655 FXUS61 KBTV 270802 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 402 AM EDT Sat Jul 27 2019 .SYNOPSIS... Another very warm day anticipated across the North Country with just a small chance of a stray shower or thunderstorm across the higher terrain this afternoon. A better chance of scattered showers and thunderstorms will arrive on Sunday, with some storms capable of frequent lightning and brief heavy downpours. Temperatures will continue above normal for Sunday into early next week, with additional chances for precipitation on Tuesday. && .NEAR TERM /THROUGH SUNDAY/... As of 401 AM EDT Saturday...Water vapor shows mid/upper level ridge across the NE CONUS with deep dry layer overhead as a result of large scale subsidence. This dry layer will limit areal coverage of potential showers/storms this aftn, along with the lack of any significant forcing. With that said, most high res guidance continues to highlight weak Lake Ontario boundary interacting with some sfc based instability to produce a few showers/storms across the southern SLV/western Dacks. In addition, an isolated storm is possible across the eastern Dacks associated with lee side trof and Lake Champlain lake breezy boundary interaction. Once again, these trrn driven showers/storms will be isolated and very limited in areal coverage, due to lack of moisture/forcing. Interesting, soundings show deep layer mixing thru 800mb with high lcl heights, resulting in high cloud bases, which if enough precip loading can occur in an updraft, would support some localized gusty winds in the stronger cells. Something to watch this aftn with any convection. Otherwise, saw BTV reached 89F yesterday, and was thinking we should be another degree or two warmer today with progged 925mb temps near 22c and good dry adiabatic mixing per soundings. Highs generally range mid 80s to lower 90s with moderate rh levels, as some mixing of drier air aloft occurs during peak heating. Tonight, any lingering precip will quickly end by sunset with soundings showing some bl moisture return as dwpts climb back into the mid/upper 60s during the evening hours. A dry night anticipated, with best chc for fog across eastern VT valleys, as low level winds increase across slv/dacks and parts of the CPV. A muggy night with lows ranging from the upper 50s slk/nek to mid/upper 60s cpv/uhi's. Sunday...active day anticipated with scattered pulse-like thunderstorms expected across the North Country. The short wave and associated mid/upper lvl trof is located over the northern Plains/western Great Lakes this morning per latest water vapor. This energy will cross our cwa during peak heating/instability on Sunday to produce several broken lines of scattered storms. The pre-storm environment will feature moderate instability parameters with cape of 1500 to 2000 j/kg, while 0 to 6 km is 20 to 25 knots per latest nested nam. The best ribbon of 700 to 500mb winds will pass to our north, along with strongest forcing associated with mid/upper level trof shearing out. However, tail of 5h vort with some modest height falls and sfc temps warming into the mid/upper 80s and dwpts in the 60s will produce enough instability to promote strong updrafts with the stronger convective elements of gusty winds. The potential for organized convection, with a widespread severe threat is low, however still expect a few stronger storms, with a couple of svr/damaging wind gusts possible given large CAPE profiles. Also, could not completely rule out an isolated dime to quarter size hail report or two, given the cape profiles, but lack of shear/wind will keep threat minimal. SPC continues to keep our cwa in general thunderstorm outlook, which maybe upgraded in future outlooks to marginal per coordination. && .SHORT TERM /SUNDAY NIGHT/... As of 330 PM EDT Friday...On Sunday, a shortwave will dig into southern Quebec province. This feature will increase chances for showers and storms across the North Country. A somewhat moister airmass will push east Sunday morning, with higher theta-e air advecting across the region. This could generate some isolated showers in the morning, but also anticipate dewpoints to climb into the mid to upper 60s as the airmass moves in. As the day progresses, expect a few storms to join the mix later in the morning into the afternoon as temperatures warm into the low to mid 80s, resulting in roughly 1500-2500 J/kg of CAPE in the afternoon. As the shortwave feature moves closer to the North Country on Sunday, favorable dynamics could result in stronger storms, with the highest chances across northern New York and the Champlain Valley. Any of these stronger storms will be capable of gusty winds and frequent lightning during the afternoon based on the following factors: By 18Z, an upper jet streak sets up with good upper diffluence developing as a result of the amplifying ridge and the digging shortwave. Flow accelerates as the shortwave approaches, bringing 700mb winds up 30 to 40 kts. However, faster flow aloft remains a bit further north. The result will be 20-25 kts of 0-3 km shear and 25-35 kts of effective shear. Low-level lapse rates remain good, at roughly 8 C/km. Anticipate mostly pulse convection late morning. With the above shear, a few could mix in gusty winds and then storms could develop into broken lines of convection with bowing segments during the afternoon. There are some limitations to convection. Better dynamics lie further north in Canada and mid-level lapse rates remain poor. Additionally, winds veer with time, which should limit inflow into developing convection. However, along the lee-side trough and lake breeze in the western Champlain Valley, inflow could be better and allow stronger storms to develop if terrain shadowing does not inhibit development too much. By late afternoon, diurnal instability decreases, but given the aforementioned dynamical support, convection should make it across eastern Vermont as well. By Sunday night, ridging and drier air will begin to filter into the region, bringing convection to an end towards midnight, though some linger showers could remain across the Northeast Kingdom. Lows should remain in the 60s for Sunday night. && .LONG TERM /MONDAY THROUGH FRIDAY/... As of 330 PM EDT Friday...Upper trough passes to our northeast late Sunday night into Monday and with shortwave ridging over the area...dry weather is expected for the start of Monday. Eventually the flow aloft back to the southwest late in the day on Monday and perhaps some convection moves in late. Its looking more like Tuesday and especially Wednesday will have the best chances for showers and thunderstorms. This is in response to a more pronounced southwest flow aloft that becomes established as the trough axis does not move east of the area until Thursday. Instability will exist but deep layer shear is weak and thus at this time severe threat may be limited. However it will be something that needs to be watched. Gradual clearing starts to take place Thursday and Friday as upper trough axis moves east...but is still close enough that could create some weak convection on the backside of the trough. Based on 925 millibar temperatures its looking like Monday through Wednesday should see above normal temperatures...but then return to normal for Thursday and Friday. && .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/... Through 06Z Sunday...High pres both aloft and at the sfc continues to produce widespread vfr conditions across our taf sites this morning. The combination of clr skies and light winds, expect some patchy/shallow ground fog/br to develop at slk/mpv btwn 08-11z this morning. Given the lack of recent rainfall duration of ifr will be 2 to 3 hour window this morning with conditions quickly improving by 12z. Otherwise, a spot shower is possible this aftn near slk, have mention vcsh, but lack of moisture will limit areal coverage. Light trrn driven winds overnight will become south 4 to 8 knots today with vfr prevailing at all sites. Outlook... Saturday Night: VFR. NO SIG WX. Sunday: VFR. Chance SHRA, Chance TSRA. Sunday Night: Mainly VFR, with local MVFR possible. Chance SHRA. Monday: Mainly VFR, with local MVFR possible. Slight chance SHRA. Monday Night: VFR. Slight chance SHRA. Tuesday: Mainly VFR, with local MVFR possible. Chance SHRA, Chance TSRA. Tuesday Night: VFR. Chance SHRA, Chance TSRA. Wednesday: VFR. Likely SHRA, Likely TSRA. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Taber NEAR TERM...Haynes/Taber SHORT TERM...Haynes LONG TERM...Evenson AVIATION...Taber