Area Forecast Discussion
Issued by NWS Burlington, VT
Issued by NWS Burlington, VT
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567 FXUS61 KBTV 281413 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 1013 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 1011 AM EDT Friday...Temperatures are warming nicely after a cool start to the day under a plethora of sunshine. Another "cool" late June afternoon remains in store for the North Country with highs topping out in the low to mid 70s. Enjoy the sunshine if you can as we have a wet weekend in store for us. Previous discussion follows: 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 initially 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 THROUGH SUNDAY NIGHT/... As of 354 AM EDT Friday...Continuing from the near term discussion, expect heavy rain showers and a few rumbles of thunder, especially towards daybreak as temperatures aloft cool. A strong jet stream to our north will aid in large scale lift in conjunction with a strong low level southwesterly jet bringing us very warm and moist air. Accordingly, an axis of greatest precipitable water in excess of 2 inches, or near the climatological maximum, will slide eastward overnight. As this happens, rich moisture will continue to stream northward as the main frontal system trails to the west. Surface dew points will be steady or slightly rise through the mid and upper 60s, while 1000 to 500 millibar relative humidity stays above 90% with high freezing levels sitting nearly at the top of this layer. Hazardous weather potential is primarily related to torrential rain, supported by CAPE with a tall and skinny profile. The heaviest rain will be in thunderstorms, with chances generally expanding eastward and increase overnight. Rainfall rates will not be overly intense outside of any thunderstorms, but even so, a long duration of moderate rainfall should provide a large swath of 0.75" to possibly 1.5" of rain through Sunday morning. Some sharp river rises are possible. Area streams and rivers will largely be near normal volume ahead of this rainfall, which helps lower the flood risk. However, the Lamoille and Passumpsic basins in Vermont are running a little high, so those may be more susceptible to seeing small stream flooding. The footprint of heaviest rain Saturday night may be important ahead of potential organized convection on Sunday that develops along a strong cold front. As typical, said cold front does appear to come through piecemeal, with showers and a few thunderstorms poised to move through our region during the morning hours and then more showers could develop towards evening. The very warm and humid low level air ahead of the first boundary suggests development of potentially moderately high CAPE Sunday morning with even modest diurnal heating. If this type of instability can be realized, the deep layer shear could support development of a squall line. Otherwise, the risk for organized convection generally will have to be watched. Winds should tend to become more westerly with mid-level drying during the afternoon, and only after a secondary front moves through do we see cold air advection at the surface usher in refreshing air by Sunday night. The incoming air mass does not look as unseasonably cool as the one currently in place, but will still be noticeably cooler. Temperatures will fall back into the 40s and 50s following a night with temperatures largely in the mid and upper 60s. Highs on Sunday will mainly be in the 75 to 80 range, although sensitive to the amount of partial sunshine that can develop ahead of the morning frontal passage. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 354 AM EDT Friday...Much quieter weather is anticipated during the long term period. Low humidity air will be in place early in the week. After some northerly flow on Monday, there is good model agreement on strong ridging and light winds for Tuesday. Then we will see the air mass modify to become more seasonably warm and gradually more humid. There are low chances of thunderstorms Wednesday afternoon/evening, mainly in western areas where more instability is expected. With outdoor activities associated with the July 4th holiday, the more humid conditions may set the stage for scattered showers and thunderstorms. At this time frame, chances look low but have included isolated thunderstorms for Thursday afternoon. Broad southwesterly flow combined with any shortwave troughs could trigger thunderstorms, especially if timing coincides with peak heating. This type of thing cannot be predicted with skill a week out, so stay tuned. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/... Through 12z Saturday...Sfc high pres will result in plenty of sunshine and VFR conditions today with light north winds 3 to 6 knots. Winds shift to the south/southeast by this evening and increase 5 to 10 knots with gusts up to 15 knots by Sat morning. Clouds will thicken overnight with some light rain showers developing btwn 09-12z acrs the northern NY taf sites. VFR conditions will be associated with these showers as they spread into VT sites toward 12z. Outlook... Saturday: Mainly VFR, with local MVFR possible. Chance SHRA. Saturday Night: MVFR/IFR conditions possible. Definite SHRA. Sunday: MVFR/IFR conditions 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...Clay/Taber SHORT TERM...Kutikoff LONG TERM...Kutikoff AVIATION...Taber HYDROLOGY...Taber MARINE...Kutikoff