Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 240806 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 406 AM EDT Sun Jul 24 2016 .SYNOPSIS... Other than areas of fog this morning it looks like we will have a break from the storms today with plenty of sunshine and high temperatures generally in the 80s. The dry weather will be short lived as the threat for more showers and thunderstorms returns Monday afternoon and evening. And as has been the case with the last couple of events...some of the storms could be strong to severe. && .NEAR TERM /THROUGH TONIGHT/... As of 406 AM EDT Sunday...Drier northwest flow aloft will prevail across the area for a good part of the day today before the flow aloft backs to the west tonight. Still some lingering clouds over the area early this morning along with some fog and these elements will be gradually eroding and should be gone by mid-morning. The resulting sunshine should help temperatures climb into the 80s during the afternoon hours. The flow aloft begins to back to the west tonight and moisture will begin to increase. Most of the night will remain dry but as shortwave trough approaches...potential for some isolated convection will exist out across the Saint Lawrence Valley by Monday morning. Lows will range from the upper 50s east to the upper 60s west. && .SHORT TERM /MONDAY THROUGH TUESDAY NIGHT/... As of 406 AM EDT Sunday...Monday: 00z guidance suite in okay agreement amongst one another, but as typically the case, it`s those subtle differences that really are the keys to locking in the details. that said, there still continue to be a number of items in the "pro strong convection" category. those being: shortwave moving into the area at peak heating time, an elevated mixed layer (EML), surface instability (model mean CAPE values 1500-2000 J/kg), decent 0-6km shear of 40- 45kt (esp later in the afternoon). in the "con strong convection" arena, question about how much sunshine we`ll be able to get as there could be some debris clouds during the morning, no strong low level convergence, fairly warm layer around 800 mb which may act as a cap to updrafts. after back and forth discussion (in my head, and with the other forecaster here), I think most things will come together for at least scattered convection to develop - that will have the potential to become locally strong. SPC`s latest Day 2 outlook keeps the region in a "Marginal Risk" for severe thunderstorms due to the uncertainty. That assessment seems reasonable at this point. Have added some enhanced characteristics to the forecast, namely to add in the potential for strong gusty winds and small hail with thunderstorms during the afternoon/early evening. Speaking of that warm layer aloft, models indicate 925mb temperatures could warm to as much as 25C. Mixing that down to the surface under perfect situation (sunshine and well mixed boundary layer) would result in temperatures reaching the mid-90s! In fact, some aspects of Monday`s setup appear similar to what we saw on Friday, where the warm layer aloft did cap convection for much of the day and allowed temperatures to soar into the 90s. At this point due to the uncertainty of cloud cover (thinking there will be some) and the fact that the majority of guidance has mid 80s for highs, I did go warmer than most guidance, but still played it a bit conservative and painted in Upper 80s to a few spot 90F in the valleys. Anticipate scattered thunderstorms to develop in the morning across northern NY and then spread east throughout the afternoon. Bulk of the storms should be east of the forecast area shortly after 21z (5pm), however some instability will continue across western half of the region into the early evening as those areas could have a chance to "reload" thanks to sunshine after the initial batch of storms earlier in the afternoon. So for PoPs, I ramp up to the 45-60% level by mid afternoon, then show a decrease, but keeping some 20- 30% PoPs going until a bit after midnight for eastern VT. Convective mode will probably start with isolated cells, a line forming during the afternoon. Primary threat would be strong wind gusts. Monday Night: residual thunderstorms wind down for the first half of the night across eastern sections. It will still be warm/muggy overnight as there isn`t any cold front out there. Tuesday: We`ll be on the backside of the trough responsible for Monday`s action. Generally means subsidence aloft, and this should be the case. Thus looking for a mostly sunny day. Guidance does suggest a little bit of moisture hung up across the Northeast Kingdom of VT and with that area being closer to the upper trough, a shower or two is not out of the question early in the day. Otherwise with 925mb temperatures in the 18-20C range, we will readily top out in the lower to mid 80s in the valleys. This is several degrees above normal. Tuesday Night: quiet and calm, but still mild. Generally lows in the upper 50s to lower 60s. && .LONG TERM /WEDNESDAY THROUGH SATURDAY/... As of 406 AM EDT Sunday...Decent agreement between the 00z GFS and ECMWF for much of the period. Wednesday should be dry and very warm. 925mb temperatures are a couple of degrees warmer than Tuesday, so we`ll see highs well into the 80s, perhaps a few lower 90s in the southern valleys. Hints of slight 500mb height falls and a weak surface front to our north that will probably be a focus for a few thunderstorms across Quebec. That feature should stay away from here based on 00z guidance, but previous runs didn`t have it as close. So perhaps that is a trend? Thursday is a little trickier. Even though the 00z suite are similar, they are differing from the 12z counterparts. At face value with the 00z models, it would be a generally sunny and hot day (925mb temperatures pushing 24C which would be mid 90s in valleys) and still show a front just to our north. Previous runs had moisture pushing up from the southwest. Thus will maintain idea of 20-30% chance of showers/t-storms. Won`t buy into the heat just yet, but even then, it will be another warmer than normal summer day (mid 80s at least). Friday a deeper southwest flow pattern should be established, and models bring increasing moisture into the region. Thus we should see more in the way of clouds and scattered showers/t-storms, and temperatures closer to normal assuming more clouds. Saturday is more "iffy". GFS continues the moist southwest flow pattern with a shortwave off to our west. That would mean a rather unsettled day. 00Z Euro has a weak ridge in place with light northerly flow, which would suggest dry and mild. Forecast will show a blend, which actually works out to climatology. Don`t cancel outdoor plans yet for Saturday. && .AVIATION /08Z Sunday THROUGH Thursday/... Through 06z Monday...Areas of fog and low clouds are expected through 14z which will cause LIFR and VLIFR conditions. Otherwise... VFR conditions are expected through the rest of the period with little in the way of cloud cover expected. Winds will generally be under 10 knots through the period. Outlook 06z Monday through Thursday... VFR conditions through much of the period. Showers and thunderstorms Monday afternoon and night could be strong to severe with gusty winds and hail and ceilings/visibilities lowering into the MVFR and IFR categories with any of the showers and storms. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Evenson NEAR TERM...Evenson SHORT TERM...Nash LONG TERM...Nash AVIATION...Evenson is the U.S. government's official web portal to all federal, state and local government web resources and services.