353 FXUS61 KBOX 051945 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 345 PM EDT Sat Jun 5 2021 .SYNOPSIS... Oppressive heat Sunday and Monday, with increasing humidity Tuesday into Wednesday. The heat likely breaks late Wednesday with a significant cool down Thursday into Friday, behind a backdoor front. Mainly dry weather this period, except a chance of scattered showers and thunderstorms late Tuesday into Wednesday. && .NEAR TERM /UNTIL 6 AM SUNDAY MORNING/... * Very mild night with lows only falling into the 60s. Boston and Hartford have both reached 90 degrees this afternoon, which marks the first day of the season's first heat wave. Mostly clear skies prevail across our CWA early this afternoon with some scattered cumulus clouds trying to pop up. Overall, dry conditions will prevail for the rest of the day due to height rises and a capped atmosphere. There is also a hazy look to the sky thanks to the low-level inversion trapping fine particulates (see Air Quality Alert). The Cape and Islands as well as the immediate south coast remain the places to go this afternoon if you are looking to cool off. As for tonight, expect mostly clear skies with relatively light southwest to west winds. Initially, low stratus and areas of fog could affect the immediate south coast. But once the direction shifts to the west, the stratus and fog will move offshore. Very mild night across southern New England with lows in the 60s with metro Boston possibly not falling below 70 degrees due to the urban heat island effect. && .SHORT TERM /6 AM SUNDAY MORNING THROUGH SUNDAY NIGHT/... * Sunny and hot across southern New England on Sunday. Sunday... Likely the hottest day of the year so far with widespread low to mid 90s away from the immediate south coast and Cape/Islands. Also less breezy compared to Saturday due to the relaxation of the surface pressure gradient so the heat will feel somewhat more oppressive compared to Saturday. 925 mb temperatures are 2 to 4C warmer than on Saturday (+23 to +25C) and with westerly downsloping flow, expect high temperatures to overperform again. Bumped up temperatures using a combination of the 95th percentile of NBM and the GEM guidance. Overall, this yields rather widespread highs in the mid 90s. There are some questions whether local sea breezes could kick in for the immediate coast given that winds aloft are not quite as strong as on Saturday (still decent nonetheless) but most locations away from the immediate coast will have a sultry day with little relief. Did contemplate hoisting a Heat Advisory for the CT River valley and Eastern MA away from Cape/Islands and the immediate south coast but there remains some uncertainty whether the Heat Advisory criteria of 95-99F heat index (first of two consecutive days) will be realized given that dew points are only in the low to mid 60s. Upon consultation with neighboring offices, opted to hold off on any heat headlines and let the next shift reevaluate. Heat Advisory or not, it will likely be the hottest day of the year so far and please take the necessary precautions to stay hydrated and cool. Sunday night... Another warm night, but depending on how high temperatures on Sunday get, lows should only get down into the mid 60s to low 70s (metro Boston may only cool off into the mid 70s). Cooler on the immediate south coast and Cape/Islands where daytime highs only reach the mid 70s to mid 80s. && .LONG TERM /MONDAY THROUGH SATURDAY/... Highlights... * Very hot temperatures through mid week. 90+F continues Mon and Tue, then less widespread Wed * A cold front late Wed/Wed night brings relief from the heat and humidity for the latter half of the week. * Mostly dry. The only exception will be some showers and thunderstorms possible late Tue into Wed Details... Monday through Wednesday... Not a whole lot of change in thinking with regard to the first half of the workweek...it's going to be hot! Under the influence of a building mid level ridge to the south, our streak of 90+F days across southern New England continues, peaking on Monday and continuing through at least Tuesday. Ensemble guidance continues to indicate high probabilities (50-100%) of >90F Monday and lesser (20- 50%) on Tuesday as 850mb temps moderate a bit and cloudcover increases significantly. Confidence is higher given the signal already shown for Mon/Tue, especially given that 06Z EPS guidance didn't show any probs of 90F today and we've already hit 90+ in many locations. Monday 850 mb temps will hit their peak, near +19C with +25C at 925 mb to boot! This regime with full sun and W/SW winds will allow for widespread mid 90s, especially further removed from the south shore where ocean cooled air keeps temps in the 70s and 80s. By Monday night into Tuesday mid and upper level moisture begins to round the top of the ridge bringing a good bit of mid and high clouds as well as increasing rain and thunderstorm potential, especially in the diurnally favored afternoon/evening hours; they would be scattered in nature with weak thunderstorms given good instability but lack of shear or a good forcing mechanism. Temperature wise, those clouds along with a slightly moderating airmass (850 mb temps down to +17 or +18C) will keep highs several degrees cooler than Monday. The increased moisture, however, will bring more humidity with dewpoints rising into the low 70s. Each day the hottest locations will be the Merrimack Valley and Connecticut River Valley. Wednesday clouds stick around but we'll likely have another day of warmer than normal temperatures, in the upper 80s to near 90. The only fly in the ointment would be a quicker than expected cold frontal passage which most of the guidance continues to indicate will be later Wednesday night. We should have a better handle on this in the next 24-48 hours as we come into range of the higher resolution guidance. Given the moisture available and approaching frontal passage, we'll also see an increased chance for scattered showers and thunderstorms late in the day. Thursday into the weekend... A drier and cooler airmass moves in behind the front for Thursday and Friday. 850 mb temps drop to near +13C and +10C Thursday and Friday allowing for highs in the upper 70s/low 80s and low to mid 70s respectively. Under persistent NW flow several disturbances moving through have the potential to bring unsettled weather back to the forecast, but there is not enough agreement on any wet solutions to feel confident in the return of rain just yet. Temperatures will continue to be quite cool through the weekend compared to this week. && .AVIATION /19Z SATURDAY THROUGH THURSDAY/... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 1730Z update...High confidence. VFR conditions across all terminals except for KACK, where broken low clouds meant alternating between LIFR and VFR conditions. WSW winds 10-20 kt with 25 kt gusts at times will preclude seabreeze development this afternoon. A few isolated afternoon showers are possible, but most if not all terminals remain dry. Tonight...High confidence away from the south coast. Moderate confidence for the south coast. VFR across the vast majority of locations, but am expecting MVFR to IFR stratus/fog across the south coast. Should see the fog/stratus diminish as winds shift from the WSW to the W late. Wind speeds of 5-10 kts. Sunday...High confidence. VFR conditions expected. Winds out of the W at 5-15 kts. There could be a few 20 kt gusts across SE MA and the Islands during the afternoon. KBOS TAF...High confidence. KBDL TAF...High confidence. Outlook /Monday through Thursday/... Monday through Monday Night: VFR. Breezy. Tuesday: VFR. Chance SHRA, slight chance TSRA. Tuesday Night: VFR. Slight chance SHRA, isolated TSRA. Wednesday through Wednesday Night: VFR. Chance SHRA, slight chance TSRA. Thursday: VFR. && .MARINE... Forecaster Confidence Levels. Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 130 PM Update... Small Craft Advisories remain in effect across all waters due to expected gusty winds with 25 kt gusts at times including near shore waters in the afternoon hours. Also building seas to near 5 ft across outer waters. Have received confirmation from ferry captains that outer waters are quite choppy and winds are blowing 10-20 kt. Today...High confidence Winds out of the SW at 10-20 kts gusts of 20-25 kts during the afternoon. Waves 4-6 ft across the outer waters and 2-4 ft elsewhere. Stratus and fog across the southern and eastern waters with visibility ranging from 1/2 to 3 nm. Tonight...Moderate confidence in stratus/fog. Winds out of the SW/W at 10-20 kts diminishing to 10-15 kts. Gusts of 20-25 kts during the evening. Waves 4-6 ft across the outer waters falling to 2-4 ft late. Stratus/fog across the southern and eastern waters with visibilities of 1/2 to 3 nm. Should see the fog/stratus move off the waters late as winds shift to the west. Sunday...High confidence Winds out of the SW at 10-15 kts could have some 20 kt gusts during the afternoon. Waves of 2-4 ft. Outlook /Monday through Thursday/... Monday: Winds less than 25 kt. Monday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Tuesday through Wednesday Night: Winds less than 25 kt. Slight chance of rain showers, isolated thunderstorms. Thursday: Winds less than 25 kt. && .CLIMATE... With the toasty temperatures arriving Sunday, here's a look at the extremes of heat and humidity for Sunday June 6 to Tuesday June 8. Record High Temps June 6 BOS 100 / 1925 PVD 96 / 1925 BDL 96 / 1925 ORH 94 / 1925 June 7 BOS 97 / 1999 PVD 96 / 1999 BDL 98 / 1999 ORH 94 / 1925 June 8 BOS 97 / 1984 PVD 94 / 2008 BDL 96 / 1984 ORH 91 / 1984 Record High Min Temps June 6 BOS 80 / 1925 PVD 80 / 1925 BDL 76 / 1925 ORH 77 / 1925 June 7 BOS 68 / 1999 PVD 66 / 1922 BDL 67 / 1973 ORH 74 / 1899 June 8 BOS 77 / 2008 PVD 74 / 2008 BDL 70 / 2008 ORH 71 / 2008 Highest Dewpoint June 6 BOS 71 / 2010 PVD 70 / 2010 BDL 71 / 2010 ORH 70 / 2010 June 7 BOS 74 / 1984 PVD 78 / 1984 BDL 73 / 2008 ORH 74 / 1999 June 8 BOS 73 / 1984 PVD 74 / 1984 BDL 73 / 2008 ORH 72 / 2008 && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...Air Quality Alert until 11 PM EDT this evening for MAZ020>024. RI...Air Quality Alert until 11 PM EDT this evening for RIZ001>008. MARINE...Small Craft Advisory until 9 PM EDT this evening for ANZ230>237-251. Small Craft Advisory until 6 AM EDT Sunday for ANZ250-254. Small Craft Advisory until 8 AM EDT Sunday for ANZ255-256. && $$ SYNOPSIS...BW/Chai NEAR TERM...Chai SHORT TERM...Chai LONG TERM...BW AVIATION...BW/Chai MARINE...BW/Chai CLIMATE...Staff