textproduct: Boston / Norton

WHAT HAS CHANGED

There have been no significant changes since the last forecast update.

KEY MESSAGES

-Near-normal to warmer than normal temperatures Wed/Thu as a weak clipper the system brings some higher terrain light snow and light rain for the coastal plain tomorrow night

-Above normal temps Thursday with gusty winds at 30 to 40mph

-Arctic front arrives Friday night, with dangerous cold and wind chills expected this weekend and possibly lasting into next week.

-We continue to monitor a potential coastal storm for late in the weekend, but confidence remains very low.

DISCUSSION

Key message 1...Near-normal to warmer than normal temperatures Wed/Thu as a weak clipper the system brings some higher terrain light snow and light rain for the coastal plain tomorrow night

A mid-level ridge builds overhead tonight with an area of surface high pressure positioned to our south. This will support a wind shift to the southwest overnight which will allow warmer air to advect into the region during the day tomorrow. After a chilly start to Wednesday with single digit low temperatures, warm advection and southwest flow will allow afternoon temperatures to approach near to slightly above normal temperatures ranging from the upper 20s across the interior northwest to the upper 30s over southeast MA and The Cape/Islands.

Models continue to resolve a subtle short-wave aloft embedded in larger upper-level trough moving overhead tomorrow night. Positive vorticity advection in conjunction with low-level warm air advection will support a period of light snow showers for much of the interior/high terrain. Moisture will be very limited with PWATs only between 0.25-04". Not expecting any significant accumulations with only a dusting to an inch tomorrow night. Areas further south and east more likely to see some spotty rain showers.

Key Message 2...Above normal temps Thursday with gusty winds at 30 to 40mph

Thursday will likely be our last mild day for the foreseeable future, before an arctic airmass moves in this weekend. Mid-level ridge and light WAA allow 850 mb temps to warm to -5C, which will translate into highs in the low to mid 40s. Thursday will be very breezy as strong westerlies develop due to a tight pressure gradient between high pressure over the Atlantic and low pressure over the Great Lakes. Bufkit soundings show a fairly deep mixed layer up to 800 mb, where winds are around 35-45mph. Gusts of 30-40mph should be able to mix down to the surface during the peak heating hours in the afternoon.

Key Message 3...Arctic front arrives Friday night, with dangerous cold and wind chills expected this weekend and possibly lasting into next week.

Arctic front arrives on Friday with highs likely peaking in the upper 20s to low 30s early in the day before plunging to near zero by Friday night. The Arctic front will bring continued gusty winds, with NW gusts of 30-40mph once again in the afternoon, and remaining gusty overnight. This will bring the windchill index/feels-like temperature into the single digits for Friday afternoon and into the negative teens to twenties for Friday night. High temperatures on Saturday will likely be the coldest of the season thus far, with highs only topping out in the single digits to low teens. It will be less windy on Saturday with NW winds gusting 15-20mph; however, this will keep the wind chill index in the -10 to -20 range. Winds finally look to diminish on Saturday night as the center of the arctic high moves overhead; however, this will set the stage for good radiational cooling conditions, allowing low temperatures to drop near or below zero by Sunday morning. Not much relief from the Cold on Sunday as highs remain well below normal in the low teens and wind chills still near or below zero. Wind chills below -15 can cause frostbite in as little as 30 minutes on exposed skin, so use caution if spending time outdoors this weekend, especially at night. Cold weather looks to continue into next week, as CPC continues to highlight much of the Northeast in a moderate risk for well below- normal temperatures.

Key Message 4...We continue to monitor a potential coastal storm for late in the weekend, but confidence remains very low.

Guidance continues to indicate a potential coastal low sometime between Sunday and Monday. There is still significant uncertainty with this system, as both deterministic and ensemble guidance are very spread out along its path, as it could travel up the coast or out to sea as it exits the mid-Atlantic. With a track out to sea, snow impacts would be little to none; however, if this system approaches the 40/70 benchmark and travels up the coast, there would be more significant snow impacts, especially with cold air already in place. The probabilistic Winter Storm Severity Index shows a 20- 30% chance for major winter storm impacts Sunday into Monday.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

Forecaster Confidence Levels...

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

Tonight: High Confidence.

VFR. West winds decreasing to 5-10 knots.

Wednesday: High Confidence.

VFR. Southwest winds 5-10 knots.

Wednesday Night: Moderate Confidence.

Increasing mid-level cloudiness. Low-end MVFR cloud bases around 3000 feet possible. Scattered -SN. KBOS Terminal...High Confidence in trends. Moderate Confidence in timing.

VFR. Gusty W winds around 20 kts decreasing tonight to 5-10 kts. Brief -SN possible Wednesday afternoon with little to no accumulation expected.

KBDL Terminal...High Confidence in trends. Moderate Confidence in timing.

VFR. W winds 5-10 kts turn SW Wednesday morning. -SN possible Wednesday afternoon with little to no accumulation expected.

Outlook /Thursday through Sunday/...

Thursday: VFR. Windy with gusts up to 30 kt.

Thursday Night: VFR. Windy with local gusts up to 30 kt.

Friday through Saturday: VFR. Breezy.

Saturday Night: VFR. Breezy. Slight chance SN.

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

MARINE

Forecaster Confidence Levels...

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

Tonight through Wednesday night

SCY criteria persists through about midnight before winds diminish and seas subside below SCY levels. This will be in response to high pressure building south of the coastal waters. A brief period of calmer conditions tomorrow morning and afternoon before before southwest winds kick back up to SCY criteria Wednesday night into Thursday. Increasing winds on Thursday as well, possibly reach gale force for the outer waters by Thursday evening.

Outlook /Thursday through Sunday/...

Thursday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Areas of rough seas. Slight chance of rain.

Thursday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas.

Friday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Seas up to 5 ft.

Friday Night: Strong winds with gusts up to 35 kt. Areas of rough seas. Chance of freezing spray, slight chance of snow.

Saturday: Moderate risk for Small Craft Advisory winds with gusts up to 30 kt. Local rough seas. Chance of freezing spray, slight chance of snow.

Saturday Night: Winds less than 25 kt. Seas up to 5 ft. Chance of snow, chance of freezing spray.

Sunday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of snow, chance of freezing spray. Visibility 1 nm or less.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 7 PM EST this evening for ANZ230- 231-236-251. Small Craft Advisory until 1 AM EST Wednesday for ANZ232>235- 237. Small Craft Advisory until 7 AM EST Thursday for ANZ250- 254>256.