Area Forecast Discussion
Issued by NWS Boston, MA

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000 FXUS61 KBOX 221436 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1036 AM EDT Sun May 22 2022 .SYNOPSIS... Near record high temps with heat indices between 95 and 100 degrees are expected Sunday away from the south coast. A few strong to severe thunderstorms are possible from mid-afternoon into early Sunday evening across western-central Massachusetts and Connecticut. Cooler and more seasonable weather returns on Monday with Tuesday and Wednesday looking to be pick of the week with delightful weather and low humidity. A warming trend begins late in the work week with the risk for a few showers and thunderstorms on Friday. Memorial Day weekend looks to feature above normal temperatures and mainly dry weather. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Highlights... * Near Record Highs in the low-mid 90s the northwest of a Providence to Taunton line with heat indices 95-100 * A few strong-severe t-storms possible across western-central MA/CT between 2 & 10 pm Sun with isolated damaging wind gusts and locally heavy rain 1030 AM Update... Forecast remains on track late this morning. Plenty of sunshine with an anomalously warm temps aloft has allowed temps to already surge well into the 80s in many locations. Still a weak sea breeze across the northeast MA coast, but this should dissipate by mid afternoon as gradient results in wind shifting to a westerly direction. This coupled with 850T near +18C/+19C should allow highs to reach the lower to middle 90s in many locales northwest of the Boston to Providence corridor. South to southwest wind gusts of 20 to 25 mph developing this afternoon will result in temps a bit lower towards the south coast. This is particularly true on the immediate south coast, Cape and Islands where highs will be in the 70s to the lower 80s. The other concern is the potential for a few strong to severe thunderstorms roughly between 2 and 10 pm this evening across interior MA and CT. Some initial isolated to scattered convection may develop by mid-late afternoon with a pre- frontal trough northwest of I-95. Another round of scattered activity that may be somewhat more numerous is possible early this evening. This is mainly across western MA and northern CT with the actual surface cold front. While we are losing the EML in place, large T/Td spreads coupled steep low level lapse rates and good DCape values will support isolated strong to damaging wind gusts with a few of the storms. Some small hail is possible, but again the main risk is localized strong to damaging wind gusts. Brief heavy rain/nuisance poor drainage street flooding is also expected with the high PWAT Values. As for eastern MA and RI we are still expecting the activity to weaken as it approaches the Boston to Providence corridor. Today... 1) Heat & Humidity Hot and steamy day ahead, with a warm start given high dew pts early this morning. Also, height falls today will promote better boundary layer mixing today vs yesterday. Thus, model soundings supporting mixing up to and beyond 850 mb, with WSW winds 10 to 20 mph. This will transport a hot and humid airmass all the way to the eastern MA coast, including the city of Boston. 850 mb temps around +18C to +19C, and mixing to this level and beyond will support highs in the middle 90s away from the south coast. As previous forecast stated, highs of 90-95 expected along and north of approximately a Providence to Taunton line. South of this line, much cooler given SW winds streaming across ocean temps in the low to mid 50s! Dew pts in the low to mid 60s, combined with air temps in the lower to middle 90s, will support heat indices of 95-100. Thus, heat headlines will remain in place. There will be a SW breeze of 10-20 mph, highest RI and eastern MA, but not offering much relief given hot and humid airmass. 2) Strong to Severe Thunderstorm Risk across western-central MA/CT Watching a weak S/WV trough advecting up the coastline from the Mid Atlantic region. This feature moves across SNE from late this morning into the afternoon. It does result in subtle height falls, which may be sufficient to erode the mid level cap. This S/WV trough does induce a prefrontal trough, which likely is sufficient as a trigger to initiate convective development. Some of the guidance global and hi res guid indicate convection developing early this afternoon, way out ahead of the main frontal boundary. This convection may be able to tap into a remnant EML before exiting offshore late this afternoon. If all these ingredients overlap briefly, some of this convection early/mid this afternoon could be strong to perhaps severe. Given inverted v signature on area soundings from temps 90-95 and dew pts in the 60s, strong to damaging winds is a concern, along with localized heavy rain given high PWATs up to 1.7 inches, and relatively weak winds aloft support slowly moving storms. Then a second round of storms are likely with the actual frontal boundary, mid to late afternoon and early evening. Lots of instability available with MLCAPES 1500-2000 J/KG along with frontal scale forcing. However, deep layer shear is only 20-25 kts, and only marginal mid level lapse rates, as remnant EML moving offshore. This will limit areal coverage of storm severity, with greatest risk of a few strong to severe storms across western-central MA/CT, closer to the approaching frontal boundary. Timeframe remains unchanged from previous forecast, 2 pm to 10 pm. Low prob of some hail given amount of CAPE. However given lack of deep layer shear and marginal mid level lapse rates, any hail should be small.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM MONDAY/... Tonight... Scattered showers & t-storms weaken this evening as the approach the I-95 corridor. Perhaps a few showers with a rumble of thunder survive, but not expecting much more than that. Otherwise...the rest of tonight will feature dry but significantly cooler weather returning. Low temps by daybreak Monday should be back down into the middle 50s to the lower 60s. Monday... Anticyclonic flow around a large area of high pressure positioned north and west of New England will result in a northerly flow for the first half of the week. Predominantly northwesterly flow on Monday will support a seasonable day with high temps in the low 70s. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... Highlights... * More seasonable temperatures return for the new work week. Tuesday and even Wednesday look to feature delightful weather and low humidity. * Turning warmer and unsettled again by late week. * Memorial Day weekend looks to feature above normal temps and dry weather. Details... Monday night into Wednesday... Monday highs will be about 5 degrees above normal but a lot more seasonable and a lot more comfortable with dew points falling into the 40s to near 50. Expect mostly dry conditions with mix of sun and clouds on Monday although there could be lingering showers around, especially across southeast MA. Indeed, a refreshing and almost fall-like air mass will dominate on Tuesday with dew points in the 30s! Despite northeast flow off the cooler ocean waters, maritime high pressure will allow for plentiful sunshine. So Tuesday may turn out to be pick of the work week with delightful weather and low humidity. This also translates to cool/chilly nights due to the dry air mass encouraging more efficient radiational cooling so went with colder guidance for overnight Tuesday. Then by Wednesday, the surface flow becomes more southeast or southerly so both temps and dew points will increase a few degrees compared to Tuesday but still very comfortable. Talk about a gorgeous stretch of weather mid week! Thursday into Saturday... Then a warming trend begins towards the latter half of the work week as low-level flow becomes more southerly and eventually southwest. Expect temps to return to near normal by mid to late in the work week and then above normal for Memorial Day weekend. For reference, average highs for late May are in the low to mid 70s. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/... Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 11Z TAF Update... Today...High Confidence. Mainly VFR conditions expected. However, scattered showers and t-storms are expected to develop across western-central MA/CT during the mid to late afternoon hours, then moving into eastern MA. A few storms may be contain brief heavy rain and locally strong wind gusts, greatest risk across western-central MA/CT. The activity will weaken as it approaches the Boston to Providence corridor, but some may survive in a weakened form by early evening. SW wind gusts of 20 to 25 knots are expected to develop by afternoon but may be briefly stronger in any thunderstorm. Sunday night...High Confidence. Scattered showers and t-storms weaken as they approach the I-95 corridor during the evening, and possibly dissipate before reaching southeast MA. Otherwise, VFR except for perhaps some low clouds/fog in the evening across the Cape/Islands before the cold front crosses the region. SW winds early in the evening will shift to the northwest at 5 to 15 knots by late evening/overnight. Monday...high confidence. Mainly VFR and dry weather. NNE winds 10-15 kt, gusts up to 20 kt over Cape Cod and the Islands. KBOS TAF...High Confidence in TAF. VCTS 18z-02z. KBDL TAF...High Confidence in TAF. VCTS 16z-00z. Outlook /Monday Night through Thursday/... Monday Night through Wednesday: VFR. Wednesday Night: Mainly VFR, with areas MVFR possible. Chance SHRA, isolated TSRA. Thursday: Mainly MVFR, with areas VFR possible. Chance SHRA, isolated TSRA. && .MARINE... Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Today/Tonight/Monday...High Confidence. Southwest wind gusts of 20 to 25 knots will develop by Sunday afternoon ahead of an approaching cold front. Strongest of those winds will likely be near shore given better mixing over the land. It is marginal, but we may need some near shore small craft headlines in the afternoon for gusty winds/choppy seas. Winds shift to the northwest late Sunday night behind the cold front; with perhaps some more marginal small craft wind gusts of 20 to 25 knots. This time the strongest wind gusts will be over the open waters; so perhaps some marginal small craft headlines may be needed for a few or our eastern waters. Outlook /Monday Night through Thursday/... Monday Night: Winds less than 25 kt. Tuesday: Winds less than 25 kt. Seas locally approaching 5 ft. Tuesday Night through Wednesday: Winds less than 25 kt. Wednesday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Slight chance of rain showers, isolated thunderstorms. Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Slight chance of rain showers, isolated thunderstorms. && .CLIMATE... Sun May 22nd... BOS 93F (1959) PVD 94F (1941, 1992) BDL 95F (1992) ORH 90F (1911, 1992) Monthly record high temperatures... BOS 97F (05/26/1880) PVD 96F (05/26/2010) BDL 99F (05/26/2010, 05/20/1996) ORH 94F (05/26/2010) && .BOX WATCHES/WARNINGS/ADVISORIES... CT...Heat Advisory until 8 PM EDT this evening for CTZ002>004. MA...Heat Advisory until 8 PM EDT this evening for MAZ003>006- 010>018-026. RI...Heat Advisory until 8 PM EDT this evening for RIZ001>004. MARINE...None. && $$ SYNOPSIS...Nocera/Chai NEAR TERM...Frank/Nocera SHORT TERM...Nocera LONG TERM...Chai AVIATION...Nocera/Chai MARINE...Nocera/Chai CLIMATE... is the U.S. government's official web portal to all federal, state and local government web resources and services.