textproduct: Boston / Norton

WHAT HAS CHANGED

Wind Advisories issued for Tuesday afternoon and evening across eastern Massachusetts and Rhode Island. Gale Warnings also issued Tuesday afternoon and evening for all nearshore waters.

KEY MESSAGES

- Windy Tue with unseasonably warm temps away from the south coast. Wind Advisory for the BOS-PVD corridor. Dry outside the low risk for a late Tue spot shower/t-stormm in NW MA.

- Periods of showers and t-storms arrive from west to east Wed and showers may persist into Thu for parts of the region.

- Turning sharply cooler late in the week and into the weekend with a few stray showers possible but mainly dry.

DISCUSSION

KEY MESSAGE 1...Windy Tue with unseasonably warm temps away from the south coast. Wind Advisory for the BOS-PVD corridor. Dry outside the low risk for a late Tue spot shower/t-storm in NW MA.

A slow moving cold front will approach the eastern Great Lakes as high pressure slides further east in the Atlantic on Tue. This will result in a strong southwest flow of unseasonably warm temperatures. 925T on the order of +18C/+19C northwest of I-95 should yield high temps in the upper 70s to the lower 80s. Strong southwest will yield much cooler temps towards the south coast...holding highs in the 60s to the lower 70s. In fact...Nantucket may not break 60!

It will also be quite windy on Tue with a strong southwest LLJ. The model guidance is indicating this 925 mb on the order of 50-60+ knots. The result will be southwest wind gusts of 30 to 45 mph developing by mid afternoon. In fact...a swath of 40-50 mph wind gusts seem reasonable in the vicinity of the I-95 corridor. This is on the northwest edge of the strongest jet and also where temps get warm enough for sufficient mixing. Therefore...we have hoisted a Wind Advisory across eastern MA/RI and onto the upper Cape from noon to 10 pm on Tue. The strongest of those winds are most likely in the 3 to 7 pm window.

Lastly...there is a low risk for a late afternoon-evening shower/t- storm or two across northwest MA with some marginal instability. However...the main threat for this will be well to our northwest given the lack of any real synoptic scale forcing.

While southwest winds will diminish some Tue night with the loss of diurnal heating...the southwest LLJ will maintain a gusty southwest breeze well into the overnight hours. This will result in an unseasonably mild night. Overnight low temps will only drop into the middle to upper 50s in most locations...except just a few degrees cooler near the south coast.

KEY MESSAGE 2...Periods of showers and t-storms arrive from west to east Wed and showers may persist into Thu for parts of the region.

A cold front approaches western MA/CT Wednesday evening/night and crosses the region fully by mid morning on Thursday. This will be the wettest stretch of the week as a plume of moisture and even some instability advects north into the region during the day on Wednesday in the warm sector. Warm is relative, though, as high temperatures will actually be quite a bit cooler than Tuesday in the upper 60s and low 70s. This, with dewpoints in the mid to upper 50s may lead to a few hundred J/kg of elevated CAPE, enough for some embedded thunder but not supportive of any severe weather. As the parent low exits to our northeast overnight a secondary low looks to form somewhere in the vicinity of our southern waters which may lead to a resurgence of moderate to heavy rain during the first part of Thursday. At this time, though, it is borderline, with some guidance indicating it forming too late/south to truly impact SNE. The best chance for Thursday moderate rain, though, would be the southern tier of the region. Ensemble guidance indicates the best chance (50- 70%) of AOA 0.1" of rain after 8am Thursday to be on Cape Cod and the islands, diminishing to the northwest with <20% chance in western MA. What's more certain is that temperatures will be cooler on Thursday in the post frontal airmass, in the low to mid 60s. This actually puts us right around normal for early May.

KEY MESSAGE 3...Turning sharply cooler late in the week and into the weekend with a few stray showers possible but mainly dry.

Beyond Thursday is when we get into the slightly below normal stretch of temperatures which persists through at least Saturday. High elevations likely don't make it out of the 50s. This, as a broad east coast trough remains overhead with below normal heights to start the weekend before things begin moderating toward next week. This trough with some weak disturbances rounding it may lead to a some scattered showers, especially over interior SNE but at the moment the forecast leans drier rather than wetter; in other words, some showers but not a washout. That being said, some guidance (the GFS in particular) hints at a more robust shortwave moving through which could through a wrench in that drier than wetter forecast for Saturday. Too soon to nail down these kind of details, stay tuned.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

Forecaster Confidence Levels...

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

00z TAF Update...

VFR conditions continue through Tuesday. Southwest wind gusts of 25 to 35 knots this afternoon with a few gusts near 40 knots will gradually diminish this evening. However...sustained southwest winds of 5 to 15 knots with a few 20+ knot gusts at times will continue overnight. SW wind gusts will strengthen again later Tuesday morning and especially Tuesday afternoon into the first half of Tuesday evening. SW wind gusts will increase on the order of 30-40 knots and a few gusts may reach 40-45 knots briefly especially near the I-95 corridor.

KBOS Terminal...High confidence in TAF.

KBDL Terminal...High confidence in TAF.

Outlook /Wednesday through Saturday/...

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

Wednesday Night: Mainly VFR, with areas IFR possible. Breezy. Chance SHRA, slight chance TSRA.

Thursday: VFR. Chance SHRA.

Thursday Night: VFR. Slight chance SHRA.

Friday: VFR. Breezy.

Friday Night: Mainly VFR, with local MVFR possible.

Saturday: Mainly VFR, with areas MVFR possible. Breezy. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

Tonight through Tuesday night...High confidence.

Near shore SW gale force wind gusts will diminish early this evening. However...another round of near shore SW gale force wind gusts is on tap for Tuesday afternoon and evening. Therefore...we have issued another set of nearshore Gale Headlines with strong small craft headlines persisting across the outer-waters.

Outlook /Wednesday through Saturday/...

Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Chance of rain showers.

Wednesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Rain showers, slight chance of thunderstorms.

Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers.

Thursday Night: Winds less than 25 kt. Local rough seas. Chance of rain showers.

Friday: Winds less than 25 kt. Local rough seas.

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

Saturday: Winds less than 25 kt. Local rough seas. Slight chance of rain showers.

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...Wind Advisory from noon to 10 PM EDT Tuesday for MAZ005>007- 013>022. RI...Wind Advisory from noon to 10 PM EDT Tuesday for RIZ002>007. MARINE...Gale Warning from 11 AM to 11 PM EDT Tuesday for ANZ230>237- 251. Gale Warning until 7 PM EDT this evening for ANZ231>234. Small Craft Advisory until 8 PM EDT Wednesday for ANZ250- 254>256.