Forecast details presented in the above posting remain mostly valid. As such, presented here are the overall weather conditions expected for August 10th for the greater Montreal area.
Temperature/Humidity
Prior to saturation under rain-cooled air, a maximum temperature of 25-26 C is more likely due to more sunlight getting through early in the day (see section below). Under very high humidity at and near saturation, a humidex of 33-34 C is favored. The air remains almost saturated throughout the afternoon to evening, with a display temperature of 18-19 C with a slight decline in humidity late-evening, governing a humidex of 23-24 C.
Precipitation
An area of low pressure will advance NE today. As previously mentioned in the above post, the cold front associated with this system, together with a series of attendant shortwave troughs, will be the principal modes of lift for ubiquitously-distributed convective rainfall during mostly the afternoon period. However, the latest thinking is that periods of sunshine will get through the cumulus cloud deck this morning into the early-afternoon in response to broken skies. As a result of this, together with very high to very high humidity, atmospheric instability would reach higher magnitudes by late-morning and, thus, support a more significant thunderstorm risk, including strong to severe thunderstorms for the afternoon to early-evening period. As such, a Severe Thunderstorm Watch could very well appear by late this morning, followed by possible Severe Thunderstorm Warnings for the afternoon. Collectively, the probability for rainfall would be 80% for the afternoon to early-evening, along with a 60% probability for thunderstorms in light of aggressive lift in the area during this time frame. The primary hazards with the more organized thunderstorm families would be locally damaging straight-line winds, intense lightning and torrential rainfall leading to significant local water accumulation. As such, there exists again some potential for technical issues during this closing display, though hopefully the outcome would be the same as it was with the Finnish display.
Nevertheless, there remain indications that the greatest lift would eject East/SE just narrowly before display time to more likely allow for drier conditions at that point. This will continue to be monitored in the newest data analyses. Under saturated air, skies would be cloudy under a low-cloud layer.
Wind
Winds would be light from the SW (8-11 km/h) until the mid-afternoon. However, differing from the above post for the late-afternoon to evening, there is further concern that the winds could become quite light (3-6 km/h) behind the convective rainfall and/or thunderstorms, and from the WSW during the evening under saturated air. As such, thick accumulations of smoke could be drifting rather gently towards right-hand and partially central portions of the La Ronde audience, from all altitudes. This could potentially obscure large portions of the display deeper into it, especially along low- to mid-altitude, and if/when smoke-rich products are used. As such, much like convective rainfall/thunderstorms, wind speed and direction need to continue to be carefully monitored.
Another update to follow throughout this afternoon (August 10th).
Trav.
