textproduct: Boston / Norton

WHAT HAS CHANGED

Confidence is increasing in dangerously cold wind chills, strong wind gusts and heavy freezing spray over the waters this weekend.

KEY MESSAGES

- Mainly dry through Thu with very cold nights. Seasonable afternoon temps today then trending colder Wed & Thu.

- More active Friday into the weekend. Chance for dangerously cold wind chills this weekend along with strong winds and heavy freezing spray over the waters.

DISCUSSION

Key Message 1...Mainly dry through Thu with very cold nights. Seasonable afternoon temps today then trending colder Wed & Thu.

Overall a quiet weather pattern for the next few days ahead. One potent shortwave and upper low passes well to the north tonight into Wed with a cold front passage. Then a second shortwave moves through on Thu. These will pass with little fanfare as moisture is very limited. Just some increased cloud cover tonight and perhaps on Thu but otherwise dry weather.

Temps today should be similar to what was observed yesterday as there is very little change in low level temps, so generally 30-35F. Then it trends colder Wed into Thu behind northern stream trough passage and cold front as 925 mb temps cool. Very cold nights expected through Thu night with lows single numbers and teens, but some below zero readings Thu night in the colder locations. Fortunately, the nighttime wind won't be much of an issue.

Key Message 2...More active Friday into the weekend. Chance for dangerously cold wind chills this weekend along with strong winds and heavy freezing spray over the waters.

A generally quiet week ends with a passing Alberta clipper and its strong arctic front passing through the region. As the previous forecast noted, this is expected to be a moisture-starved system that will push through quickly, which will limit any snowfall totals that accumulate. Generally, a coating to an inch can be expected, with the greater chance for an inch mainly along the eastern coastline as ocean effect showers may linger through the day Saturday.

An arctic front moves through southern New England, leaving what may be the coldest wind chills we've seen this season in its wake. The general trend has not changed significantly; a low is expected to deepen over the Maritimes and southern New England will be caught in the tightening pressure gradient as high pressure remains towards the Great Lakes. Gale-force winds are a possibility over the waters, and winds could possibly climb into storm force criteria. Those of us on land will also likely see elevated winds that will only make it feel even colder. Temperatures aloft sink to around -25C at 925 mb Saturday night, which when combined with the winds, it could end up feeling like -30F in parts of the Berkshires and between -20F and -10F elsewhere. Ensemble guidance continues to center the higher probabilities for wind chills below -25F over the Berkshires and the higher elevations of central MA. NAEFS guidance also indicates low level temperatures reaching 2 to 3 standard deviations below normal. Bottom line, it will very likely be dangerously cold and windy this weekend, especially heading into Sunday morning.

With the elevated winds and very cold temperatures, confidence is increasing in the chance for heavy freezing spray over the waters this weekend.

AVIATION /06Z TUESDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

06z TAF Update...High confidence.

VFR through Wednesday. SCT-BKN cigs 5-7k ft developing this afternoon and evening. Light NW wind becoming SW 5-10 kt after 18z, then SW-W wind 4-8 kt tonight. NW wind 10-20 kt developing Wed.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High Confidence in TAF.

Outlook /Wednesday Night through Saturday/...

Wednesday Night through Thursday Night: VFR.

Friday: VFR. Slight chance SN.

Friday Night: Mainly VFR, with local IFR possible. Breezy. Chance SN.

Saturday: VFR. Strong winds with local gusts up to 40 kt. Slight chance SN.

MARINE

Forecaster Confidence Levels...

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

Through Wednesday...High confidence.

Winds below SCA through the period. NW winds becoming W 10-15 kt this afternoon and evening, then NW gusts to 20 kt developing Wed. 5 ft seas over outer waters will subside to 3 ft this afternoon.

Outlook /Wednesday Night through Saturday/...

Wednesday Night through Friday: Winds less than 25 kt.

Friday Night: Winds less than 25 kt. Local rough seas. Chance of snow, freezing spray.

Saturday: Moderate risk for gale force winds with gusts up to 45 kt. Rough seas up to 15 ft. Freezing spray, chance of snow.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 9 AM EST this morning for ANZ250- 254-255. Small Craft Advisory until 7 AM EST this morning for ANZ251- 256.