textproduct: Boston / Norton

WHAT HAS CHANGED

Confidence continues to grow in the likelihood for at least some wind headlines Saturday. Otherwise, no significant changes.

KEY MESSAGES

- Dry & seasonably cool today. A few brief passing rain/snow showers tonight with focus across northern MA.

- Strong westerly wind gusts of 35-55 mph on Sat...Wind Headline will likely be needed at least for parts of the region.

- A period of heavy rainfall, strong winds and unseasonably mild temps Mon into Mon night. Some river and small stream flooding expected.

- Trending colder with mainly dry weather Tue through Thu.

DISCUSSION

KEY MESSAGE 1...Dry & seasonably cool today. A few brief passing rain/snow showers tonight with focus across northern MA.

Post frontal/dry airmass overspreading the region early this morning, on gusty NW winds 25 to 35 mph during the predawn hours. Strong CAA with 850 mb temps lowering to -10C to -12C early this morning, yielding lows in the 20s before sunrise, along with colder wind chills. Although, partly to mostly sunny conditions later this morning, combined with diminishing winds will take the edge off the cool temps. Highs this afternoon will be in the 40s, which is just about on track for this time of year. Fast/progressive flow aloft yields a WAA pattern overspreading the region this afternoon, yielding increasing clouds and SW winds increasing 15-20 mph. Hence, morning hours brighter than the afternoon.

A shortwave and associated warm front will likely bring a few brief passing rain/snow showers to the region tonight...particularly across northern MA.

KEY MESSAGE 2...Strong westerly wind gusts of 40-50 mph on Sat. Wind headlines will likely be needed at least for parts of the region.

Mainly dry weather Saturday, with partly to mostly sunny conditions, but windy and chilly. Deepening low over the maritimes will yield a strong pgrad along with strong CAA. Increasing March sun angle will combine with strong CAA to yield steep low level lapse rates. Model soundings support WNW winds gusting up to 40 to 50. Thus, wind headlines may be required. Given the aforementioned attributes, our wind forecast incorporates some of the higher guidance (NBM 90 percentile), supporting wind gusts up to 40-50 mph at times Sat. Seasonably cool with highs in the mid to upper 40s, but feeling much cooler given the strong winds.

KEY MESSAGE 3...A period of heavy rainfall, strong winds and unseasonably mild temps Mon into Mon night. Some river and small stream flooding expected.

Guidance has trended a bit slower with the heavy rainfall and wind event and is more focused in the Monday to Monday night period. Initial wave of showers will overspread the region late Sun night into Mon associated with the low level jet and moisture transport lifting northward into the region. Winds will also ramp up in this period but the period of strongest winds and heaviest rainfall will likely come late Mon and especially Mon night with the second and stronger LLJ ahead of the advancing cold front. Wind and PWAT anomalies are 3-4 SD above normal which is a pretty strong signal for heavy rainfall and strong winds. The other wildcard is the potential for convective elements and a few t-storms and can't rule out a fine line of convection along the cold front Mon night given strong forcing for ascent and elevated instability. We are expecting 1-2 inches of rain with localized 3 inch amounts if convection gets involved. 90th percentile of the ensemble guidance is indicating up to 3 inches which would be a worst case scenario but think these higher amounts would be localized.

The expected rainfall amounts would be enough to cause flood concerns along some rivers and small streams. MMEFS ensemble guidance from the NAEFS continue to show several rivers reaching flood stage, especially the Pawtuxet, Pawcatuck and Wood Rivers in RI. Probs are 60-80% for minor flooding and there are even low probs (20-30%) of moderate flooding. Other rivers to watch for potential minor flooding include the Assabet River at Maynard, Deerfield River at West Deerfield and the lower reaches of the CT River from Hartford to Middle Haddam.

Regarding strong wind potential, while winds will be increasing Monday the greatest concern for a period of strong to damaging wind gusts will be Mon night ahead of the cold front. Some of the global guidance is indicating a 70-80 kt LLJ which is pretty impressive at this time range, but it's always a challenge determining how much wind will mix down to the surface with these southerly LLJ events. Temps will likely make a run at 60 or even lower 60s late Mon into Mon evening which would increase potential for strong to damaging gusts. Also, any fine line would help to mix down stronger winds. These are factors that we will have a better handle on this weekend.

KEY MESSAGE 4...Trending colder with mainly dry weather Tue through Thu.

Looks mainly dry on Tue but this will depend on the cold front moving to the east by Tue morning. If timing of fropa is further delayed it's possible showers could linger into Tue morning, especially in the east. Otherwise, drying out and turning cooler and blustery Tue behind the cold front. Core of coldest air aloft will be over New Eng on Wed which will be the coldest day of the week with highs mostly in the 30s, with slight moderation on Thu.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Forecaster Confidence Levels...

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

Today...High confidence.

VFR, though with increasing mid-level clouds as the day wears along. WNW winds becoming SW this afternoon at 7-13 knots.

Tonight...High confidence.

VFR dominates...but brief MVFR conditions possible mainly later tonight in a few brief passing rain/snow showers. Greatest risk for this will be across northern MA. Southerly wind gusts increasing to between 20 and 30 knot for a time overnight.

Saturday...High confidence.

Mainly VFR conditions expected outside a few brief passing rain/snow showers possible mainly in northwest MA. Westerly wind gusts of 30-40 knots with a few gusts up to 45 knots possible across the higher terrain.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Saturday Night through Tuesday/...

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

Sunday: VFR. Breezy.

Sunday Night: Mainly VFR, with local IFR possible. Windy with gusts up to 35 kt. Chance RA, slight chance FZRA.

Monday: Mainly MVFR, with areas IFR possible. Strong winds with gusts up to 40 kt. RA, isolated TSRA.

Monday Night: Mainly MVFR, with local IFR possible. Strong winds with gusts up to 45 kt. RA.

Tuesday: VFR. Windy with gusts up to 35 kt. Slight chance RA.

MARINE

Forecaster Confidence Levels...

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

Rough seas linger across the outer coastal waters into Friday morning. Winds expected to briefly diminish Friday afternoon, before increasing once more from the south Friday night.

Outlook /Saturday Night through Tuesday/...

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

Sunday: Winds less than 25 kt.

Sunday Night: Low risk for gale force winds with gusts up to 35 kt. Local rough seas. Chance of rain.

Monday: gale force winds with gusts up to 45 kt. Rough seas up to 16 ft. Rain, isolated thunderstorms.

Monday Night: gale force winds with gusts up to 45 kt. Rough seas up to 18 ft. Rain.

Tuesday: Strong winds with gusts up to 35 kt. Rough seas up to 13 ft. Chance of rain.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 AM EDT this morning for ANZ231>235-237-251. Gale Watch from Saturday morning through Saturday afternoon for ANZ232>235-237. Small Craft Advisory until 10 AM EDT this morning for ANZ250- 256. Small Craft Advisory until 4 PM EDT this afternoon for ANZ254- 255. Gale Watch from late tonight through Saturday afternoon for ANZ254>256.