textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes. Becoming more confident in springtime warmth, especially Tuesday, along with the potential for minor river flooding within the next 7 days.

KEY MESSAGES

- A brief round of showers, and perhaps a rumble of thunder, late tonight into very early Sunday morning.

- Above normal temperatures next week. Trending more unsettled mid to late week with a round or two of precipitation possible.

- Expecting significant snowmelt over the coming week. Minor river flooding possible.

DISCUSSION

KEY MESSAGE 1...A brief round of showers, and perhaps a rumble of thunder, late tonight into very early Sunday morning.

Southern New England remains on the cool side of a warm front tonight, until a cold front passes by late Sunday. This gives our region a brief period of time within the warm sector of a low pressure moving east across northern New England Sunday.

Areas of fog and patchy drizzle finally ended for a time this afternoon, but are likely to return later tonight. With dew points expected to remain above freezing through Sunday, we're looking at continued snow melt during this time.

Expecting a round of rainfall ahead of a pair of fronts starting late this evening before winding down from west to east during the day Sunday. It could be late afternoon before this rainfall finally clears the Cape and islands. While it's not impossible for there to be a few rumbles of thunder given the observed convection farther to our west, thinking the time of day and year does not favor thunderstorms across southern New England and left them out of this forecast.

KEY MESSAGE 2...Above normal temperatures next week. Trending more unsettled mid to late week with a round or two of precipitation possible. Minor river flooding possible.

A thermal ridge is expected to build in further from the south next week bringing light S/SW winds. In response, 850mb temperatures rise to 10-15C through the week, supporting above normal temperatures. Highs will likely rise into the upper 50s and 60s Monday through Thursday for many spots. Tuesday will likely be the warmest day with highs in the 60s with a some interior/valley areas potentially approaching 70. This runs round 20-25 degrees above normal. Immediate coastal areas will run a bit cooler, especially along the immediate south coast and the Cape and Islands given the onshore southerly component flow. Those mentioned areas will more likely stay in the 40s and 50s. Some guidance continues to hint at the potential for a backdoor front later Wednesday which could bring down temperatures, at least in northeast MA. Highs will depend on how far south this front extends.

The pattern trends more unsettled Wednesday onward with the passage of a few shortwave troughs bringing a few rounds of precipitation through late week. There is still uncertainty in the timing/coverage of showers on Wednesday. Thursday's wave will be more organized with a stronger cold front accompanying it. This will support more widespread precipitation later Thursday, likely rain to start, with potential snow mixing in for the higher terrain as the front works through.

KEY MESSAGE 3...Expecting significant snowmelt over the coming week. Minor river flooding possible.

The extended period of warmer conditions does raise concern for rises in rivers/streams from the quicker melting of snowpack. Ensemble guidance indicates rising river/stream levels through the week. Ensembles show some locations, particularly on the CT and Merrimack Rivers, reaching at least action stage, if not minor flood stage within the next week. By late next week, ensemble guidance indicates 40-60% probabilities for CT river locations to exceed minor flood stage and low probabilities (< 15%) for moderate flood stage.

For some rivers across RI and eastern MA (e.g. Taunton River at Bridgewater), snowmelt could lead to potential minor flooding as early as Monday or Tuesday. We will also need to watch some of the smaller rivers, such as the Pawcatuck River at Westerly, the Assabet River at Maynard and the Shawsheen River at Wilmington for possible flooding later next week.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

Through Tonight...Moderate confidence.

IFR/LIFR conditions dominate through tonight. SSW surface winds 8-15 knots with some 20+ knot gusts through the afternoon and evening. Cigs/vsbys improve very slightly to IFR levels in some locations away from the south coast this afternoon and evening. However...LIFR conditions will be favored near the south coast where advection fog, dense at times, will impact areas near the south coast, Cape and Islands.

A band of of showers will approach western MA/CT after 03z/04z tonight and may reach the coastal plain 06z/07z. While the showers will be undergoing a weakening trend...they still may survive in some form and reach the coast. Perhaps even an isolated rumble of thunder. S-SW winds will gust between 15 and 25 knots. We also will have LLWS in the TAFS given an 850 mb southwest LLJ on the order of 55-70 knots.

Sunday...High confidence in trends with moderate confidence in timing.

Gradual improvement will occur on Sunday with many locations eventually improving to VFR by mid afternoon...except for areas near the south coast, Cape & Islands where low clouds and fog may persist. SW winds should shift to the W at 10 to 15 knots.

Sunday Night...High confidence.

VFR with light WSW winds.

KBOS Terminal...Moderate confidence in TAF.

Moderate confidence in overnight visby's. Wind speed performance has been below model guidance today, so if gusts don't kick in this evening then visby's will likely drop rapidly after sunset.

KBDL Terminal...High confidence in TAF.

Outlook /Monday through Thursday/...

Monday: VFR. Breezy.

Monday Night through Tuesday: VFR.

Tuesday Night:

Wednesday: Breezy. Chance RA.

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

Thursday: Windy with gusts up to 30 kt. Chance RA, SN likely.

MARINE

Forecaster Confidence Levels...

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

Today through Sunday Night...High confidence.

Lingering rough seas across the outer waters through this weekend. In addition, a period of southwest wind gusts of 20 to 30 knots tonight into Sunday morning for most of our waters. Therefore, Small Craft Advisories continue for most souther New England Waters.

Lastly, areas of fog and poor visibility will be an issue for mariners this entire weekend, especially near the south coast.

Outlook /Monday through Thursday/...

Monday through Monday Night: Winds less than 25 kt. Areas of seas approaching 5 ft.

Tuesday through Tuesday Night: Winds less than 25 kt.

Wednesday: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain.

Wednesday Night: Strong winds with gusts up to 30 kt. Seas up to 5 ft. Chance of rain.

Thursday: Strong winds with gusts up to 35 kt. Rough seas up to 11 ft. Chance of rain.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory from 6 PM this evening to 10 AM EST Sunday for ANZ231-234. Small Craft Advisory from 6 PM this evening to 7 PM EST Sunday for ANZ232-233. Small Craft Advisory from 6 PM this evening to 1 AM EST Monday for ANZ235-237. Small Craft Advisory until 10 PM EST Sunday for ANZ250. Small Craft Advisory until 1 PM EST Sunday for ANZ251. Small Craft Advisory until 7 AM EST Monday for ANZ254>256.