Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 011119 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 719 AM EDT Fri Jul 1 2016 .SYNOPSIS... Increasingly unsettled weather today as a upper level disturbance and cold front spark heavy showers and strong to severe thunderstorms this afternoon and tonight. Storms will be capable of gusty winds, small hailstones and localized heavy rainfall. Showers and thunderstorms move eastward by midnight tonight. Breezy conditions, cooler temperatures and chances for showers start the Independence Day Weekend Saturday. Mostly sunny skies and dry conditions should lead to good conditions for outdoor holiday plans Sunday and on Independence Day. && .NEAR TERM /THROUGH TONIGHT/...
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As of 718 AM EDT Friday...No significant changes made to the forecast. With this update, I`ve just accounted for current observations in the forecast grids. Strong sunshine underway this morning, but watching deck of mid-level cloudiness across western PA/NY move pretty quickly eastward and will begin to overspread our western zones arond noon. Steadier showers and embedded thunder associated with cold front extends from near Toronto ON southward to Cleveland OH. Prospects for strong to severe thunderstorms today remains on track after reviewing some of the more recent HRRR output. Highs should top out in the 70s to low 80s. Previous near-term discussion issued at 429 AM follows... Forecast remains on track toward an active Friday afternoon and evening featuring strong to severe thunderstorms capable of gusty winds, small hail and localized heavy rainfall posing some hydrologic concerns as well. Generally clear skies continue this morning under weakening surface ridge, with 2-m temps running in the 50s to low 60s and dewpoints in the upper 40s to mid 50s. However starting to see mid-level height falls ahead of a neutrally-tilted 500 mb shortwave trough with axis extending along the eastern shore of Lake MI, with an associated cold front from the northern corner of IN/OH into the lower Ohio Valley. Expect to see at least mostly clear to partly sunny skies this morning, gradually filling in by this afternoon from the southwest. Stage will then be set for developing thunderstorms. Overall, no significant changes noted from earlier thinking in terms of instability/shear parameter space and setup. While we should see steeper low-level lapse rates set up with the sunshine, instabiilty will be limited to 1000 to 1300 J/kg of SBCAPE at best due to surface dewpoints in the upper 50s to lower 60s. Dewpoints only start to climb in the few hours ahead of developing storms, as southeast low-level winds help tap into reservoir of mid/upper 60s dewpoints over the mid-Atlantic states. In terms of wind fields and vertical shear, 500mb trough axis becomes negatively tilted and we should then start to see an increase in mid-level winds by mid afternoon into the evening, leading to southwesterly 0-6km shear vectors increasing into the 30-35 knot range by early evening. Also noting that the sfc-1km shear is around 20 knots. So CAPE and shear at least support stronger storms but will be aided by forcing for ascent owing to the negative-tilt mid-level trough and diffluent nature to the mid/upper flow. Nearly all convection- allowing models (HRRR, BTV-4/6 and the ARW/NMM) show initial storms developing in the central Adirondacks/Mohawk Valley region of NY by around 17-18z and move northeast and merge into clusters/small- scale bowing lines late this aftn into the evening across the North Country. Think we end up seeing several strong to a few severe storms late afternoon and evening, capable of gusty winds (given DCAPEs of 1000 J/kg) and small hail (WBZ heights are around 10 kft). See the Hydrology section for more details on the hydro aspects, which will need to be carefully monitored even though storms should be moving along. Have maintained enhanced wording for gusty winds, heavy rain and small hail in the Wx grids, with highest PoPs in the 20-03z period. Storms should pass into NH by midnight, with residual slight chance PoPs west to east. Looking at highs today in the 70s to lower 80s, with lows in the 50s with lowest low temps in NY and on the warmer end of that range across VT.
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&& .SHORT TERM /SATURDAY THROUGH SUNDAY/... As of 429 AM EDT Friday...Saturday becomes our typical post frontal regime with the upper low settling in over the area with lowering heights, residual low level moisture and west to northwest upslope flow allowing for showers, mainly across the northern portion of the area closer to the upper low centered over Quebec. It will be cool and breezy as well with highs only around 70 and northwest winds 15-25 mph. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... As of 429 AM EDT Friday...Daytime showers end and turning dry for any firework displays sunday night. Monday(4th) will be dry and seasonably warm. Late morning temperatures in the 60s/70s will be ideal for any parades. Broad ridge over the central US sets up for the rest of the week with westerly flow and building heights thus warming trend through the week and dry. Late week there are slight differences in the models on a potential disturbance in the wnw flow but for now...warm and dry. Dewpoints/moisture seem manageable until late week when surface high slides east allowing southwest flow and greater humidity with perhaps another northern stream upper low and trough for stormy next weekend. && .AVIATION /11Z Friday THROUGH Tuesday/...
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Through 12Z Saturday...VFR through the morning hours, though focus shifts the afternoon and evening with strong to potential severe thunderstorms. Showers and strong storms starting around 18-21z as a cold front nears and eventually sweeps across the area. Frequent lightning, gusty winds capable of localized turbulence, at least small hail and heavy downpours capable of brief IFR visiblility restrictions are all possibilities in the strongest cells. Maintained MVFR +SHRA group in the TAFs to reflect when the period of greatest strong thunderstorm threat would be. Later TAFs issuances can better define specific timing/impact. Cold front exits into NH by 06z with dissipating showers and a west wind shift. Will need to watch for possible MVFR ceilings after 06z, particularly for the NY TAF sites. Outlook 12Z Saturday through Tuesday... 12Z Saturday through 12z Sunday...Generally VFR, though daytime VFR/MVFR visibility showers as an upper level disturbance passes to our north. Gusty northwest winds of 25-30 knots likely to be biggest impact on aviation, strongest during the afternoon hours. 12Z Sunday through Tuesday...VFR under high pressure during the day. Possible overnight IFR to VLIFR fog at SLK and MPV each evening.
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&& .HYDROLOGY... As of 429 AM Friday...We continue to monitor potential for localized heavy rainfall in strong to severe thunderstorms this afternoon and evening. Strong QG forcing should help produce a widespread rain for the area. Precipitable water values increase during the afternoon and evening to around 1.3 to 1.5", moderately high but again not excessive. The progressive nature of the mid- level trough and storm motions should keep cells/lines moving, but NEly Corfidi vectors of 10-15 kts supports potential for some backbuilding. Will need to monitor convective evolution today for this potential. Flash flood guidance still is rather high, but areas that will need to monitor for heavy rainfall capable of small areas of flash flooding are in Franklin and western Clinton Counties in NY and Orleans, Caledonia and Essex Counties in VT given the flash flooding that occurred in these areas early in the week. Urbanized areas and mountainous terrain are common trouble spots as well. Main-stem river flooding is not anticipated. && .MARINE... As of 429 AM Friday...Those boating on Lake Champlain today should be aware of the potential for strong to severe thunderstorms near the Lake during the afternoon and evening hours. Storms will be capable of lightning, small hail and gusty winds creating choppy waves. A Lake Thunderstorm Advisory may become necessary today as storms potentially develop/move toward Lake Champlain. Be prepared to seek safe harbor if threatening weather approaches today. Saturday will feature gusty northwest winds, likely in the 15 to 25 knot range. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Loconto NEAR TERM...Loconto SHORT TERM...SLW LONG TERM...SLW AVIATION...Loconto HYDROLOGY...Banacos/Loconto MARINE...Loconto

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