396 FXUS61 KBOX 281331 AFDBOX Area Forecast Discussion National Weather Service Boston/Norton MA 931 AM EDT Mon Sep 28 2020 .SYNOPSIS... Increasingly moist southerly flow out ahead of a cold front will bring unseasonably mild conditions and scattered showers through Tuesday. A series of frontal systems will bring widespread, potentially heavy rainfall in two rounds from Tuesday night to early Thursday. More scattered showers are possible Friday but a cool dry weekend follows. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 930 AM Update... * Summer-like Humidity today * Scattered showers/isolated t-storm threat with brief heavy rain towards the Cape & Islands but mainly dry elsewhere Meridional upper level flow has allowed summer-like humidity to return to southern New England. The deep moisture in place will result in a scattered to broken deck of clouds today, but still expect peeks of sunshine. This should allow high temps to reach between 75 and 80 degrees with perhaps a few locations breaking the 80 degree mark. The other issue will be shortwave energy lifting up from the south. The bulk of the forcing/moisture with this shortwave is located towards the Cape & Islands. This is where we expect most of the scattered shower threat today with even brief downpours. SPC meso- analysis indicating several hundred J/KG of MUCape, so an isolated t-storm or two is also possible towards the Cape/Islands. Meanwhile, across the rest of the region mainly dry weather will prevail other than perhaps a brief spot shower. && .SHORT TERM /6 PM THIS EVENING THROUGH TUESDAY NIGHT/... Tonight: Another mostly dry, muggy and mild night with an isolated shower. with winds from the south advecting air with dew points in the mid to upper 60s over waters with SSTs in the low 60s, there could be another round of widespread but locally dense fog. Tuesday: One more muggy, mild and mostly dry day ahead of the cold front and a potential pattern change. Looks like bulk of the rain associated with the cold frontal passage will hold off till the evening hours. In other words, very similar to Monday and have continued to use a blended approach for the forecast. Eastern MA could see more sunshine than Western MA, so have trended temperatures warmer for the former and cooler for the latter. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... * Widespread, potentially heavy rainfall comes in two rounds from Tuesday night through early Thursday along with some gusty winds. * There is another chance at showers Friday into Saturday but the weekend brings much cooler and drier weather. Details... Tuesday night through Thursday... Things are falling into place to bring a prolonged period of potentially drought busting (or at least drought alleviating) rainfall to southern New England between Tuesday night and Thursday morning. This welcomed pattern change has been well advertised by global guidance for many days and confidence that we'll see some good rainfall somewhere in New England is high. That said, the location of the highest rainfall totals remains uncertain. The first round of more widespread rain comes Tuesday night into early Wednesday as a cold front stalls around eastern NY/western MA and a sfc low rides up the stalled frontal boundary. Anomalously warm and moist southerly flow continues ahead of this front with PWATs approaching 2 inches, so there is plenty of moisture to work with. The highest rainfall totals (1 to 2 inches) with this round will likely be over western/central New England in closer proximity to the frontal forcing. Further east the potential for a decent soaking remains, but to a lesser degree. Again, confidence in the location of the highest QPF remains low but confidence that we'll see a good rainfall is high. The moisture is there, as is the forcing; we're placed beneath the right rear quadrant of a 150 kt upper jet, with 40-50 kts at 925 mb as well. The story is the same with the second round Wednesday night into Thursday, only this time the surface low is deeper and the low level jet is even stronger. The secondary surface low lifts up the east coast bringing strong forcing for ascent and the potential for another 1 to 2 inches somewhere over southern New England. The other impact would be potential for gusty winds Wednesday and Wednesday night. Model soundings don't show especially deep mixing, but depending on the track of the low and magnitude of the winds some decent gusts could reach the surface. This will also make for rough seas on area waters. There may be a decent gradient in high temps on Wednesday between western MA (50s) and eastern MA (mid 70s) depending on how far east that cold front can make it. Seasonable temperatures return Thursday in the upper 60s and low 70s. Friday through Sunday... The cold front ushers in a cooler and drier airmass to end the week. The respite may be short lived as another low traverses the region Friday afternoon into Saturday morning bringing more rain chances. Beyond that, though, guidance is in good agreement that high pressure will bring dry and cool weather for the weekend. && .AVIATION /13Z MONDAY THROUGH FRIDAY/... Forecaster Confidence Levels... Low - less than 30 percent. Moderate - 30 to 60 percent. High - greater than 60 percent. 14Z Update... Today...Moderate confidence. VFR conditions dominate today. The exception will be towards the Cape & Islands where MVFR-IFR conditions are expected. Scattered showers and even an isolated t-storm or two will be possible towards the Cape and Islands as well. S winds may gust to 15 to 20 knots by afternoon. Tonight...Moderate confidence. VFR to start, except MVFR on the Cape and Islands. Then deteriorating to widespread MVFR and localized IFR cigs by Tue 04z. Locally dense fog possible after 06z. S winds at 5 to 10 kts. Tuesday...Moderate confidence. MVFR to localized IFR ceilings to start, improving to VFR for Eastern MA and RI terminals by 15z. Western MA and CT terminals could stay in MVFR ceilings much of the day. S winds 5 to 10 kts. KBOS Terminal...Moderate confidence in TAFs. KBDL Terminal...Moderate confidence in TAFs. Outlook /Wednesday through Friday/... Wednesday: Mainly VFR, with local IFR possible. Windy with local gusts up to 30 kt. SHRA likely. Wednesday Night: VFR. Breezy. SHRA likely. Thursday: VFR. Windy with local gusts up to 30 kt. Chance SHRA. Thursday Night: VFR. Breezy. Friday: VFR. Chance SHRA. && .MARINE... Expect increasing south winds and building seas. Small Craft Advisory continues for some of the southern coastal waters due to marginal rough seas. Scattered showers move off to the east Monday night. Reduced vsbys in patchy fog overnight. South winds less than 20 kt. Seas up to 5 feet on the exposed southern waters, less than 5 feet on all other waters. Outlook /Wednesday through Friday/... Wednesday: Moderate risk for Small Craft Advisory winds with gusts up to 25 kt. Rough seas up to 8 ft. Rain showers likely. Wednesday Night: Low risk for Small Craft Advisory winds with gusts up to 30 kt. Rough seas up to 9 ft. Rain showers likely. Thursday: Moderate risk for Small Craft Advisory winds with local gusts up to 30 kt. Rough seas up to 10 ft. Chance of rain showers. Thursday Night: Winds less than 25 kt. Areas of rough seas. Friday: Winds less than 25 kt. Seas up to 5 ft. Chance of rain showers. && .BOX WATCHES/WARNINGS/ADVISORIES... CT...None. MA...None. RI...None. MARINE...Small Craft Advisory until 8 PM EDT Tuesday for ANZ254>256. && $$ SYNOPSIS...BW/Chai NEAR TERM...Frank SHORT TERM...Chai LONG TERM...BW AVIATION...Frank/BW/Chai MARINE...BW/Chai