Area Forecast Discussion
Issued by NWS Boston, MA
Issued by NWS Boston, MA
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385 FXUS61 KBOX 241447 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 1047 AM EDT Mon Jun 24 2024 .SYNOPSIS... Other than the chance of a spot shower, dry weather prevails Monday along with lowering humidity this afternoon and not as hot as Sunday, as a cold front exits offshore. Dry and very warm weather is on tap for Tuesday, but with comfortable humidity. Hot and humid weather returns Wednesday with another round of showers and thunderstorms possible Wednesday afternoon and night as a cold front approaches from the west. The showers may linger into Thursday as the front moves through, followed by dry and seasonable conditions Friday and Saturday. Another cold front will bring an increasing risk of showers and thunderstorms Saturday night into Sunday. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 1030 AM Update: Minor update to the forecast to bring down dewpoints a bit sooner in interior CT, MA and RI now that westerly flow has taken hold. Dewpoints here were falling into the 50s so a much more refreshing air mass advecting in. It still is quite a bit humid in southern RI and the Cape and Islands but anticipate lowering dewpoints into the afternoon for these locations. All in all, forecast holding up well with no significant changes. Previous discussion: * Turning less humid * Mainly dry weather and seasonably warm Cold front in the CT valley and will likely stall near the coast later this morning before pushing offshore by evening. The front will be followed by a notable dewpoint drop into the 50s a few hours after the passage so lowering humidity values from west to east today, although it may take until late afternoon or evening before the drier air is felt along the SE New Eng coast. Showers and t-storms south of ACK within the deep moisture axis which moves offshore this morning. The column is drying this morning, but moisture returns this afternoon as mid level low drops SE across New Eng. The cooing temps aloft acting on the increase in moisture may lead to a few spot showers developing this afternoon but areal coverage will be limited. Otherwise, sunshine gives way to SCT-BKN diurnal CU/SCU. 850 mb temps lower from +15C at 12z to +11C by days end. This will result in a very tranquil/pleasant day with highs 80-85, upper 70s western- central MA into northern CT. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 PM TUESDAY/... 4 AM update... Tonight... * Dry, cooler and comfortable humidity Dry, cool NW flow across SNE in response to vertically closed low over the Gulf of Maine. Derived mins from a blend of the cooler MOS guidance and the milder NBM. Should be enough WNW pgrad to preclude cooler MOS guidance from verifying, thus followed a blend, which still yields cool temps, with lows in the upper 50s to lower 60s. Tuesday... Could be pick of the week, with dry NW flow continuing. However, temps will be warming aloft as vertically stacked low over the Gulf of ME exits into the Maritimes. 850 temps warm from +12C to +16C by days end, along with 925 mb temps warming to +22C. These temps aloft combined with WNW winds 10-15 mph shifting to WSW support highs of 85-90 Tue afternoon. Although, not humid with dew pts in the 50s. Given dry column (PWATS ~0.75 inches) and dew pts in the 50s, not expecting much if any clouds, hence full sun. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Key Points... * Hot and humid Wed with showers/t-storms Wed afternoon and night * Showers may linger SE New Eng Thu AM, otherwise improving conditions * Dry & seasonable Fri and Sat * Humidity increases Sat night and Sun with risk of showers/t-storms Wednesday into Thursday... Next mid level trough and shortwave amplifies across the Gt Lakes Wed before moving into northern New Eng Thu. Pre-frontal SW flow will bring increasing temps and humidity with highs likely reaching upper 80s to lower 90s away from the south coast, while dewpoints increase to near 70. The heat and humidity will help to generate modest instability beneath favorable mid level lapse rates from a remnant EML. While we do expect scattered showers and t-storms to develop in the afternoon, better chance will likely be during Wed night when best height falls move into the region along with right entrance region of upper jet at a time when diurnal instability will be diminishing. So there is some uncertainty with severe weather risk as peak forcing will not be lining up with peak diurnal instability. Still have to monitor this closely as deep layer shear will be increasing and it is possible we have a narrow window for severe potential late Wed and Wed evening when instability and shear overlap. It is interesting that CSU machine learning probs have ramped up on severe wind potential for Wed-Wed evening. Heavy rainfall will also be a concern Wed night as deep moisture axis moves across the region with PWATs increasing to near 2 inches. Cold front will be moving across SNE overnight Wed night and likely stalling in the coastal plain on Thu. However, moisture axis will shift to SE New Eng by 12z Thu with good drying moving in from the west during the day. Showers may linger in SE New Eng during Thu morning, otherwise expect improving conditions with increasing sunshine developing from west to east. Highs will reach upper 70s to mid 80s with decreasing humidity in the afternoon, especially interior. Friday and Saturday... High pres builds across New Eng Fri which will bring sunshine and somewhat cooler temps, especially along the coast as sea-breezes develop. High pres moves offshore Sat with increasing SW flow developing which will result in dewpoints increasing. Dry weather should hang on for much of the day, but can`t rule out a few showers in the afternoon. Saturday night and Sunday... Unsettled weather returns as next mid level trough approaches from the Gt Lakes with moisture axis moving into SNE with 2+ inch PWATs. Expect scattered showers and t-storms through Sunday as cold front may be delayed until later Sun or Sun night. Rather humid conditions likely Sun as 70+ dewpoints return. && .AVIATION /15Z MONDAY THROUGH FRIDAY/... Forecast Confidence Levels: Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 15z TAF Update: Today: High confidence. VFR continues for most; lingering IFR over ACK expected to be short-lived, by 17z, with conditions improving there to VFR thereafter. W to WNW winds 10-15 kt with gusts 20-25 kt for most, although winds along the South Coast, Cape and Islands start SW around 10-12 kt and will shift to WSW/W by aftn. Monday night...High confidence. VFR cloud bases with an isolated shower/sprinkle possible during the evening. West winds 10-20 kt in the evening, shifting to NW 10-15 kt after midnight. Tuesday...high confidence. NW winds 10-15 kt in the morning, becoming SW 10-15 kt in the afternoon. VFR and dry runways. KBOS TAF...High confidence in TAF. VFR with WNW winds around 10-15 kt with gusts up to 25 kt today. Low (< 15%) chance of an unrestricted-visby shower tonight with winds shifting to NW around 15 kt overnight. Winds then shift back to WNW/W Tue AM with decreasing speeds, becoming SW late in the day on Tue. KBDL TAF...High confidence in TAF. VFR. W winds around 10-15 kt become NW/N late this aftn and tonight at similar speeds. Winds then shift early Tue to W and then SW later Tue aftn. Outlook /Tuesday Night through Friday/... Tuesday Night: VFR. Breezy. Wednesday: Mainly VFR, with local MVFR possible. Breezy. Chance SHRA, slight chance TSRA. Wednesday Night: Mainly MVFR, with local IFR possible. Breezy. SHRA likely, isolated TSRA. Thursday: Mainly VFR, with local MVFR possible. Slight chance SHRA. Thursday Night through Friday: VFR. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. *** SCA remains in effect *** Today... Robust low level SW jet of 40-45 kt at 2 kft over Cape Cod and Nantucket, slow exits offshore today. Therefore, SW winds surface winds of 15-25 kt during the predawn hours, ease this afternoon and shift to the WSW and then west late. Although, given the long wind fetch, it will take sometime for seas to subside across the southern RI/MA waters. Scattered showers and thunderstorms south of the islands in the predawn hours, slowly moves offshore late this morning. Tonight... Wind shift to the NW 15-20 knots. Seas continue to slowly subside. Dry weather and good vsby. Tuesday... Low pressure over the Gulf of Maine exits into the maritimes. This yields NW winds 10-15 kt in the AM, WSW in the afternoon. Dry weather and good vsby prevail. Outlook /Tuesday Night through Friday/... Tuesday Night: Winds less than 25 kt. Areas of seas approaching 5 ft. Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Seas up to 5 ft. Slight chance of rain showers. Wednesday Night: Low risk for Small Craft Advisory winds with gusts up to 25 kt. Local rough seas. Rain showers likely, isolated thunderstorms. Thursday: Winds less than 25 kt. Areas of seas approaching 5 ft. Chance of rain showers. Thursday Night: Winds less than 25 kt. Seas locally approaching 5 ft. Friday: Winds less than 25 kt. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...High Surf Advisory until 7 PM EDT this evening for MAZ020>024. RI...High Surf Advisory until 7 PM EDT this evening for RIZ006>008. MARINE...Small Craft Advisory until 8 PM EDT this evening for ANZ232>235-237. Small Craft Advisory until 2 AM EDT Tuesday for ANZ254>256. && $$ SYNOPSIS...KJC/Nocera NEAR TERM...KJC/Loconto/Nocera SHORT TERM...Nocera LONG TERM...KJC AVIATION...KJC/Loconto/Nocera MARINE...KJC/Nocera