textproduct: Boston / Norton

WHAT HAS CHANGED

Small Craft Advisories extended for some waters into Friday. Cold front moving across our region late tonight into Friday could allow for hit-or-miss showers or even a rumble of thunder tonight for some.

KEY MESSAGES

- Cold front moves across our region late tonight into midday Thursday. Expecting falling temperatures through the day. Even a risk for minor snow accumulation across interior southern New England, depending on the timing of the subfreezing air.

- Light snow Friday PM. Minor accumulations possible for higher elevations. Gusty winds Saturday.

- Widespread rain with locally heavy rainfall Sunday night into Monday which may lead to minor river flooding. Another period of gusty winds Monday.

DISCUSSION

KEY MESSAGE 1...Cold front moves across our region late tonight into midday Thursday. Expecting falling temperatures through the day. Even a risk for minor snow accumulation across interior southern New England, depending on the timing of the subfreezing air.

Much of our weather into Thursday will depend on the timing of a cold front moving past southern New England. Expecting scattered showers for most, with the possibility of a thunderstorms closer to the cold pool aloft moving across the Great Lakes into northern New England. Once this front moves on by, colder air should arrive. Air cold enough to result in falling temperatures during the daytime. That said, expecting low temperatures to return to near normal for mid March by Thursday night.

Thinking showers will be most widespread across our region after midnight into mid morning Thursday. Depending on how quickly temperatures fall, there is the possibility for light snow across the higher terrain towards the Berkshires mainly, but perhaps also into the Worcester Hills. Conditions should be drying as this snowfall develops, so not expecting much more than a coating to an inch.

KEY MESSAGE 2...Light snow Friday PM. Minor accumulations possible for higher elevations. Gusty winds Saturday.

Mainly dry conditions expected on Friday with seasonable temperatures. Next shortwave trough is expected to move through the region Friday night into Saturday. Model guidance shows a signal for marginal moisture to push into the region ahead of the wave. Scattered showers are possible Friday afternoon and Friday night. These showers are more likely to be snow showers for the high elevations. Rain/snow mix is possible for the lower elevations. Any accumulations are likely to be light. Generally up to an inch for northwest/north-central MA higher elevations, perhaps locally higher amounts for the highest elevations of the northern Berkshires. Elsewhere, a coating to a half an inch is more likely for the remainder of MA, northern CT (excluding the Cape). A cold front swings through overnight into Saturday morning. A moderate jet and enhanced gradient along with CAA will allow mixing down of stronger winds aloft to the surface. There is some uncertainty among guidance on how strong the jet will be. Gusts 35-45 mph are possible with the higher winds across the higher elevations and Cape/Islands. There are moderate probabilities 50-60% for gusts greater than 45 mph for the highest terrain of the Berkshires and Worcester Hills. Something that we will have to keep an eye on for potential Wind Advisory headlines.

KEY MESSAGE 3... Widespread rain with locally heavy rainfall Sunday night into Monday which may lead to minor river flooding. Another period of gusty winds Monday.

A shortwave trough approaches the region Sunday with a LLJ ahead of it. This will shift winds southwest and help advect in moisture rich air northward into southern New England. Moisture will be fairly above normal with precipitable water amounts 200-280% of normal. Marginal instability associated with this system along-side the anomalous precipitable water values raises the potential for locally heavy rainfall, convective cells, and perhaps an isolated thunderstorm embedded in the rain. Ensemble probabilities for greater than 1" of rain range from 30-60% generally. The ECMWF ensemble members are leaning wetter than the GEFS, even highlighting higher probs closer to 70% for RI, CT, and SE MA for 1" or greater of QPF. Upper percentiles for total QPF run 1 to a little over 2" across ensemble guidance. This does raise concern for rising river/stream levels from snowmelt and additional rain. MMEFS ensemble guidance shows potential (40-60%) for rivers reaching minor flood levels early next week (Pawtuxet, Taunton, Pawcatuck rivers). Low probs to reach minor flood along the lower reaches of the mainstem Connecticut River from Hartford through Middle Haddam.

A strong southerly LLJ shifts across the region Monday. This will produce gusty south winds. There is uncertainty in the degree of mixing we will get to the surface from that LLJ, so the magnitude of gusts remains less certain. Regardless, it will likely be generally gusty Monday with milder temperatures.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

Forecaster Confidence Levels...

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

Moderate confidence.

IFR stratus lingering across the waters east of MA. This stratus should move farther onshore as we approach and get past sunset. Elsewhere, VFR with areas of MVFR in rain showers ahead of a strong cold front. Probability of TSRA at this point is 15-25% during the 11/02-06z timeframe, so have left explicit mention of TS out of the TAFs at this point. Powerful SW low-level jet of 40-50 kt about 015-020 should impact most terminals late this evening into early morning Thursday. LLWS should be over by the Thursday morning push.

As we get into Thursday morning, a front will swing through the region, and VFR conditions are expected to develop after the front along with surface winds turning more W, with gusts over 20 kt at times.

KBOS Terminal...Moderate confidence in TAF. Stratus is literally just east of the terminal and could move over at just about any time now. Latest satellite showed a little bit of a wake effect with Cape Ann. Delayed the onset of the lower clouds bases by a couple more hours.

KBDL Terminal...Moderate confidence in TAF. Expect MVFR conditions to develop by 01z, but it could be earlier. Uncertainty in the specific timing of SHRA and perhaps a brief TSRA late today/this evening. Confidence of TS is too low to include in TAF at this point, but could occur between 00-05z time.

Outlook /Friday through Monday/...

Friday: VFR. Breezy. Slight chance RA.

Friday Night: Windy with local gusts up to 30 kt. Chance RA.

Saturday: Windy with gusts up to 30 kt.

Saturday Night: Breezy.

Sunday: Breezy. Slight chance RA.

Sunday Night: Strong winds with local gusts up to 40 kt. Chance RA, chance FZRA, slight chance TSRA.

Monday: Strong winds with areas of gusts up to 45 kt. 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. A cold front moving across the waters late tonight into Thursday will also generate gusty SW winds at times until it passes. Poor visibility at times in fog expected tonight, and also the risk for a few showers. Becoming clearer with gusty W to NW winds Thursday into Thursday night.

Outlook /Friday through Monday/...

Friday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft.

Friday Night: Strong winds with gusts up to 35 kt. Areas of rough seas. Chance of rain.

Saturday: Strong winds with gusts up to 35 kt. Rough seas up to 11 ft.

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

Sunday: Winds less than 25 kt.

Sunday Night: Strong winds with gusts up to 40 kt. Areas of rough seas. Rain likely, slight chance of thunderstorms.

Monday: gale force winds with gusts up to 45 kt. Rough seas up to 13 ft. Rain.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 8 PM this evening to 7 PM EDT Thursday for ANZ232-233. Small Craft Advisory from 8 PM this evening to 1 PM EDT Thursday for ANZ234. Small Craft Advisory from 8 PM this evening to 7 AM EDT Friday for ANZ235-237-250-254>256.