Area Forecast Discussion
Issued by NWS Burlington, VT

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000 FXUS61 KBTV 221407 AFDBTV Area Forecast Discussion National Weather Service Burlington VT 1007 AM EDT Fri Jul 22 2016 .SYNOPSIS... scattered showers and thunderstorms, some possibly severe, are expected through Saturday as a frontal system moves slowly through the region but there will be partly sunny rain free periods as well. It will be hot today with high temperatures in the mid 80s to lower 90s. Another round of thunderstorms is possible on Monday. Meanwhile Sunday looks dry and seasonable. && .NEAR TERM /UNTIL 11 PM THIS EVENING/...
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As of 957 AM EDT Friday...Scattered clouds about in fast flow and on visible you can see the tubulent nature of the clouds. At 10 am...already 82F here at BTV and likely getting into L90s if not a few degrees higher. SFC based CAPES already 500-1000 J/KG across St Lawrence Valley where Td are in M-U60s. Dry Air aloft has developed a CAP and basically awaiting some trigger. VSB satellite showing linear feature which looking at model data I attribute it too mid-lvl trof and pre-fntl trof. Although we and high resolution models have backed off for any thunderstorm show to begin after 4 pm and come from quebec...will still need to watch closer to home for early afternoon. Confidence is low as High RES models have not handled well. No changes to current forecast. Previous Discussion issued at 751 am...The shortwave and scattered early morning showers/storms have exited the area and some shortwave ridging is resulting in some temporary stabilization. Model soundings mix down decent dry air advection that should allow for plenty of sun to develop and thus heat up for high temperatures reaching the mid 80s to lower 90s especially where westerly to southwest winds downslope into the valleys. Surface instability should start to return this afternoon but will depend on how much dry air gets mixed down to the surface and what the resulting dew points are. Right now it looks like low to mid 60s should do it which will give us CAPES around 1000 J/kg, some of the models suggest dew points will be peaking into the upper 60s later in the day when CAPE may rise to 1500 to 2000 J/kg. It will probably end up somewhere in between. Very dry mid-levels support downward momentum for potentially damaging winds and hail given wet bulb zero levels drop below 10K. 0-6km shear values are around 40 kts which also support the severe potential. SPC outlook has us in the slight chance category for today. The main trigger for thunderstorms should be toward late afternoon and evening hours. Low level instability still prevalent early and area in closer proximity to approaching stronger nrn stream shortwave...surface front as well as nose of 300mb and 500mb jets moving into area by 00z Sat enhancing any lift. Tonight...Any shower/thunderstorm activity wanes after midnight but still influenced by northwest cyclonic flow which will keep shower threat especially across NC-NE Vermont. Could be some patchy fog around especially where it rains this evening. lows mainly in the 60s.
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&& .SHORT TERM /11 PM THIS EVENING THROUGH SUNDAY NIGHT/... As of 414 AM EDT Friday...00z guidance suite still inconsistent with some of the details for Saturday, especially with respect to the coverage and specific timing of convection. Synoptically, a potent shortwave, currently moving into the far reaches of western Ontario will move east- southeast over the next 36 hours and should be reaching into our area sometime Saturday afternoon. The dynamics are expected to kick off thunderstorms (actually, there will likely be a cluster of thunderstorms as well with that shortwave that will move southeast out of Quebec and into our region). Each model has a differing evolution of the convection, and is again a symptom of just how sensitive the models are to this type of weather pattern that is driven by mixed layers, elevated and low level instability and boundary layer details. Taking a blend of the models suggests that we`ll have CAPE values perhaps up to 1000 J/kg which is decent enough to drive convection. Not seeing any strong signals with other convective indices to suggest additional severe t-storms. GFS hints at a bit of an elevated mixed layer (EML) but not the NAM. NAM has 30-40kts of shear, GFS is less than 30kt. Suppose we can`t totally rule out a stronger storm with gusty winds here or there. Looks like the highest chances for storms will be from mid-day through the evening and more so from the `Dacks and points eastward. SPC has this same region marked with "Marginal Risk" and at this point, that seems like a good assessment. Storms come to an end during the evening. An upper ridge moves over the region for Sunday. If you want a day with no weather worries for outdoor activities, Sunday will be the day. Temperatures both days will probably be within a couple of degrees of normal. Upper 70s to lower 80s. A bit humid on Saturday, but in the wake of the upper trough, drier air will come on in as flow becomes northerly. && .LONG TERM /MONDAY THROUGH THURSDAY/... As of 414 AM EDT Friday...No huge changes with the overall synoptic pattern depicted by the 00z guidance. In general our area will be underneath westerly flow. One moderately strong shortwave comes across somewhere in the late Monday/early Tuesday timeframe. Some instability depicted in the models, as well as decent 0-6km shear (GFS has 40-50kt), however the big question is timing. If all of this comes together with peak heating time Monday afternoon, we would have the chance for strong/severe t-storms. If it comes through at night, then it`s nothing much more than showers with embedded rumbles of thunder. 00Z GFS is a little slower than it`s previous runs and suggests a Monday night passage. 00z ECMWF is quicker and suggests Monday could be somewhat active. At this point, trying to pin this feature down to within 6 hours is beyond my skill level. Thus have maintained a more broadbrush forecast indicating roughly 50% chance of t-storms Monday and Monday night. With the westerly flow, temperatures aloft do warm a few degrees so we should be a bit warmer than normal (lower- mid 80s). Depending on the timing of the Monday/Monday night system, there could be some residual showers around first thing on Tuesday. Otherwise Tuesday will be the beginning of a stretch of some fine mid-summer weather. With westerly flow, temperatures won`t vary much from day to day and will top out several degrees above normal. Looking for widespread lower/mid 80s into Thursday. At this point it looks dry for Wednesday, and pretty much Thursday. Couldn`t rule out an isolated t-storm Thursday however as at least the ECMWF indicates some moisture around with moderate levels of instability. Looks like the next system will be coming in sometime Thursday night into Friday. && .AVIATION /14Z Friday THROUGH Tuesday/... Through 12z Saturday...mainly VFR cigs through 15z with some stratocumulus MVFR at KSLK. expect all VFR by 15Z with daytime heating. Expecting another possible round of showers/thunderstorms in the late afternoon or evening with another upper level short wave and surface trough, again producing mvfr vis in scattered rain showers perhaps some very brief IFR in thunderstorms. These storm coincide with daytime heating and may produce strong gusty winds and hail. Lull between rain episodes with no precip through much of midday. Confidence low on thunderstorm occurrence and location, so didn`t put in the TAFs until it becomes more certain. Best guess is northern NY and VT in the 21-03Z period. Showers and storms will wind down by midnight. Some patchy fog or mist possible where it rains, but for now just put in at MPV where climatology favors it. South to southwest winds will be 10-15G23KT today, perhaps veering more to west by afternoon. Outlook 12z Saturday through Tuesday... Sat...VFR, with scattered brief MVFR/IFR in showers and thunderstorms. Some thunderstorms may contain strong winds and hail. Sun...Mainly VFR under weak high pressure. Mon/Monday night...VFR with scattered brief MVFR/IFR in showers and thunderstorms with frontal passage. Tuesday...VFR/high pressure. && .BTV WATCHES/WARNINGS/ADVISORIES... VT...None. NY...None. && $$ SYNOPSIS...Sisson NEAR TERM...Sisson/SLW SHORT TERM...Nash LONG TERM...Nash AVIATION...Sisson

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