Area Forecast Discussion
Issued by NWS Burlington, VT
Issued by NWS Burlington, VT
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957 FXUS61 KBTV 280747 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 347 AM EDT Fri Jun 28 2024 .SYNOPSIS... A beautiful day is on tap with plenty of sunshine and mild temperatures in the upper 60s to mid 70s. Clouds increase tonight with occasional showers developing on Saturday, along with breezy south to southwest wind gusts of 30 to 45 mph. Localized heavy downpours are possible on Saturday afternoon into Sunday, which will need to be watched closely for the potential for localized flooding. Drier weather returns by the start of next week. && .NEAR TERM /THROUGH SATURDAY NIGHT/... As of 342 AM EDT Friday...A chilly morning acrs our cwa with SLK down to 36F as of 3:45 AM and BTV at 50F which is the coldest for the date since 1990. The near term concerns wl be gusty winds and developing precip on Saturday acrs our fa. Today is very quiet with 1022mb high pres shifting from the northern NY into the Gulf of Maine by 00z this evening. Plenty of sunshine expected with comfortable temps in the upper 60s to mid 70s. Light and variable winds become south by this evening at 4 to 8 mph. Tonight-Saturday...As sfc high pres shifts to our east, deep south/southwest flow develops ahead of our next s/w trof with strong moisture advection. Pw values surge to near 2.0" by 00z Sunday, which are near daily maximum for the date or 2 to 4 std above normal for late June. The dynamics associated with approaching mid/upper lvl trof and orientation of the jet stream aloft wl help us to maximize qpf amounts, but intially instability is limited so rainfall rates should be held in check. Helping to advect this deep layer moisture into our region with be an anomalously strong 850mb jet of 50 to 60 knots from the southwest on Sat. Sounding profiles show a sharp inversion around 2.5kft, with top of the mixed layer winds of 35 to 42 knots on Sat. We should see enhanced southerly flow given inversion height, especially acrs the central/northern CPV with localized gusts 40 to 45 mph likely midday Saturday. Also, secondary enhanced area of gusty winds are likely over the northern Dacks along the route 11 corridor from near Malone to Altona, where gusts to 40 mph is likely. A few isolated power outages are possible in these areas on Saturday. Timing of rain showers on Saturday acrs our cwa is rather challenging, especially in the morning into early aftn hours. Initially airmass is rather dry at all levels and expect some virga associated with first surge of warm air/moisture advection. However, secondary s/w energy and another surge of moisture advection develops btwn 18-21z from sw to ne acrs our region and expect showers to increase in areal coverage, with developing widespread wetting rainfall likely acrs most of the region by 21z Saturday. I have tried to integrate this thinking into the pop grids for Sat. As we have mentioned multiple times over the past several days, many ingredients are coming together for localized heavy downpours on Sat aftn/evening, including warm cloud depths of 12.0 to 13.0 kft, pw values near 2.0", sw orientation of 850mb jet of 50 to 60 knots, and rrq of 250mb jet passing to our north acrs central Canada. Given the orientation of the llvl jet toward the High Peaks, this area wl need to be watched closely for localized heavy rainfall and potential flooding, especially overnight as instability aloft increases to help enhance localized heavier rainfall rates. WPC has upgraded parts of northern NY in their latest day 2 ERO to slight risk, which from our perspective looks reasonable given the synoptic scale setup. Difficult to pin point exact qpf amounts thru 00z Sunday, but generally 0.25 to 0.75 with highest values over northern NY with a tenth of an inch or less over eastern/southern VT. Have placed localized heavy rain wording into the grids btwn 21-00z acrs northern NY on Sat, as elevated instability increases btwn 150-400 J/kg from west to east. Also, given the increasing elevated instability parameters off both the NAM 3KM and HRRR have mention isolated thunder. SPC has expanded their day 2 marginal risk to cover all of northern NY, but feel the greatest threat maybe aft 00z, when instability increases further. Highs on Sat in the upper 60s to mid 70s, with increasing humidity toward sunset. && .SHORT TERM /SUNDAY/... As of 244 PM EDT Thursday...A 50 knot southwesterly low-level jet will move directly overhead Saturday afternoon into Saturday evening, as our area is squeezed between high pressure to our east and a low lifting to our north. With the resultant warm air advection on southwesterly winds, a temperature inversion will develop in the 850 to 950 mb layer, which will prevent the strongest momentum air from mixing to the surface in lower elevations. Nonetheless, expect a gusty day with south/southwest wind gusts 20 to 30 mph for most locations. Higher elevations (above 2500 ft) will gust higher, potentially 45+ mph. The Champlain Valley will also see stronger winds in the 25 to 35 mph range as flow is channeled up the valley. Peak wind gusts will be observed Saturday afternoon/early evening just before the onset of rain. Once steady rain moves into the area, winds will diminish slightly as the rain stabilizes the air. Latest thinking on the timing for arrival of steadier precipitation will be Saturday afternoon for northern NY, and late afternoon/early evening for VT. However, some earlier scattered showers are possible before the arrival of the steady precipitation. Given the low-level inversion, instability will be marginal if any, and thus have kept mention of thunderstorms out of the forecast for Saturday. However, ingredients are favorable for some heavy rainfall overnight. Precipitable water values climb to around 2.0 inches, which is around 200% climatological normal. In addition, deep warm cloud depths of over 12 kft will increase precipitation rates, though lack of instability will temper heavy rainfall potential. At this point, it appears system will be just progressive enough to preclude any widespread training threat, though some isolated areas may have multiple heavy rain showers move overhead and thus may see some ponding of water in poor drainage areas. Current Excessive Rainfall Outlook from WPC for Saturday has our forecast area outlined in the Marginal Risk. Will be watching things closely, but not expecting widespread issues at this point. Storm total amounts for Saturday through Saturday night will be in the 0.5 to 1.0 inch range. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... As of 244 PM EDT Thursday...Steady rain will come to an end Sunday morning, but showers will continue thanks to a series of fronts that will move through during the day. As the fronts/troughs move through, will see decreasing moisture and thus potential for any moderate to heavy rain within showers will be lessening. However, steepening low and mid-level lapse rates will result in some marginal instability, though depth of moisture and instability will be relatively shallow. Thinking we will see a few embedded thunderstorms during the day within the rain showers, though limited instability will temper severe potential. Once the final cold front sweeps through late Sunday, will be in for a drier start to the work week as expansive high pressure builds in from the west. Highs in the 70s/low 80s with dewpoints generally in the 50s will feel quite refreshing and should be a beautiful stretch of weather overall. A gradual warming trend can be expected going into midweek. The next chance for showers will be in the Wednesday/Thursday timeframe. && .AVIATION /08Z FRIDAY THROUGH TUESDAY/... Through 06z Saturday...VFR conditions expected at all taf sites for the next 12 to 24 hours as sfc high pres is building directly overhead. Given the 1 degree spread at SLK and crnt temp at cross over value, expect some periods of fog and associated IFR vis is possible btwn 07-11z. Feel the potential is in the 30-40% range, so have utilized a tempo group to highlight the potential, otherwise light and variable winds will become south 4 to 8 knots toward 00z this evening. Outlook... Friday Night: VFR. NO SIG WX. Saturday: Mainly VFR, with areas MVFR possible. Chance SHRA. Saturday Night: Mainly MVFR, with areas IFR possible. Definite SHRA. Sunday: Mainly VFR, with areas MVFR possible. Chance SHRA, Slight chance TSRA. Sunday Night: Mainly VFR, with local MVFR possible. Slight chance SHRA, Slight chance TSRA. Monday: VFR. NO SIG WX. Monday Night: VFR. NO SIG WX. Tuesday: VFR. NO SIG WX. && .HYDROLOGY... The threat for localized heavy downpours and isolated flash flooding is possible this weekend across our region. The Weather Prediction Center Day 2 Excessive Rainfall Outlook has northern NY in slight risk or at least 15% chance of rainfall exceeding flash flood guidance within 25 miles of a given point. The area of greatest concern based on anticipated precipitation amounts would be across the High Peaks of northern NY, with a secondary area of concern over central VT, given recent rainfall amounts. Current forecasts indicate between 0.60 and 1.50 inches of rainfall is expected with localized amounts of 2.0 to 3.0 inches possible in the heavier thunderstorm activity late Saturday into Sunday. Please continue to monitor the latest forecast for additional details over this upcoming weekend. && .MARINE... Unseasonably strong winds are expected on Saturday when a Lake Wind Advisory will be needed for Lake Champlain. South winds may exceed 25 knots by daybreak and may be be above 30 knots on the broad lake at times during the day. Rough waves could develop quickly. Wave heights on the broad lake and inland sea may build into the 3 to 5 feet range briefly Saturday. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Taber NEAR TERM...Taber SHORT TERM...Duell LONG TERM...Duell AVIATION...Taber HYDROLOGY...Taber MARINE...Kutikoff