130 FXUS61 KBTV 202324 AFDBTV AREA FORECAST DISCUSSION National Weather Service Burlington VT 724 PM EDT Sat Apr 20 2019 .SYNOPSIS... Rainfall will continue to taper off from west to east this afternoon and evening with drier conditions expected heading into the overnight period and Sunday. Rivers will continue to rise through Sunday morning as snowmelt and rainfall enter already swollen rivers but should begin to crest and fall by late Sunday morning. Temperatures will rebound nicely on Sunday with afternoon highs in the upper 60s to lower 70s. This period of dry weather will be short lived as a weak coastal system will work it's way into New England on Monday and bring another round of rain showers to the region. Following Monday, unsettled weather under zonal flow aloft will continue through the week with temperatures near or slightly above normal. && .NEAR TERM /THROUGH SUNDAY NIGHT/... As of 709 PM EDT Saturday...Fog has begun to settle into the deeper valleys this evening after multiple round of rainfall over the past week. There is an impressive temperature gradient in place between the Champlain Valley and the western slopes of the Green Mountains which shows a very stout inversion in place. For example, it's currently 45 degrees in Burlington while Underhill, just above 1000 ft, is 62 degrees. With continued light drainage northerly flow, it looks like these low clouds and fog could be around for a while this evening. This is a prime example of cold air damming across both the Champlain and St. Lawrence Valleys. In these types of scenarios, fog and low clouds can stick around a lot longer than expected and given the strength of the inversion, it could be after midnight that clouds begin to break and fog lifts. Warmer air should start mixing down early Sunday morning and we should see the deeper valleys finally warm back up with the rest of the North Country. After stalling out over the Ohio River Valley this afternoon, the upper level low which has been the main contributor to rainfall today has finally begun to slide eastward. This has allowed winds aloft to shift from the southeast (bringing in a plethora of Atlantic moisture) to the southwest (bringing in drier continental air). In addition, the stacked low pressure system is now beginning to weaken and the associated strong jet dynamics are quickly fizzling out. With all that said, radar reflectivities have been waning with the combination of the drier air and weakening upper level support. Any lingering rain showers will taper off from west to east through the remainder of the afternoon and early evening hours. All guidance now suggests that the main band of rainfall will exit the state no later than 8 PM. Scattered showers will be possible through the evening hours as we remain under broad cyclonic flow aloft but dwindling low level moisture will limit areal coverage of such showers. Temperatures have been all over the place today with the frontal boundary stalled across central Vermont. At times today, St. Johnsbury was in the low 70s while just a few miles north was in the 50s. This has made the temperature forecast through the evening hours quite tricky. When looking at temperatures aloft at KMMN and KWTF, temperatures in the low to mid 50s have been observed while temperatures behind the frontal boundary remain trapped under a strong low level inversion. This inversion should begin to mix out this evening with temperatures beginning to warm as warmer temperatures aloft are finally able to make it down to the surface. This will likely allow high temperatures for much of northern New York and northern Vermont to be reached just shy of midnight. Sunday looks to be a complete 180 from today with temperatures warming nicely into the upper 60s to low 70s under southerly flow. To top it off, winds should generally be 10 knots or less with a few gusts mixed in through the afternoon hours as winds aloft will be weak. It wouldn't be surprising to even see some breaks in the clouds during the afternoon hours. && .SHORT TERM /MONDAY THROUGH MONDAY NIGHT/... As of 338 PM EDT Saturday...Monday into Monday night the upper low just off the mid-Atlantic coast will move slowly northeastward and will gradually weaken/open up as it heads toward the Gulf of ME by Tuesday morning. The models handling of the sensible weather effects are all quite varied. At the surface low pressure off the coast on the GFS to low pressure over southern New England on the NAM. At this point it looks like the idea of showers developing during the day especially in the afternoon is the way to go, whether it be partially due to afternoon heating or showers rotating westward from a low off the coast. Expecting the showers to diminish overnight Monday night as the low moves east and weakens. High temps on Monday a bit tricky as they may range anywhere through the 60s to around 70 further west. Monday night low temps in the 40s with still plenty of clouds around. && .LONG TERM /TUESDAY THROUGH SATURDAY/... As of 338 PM EDT Saturday...The April showers theme continues for the week. We get a short break in the action for much of Tuesday before another shortwave trof digs through the Great Lakes into southern Quebec later Tuesday into early Wed. If we see some sun, it could be a bit warmer than we are currently advertising in the 60s with 850 temps getting back up around 9C. This will bring additional showers through the North Country late Tuesday through Wednesday morning. We may see another break in the action Thursday as short wave ridging moves in. More troffing moves in Friday into Saturday with a chance of showers but there really hasn't been much run to run consistency with the models. Temperatures through next week start above normal drop towards near normal through the middle of the week into next weekend. && .AVIATION /23Z SATURDAY THROUGH THURSDAY/... Through 00Z Monday...Cold air damming has set up across the Champlain and St. Lawrence Valleys with IFR to LIFR ceilings at KMSS and KBTV locations and dense fog at KBTV. The biggest question is to when these low clouds and fog will lift but in these types of situations, they could hang around for a while. The best guess based on hi-res guidance is that between 06Z and 09Z the inversion blocking all the clouds in the deeper valleys should break down and bring the aforementioned sites to MVFR and ultimately VFR by daybreak. Other locations across the North Country have been variable between MVFR and VFR ceilings but have trended toward VFR over the past hour. Winds will generally be light and variable but will start switching to the south over the next few hours with some gusty winds up to 20 kt possible Sunday afternoon. Outlook... Sunday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA. Monday: Mainly VFR, with areas MVFR possible. Chance SHRA. Monday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA. Tuesday: Mainly VFR, with local MVFR possible. Chance SHRA. Tuesday Night: Mainly VFR, with local MVFR possible. Likely SHRA. Wednesday: Mainly VFR, with areas MVFR possible. Chance SHRA. Wednesday Night: Mainly VFR, with areas MVFR possible. Slight chance SHRA. Thursday: Mainly VFR, with areas MVFR possible. Slight chance SHRA. && .HYDROLOGY... As of 345 PM EDT Saturday...A Flood Watch remains in effect until Noon on Sunday for northern, central and eastern Vermont. Rainfall has largely tapered off across the North Country with a few lingering showers residing across eastern and northern Vermont. Any new rainfall amounts will be a tenth of an inch or less which will help bring the flood threat to an end. In the mean time, a combination of snowmelt and rainfall will continue to run-off into already swollen rivers. This will allow rivers to continue to rise through the evening and overnight hours before cresting after midnight. Drier conditions developing this evening and Sunday will help mitigate any additional flood threats once rivers crest. Those with interests in low-lying or flood prone areas should continue to monitor the latest forecasts. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...Flood Watch through Sunday morning for VTZ001>008-010-016-017. NY...None. && $$ SYNOPSIS...Clay NEAR TERM...Clay SHORT TERM...Sisson LONG TERM...Sisson AVIATION...Clay HYDROLOGY...WFO BTV