textproduct: Boston / Norton

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

- Scattered showers this afternoon following morning fog.

- Warming trend takes hold, though could see dangerous heat Wednesday through Friday.

- Risk for showers and thunderstorms mid to late week.

DISCUSSION

KEY MESSAGE 1...Scattered showers this afternoon following morning fog.

Fog this morning that had been lurking over the waters and took hold over much of the region this morning will likely stick around until sunrise. Fog recedes, though cloudier skies will take a bit longer to decrease. High pressure will start to take hold over the region, keeping winds light. We do remain under some troughing aloft, though, keeping the chance for some showers in play this afternoon. The chance for scattered showers over southern New England makes a return, yet the risk for these becoming thunderstorms remains low - - much like yesterday. MLCAPE values will remain mostly below 500 J/kg and MUCAPE generally maxes out around 500 J/kg as well. So, a rumble or two cannot be entirely ruled out, but is unlikely. Highs today will be mostly in the 80s.

KEY MESSAGE 2...Warming trend takes hold, though could see dangerous heat Wednesday through Friday.

A strong upper level ridge continues building in from the west to start the week, which will be a key factor in this week's heat. Ensembles and deterministic guidance suites are in good agreement that this ridge will continue into the Ohio Valley to start the work week, then continuing further east into the northeast CONUS. The signals for intense heat heading into the middle of the week have not changed too much from the previous forecast: ensembles continue to keep the highest probabilities of highs reaching and/or exceeding 100F over urban areas and the river valleys, especially on Thursday. GEFS probabilities for Thursday afternoon range generally between 20- 40 percent with Canadian ensemble probabilities slightly higher at 30-60 percent. This ensemble is also highlighting the CT River Valley more aggressively than other aforementioned areas, with some spots in the range of 60-70 percent. The continued overall consensus across the different guidance suite aids in increasing confidence in the risk for this dangerous heat overall. Mean 850 mb temperatures across the ensembles continue to reach 20-23C, and 925 mb temperatures in the deterministic guidance continue to key in on 25C temperatures and higher, even to 30C(!). This is all before dew points and overall moisture are being taken into account. With ambient temperatures possibly reaching 100F, heat indices could soar into the triple digits, lending to a Major (3/4) level Heat Risk. Urban areas, the Merrimack Valley, and the CT River Valley could see Extreme (4/4) Heat Risk impacts, especially on Thursday.

Another issue with these high daytime temperatures is that not much relief is expected overnight. NBM has low probabilities for temperatures getting below 70F overnight between Wednesday and Friday (generally at 20 percent and lower). The other ensembles are equally pessimistic; GEFS, ECMWF ENS, and the Canadian ensemble all have probabilities generally higher than 60 percent for temperatures staying above 70F overnight.

KEY MESSAGE 3...Risk for showers and thunderstorms mid to late week.

As the ridge builds in heading into the middle of the week, a few shortwaves may track along the eastern edge. Some showers and/or thunderstorms associated with them may move through the region Tuesday, briefly bringing a little bit of relief from the heat. Once the ridge has built up into southern New England for Wednesday and Thursday, chances for showers and storms drop significantly. Chances increase for the end of the week as the ridge breaks down. More refined details will come into the picture as we get closer to both events.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

Forecaster Confidence Levels...

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

12Z TAF Update...

Through this afternoon...High confidence in conditions. Moderate confidence in timing.

IFR/LIFR ceilings and vsbys slowly improve to VFR after 15Z. Some uncertainty in timing of improvements for BOS and Cape/Islands with onshore flow possibly supporting IFR/MVFR ceilings into the early afternoon.

Tonight...Moderate confidence.

IFR/MVFR returning tonight mostly around SE MA, Cape Cod, and the Islands. Fog may develop in the river valleys as well. Winds going light to calm will only help support this.

Monday...High confidence.

VFR. Fog banks near the coasts diminish and ceilings lift. Winds remain mostly light and steadily shift more southerly from NE heading into the evening.

KBOS Terminal...Moderate confidence in TAF. Onshore flow may support lower ceilings around 1000 feet into the early afternoon hours, but the expectation is for VFR conditions to return by 16-17Z.

KBDL Terminal...High confidence in TAF.

Outlook /Monday Night through Thursday/...

Monday Night: VFR.

Tuesday: VFR. Breezy. Slight chance SHRA, slight chance TSRA.

Tuesday Night: VFR. Breezy. Chance SHRA, slight chance TSRA.

Wednesday through Thursday: VFR. Breezy.

MARINE

Forecaster Confidence Levels...

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

Through Monday...High confidence.

Fog and/or stratus continues to impact the waters. This should erode a bit heading into this afternoon, though continued onshore flow could limit the speed of improvement. Seas will range from 2-3 ft. Winds remain quite light through Monday and will generally keep an easterly component to them. Fog may once again impact the waters tonight, though it should clear the waters heading into Monday.

Outlook /Monday Night through Thursday/...

Monday Night through Tuesday: Winds less than 25 kt.

Tuesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Areas of seas approaching 5 ft. Chance of rain showers, slight chance of thunderstorms.

Wednesday: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft.

Wednesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain showers.

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

BOX WATCHES/WARNINGS/ADVISORIES

CT...None. MA...None. RI...None. MARINE...None.