275 FXUS61 KBTV 161921 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 321 PM EDT Thu Jul 16 2020 .SYNOPSIS... Showers and thunderstorms will develop across northern New York this afternoon ahead of a warm front and spread eastward as we head into the evening and overnight hours. These showers and thunderstorms will persist into Friday afternoon when a cold front allows these storms to taper off from west to east. Quiet weather will return for Saturday but as we head into Sunday we will see afternoon highs climb into the upper 80s to lower 90s with heat indices pushing 95 to 100 degrees across the region. A cold front pushing through Sunday night and Monday will bring a reprieve to these very warm temperatures with temperatures expected to return to near normal values behind the front. && .NEAR TERM /THROUGH FRIDAY NIGHT/... As of 317 PM EDT Thursday...We are beginning to see cloud cover increase across the St. Lawrence Valley in response to a progressive shortwave trough. This feature is the leading edge of strong moisture advection and over the next several hours we will see our PWAT values across the region climb from around 1.2" to around 1.8". This will begin to set the stage for rain showers to develop this evening and persist through much of the day on Tuesday. In the mean time, we should see enough elevated instability develop across the St. Lawrence Valley this afternoon to support some convective showers with some embedded thunderstorms. This will largely be associated with the shortwave trough as it quickly pushes through our region. With all instability of the NAM3, BTV4 and ARW/NMM cores all being elevated and not rooted at the surface, the chances for gusty winds looks very unlikely. In addition, with the rapidly increasing moisture within the atmosphere (increasing PWATS), lapse rates in the low to mid-levels will likely be moist adiabatic which will not support any hail development. Thus, any showers or thunderstorms this afternoon could produce some moderate to heavy rainfall but remain well below severe limits. Showers with embedded thunderstorms will become more widespread during the overnight hours as a warm front pushes through the North Country. The best chances for thunderstorm activity will be prior to midnight with a strong capping inversion developing behind the warm front which should keep much of the thunderstorm activity at bay. However, some nice channeled flow up the Champlain Valley will lead to winds gusting between 20 and 30 mph across the northern Champlain Valley through much of the overnight period; especially around Lake Champlain. Shower activity probably won't make it into Vermont until around midnight but on and off showers are expected to continue into Friday afternoon when a cold front ultimately comes through and brings an end to the rainfall. Rainfall totals of 0.5" to 0.9" will be common across northern New York with the highest amounts expected across the rain-starved St. Lawrence Valley. Rainfall totals across Vermont will range from 0.3 inches across southern Vermont to 0.6 inches near the international border and across northeastern Vermont. Flooding is not anticipated with this system as it'll be quick to exit the region with the 40-50 knot jet helping to push the rainfall through the region. However, we will continue to monitor the situation closely as it unfolds. Any lingering shower activity will come to an end by Friday evening with decreasing cloud cover and weakening winds being observed across the region. Dewpoints will drop slightly behind the cold front which will help make the overnight hours feel pleasant as temperatures drop into the upper 60s to lower 70s. Fog looks likely to develop across the North Country Friday night in response to the rainfall and stabilizing atmosphere but we won't have a good idea of exactly where until once we see where the heaviest rainfall occurs. && .SHORT TERM /SATURDAY THROUGH SUNDAY/... As of 317 PM EDT Thursday...Main highlight and for the weekend continues to be a return of unwelcome heat and humidity. High pressure anchored off the Atlantic seaboard combined with a slowly evolving upper trough over Saskatchewan and Manitoba will usher in increasing humidity from the mid-west on southwesterly low level flow. Mid/upper level flow will remain generally out of the west though which should help to moderate the air mass a bit, but 925mb temps of +22-24C Saturday and +24-28C Sunday will support highs of 85-90F and 88-95F respectively. Dewpoints will be bearable Saturday, but jump into the oppressive category Sunday which may support heat indices of 95-100F in the deeper valleys. The need for a heat advisory in these areas will need to be monitored. Saturday night will be muggy with temps only falling into the mid 60s to low 70s and humidity near 100%. In regard to convective potential, there remains little forcing for storms to develop through the period, but models continue to hint at the idea of afternoon/overnight convection over southern Ontario riding over the ridge Saturday night but mainly remaining north of the border. Still could see something possibly drift south, but with much uncertainty will keep the forecast dry for now. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... As of 317 PM EDT Thursday...Heading into next week, conditions look more favorable for several chances of showers and thunderstorms. First comes with the aforementioned upper trough translating eastward along the intl border Sunday night which the parent surface low well north will drag a cold front through the region. It currently appears that the timing will support a lack of convection due the overnight passage, but with progged PWATs up to to 2" the threat of locally heavy rain will be possible. A brief period of high pressure builds in for Monday and Tuesday with generally dry conditions expected, followed by increasing chances for more showers and thunderstorms Tuesday night through Wednesday as another trough drops out of Canada into the Great Lakes. Temps through the period begin well above normal with highs Monday ranging through the 80s to locally 90 possible in the deeper valleys, but cool closer to seasonal normals in the lower 80s for the remainder of the week. Low remain mild in the 60s, with modest humidity. && .AVIATION /19Z THURSDAY THROUGH TUESDAY/... Through 18Z Friday...A mix of MVFR and VFR ceilings prevail across the North Country this afternoon ahead of an approaching warm front. Conditions will likely deteriorate as we head into the evening and overnight hours as we begin to see moisture surge into the region with ceilings dropping to 1500 to 2500 ft by 12Z on Friday. Isolated pockets of IFR conditions will be possible, especially at KSLK during the morning hours initially behind the warm front until a cold front swings through. We are expecting convection to move into KMSS between 22Z and 00Z and spreading eastward into Vermont just prior to 12Z. We could see some embedded rumbles of thunder but we are generally looking at some decent rain makers tonight and again on Friday. Visibilities look to stay above 6SM but some stronger showers or thunderstorms could briefly drop visibilities to 3-5SM. Wind shear will also be a concern tonight into the early morning hours as a strong low level jet moves overhead. We will likely lose our gusty winds between 6Z and 14Z when we will see 40-50 knots of wind at 2000 ft. This will likely lead to some decent turbulence during the morning hours across much of northern New York and Vermont. Conditions will slowly improve throughout the day on Friday as precipitation ends from west to east and ceilings begin to slowly improve and the stronger winds aloft exit to the east. Outlook... Friday Night: VFR. NO SIG WX. Saturday: VFR. NO SIG WX. Saturday Night: VFR. NO SIG WX. Sunday: VFR. Chance SHRA. Sunday Night: Mainly VFR, with local MVFR possible. Chance SHRA. Monday: Mainly VFR, with areas MVFR possible. Chance SHRA. Monday Night: VFR. NO SIG WX. Tuesday: VFR. Chance SHRA. && .MARINE... South winds have increased to 20-30 knots this afternoon as the pressure gradient has increased between a departing high pressure system across the Gulf of Maine, and a frontal system across the Great Lakes. Waves will build to 3 to 5 feet by this evening, likely highest across the northern portion of the broad lake. These strong and gusty winds will continue through early Friday afternoon before tapering off. Waves will take a little longer to settle down Friday afternoon with waves gradually subsiding to 1-3 feet Friday evening. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Clay NEAR TERM...Clay SHORT TERM...Lahiff LONG TERM...Lahiff AVIATION...Clay MARINE...Banacos/Clay