the day, then drop into the upper 20s in the afternoon. With the core of the arctic airmass over the region by Sunday night, low temperatures bottom out in the single digits, possibly near zero in the western interior. High temperatures on Monday only rebound into the mid to upper 20s, even with the strong sun angle under sunny skies. Low temperatures Monday night bottom out in the single digits once again. Wind really wont be much of a factor during this arctic outbreak, which will keep the wind chill index from falling well below zero, as we saw in January's arctic outbreaks.

Key Message 3...Unsettled and warmer weather remains possible through much of next week, but uncertainty remains high.

Temperatures are expected to warm back to more seasonal levels Tuesday through the rest of next week, with highs in the upper 30s to low 40s. Precipitation outlook still looks murky for much of next week, with several weak waves of shortwave energy arriving from the Great Lakes and Ohio River Valley during the middle to end of next week. Given the cold air in place ahead of the first wave on Wednesday, any WAA will lead to a messy mixed precipitation setup with anything from snow to sleet to freezing rain. The active pattern may continue beyond Wednesday as guidance hints at a stalled frontal boundary near Southern New England, but confidence remains low.

AVIATION /07Z FRIDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

Today...High Confidence.

VFR. Light NW-ly winds below 10 knots back to SW-lies.

Tonight...Moderate Confidence.

VFR with areas of MVFR possible in BR over the CT Valley, RI, and into NE MA. Light SW winds, becoming calm in some locations.

Saturday...High Confidence.

VFR. Light SW-ly winds 5-10 knots. Increasing mid-level cloudiness into the afternoon.

KBOS Terminal...High confidence

KBDL Terminal...High confidence

Outlook /Saturday Night through Tuesday/...

Saturday Night: VFR. Slight chance FZRA.

Sunday: Mainly VFR, with local IFR possible. Breezy. Chance SN, slight chance FZRA.

Sunday Night: VFR. Breezy.

Monday through Monday Night: VFR.

Tuesday: VFR. Slight chance RA, slight chance SN.

MARINE

Forecaster Confidence Levels...

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

Through Saturday Morning...High confidence.

SCA remain in effect through tonight for seas lingering above 5 feet across the outer waters. Winds generally below 15 knots, with the exception of the occasional gust up to 20 knots over the far northeast waters later tonight into Saturday morning.

Outlook /Saturday Night through Tuesday/...

Saturday Night: Winds less than 25 kt.

Sunday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of snow, slight chance of freezing rain.

Sunday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of freezing spray.

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

Monday Night: Winds less than 25 kt.

Tuesday: Winds less than 25 kt. Slight chance of rain.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 1 AM EST Saturday for ANZ254>256.