Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 191149 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 749 AM EDT Mon Jun 19 2017 .SYNOPSIS... Showers and thunderstorms with very heavy rainfall will form today, mainly in Vermont and the Champlain Valley of northern New York. A flash flood watch is in effect this afternoon and evening. Small hail and gusty winds are also possible in the stronger storms. The threat for heavy rainfall and wind will lessen after tonight, however the weather will remain unsettled this week as a trough of low pressure slowly moves through the area. && .NEAR TERM /THROUGH TONIGHT/...
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As of 747 AM EDT Monday..Tweaked the pops a bit through the morning hours to lower them based on radar trends. Precip is dissipating as it moves northeast, and showers further south in NY will take until mid morning to make it up here. No other changes. 500 mb trough remains to the west during the near term period with southwest flow across the region. As noted in previous forecast cycles expecting heavy rainers today as atmosphere is primed for highly efficient rainfall processes. Warm cloud depth to 10K-12K feet, tall skinny CAPE, and Precipitable Water nearing 2 inches, which is 2-3 standard deviations above normal and near max for the day based on SPC sounding climatology for KALB. Best moisture/thermodynamic support for heavy rainfall is in east and south Vermont, tapering off to the northwest into northern NY. A weak surface boundary will move out of northern New York into Vermont around midday and provide a focus for convection. Difficult to call it a front with wind shift only from south to southwest and no real airmass change. However with southwest flow aloft ahead of the upper trough expect convective cells to move northeast along the boundary, and training cells certainly a possibility. BUFKIT soundings show Corfidi vectors less than 10 knots in central and southern Vermont this afternoon, favoring training/back building. A weak shortwave trough will rotate through the base of the 500 mb trough and move along the surface trough today to provide a trigger and help sustain convection. Severe threat this afternoon is less than prior days. Cooler surface temps under cloudy skies will limit instability. Highs in the upper 70s to low 80s, although east/south VT ahead of the boundary has forecast CAPE this afternoon nearing 2000 j/kg. Shear and instability don`t quite line up today, with 0-6km Bulk Shear of 40-50 kts is displaced to the northwest of the best instability. Kept mention of gusty winds/small hail in forecast today, but expect sub- severe with gusts to 30 mph in a wet downburst and pea hail possible but not very likely with warm cloud depth. Pops decrease tonight with loss of surface heating, however with proximity of upper low to west and weak shortwaves kicking out can`t rule out continued showers entirely. Drier surface air works into the area on the southwest low level flow, reducing dewpoints from upper 60s to low 70s down into the 60s for a little relief from the humidity.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY/... As of 432 AM EDT Monday...Large upper trough extending from Eastern Canada down into the Great Lakes will be the dominant feature in the short period. The axis of deeper moisture shifts east but area remains in southwest flow aloft with upper trough still to the west leading to potential for showers and possible thunderstorms, especially terrain enhanced activity through the early evening of Tuesday. Another round of mainly terrain driven showers is expected for Wednesday as the trough axis passes over the region. An afternoon rumble of thunder can`t also be ruled out as well. Highs for Tuesday will be in the 70s to low 80s with lows in the upper 50s to 60. Wednesday will see highs in the upper 60s to 70s. && .LONG TERM /WEDNESDAY NIGHT THROUGH SUNDAY/... As of 256 PM EDT Sunday...One broad trof at the beginning of this period being replaced by another trof late in the period with a series of disturbances and fronts makes for a messy forecast period with seasonable temperatures and shower threat through the period. Wed night/Thu: minor shortwave ridging for Wed ngt/ early Thu for a dry period, It appears some minor energy and push if some warmer air will bring about some warm frontal showers possibly late Thu/Thu ngt. Fri: Developing Great Lakes trof with a decent shortwave moving toward area Fri Ngt-Sat will send a cold front across the area late Fri-Fri ngt for showers/t-storms. Sat: Some shortwave ridging developing thus mainly dry but can`t rule out an instability shower on Sat. Sun: Another shortwave dropping across Great Lakes toward Northeast with more showers/t-storms possible Late Sunday-Sunday night across NY moving into VT. && .AVIATION /12Z MONDAY THROUGH FRIDAY/... Through 12Z Tuesday...VFR at most locations with KSLK currently seeing MVFR being the lone exception. The next potential for MVFR to IFR conditions will be across parts of northern NY and Vermont after 18z on Monday as showers and storms become more numerous once again. Winds will be southerly at 05-10 knots for most locations with KMSS seeing some late morning gusts up to 20 knots. Outlook... Tuesday: VFR. Breezy. Chance SHRA...Slight Chance TSRA. Tuesday Night: VFR. Chance SHRA. Wednesday: VFR. Chance SHRA...Slight Chance TSRA. Wednesday Night: VFR. Slight Chance SHRA. Thursday: VFR. Chance SHRA...Slight Chance TSRA. Thursday Night: VFR. Chance SHRA. Friday: VFR. Chance SHRA. && .HYDROLOGY... A flash flood watch continues from noon today through this evening for the potential for flash flooding associated with very heavy rainfall rates in thunderstorms across Clinton and Essex counties in New York and all of Vermont. High rainfall rates of 1 to 2 inches per hour with isolated higher amounts possible in the stronger convective elements will increase the potential for flash flooding this afternoon and night. The greatest potential for flash flooding will be across the higher terrain and urban areas with poor drainage, and areas that have received rainfall in the past week, including Washington, Orange, and Windsor counties in Vermont. Small streams in those areas continue to run above normal for this time of year, and can be quickly overcome by excessive rainfall. Rapid rises on smaller streams and rivers are possible in areas of the most persistent showers and thunderstorms. We also tend to see washouts of ditches and the edges of unpaved roads in steeper terrain in storms with very high rainfall rates of 2-3 inches per hour, even if they are short lived. && .MARINE... A Lake Thunderstorm Advisory is in effect for tonight. Scattered showers and thunderstorms moving across the lake though midnight will have the potential to produce gusty winds...frequent lightning..and very heavy rainfall. Storms during the overnight hours will still have the potential to produce frequent lightning and very heavy rainfall. A Lake Wind Advisory remains in effect tonight for south winds at 15 to 25 knots. These winds will continue to create very choppy conditions with waves of 1 to 3 feet and some higher swells possible over the north end of the late. Strong to possibly severe thunderstorms are expected to develop by this evening...which could cause gusty and erratic winds. Boaters should keep a close eye on the sky this evening and seek harbor if threatening weather approaches. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...Flash Flood Watch from noon EDT today through this evening for VTZ001>012-016>019. NY...Flash Flood Watch from noon EDT today through this evening for NYZ028-031-034-035. && $$ SYNOPSIS...Hanson NEAR TERM...Hanson SHORT TERM...MV LONG TERM...SLW AVIATION...MV HYDROLOGY...Hanson MARINE...Evenson/Taber

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