textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes to prior forecasts.

KEY MESSAGES

- Scattered snow showers across portions of southern New England late today through midnight.

- Milder Wed, then spring-like Thu, followed by showers accompanying a cold front Thu night into early Fri.

- Behind the front, dry, but blustery and colder later Friday into Saturday

DISCUSSION

KEY MESSAGE 1...Scattered snow showers across portions of southern New England late today through midnight.

Fairly impressive shortwave aloft, that is also associated with a pocket of cold air (500mb temperatures colder than -30C) will rotate across the region this evening into early overnight. Although it's coming through overnight, the cold air aloft will be enough to generate enough instability for scattered snow showers to develop, with activity waning after midnight. Just like summer time convection, not everyone will see these snow showers. Snow Squall Parameter is not overly impressive (values just above 1), but suggests the better chances for any briefly heavier snow showers will be across the western half of the area. Points further east may just see flurries. Accumulations will be light (generally less than 1/2") and be confined to those localized areas that see the brief heavier bursts. No impacts to roads are anticipated.

On a side note, ahead of the main trough, a ribbon of vorticity aloft will result in a general area of light snow & rain that will traverse the region through 6pm, but also not have any real impacts.

KEY MESSAGE 2...Milder Wed, then spring-like Thu, followed by showers accompanying a cold front Thu night into early Fri.

Active upper air pattern will bringing a series of shortwave troughs through the region. The first short wave will move across the region Wed night. This first wave will have limited moisture and jet dynamics. Therefore, shower activity should be more scattered in coverage. Hence, not everyone will have measurable rainfall. WAA ahead of the short wave will result in milder temps Wed, with highs around 50, cooler near the south coast, in response to gusty SW winds. Morning sunshine likely gives way to afternoon clouds, in response to WAA pattern.

Then spring-like warmth Thursday ahead of the next short wave. Highs should rise to around 60 away from the south coast, given another day of SW winds. This second wave moves through Thursday night into early Friday and has more moisture and forcing for ascent. Therfore expecting showers Thu night into early Fri to be more widespread.

As previous forecaster noted, each shortwave (Wed ngt & again Thu ngt) will be accompanied by a robust low level SW jet. But given the timing, a nocturnal inversion will preclude these stronger winds aloft from mixing to the surface.

KEY MESSAGE 3...behind the front, dry, but blustery and colder later Friday into Saturday.

FROPA occurs sometime early Friday, followed by drier but blustery and colder conditions. Some of the model guidance (GFS & UKMET) advects -12C air at 925 mb temps across SNE 12z Sat! Not very spring- like, then again, March in New England. Lows in the teens and 20s, highs only 35-40 Saturday.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

18z TAF Update...

Moderate confidence through tonight, high confidence Tuesday.

IFR pretty much across the entire area. Have a mix of -DZ, -RA, or -SN depending on where you are. Through 22z or so, expect an area of light precipitation to trek from west to east across the region. This will produce -SN, mixing with -RA in lower elevations. As that moves off the coast, scattered snow showers are expected to develop and also traverse across the region through about 05-06z or so. Confidence in specific location and timing of those scattered snow showers is only at the level to use PROB30 lines in most of the TAFs.

Conditions should start to slowly improve to MVFR after 06z from west to east, and then VFR pretty much everywhere (except the Cape and Islands) by 12z. For the remainder of Tuesday, VFR conditions will prevail. Surface winds will start out from the NW and transition to SW and range from 8-12kts.

KBOS Terminal...Moderate confidence. Should see light precipitation in the form of a light RA/SN mix begin by 19z and last a few hours. Snow showers will be scattered about after that through 04-06z. Uncertainty if any impact BOS, however they would be short lived and given temperatures remaining above freezing, no accumulations are expected. Low probability of precipitation and IFR continuing through 10z, but not enough to include in the forecast. NW to SW winds on Tuesday, though some guidance suggests a brief onshore sea breeze will develop around 18z.

KBDL Terminal...Moderate confidence. Light precipitation through 21z gives way to scattered snow showers. Uncertainty if any impact BDL, but it's possible a coating of snow does occur.

Outlook /Tuesday Night through Saturday/...

Wednesday: VFR. Breezy.

Wednesday Night: VFR. Breezy. Slight chance RA.

Thursday: Mainly VFR, with local MVFR possible. Breezy. Slight chance RA.

Thursday Night: MVFR/IFR conditions possible. Breezy. RA likely.

Friday: VFR. Breezy. Slight chance RA.

Friday Night: VFR. Slight chance SN.

Saturday: VFR.

MARINE

Forecaster Confidence Levels...

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

Through Tuesday...High confidence.

Northerly winds that were gusty earlier today are slowly decreasing, and have taken down the Small Craft Advisories for Boston Harbor and Narragansett Bay. The trend will be for the winds to continue to diminish and then shift to NW later this evening. Winds continue to weaken Tuesday, and it's possible the SCA for the more outer waters will be taken down prior to Tuesday afternoon, although seas will remain a little rough beyond that time.

Outlook /Tuesday Night through Saturday/...

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

Wednesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain.

Thursday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Slight chance of rain.

Thursday Night: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Local rough seas. Chance of rain.

Friday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of rough seas. Chance of rain.

Friday Night: Winds less than 25 kt. Seas up to 5 ft. Slight chance of rain, slight chance of snow.

Saturday: Winds less than 25 kt. Seas locally approaching 5 ft.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ231>235-237. Small Craft Advisory until 2 PM EDT Tuesday for ANZ250-251- 254>256.