Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 191143 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 743 AM EDT Sat May 19 2018 .SYNOPSIS... A warm front will bring widespread rain showers to the North Country mainly this afternoon. Scattered showers and a slight chance of thunder are expected tonight as temperatures warm overnight. Sunday morning a frontal system will pass through the region with showers ending and some clearing behind it for Sunday afternoon with temperatures in the 60s to around 70. High pressure quickly builds back in to start the work week with above normal temperatures and dry weather. && .NEAR TERM /THROUGH SUNDAY/... As of 743 AM EDT Saturday...Current forecast still on track but had to tweak temps up a bit based on current readings and expectation that northern areas will make it in to the mid 60s before a dramatic wet bulb cooling 10+ degrees back into the 50s when the rain starts. RAP/HRRR even suggest it may make to 70 degrees before falling back. Previous discussion...Clouds starting to increase this morning ahead of a warm front. Expecting breezy south winds associated with developing low level jet of 20 to 30 knots at 1000 feet. This jet will help to increase moisture with clouds lowering and thickening during the late morning. Mainly light rain showers should arrive between 10-noon south and noon- 2pm central and 2-4pm near the international border. Some downslope shadowing is possible in the Champlain valley with developing 850mb southwest jet of 40 to 50 knots off the Adirondacks. Temps warm into the 50s south to mid 60s north through midday, but cool back into the lower to mid 50s this afternoon after the rain arrives and wet bulb cooling takes place. Rain will become more showery in nature Saturday night as the best warm advection and overrunning lifts northeast of the area by the evening hours. Some of the area, especially in northern NY may get into the warm sector while east of the Greens its less likely. South to southwest winds pick up in the Champlain Valley westward with a low level jet aloft with gusts of 20-30 mph. Shower chances become less early tonight as the warm sector aloft and dry slot moves in tonight there could be a period during the night without much going on before a cold front approaches the St. Lawrence Valley by early Sunday with an increase in precip probabilities. Models continue showing some CAPE to around 250 J/kg, mainly elevated, while the GFS is less. The Showalter index is slightly negative and Ks in the 30s, so a rumble of thunder is not out of the question and have slight chance in the forecast but coverage is low. Simulated satellite from the BTV WRF continues to show some embedded convective cells in the warm sector on the edge of the warm front aloft and the cold front closer to the St Lawrence Valley. The cold front on our doorstep by 12z Sun with showers ahead and along the front but clearing behind. The front will move steadily southeast Sunday with a decreasing probability of precipitation from northwest to southeast but should clear most of our area by early afternoon. Timing will play a role in the instability ahead of the front and indications are that some weak instability will develop mainly southeast VT (near VSF) and points south. Again MUCAPE only near 250 J/kg so not including thunder for Sunday morning. Looking like about a half inch of rain is expected with locally 0.75 in any heavier showers or embedded thunderstorms. Temperatures Saturday night will be steady or rising ranging from early evening lows the upper 40s east of the Greens to mid to upper 50s in the St. Lawrence valley rising through the 50s to around 60 by Sunday morning. Gradual clearing is expected on Sunday afternoon behind the front with NW winds of 10 to 20 kts and high temperatures close to normal with readings in the mid 60s mountains to lower 70s in the lower Champlain and CT valleys. && .SHORT TERM /SUNDAY NIGHT THROUGH MONDAY NIGHT/... As of 340 AM EDT Saturday...Pretty quiet 24 or so hour period. Should be mostly clear Sunday night in the wake of the front. Overnight low temperatures will be seasonable for this time of year. Monday the region will still be under dry northwest flow. With the strong late May sunshine heating the ground, that should result in a super-adiabatic lapse rate near the surface and excellent boundary layer mixing. Thus I leaned more toward the warmest guidance I could find. We should top out in the mid to upper 70s in most areas, with a spot 80F not out of the question either. Given the boundary layer mixing, did opt to lower the dewpoints given the progged dry air aloft. Should see afternoon relative humidities in the lower 20s% range, so it will be something for the fire community to monitor. Monday night should be similar to Sunday night -- lots of clear skies and light winds. Lows will range from the 40s to lower 50s. && .LONG TERM /TUESDAY THROUGH FRIDAY/... As of 340 AM EDT Saturday...00z guidance suite in "okay" agreement, and at the very least it doesn`t appear that any significant storms will affect the area for the period. Just a couple of minor systems. The model blend guidance appeared fairly reasonable, and only made a few tweaks from that. My commentary, if you wish to read it, for each of the days follows... Tuesday: a weak shortwave combined with southwest flow will result in an increase in clouds and the potential for showers, especially later in the day and into Tuesday night. As the previous forecaster noted, guidance hints at a little bit of instability, mainly elevated Tuesday night. So although a thunderstorm can`t be ruled out, given any strong signals, I have opted to keep mention out of the forecast at this point. With 925mb temperatures on the rather warm side (15-18C), we should again be well above normal for temperatures, with highs in the 70s. Could make a run at 80F in northern areas where the clouds will hold off til later in the day. Despite the talk of showers, the PoPs aren`t all that high - just 25-35% late Tuesday and Tuesday night. That means most of the time for most of us it will be rainfree. The clouds Tuesday night will also keep lows well above normal (mainly 50s). Wednesday: as the shortwave passes by early in the day, an associated weak surface low will pass by to our north. As that happens, winds switch to the northwest and some cooler air comes in. GFS has a fairly noticeable cold front, while the Euro is weaker and keeps most of the cooler air to the north. Played middle of the road for temperatures at this point with highs upper 60s to lower 70s. Not a lot of dynamics or instability around, so although there could be a few showers with the front, not expecting any t-storms. Kept the PoPs generally in the 25-30% range. Thursday: GFS and ECMWF both offer solutions which suggest a mostly sunny and dry day with northwest flow aloft and a ridge of high pressure at the surface. Big differences in temperatures. The cooler GFS has 925mb temperatures of 8-10C (which equate to highs in the 60s), while the EC is already pushing away the slight bit of cool air from Wednesday and has 925mb temperatures in the 16-18C range (which equates to highs well into the 70s if not lower 80s). However the EC solution is a fairly big change from it`s previous runs which were considerably cooler. So I stuck with the model blend which at this point still skews toward the "cooler" solution, which is still near normal. Obviously a fairly large forecast error bar exists. Friday: still northwest flow aloft and looks mostly dry. Now it`s the 00z GFS that is warmest (925mb temps 16-18C) vs the EC which cools slightly to 14-16C at 925mb. In either case, it`s looking like temperatures in the 70s is a good bet, though like Thursday, there is a wide error bar on the forecast, and it could be more summer like as we end the week and transition into the Memorial Day holiday weekend. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/... Through 12Z SUNDAY...VFR conditions are expected this morning then trending MVFR late this afternoon in rain through this evening with IFR and LLWS possible late tonight. A warm front will approach tonight preceded by light rain showers that will move north into the area 16-19z continuing through 23-01z. Flight conditions will trend toward MVFR as the rain showers taper off but with the warm frontal surface lowering could be some IFR cigs later tonight. Keeping a chance of showers through 12z with the warm front aloft. There is a slight chance of thunder with instability aloft, but not enough to include in the TAFs. Showers will move back in late as a cold front approaches Sunday morning with variable MVFR locally IFR conditions. Winds will increase from the S around 10-15 kt with gusts up to 20 kt or so. Gusts should be limited after 18z during the rain, however the exception may be RUT with may maintain gusty SSE winds through 00z. Areas of LLWS and turbulence area expected after 03z around 2000 ft but lowering to 1000 ft with the warm front aloft with a strong 35-50 kt SW jet just above the surface. Showers will move back in late as a cold front approaches Sunday morning. Outlook... Sunday: Mainly VFR, with local MVFR possible. Chance SHRA. Sunday Night: VFR. NO SIG WX. Monday: VFR. NO SIG WX. Monday Night: VFR. NO SIG WX. Tuesday: VFR. Slight chance SHRA. Tuesday Night: Mainly VFR, with local IFR possible. Chance SHRA. Wednesday: Mainly VFR, with areas MVFR possible. Chance SHRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Sisson NEAR TERM...Sisson SHORT TERM...Nash LONG TERM...Nash AVIATION...Sisson is the U.S. government's official web portal to all federal, state and local government web resources and services.