textproduct: Boston / Norton

WHAT HAS CHANGED

Only change was to increase probability of precipitation overnight with some isolated showers.

KEY MESSAGES

- Streak of well above normal temperatures Sunday through Wednesday. There is an increasing chance for record warm temperatures Tuesday and Wednesday. Isolated thunderstorms are possible Tuesday, some of which may be strong.

- Unseasonably warm Wednesday with scattered thunderstorms possible later in the day with some potentially strong to severe.

- Cooler, more seasonable temperatures late week.

DISCUSSION

KEY MESSAGE 1...Streak of well above normal temperatures Sunday through Wednesday. There is an increasing chance for record warm temperatures Tuesday and Wednesday. Isolated thunderstorms are possible Tuesday some of which may be strong.

Mainly dry and warmer for the rest of the day with high pressure largely in control of the weather pattern. A few widely scattered showers are possible overnight as a weakening batch of convection makes its way through the region. Best chance will be across portions of northern and central Massachusetts where forcing will be a bit more concentrated.

High confidence continues in a pattern change to unseasonable warm temperatures for the first half of next week and potentially flirting with record highs on Tue/Wed. Strong Bermuda ridge pushes 500mb heights to 588-590 dm. GEFS/EPS ensembles show a 60-80 percent chance of high temps of at least 90 across the CWA. This is a strong signal considering we are still several days away from this event!

More significant warm up begins Sunday as southwest flow helps warm temps into the middle 80s for much of the interior. Elsewhere, water temps in the 50s will help keep temperatures about 10 to 15 degrees cooler. High pressure to the N of the region shifts winds to the NE on Monday resulting in slightly cooler temperatures, especially near the coast. Highs Mon on the immediate coast probably in the upper 60s and 70s while 80+ risk will be confined to the interior. The hottest days look to be Tue and/or Wed depending on the timing of a cold front. 925T near +24C should result in the potential for high temperatures to climb into the 90s away from any modified marine influences. This may result in record high temperatures being challenged at least in areas away from the south coast. Main factor acting against realizing the widespread mid 90s advertised by the NBM will be cloud cover extent. Should be a somewhat drier heat with dewpoints in the lower 50s Tuesday.

Finally, guidance continues to show a chance for isolated strong to sever thunderstorms Tuesday afternoon. There should be plenty of instability for storms with the NBM showing a widespread 40-60% chance of values exceeding 1000 J/kg Tuesday afternoon. The limiting factor at this time is the lack of wind shear and forcing as a front remains well to the west. Thus, at this time, the coverage of storms remains in question.

KEY MESSAGE 2...Unseasonably warm Wednesday with scattered thunderstorms possible later in the day with some potentially strong to severe.

A low pressure system and attendant cold front is expected to track across the northeast Wednesday into Thursday. Depending on the timing of the cold front, we may see one last day of above normal high temperatures in southern New England. This is supported by warm 925mb temperatures bumping up to 23-25C with enhancement from the WAA ahead of the approaching system. There is high confidence for temperatures 80F+ with ensembles indicating potential for highs around 90 in the valleys inland. South coast and Cape and Islands will stay in the 70s and low 80s from the southwesterly onshore flow. Another early season hot day, so be sure to hydrate, take breaks, and have a cool place to do so.

Ahead of the cold front, southwesterly flow aloft helps to advect in Gulf moisture as instability builds ahead of the frontal system with the ample heating. MLCAPE values appear on the marginal side, although shear appear sufficient with the help of a jet. With the added forcing of the front, this should support scattered thunderstorms developing later in the day with potential for some storms being strong to severe. Forecast soundings indicate a good amount of dry air at the surface which may be a signal for strong downdrafts (gusty winds) within any strong-severe storms. The assorted ML guidance shows a signal with low probabilities for severe at this time. We are still a ways out and details on the timing of the front will need to be ironed out more before confidence increases in the severe potential. Stay tuned.

KEY MESSAGE 3...Cooler, more seasonable temperatures late week.

A cold front will swing through by Thursday bringing in a cooler airmass. This will bring in more seasonable/seasonably cool temperatures late-week with mainly dry conditions and northerly component flow.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

00Z TAF Update:

Tonight...High Confidence

VFR conditions. Period of midlevel ceilings overnight with a low chance for an isolated shower. SW winds 5-10 kts in west/central MA and 9-14 kts for east terminals. Winds shift more WSW toward 12Z. Areas of LLWS overnight from BOS points SE.

Sunday & Sunday Night...High confidence

VFR. WSW to W winds 8-13 kts with gusts around 20 kts developing after 15Z. Winds shift WNW later in afternoon-early evening. Winds becoming light and briefly variable after 00Z, becoming easterly overnight.

KBOS...High confidence in TAF

KBDL...High confidence in TAF.

Outlook /Sunday Night through Thursday/...

Monday: VFR. Breezy.

Monday Night: VFR.

Tuesday through Tuesday Night: VFR. Breezy.

Wednesday through Wednesday Night: VFR. Breezy. Chance SHRA, slight chance TSRA.

Thursday: VFR. Slight chance SHRA.

MARINE

Forecaster Confidence Levels...

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

SCAs remain in effect on most waters as easterly swell that brings elevated seas in the 4-7 ft range tonight. Winds shift W tonight into Sunday. Given the continued elevated seas and increase in winds tomorrow, SCAs have been extended through Sunday afternoon. Winds and seas are expected to remain elevated then gradually fall as high pressure builds in.

Outlook /Sunday Night through Thursday/...

Monday through Monday Night: Winds less than 25 kt.

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

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

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

Wednesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, slight chance of thunderstorms.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ231>234. Small Craft Advisory until 2 AM EDT Sunday for ANZ235-237-251. Small Craft Advisory until 2 PM EDT Sunday for ANZ250-254>256.