Area Forecast Discussion
Issued by NWS Burlington, VT

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523 FXUS61 KBTV 242347 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 747 PM EDT Sun Jul 24 2016 .SYNOPSIS... After a beautiful end to the weekend, hot and active weather returns to the North Country again on Monday as an occluded front will bring a return of showers and thunderstorms during the afternoon to evening hours. Much like the past few active days, some storms may be strong, accompanied by gusty winds and small hail. High pressure returns to the region for Tuesday and Wednesday with seasonable temperatures and just a few isolated showers possible in the Northeast Kingdom. && .NEAR TERM /THROUGH MONDAY/...
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As of 747 PM EDT Sunday...Going forecast remains in good shape and only some nominal adjustments to sky cover and t/td datasets were needed as of 700 pm to blend with current trends. Radar returns showing some very light activity skirting into the St Lawrence Valley on the nose of deeper warm thermal advection aloft, but given large surface dewpoint depressions I have to imagine most if not all of this is just virga. Did paint in a token 10 pop across the northern border zones through midnight (mainly NY) to account for the possibility of a stray sprinkle, but essentially inconsequential. Have a great evening. Prior discussion follows. A quiet night is on tap for the North Country tonight as an upper ridge currently over the eastern Great Lakes shifts overhead. Skies won`t be particularly clear with some convective debris clouds from activity currently over Michigan/Ohio drifting in, but conditions will remain dry with temps comfortable again in the mid/upper 50s east to the mid/upper 60s west. Monday still looks like another active day here, but the devil`s in the details as to timing and subsequent intensity of convection. Afternoon upper air and surface analysis show our forcing mechanism for convection on Monday is an occluded front shifting into the Great Lakes with the parent low well north approaching James Bay and triple point over western Lake Superior. As the parent low shifts to the southern tip of James Bay by 18z tomorrow, the occlusion lifts northeastward allowing the attending warm front to move into the BTV CWA mid/late morning, and the cold front after 18z. This is a slightly later arrival than previously forecast, but may actually work better for convective development as we`ll have a chance for overnight debris clouds around Monday morning to lift out. The con will be that we`ll be on the downward trend of peak instability by the time the front gets here. As the previous shift mentioned though, we`ll have a lot of ingredients in place to support convective development, that being an elevated mixed layer with modest mid-level lapse rates around 7C/km, decent 0-6km shear of 35-45kts, and ample surface instability of 1000-2000 J/kg. Hindering convective development will be the morning debris clouds, and a fairly warm layer aloft, both of which will act as a cap at least through mid- day. All this said, still siding on the idea of scattered to numerous showers and thunderstorms developing over the area after 18z, with a focus from the Adirondacks eastward where the greatest instability will develop due to dewpoints pushing into the upper 60s to low 70s, and mean 925mb temps around +23-25C supporting highs well into the upper 80s and a few lower 90s. SPC`s latest Day 2 outlook upgraded portions of the region to "Slight Risk" and expect by tomorrow morning that risk will be expanded to more of the area. Primary threat will be like yesterday, mainly gusty to locally strong winds with a secondary threat of large hail due to high freezing levels.
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&& .SHORT TERM /MONDAY NIGHT THROUGH TUESDAY NIGHT/... As of 352 PM EDT Sunday...Going into Monday Night, likely to have some convective activity ongoing across eastern portions of the area through at least 8-10pm, dissipating thereafter as the front shifts east and high pressure begins to build in from the Great Lakes. The parent upper trough lingers behind though so after a brief wind shift to the west/northwest behind the front, the prevailing low level flow will remain out of the south/southwest keeping overnight temps on the mild and muggy side ranging through the 60s. Quieter conditions return for Tuesday and Tuesday night as high pressure builds over the area. We`ll still be under cyclonic northwest flow aloft so scattered afternoon fair weather cumulus are likely, along with a few isolated showers across the Northeast Kingdom. Highs will be around seasonal normals in the upper 70s to low 80s. Skies clear out Tuesday night with any lingering showers dissipating by midnight, and lows drop into the mid 50s to low 60s. && .LONG TERM /WEDNESDAY THROUGH SUNDAY/... As of 352 PM EDT Sunday...Decent agreement between the 00z/12z GFS and ECMWF for much of the period with any differences in the late week/weekend somewhat less but still problematic for the details. Wednesday should be dry and 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/12z guidance. Both models in agreement that above mentioned front does shift south across area Thursday which should be the focus of storms. Latest models push it further than previous runs and given still some uncertainty feel it could still be quite warm in southern sections perhaps L-M80s in North with L90s in southern sections. Friday and Saturday are as described by previous forecaster "iffy" as both have a southwest moist flow but timing of shortwave ridging impacts when we would actually witness precipitation. A threat of showers/t-storms thu ngt into early friday with perhaps a dry period but when is the question...thus went with previous fcst of a blend. There may be a better chance of rain, showers, t-storms on Sunday as a deeper, broader trof moves into fa with perhaps a weak wave moving along a stationary boundary that remains from thursday/friday. Confidence is low on timing but frequent threat of showers/rain seems reasonable. && .AVIATION /00Z Monday THROUGH Friday/...
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Through 00z Tuesday...VFR through 16Z Monday. Sct/bkn high clouds from 150-250 agl to advect across the region tonight under light and variable winds. After 12Z flow trends south to southwesterly 6 to 12 knots in advance of approaching energy from the Great Lakes. Increasing threat of sct/numerous showers and storms from 18Z onward west to east. Per model diagnostics and SPC SWODY2 progs some of the storms will likely trend strong to perhaps severe with brief MVFR/IFR, gusty winds and moderate to severe turbulence. Confidence on occurrence of strong to severe convection is moderate at this time, though aviation interests in the 18-00Z time frame should plan for this potential. Outlook 00z Tuesday through Friday... 00z Tue - 06z Tue: Mainly VFR with scattered to numerous showers and thunderstorms exiting east by 02Z if not sooner. Brief IFR/MVFR possible with this activity. 06z Tue - 00z Fri: Mainly VFR under high pressure. Isolated showers possible Wed/Thu afternoons. 00z Fri - 00z Sat: Increasing chances for widespread MVFR showers and isolated thunderstorms.
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&& .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Lahiff NEAR TERM...JMG/Lahiff SHORT TERM...Lahiff LONG TERM...SLW AVIATION...JMG/Lahiff is the U.S. government's official web portal to all federal, state and local government web resources and services.