textproduct: Boston / Norton

SYNOPSIS

An arctic cold front crosses the region today with a few snow showers and a localized snow squall or two, particularly for western MA. Windy conditions and bitterly cold temperatures tonight. The winds quickly diminish by Friday, but it remains unseasonably cold. Scattered snow showers possibly mixing with rain showers late Friday night into Saturday with a low pressure system passing well to our south. Another arctic cold front crosses the region Sunday followed by well below normal temperatures Sunday night into Tuesday. A low pressure system approaching from the west may bring some more rain/snow showers by Tuesday night and/or Wednesday.

NEAR TERM /UNTIL 6 PM THIS EVENING/

Key Messages:

* Arctic cold front passes through southern New England, bringing scattered snow showers and the chance for localized snow squalls

Not much has changed for today from the previous forecast. An arctic cold front will cross over southern New England this afternoon. Some clouds and sunshine before that should bring highs up to the 30s and low 40s. Forecast soundings from the high-res guidance still indicate dry low to mid levels across much of the region, though snow squall parameter values from the NAM and GFS do remain elevated. Lapse rates and some elevated instability could point more favorably for the development of localized snow squalls, particularly in NW MA, but the key limiting factor will still be the drier air aloft. Scattered snow showers with some flurries are more favored elsewhere as the front passes through.

As the front moves through, winds will pick up from the NW. Gusts between 25-40 MPH can be expected during the late afternoon hours, continuing through the evening into the first half of tonight.

SHORT TERM /6 PM THIS EVENING THROUGH 6 PM FRIDAY/

Key Messages:

* Bitterly cold with lows well below normal in the single digits and wind chills between -10F and +10F

* Unseasonably cold conditions continue for Friday

Gusty NW winds fall off over the second half of tonight as high pressure starts to creep in from the west. 925 mb temperatures fall between -15C and -18C as the arctic airmass behind the day's front moves over the region. Wind chills could fall to -10F in some spots in NW MA. Skies also clear out tonight, and if winds diminish enough, this combined with the snowpack could be enough for lows to fall below zero there. Elsewhere, wind chill values could end up maxing out at +10F with lows in the teens and single digits.

High pressure builds in from the west during the day Friday. Sunny skies with light winds will prevail, but high temperatures are still expected to be colder than normal for this time of year. 925 mb temperatures do improve to between -8C and 10C, but given limited mixing during the day, high temperatures stay in the 20s and low 30s.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/

Scattered snow showers possibly mixing with rain showers late Friday night into Saturday with a low pressure system passing well to our south. Another arctic cold front crosses the region Sunday followed by well below normal temperatures Sunday night into Tuesday. A low pressure system approaching from the west may bring some more rain/snow showers by Tuesday night and/or Wednesday.

Key Messages:

* Scattered snow/rain showers possible late Fri-Saturday, potentially changing over to rain Sat, especially east of I-95. Any snow accumulation likely to be minor.

* Another shot of arctic air Sun night into Tue with well below normal highs and very chilly nights in teens/single digits.

Details...

Friday Night & Saturday:

High pressure shifts offshore by Friday night as a weak shortwave trough approaches southern New England. An associated surface low tracks off the mid-Atlantic coast, passing to the south and east of the region Friday into Saturday. This will bring the risk for some scattered snow or rain showers. Without a strong, anchored cold air mass, there is a chance for rain to mix in, potentially changing to rain showers (Inside I-95, SE MA) in the afternoon. Snow accumulations will be light with ensembles means showing amounts less than an inch. Total QPF is on the light side as well (< 0.25") with the highest chances for precip (rain) for the Cape/Islands. Model guidance continues to show an inverted trough positioned across the region late Fri into Sat with subtle hints of convergence in the wind fields. This could potentially provide better forcing for a more organized band of precipitation. Can't rule out a brief deformation-type band on the backside of the system later Saturday as cooler air pushes in from the west. Details still to be ironed out for timing of these more organized bands of showers and precip type. Temperatures will lean slightly below normal Saturday in the 30s and low 40s for the Cape/Islands.

Sunday through Wedneday:

Another weak shortwave in the zonal flow aloft moves through Sunday, with another arctic front sweeping across Sunday night-early Monday. Most of Sunday should be dry with highs in the mid-upper 30s and low 40s for the Cape/Islands. Can't rule out a snow shower/flurry Sunday night with the passage of the arctic front. No concerns for impacts.

Below normal temperatures and breezy NW winds on Monday with highs in the 20s to low 30s and wind chills in the teens. Below normal temperatures continue Tuesday, although slightly moderated from Monday with highs in the mid-upper 20s for the higher elevations and 30s elsewhere. Confidence in the pattern decreases toward mid-week, but there are indications of a another weak disturbance moving through later Tuesday into Wednesday with potential for showers. Details are still uncertain (timing, amounts, precip type), but will become more clear as we gain a better consensus on the upper level pattern.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

12Z TAF Update...

Today and Tonight...High confidence. Moderate for snow shower chances.

Mainly VFR conditions. An arctic cold front may bring a few snow showers and the low chance for a localized snow squall or two in the afternoon. This would bring brief localized lower cigs/vsbys. Due to the very scattered nature of the showers, confidence isn't high enough to include snow showers in TAF. Highest chances for seeing a shower/flurry or isolated squall will be in the afternoon, with western MA having the highest chance for localized squalls.

WSW winds today with gusts 20-25 kts. Front moves through 18-22Z with winds shifting to WNW/NW with gusts increasing to 25-35 kts. Winds gradually diminish late Thursday night into early Friday.

Friday...High confidence.

VFR. Light winds becoming SW at 5-10 knots.

KBOS Terminal...High confidence in TAF. Low for SNSH chances.

KBDL Terminal...High confidence in TAF. Moderate for SNSH chances.

Outlook /Friday Night through Monday/...

Friday Night: Mainly VFR, with local MVFR possible. Slight chance FZRA, slight chance SN.

Saturday: Mainly VFR, with local MVFR possible. Chance RA, chance SN, chance FZRA.

Saturday Night through Sunday: VFR.

Sunday Night: VFR. Breezy. Slight chance SN.

Monday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

Today through Friday...High confidence.

* Gale Warnings this afternoon and tonight

The main concern will be an arctic cold front that crosses the region today. This will bring NW wind gusts of 30 to 40 knots this afternoon and tonight. This has prompted the issuance of Gale Warnings for our waters given excellent mixing given the amount of cold air crossing the relatively warm waters. High pressure quickly builds in from the west Fri allowing winds/seas to diminish significantly.

Outlook /Friday Night through Monday/...

Friday Night: Winds less than 25 kt. Chance of rain, slight chance of freezing rain.

Saturday: Winds less than 25 kt. Chance of rain.

Saturday Night: Winds less than 25 kt. Slight chance of rain.

Sunday: Winds less than 25 kt.

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

Monday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Slight chance of snow.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Gale Warning from 4 PM this afternoon to 1 AM EST Friday for ANZ230-236. Gale Warning from 1 PM this afternoon to 4 AM EST Friday for ANZ231>235-237-250-251-254>256.