516 FXUS61 KBOX 300151 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 951 PM EDT Fri Jul 29 2022 .SYNOPSIS... Weak low pressure tracks south of New England, resulting in periods of light rain overnight, with steadiest rain over RI and southeast MA. Not a drought buster, but beneficial rains. Then dry weather this weekend with warm days, cool nights and comfortable humidity. Very warm to hot temperatures with increasing humidity levels anticipated for the upcoming workweek, with the most oppressive days looking to be Thursday and Friday. Showers and thunderstorms are possible on Tuesday, but significant rains are not anticipated and dry weather should prevail much of the workweek. && .NEAR TERM /UNTIL 5 AM SATURDAY MORNING/... 10 PM Update: Forecast dilemma remains unchanged, will short wave trough over Lake Erie this evening have sufficient amplitude to back the mid level flow to capture deep layer moisture over VA/MD northward into SNE? 18z guidance continues the theme from the 12z CAMs on a period of steadier rains after midnight across RI and southeast MA. This is response to a strengthening 850 mb SW jet over the ocean south of New England, with max moisture and thermal advection into RI and southeast MA, especially the Cape and Islands. Previous forecast captures this well, thus no major changes with this update. Earlier discussion below. ================================================================ Following trends, the 18z guidance and HRRR runs, adjusted PoP/Wx/QPF for anticipated rains overnight tonight. Changes essentially focus less QPF north and west of I-95, with similar or slightly more towards central/southern RI, South Coast, Cape and Islands. Axis of surface wind convergence and CAPEs on the order of 1000 J/kg appear the culprits in developing a cluster of scattered convection across the Berkshires into western Hampshire and Franklin Counties (with additional development in east-central NY). Suspect these are probably high-based and while a brief downpour looks possible given radar trends, with 25-30 degree dewpoint spreads it certainly could make it tough to generate much rain. The dry profiles look to exist thru still a decent depth of the lower atmosphere across all of SNE. While radar is indicating showers mainly near or south of Route 6 from Hartford to west of Providence, falling from lower to mid-based clouds. None of these showers appear to be reaching the ground but expect that to change moving toward late evening/midnight with mainly light rains within a few miles north of I-84 northeastward to the North Shore. For these locations in interior CT and MA though, duration of rain looks fairly short and I've reduced rain totals for these areas to a few hundredths to a tenth of an inch. Rain looks to become steadier across southeast New England and particularly central/southern RI, South Coastal towns and the Cape and Islands overnight as convectively enhanced surface wave low passes over the 40/70 benchmark. Though rain should predominate, some limited instability (LIs 0 to -1) in fcst soundings across southeast New England could result in some thunder and in-cloud lightning flashes as low approaches. Rain then diminishes by the pre-dawn/early Sat AM hrs. Made a little bit of an increase in QPF towards a half to two-thirds of an inch, with 2 inch PWAT values contrasting with a rather progressive system. No changes to lows which look on track attm. && .SHORT TERM /5 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/... Highlights... * Warm and less humid for Saturday under mostly sunny skies. Saturday: Surface low departs the near shore waters of southeastern Massachusetts during the early morning hours. An isolated shower or two isn't out of the question along with areas of patchy fog through mid Saturday morning. High pressure builds in from the west and provides all of us a wonderful day under mostly clear skies. As we are located on the eastern edge of the area of high pressure the flow is out of the northwest and this ushers in a drier air mass with dew points in the mid 50s. Winds are northwest 8 to 12 knots. Afternoon temperatures are seasonable in the middle and upper 80s. Saturday night: Quiet night with clear skies and light winds. Should expect good radiational cooling with many locations outside of the urban centers falling into the mid 50s, great night for sleeping with the windows open. The urban centers will retain some heat, resulting in lows 63 to 65 degrees. && .LONG TERM /SUNDAY THROUGH FRIDAY/... Highlights: * Warm, dry and tranquil weather Sunday with still comfortable humidity levels. * Very warm to hot weather with increasing humidity levels for most of the upcoming workweek, potentially to oppressive levels mid to late in the week. * Best chance for showers and storms is with a cold front Tuesday, though significant rain is not expected. Details: Sunday: Tranquil and dry weather prevails as surface ridge remains in place with shortwave ridge aloft. Good weather for outdoor plans Sunday, and while it will be a touch more humid than Sat, still fairly comfortable with dewpoints in the upper 50s to lower 60s and highs in the mid 80s to perhaps a spot 90F reading away from the coast (mid 70s to low 80s for the coasts). Low-amplitude shortwave trough induces weak height falls and spreads increased cloudiness late-day Sunday into overnight, but the cloud cover looks to be of the mid to high variety and not likely to produce rains. Decreasing clouds second half of the night but dewpoints rise into the mid to upper 60s. Fairly mild lows in the mid 60s to near 70. Monday: High pressure offshore brings SW flow to SNE. Very warm, humid but also with some modest southwest breezes. Possible sea-breezes near the coast as synoptic gradient at the moment looks on the weaker side. Highs in the upper 80s to low 90s inland, lower 80s coastal locales. Mostly clear to partly cloudy skies for the evening with muggy lows mid-upper 60s to lower 70s. Tuesday: Tuesday still looks to feature the best chance for showers and possible storms as a cool front moves eastward through New England. Despite this, differences in deterministic and ensemble QPF both placement and amounts are apparent as well as some minor variance in frontal timing (at the moment, a frontal passage around the afternoon to mid evening hours are favored but 12z ECMWF is a few hours slower). Any rains will help and precipitable water values are around 1.8 to 2 inches, but front seems too progressive to bring significant wetting rains. Clearing by evening with highs in the upper 80s to lower 90s inland, lower to mid 80s coastal areas. Lows upper 60s to lower to mid 70s. Wednesday through Late Week: Ensemble means still indicate even warmer to hot weather and more humid conditions are in store for Southern New England. While deterministic global guidance is a few degrees higher, there are strong probabilities for 850 mb temps at or greater than 20C. Latest guidance indicates Thursday projects as the hottest and most humid of the stretch; however Friday may also feature mid/upper 90s highs as prior guidance has backed off on the timing of a sagging cold front toward the weekend. Potential exists for heat headlines for at least a part of this period but exact heat indices are still unclear. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. 02z TAF Update: no change from previous forecast thinking. Best chance for a period of steady rains with MVFR conditions after midnight over RI and southeast MA, then exiting 09z-12z. Earlier discussion below. ================================================================= Tonight: High confidence in trends, moderate on timing. VFR initially begins to deteriorate approx. 03-05z as rain expands NE. Rain however looks light enough for airports north and west of I-95 that prevailing VFR looks more likely with mainly dry runways. Best chance at MVFR/brief IFR ceilings/vsby for PVD, Cape Cod and Islands after 06z. Rain begins to taper off in the 08-12z timeframe. SW winds 6-10 kt ease a bit thru midnight then to trend NW/N. Saturday...High confidence. VFR. NW winds 8-12 kt. Saturday Night...High confidence. VFR. NW winds 5-8 kt. KBOS...High confidence in TAF. KBDL...High confidence in TAF. Outlook /Sunday through Wednesday/... Sunday through Sunday Night: VFR. Monday: Mainly VFR, with local MVFR possible. Breezy. Monday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA. Tuesday: Mainly VFR, with areas MVFR possible. Slight chance SHRA, isolated TSRA. Tuesday Night through Wednesday: VFR. && .MARINE... Forecaster Confidence Levels: Low - less than 30 percent. Medium - 30 to 60 percent. High - greater than 60 percent. Winds and seas expected to remain below SCA thresholds through Sunday. Rain showers move in this evening and exit on Saturday morning. Can't rule out a few thunderstorms for the waters south of Block Island to Nantucket. Outlook /Sunday through Wednesday/... Sunday through Sunday Night: Winds less than 25 kt. Monday through Monday Night: Winds less than 25 kt. Slight chance of rain showers. Tuesday: Winds less than 25 kt. Slight chance of rain showers, isolated thunderstorms. Tuesday Night through Wednesday: Winds less than 25 kt. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...None. && $$ SYNOPSIS...Loconto/Gaucher NEAR TERM...Nocera/Loconto/Gaucher SHORT TERM...Gaucher LONG TERM...Loconto AVIATION...Nocera/Loconto/Gaucher MARINE...Loconto/Gaucher