textproduct: Boston / Norton

SYNOPSIS

An approaching warm front will bring a period of light rain tonight into Thursday morning, with pockets of mixed wintry precipitation possible across northern MA tonight. Milder conditions arrive Thursday into Friday, with a stalled front possibly bringing a few showers near the south coast Thursday night into early Friday. Unsettled conditions continue this weekend, as a frontal system impacts the region, with cooler temperatures Saturday followed by milder conditions Sunday. Saturday appears to be the wetter of the two days. Drying out Monday, as the frontal system exits the region, along with cooler than normal temperatures overspreading the area much of next week.

NEAR TERM /UNTIL 6 AM THIS MORNING/

740 PM update...

Forecast remains on track. WAA precip overspreading the region from the west. Airmass is initially dry, so leading edge of precip shield is partially evaporating before reaching the ground. This is also resulting in evaporative cooling thru the column, yielding some ice pellets mixing in with the rain at KALB. Although, with surface temp there at 43F, no impacts. Eventually, mid level warm nose climbs to +6C, too warm to support sleet. Thus, all rain overnight, with the only exception across the high elevations of western/central MA, where temps may lower to near freezing, supporting some spotty freezing rain at elevations above 1,000 ft. This remains a low prob, thus no changes to the forecast. Farther south across CT/RI and SE MA, less rainfall expected with best WAA farther northward. Earlier discussion below.

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Key Messages:

* Periods of rain developing tonight

* Pockets of mixed wintry precip across the interior with spotty freezing rain possible over the higher elevations. Any travel impacts will be limited.

Higher clouds were already starting to arrive ahead of an approaching warm front, While the surface part of this front will probably not reach southern New England by daybreak Thursday, there will be plenty of warm air higher up. Most model soundings had peak warm nose temperatures of 4-6C. These soundings also showed a 4-6km deep layer of colder air beneath that warm nose. Overall, this should result in a period of sleet between about 8 PM to 1 AM before transitioning to all rain the rest of the night. Rainfall amounts for most anticipated to be between 0.10-0.50 inches.

The other possibility is freezing rain. We had plenty of sunshine today, which should mean surface, not the standard air, temperatures well above freezing. The areas which would support this precipitation type should be isolated. With limited impact of icing this time of year, opted to not issue Winter Weather Advisories for either the freezing rain or sleet. The main areas of concern will be the higher terrain of the Worcester Hills and towards the Berkshires.

SHORT TERM /6 AM THIS MORNING THROUGH 6 PM FRIDAY/

Key Messages:

* Milder Thu with rain becoming more spotty in the afternoon

The approaching warm front should finally move to our north during the day Thursday. This will lead to well above normal temperatures. Any precipitation should be in the form of rain. Once our region gets into the warm sector, then the rainfall chances become more spotty by late morning into the afternoon. A weak cold front should then try to pass through Thursday night.

One forecast concern is temperatures, and the corresponding impact on winds. Should more sunshine develop than currently forecast, we likely get deeper boundary layer mixing. With a 40-50 kt low level jet at 925 mb, that could lead to stronger winds than currently forecast, which is closer to the 90th percentile of the NationalBlend guidance but still below Wind Advisory thresholds. Forecast high temperatures in the 60s away from the immediate coasts could reach the 70s in a few spots.

Drying out from north to south behind the aforementioned weak cold front.

LONG TERM /FRIDAY NIGHT THROUGH WEDNESDAY/

Long Term

Key Messages

* Cooler on Saturday followed by increasing warmth and shower chances Saturday night into Sunday

* Unsettled early next week with seasonable temperatures

Saturday through Sunday night.

High pressure builds north and east of southern New England Friday night into Saturday. This will allow a backdoor cold front to advect cooler air into the region with 925 hPa temps dipping near the freezing mark by Saturday morning. This will support a cool/raw day with highs peaking in the mid to upper 40s for much of southern New England. Saturday will as mark the beginning of a wet/unsettled period for the forecast area that will carry into next week. As the aforementioned area of high pressure continues to shift east, return flow from the south will support WAA driven showers over southern New England likely beginning Saturday afternoon. Expect precipitation to persist through Sunday as the associated low- pressure system traverses over The Northeast Saturday night through Sunday evening.

As warm sector air lifts over the region on Sunday, 925 hPa temps rise dramatically to the 15 to 20C range. So while Sunday is expected to be wet/rainy, it will also be on the warm/humid side with temperatures in the low to mid 60s and dewpoints in the 50s. Ensemble mean precipitation forecasts for Saturday afternoon through Sunday night are ranging from 0.75 to 1 inch across southern New England. Some of this precip may come in the form of convective showers Sunday night as the associated cold front drives the warm sector air out of the region. Model derived CAPE values are unimpressive at this time, but with ensemble mean SBCAPE values around 250 J/kg, a few showers could have a rumble of thunder, particularly along the south coast.

Monday through Wednesday

Showers associated with a passing cold front exit off the east coast early Monday. Despite the dry/northwest flow that will follow, unsettled weather looks to continue Monday and Tuesday as a second pulse of short-wave energy digs east over The Midwest toward southern New England. Moisture will be lacking, so while we aren't anticipating any substantial precipitation from this short-wave, we do expect more clouds than sun with some sporadic showers. Temperatures looks to be seasonable with ensemble means supporting highs/lows in the upper 40s to 50s and mid to upper 30s respectively Monday and Tuesday. Details become vague as we reach the middle of next week, but there is strong support from ensembles for below normal temperatures as a broad upper-level trough is expected to bring a surge of cooler air to the Northeast for the midle of next week.

AVIATION /06Z THURSDAY THROUGH MONDAY/

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

06Z update

Through 12Z...High Confidence

Ceilings conitnue to fall to MVFR/IFR by 12Z with -SHRA and steady south/southeast winds from 10 to 15 knots.

Thursday...Moderate Confidence.

Mainly IFR/MVFR with -SHRA in the morning becoming more spotty in the afternoon. Increasing SW winds with gusts to 25-35 kt developing.

Thursday Night...Moderate Confidence.

IFR/MVFR improving to VFR from NW to SE with passage of a cold front.

Friday... HIgh Confidence

VFR. West/northwest winds around 10 knots.

BOS TAF...High confidence

BDL TAF...High confidence

Outlook /Friday Night through Monday/...

Friday Night: VFR.

Saturday: Mainly MVFR, with local IFR possible. SHRA.

Saturday Night: MVFR/IFR conditions possible. Breezy. SHRA.

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

Sunday Night: Mainly MVFR, with local IFR possible. Breezy. SHRA likely.

Monday: MVFR/IFR conditions possible. Breezy. Chance SHRA.

MARINE

Forecaster Confidence Levels:

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

Winds and seas briefly diminish late this afternoon and early evening. Increasing SE winds then develop overnight, building seas once more. Considered gale force gusts during Thursday, but have more confidence in strong Small Craft Advisory conditions. Staggered the timing through tonight into Thursday. Winds should diminish closer to sunset, but rough seas likely to linger across the outer coastal waters.

Greater risk for reduced visibility in showers and fog across the waters east of MA than the southern waters. A warm front should move past the waters Thursday, with a cold front passing the waters late Thursday night.

Outlook /Friday Night through Monday/...

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

Saturday: Winds less than 25 kt. Seas locally approaching 5 ft. Chance of rain showers.

Saturday Night: Winds less than 25 kt. Seas up to 5 ft. Rain showers.

Sunday: Winds less than 25 kt. Areas of rough seas. Chance of rain showers.

Sunday Night: Winds less than 25 kt. Areas of rough seas. Rain showers likely.

Monday: Winds less than 25 kt. Areas of rough seas. Chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...Small Craft Advisory from 10 AM this morning to 10 PM EDT this evening for MAZ020-021. RI...None. MARINE...Small Craft Advisory from 10 AM this morning to 7 PM EDT this evening for ANZ230. Small Craft Advisory from 7 AM this morning to 10 PM EDT this evening for ANZ231. Small Craft Advisory from 7 AM this morning to 1 AM EDT Friday for ANZ232-234. Small Craft Advisory from 7 AM this morning to 7 AM EDT Friday for ANZ233. Small Craft Advisory until 7 AM EDT Friday for ANZ235-237-255. Small Craft Advisory from 10 AM this morning to 7 AM EDT Friday for ANZ236. Small Craft Advisory from 5 AM early this morning to 7 AM EDT Friday for ANZ250-254. Small Craft Advisory from 5 AM early this morning to 10 PM EDT this evening for ANZ251. Small Craft Advisory until 7 AM EDT Friday for ANZ256.