textproduct: Boston / Norton

SYNOPSIS

Overcast today with very light snow or rain showers during the first part of the day before clouds decrease in the evening. Another round of scattered showers is possible in the afternoon. Arctic front moves through overnight Sunday into Monday morning with a some brief scattered snow showers possible. Well below normal temperatures Monday before slowly moderating Tuesday/Wednesday. More unsettled overall next week with a few disturbances moving through bringing periodic chances for rain/snow showers late Tue-Wed and Wed- Thu.

NEAR TERM /UNTIL 6 PM THIS EVENING/

Key Message:

* Scattered snow/rain showers possible early this morning and in the afternoon

* Cloudy conditions for most of the day

A warm/moist air advection pattern continues through today with light southerly flow. Temperatures this morning have been improving from the earlier nighttime hours as a result, and should continue to do so through the day today. Improvement will be limited by mostly overcast conditions across the region, but highs should at reach the mid 30s today for most with low 40s possible for the Cape and Islands.

Showers this morning over Long Island haven't moved much northeast, however some echoes are starting to pop up along the south coast where some surface fgen sits as of 2 AM. Light snow showers with occasional drizzle mixed in will be possible this morning through around noon across southern New England. No major impacts are expected with these showers; at most, some drizzle freezing to the surface could lead to some slick spots on the roads this morning. But given the latest radar data and forecast soundings, confidence is lower in more persistent bands of precipitation developing that would lead to this. Spotty showers of snow and rain are the primary expectation this morning. CAMs indicate the chance for some showers over eastern MA and Cape Cod for the afternoon as well, but confidence in spatial extent and exact timing is not as high.

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

Key Messages:

* Clearing skies and dry conditions with light WNW winds overnight

* Partly sunny through the day ahead of a disturbance approaching from the Great Lakes

Skies clear a bit heading into tonight with drier air aloft flowing in. Light WNW winds prevail as well as the warm air advection pattern starts to come to an end. 925 mb temperatures fall towards - 5C again overnight. Lows are expected to be in the upper teens in the interior and in the low to mid 20s elsewhere, aside from the outer Cape where temperatures should be closer to freezing. With most everyone falling below freezing again tonight, any melting snowpack will most likely refreeze.

Another shortwave disturbance moves east from the Great Lakes region during the day Sunday, but we shouldn't see impacts from it until the evening/overnight hours. Ahead of this shortwave, cloud cover will increase and NW winds will remain weak before shifting more southerly in the evening. Highs Sunday should be similar to today, reaching the mid 30s and low 40s ahead of an arctic front.

LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/

Key Messages:

* More arctic air arrives Sunday night into the early part of next week.

* Few snow showers possible Sun night-early Mon. Very light accumulations, if any (< 1.0").

* Periodic chances for precipitation next week (Tue-Wed & Wed-Thu), exact timing, amounts lower confidence.

Details...

A weak mid-level shortwave trough is expected to move through the region Sunday night into Monday morning. Deterministic/ensemble guidance has come into better agreement on the details of the system. Lack of forcing and moisture will keep this as a lighter precipitation evening. However, the arctic front should provide enough lift to support showers as it drops across southern New England late Sun night into early Monday morning. Ensembles indicate mainly low-moderate (15-50%) probabilities for greater than 0.01" of liquid precipitation with the higher chances north of the Mass Pike. Overall this means scattered snow showers are possible with the passage of the arctic front. Accumulations are likely to be very light with ensembles displaying zero to low probs of snow greater than an inch, so perhaps a quick trace to a few tenths for the higher elevations of MA. A strong arctic front will follow bringing another shot of arctic air into the region.

Arctic airmass will continue to advect into the southern New England on Monday with 850mb temperatures falling to -15 to -18C. This will support well below normal high temperatures in the 20s and low 30s for the Cape/Islands. There is also a signal for gusty winds to develop Friday with a LLJ/tightened gradient positioned over the region. The overall strength of the LLJ varies across model guidance, but there is a good consensus that with the help of the CAA, there should be ample mixing of higher winds aloft to the surface. Gusts 25-35 mph are most likely, but will have to keep on eye on the strength of the LLJ and depth of mixing to see if there is potential for highs gusts (up to 40 mph) in areas such as the Cape. The added wind will make it feel considerably colder, potentially bringing wind chills into the teens and low 20s. Mainly dry conditions with the exception of a few ocean- effect showers for the Cape/Islands. Monday night will be a chilly one thanks to optimal radiational cooling under the well below normal airmass. Temperatures will likely drop into the single digits for most of the interior and teens for the coastal areas.

Temperatures moderate Tuesday with flow from the SW. Highs still lean a little below normal in the mid/upper 20s for the higher elevations and 30s elsewhere.

Confidence in the pattern decreases toward mid-week. There is a consensus among ensembles for quasi-zonal flow aloft with a few embedded disturbances moving through. However, there still are differences in the details in the timing/amounts. This should bring periodic chances for showers through the week with the first shot at some showers later Tuesday and another round of more widespread chances late Wednesday into Thursday. Precip type will become more clear as we gain more details about the system track, but temperatures lean warmer for Wednesday (rain or rain/snow showers higher up). Highs Wednesday range in the upper 30s to mid 40s. Stay tuned for updates.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

Forecaster Confidence Levels...

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

12Z TAF Update:

Today...Moderate confidence.

Low end VFR to MVFR stratus. Widely scattered light showers both SN and RA ending by mid afternoon. Confidence is moderate regarding exact ptype. Accumulating or measurable precip isn't expected with either type. TEMPOs and VCSHs included across the region for spotty coverage of precip.

MVFR stratus improves to VFR levels between 16-18z from west to east, 19-22z for BOS, and 22-01z for Cape/Islands. Light southerly winds shifting SW/SSW this morning, then shifting to light WSW/W accompanying the improvement to VFR.

Tonight...High confidence.

VFR. W to NW winds around 5 kt. Low chance for patchy fog in the valleys.

Sunday...High Confidence.

VFR. NW winds 5-10 kts.

KBOS Terminal...Moderate to high confidence in TAF. MVFR. Very light SN possible through 15z-18z, with potentially a last round of showers early afternoon. No accums are expected and any -FZDZ probably not persistent enough for runway impacts. MVFR cigs improve to VFR after 19z.

KBDL Terminal...Moderate to high confidence in TAF. MVFR. Very light SN possible through 16z. No accums are expected and any FZDZ probably not persistent enough for runway impacts. MVFR cigs improve to VFR after 16z. Low visbys possible for bands of SN.

Outlook /Sunday Night through Wednesday/...

Sunday Night: VFR. Breezy. Slight chance FZRA, slight chance SN.

Monday: VFR. Breezy. Slight chance FZRA.

Monday Night through Tuesday: VFR. Breezy.

Tuesday Night: VFR. Breezy. Slight chance SN.

Wednesday: Mainly VFR, with local MVFR possible. Breezy. Chance RA, slight chance SN.

MARINE

Forecaster Confidence Levels...

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

Tranquil boating conditions expected through Sun, with winds and seas below small craft advisory thresholds. Light S winds continue into most of today, then become NW tonight around 10-15 kt. Seas 3 ft or less all waters thru Sun.

Outlook /Sunday Night through Wednesday/...

Sunday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas locally approaching 5 ft. Chance of snow, slight chance of rain, slight chance of freezing rain.

Monday: Strong winds with gusts up to 30 kt. Seas up to 5 ft. Slight chance of freezing rain, slight chance of snow.

Monday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas.

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

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

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

TIDES/COASTAL FLOODING

Coastal Flood Statement issued for this morning's high tide cycle along the eastern MA coast and Nantucket due to astronomical king tides. This is expected to be marginal as winds and swell aren't as favorable. Some splashover and some minor coastal flooding are possible in low lying areas/roads.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...None.