Hi everyone,

As we are all well aware, the 2020 edition of Montreal fireworks has been cancelled in light of the global pandemic known as COVID-19. Traditionally, preliminary and finalized weather forecasts would be prepared in these threads within 48 hours of each display, addressing temperature, humidity, precipitation risks, and wind speed/direction.

Although no displays this year, at Fred's suggestion, I have decided to create this thread for fun to see what weather conditions would be like during the fireworks days/nights originally scheduled for this year. While no weather forecasts would be provided, this thread could perhaps still be used as a form of monitoring conditions for each of the fireworks days to see what would have likely been present for each of the eight display days, even though it would be difficult to actually verify on-site conditions during the 10:00-10:30 p.m. period. Everyone is free to participate if they wish to. I would have added "Watch" in the thread heading, as it is appropriate, but it probably would not have fit. Haha

Today (June 20th, 2020 - the first official day of Summer 2020) would have featured the opening display. As it turns out, weather conditions would have likely been practically perfect for this first show. More fitting is that this opening night and first day of Summer are part of a significant heat wave - possibly the lengthiest June heat wave in recorded history for the island if it can last for seven consecutive days.

I would expect the light SSW winds (7-9 km/h) to blow the smoke gently clear to the right of the La Ronde audience, and although thunderstorms were in the general area this afternoon (South of the island, near the New York border), they were largely driven by solar heating and so weakened quickly by late-afternoon-evening. This leaves mostly clear skies with a few clusters of cirrus for this evening. The high humidity and fairly light winds would encourage some periods of smoke accumulation, but these would usually be displacing relatively quickly enough to not obscure viewing much (depending on how many active segments there might have been). Likely 27-28 C on the Molson display, too!

Que tombe la nuit!

Trav.

It would have been a great, warm summer night to open the season! Thank you, Trav.

Fred

Thanks Trav! I was hoping you'd continue the tradition of your weather reports/predictions!

Paul

No problem, Fred and Paul! I think that I will ultimately go ahead and follow the same layout for the rest of the originally scheduled display nights as I would have done in a normal year.

Weather conditions for the second scheduled display night (June 27th) will favorably carry on with the warmer than normal pattern.

Temperature/Humidity

Temperatures should be very warm (maximum of 28-29 C), together with borderline moderate-high humidity. This is especially true as the sun gradually breaks through the cloud by late-morning This would suggest a late-evening temperature of 21-22 C (humidex of 25-26 C) at and around the firing site.

Precipitation

Due to an advancing warm front, however, isolated convective rainfall and non-severe thunderstorms will become increasingly possible, especially by late-afternoon. This would include a 30% probability of precipitation during the late-afternoon, and then 40% for the evening as convective coverage increases. Should rainfall occur persistently during the evening, then the air would cool to 18-19 C (humidex of 24-25 C).

Wind

Winds should be in the form of SSW, with speeds of 13-17 km/h during the evening period. Much like during the opening night, this would have likely allowed the smoke to blow reasonably quickly clear to the right of the La Ronde audience, despite some periods of smoke accumulation. Note that if thunderstorms are in the area, the local wind flow would temporarily be disrupted.

Trav.

I think just a light rain was present during the second half of the 10:00-10:30 p.m. (June 27th) timeframe - largely the last 10 minutes. Occasional distant lightning was also observed around the Mirabel-Saint-Jerome corridor for about 35 minutes prior to 10:00 p.m.

Trav.

Yeah, in my area, a light rain began around 10:20pm. I live in the Northern part of Montreal, and I had seen, early tonight, the rainy zone on the radar moving from the Laurentides region towards us. So I thought the rain could be starting somewhat later at La Ronde, just before or (hopefully) after the finale.

Fred

Hi Fred,

Thank you for kindly sharing these observations! Out here, in the SW West Island-Vaudreuil corridor, the light rain began at about 9:50 p.m. before gradually evolving into more of a moderate rainfall. But yes, I think the most significant of the rainfall only occurred until after display time (while during the last 5-10 minutes, a light rainfall or even drizzle was present around the firing site). Saint-Hubert airport also reported moderate to heavy rainfall by 10:50 p.m. So, very likely, the display would have been largely dry, though meeting with some light precipitation during its final 33%, or perhaps closer to the finale and/or penultimate piece (unless the display would have extended beyond 10:30 p.m.!).

Thanks, again, Fred!

Trav.

Yeah, this scenario reminds me the weather during, and shortly after the opening show on July 1, 2017. I wrote in my report of that show:

Whereas rainy and windy weather conditions were forecast for this very humid day, the sky was partially clear during the evening and wind were not strong at all. As predicted by Trav, the smoke moved gently toward the right of the audience. However, during the last two segments, the wind suddenly turned toward the audience, then toward the left of the audience. As Trav sometime writes, such fuzzy wind patterns may be associated to rainfall. Indeed, just a couple of minutes after the show (before I even put my tripod into its bag), the rain began and it soon became heavy. We were fortunate to not have such precipitations during the show itself !

Fred

Yes, as I read the weather observations of your report, the situation for June 27th, 2020 was very similar to that of July 1st, 2017! And, yes, convective rainfall and/or thunderstorms often disrupt the wind flow at the local scale, since they produce their own winds. Thus, under these circumstances, a variety of wind directions can suddenly be observed over even a matter of minutes before the broader-scale wind flow can be restored following the influence of the rainfall event. In cases of heavy rainfall approaching the firing site (usually from the West), the winds, if they aren't already, can suddenly blow towards the on-site audience.

In the absence of rainfall, when the winds are very light (i.e. less than 6 km/h), a variety of wind directions can also further be observed during a display in progress. This is because local scale factors become more important in controlling directional tendencies at those speeds, making their patterns frequently erratic.

Trav.

Weather conditions for the third display day (July 4th) should continue with the very warm/hot tendency that had developed since June 16th. As such, this day may be part of an official heat wave. While convection would be inhibited, some lift in the area would support a near-continuous layer of cirrus later in the afternoon into the evening. Therefore, a maximum temperature of 29-30 C would be favorable before cloud cover interferes by late-afternoon, but the extent of the cloud coverage would limit cooling during the evening. Consequently, the temperature would not fall lower than 26-27 C for display time. Together with moderate humidity, a humidex of 30-31 C is favorable during the late-evening.

Wind speeds would be light throughout the day (4-7 km/h), and from the North/NNW. However, by display time, speeds should increase to 11-14 km/h and from the WSW. This suggests that the smoke would frequently be displacing somewhat slowly but towards central and right-hand sections of the La Ronde audience, although particularly thick smoke accumulation is not favorable.

Another update will follow by later this evening (July 3rd).

Trav.

Conditions presented in the above post continue to be largely applicable. As such, here are the dominant weather details for the 3rd fireworks day (today - July 4th) scheduled for this year for the greater Montreal area:

Temperature/Humidity

Temperatures will continue to be very warm to hot. This would suggest a maximum of 29-30 C by mid-afternoon, potentially expanding on what is now the island of Montreal's second official heat wave for this year. By late-evening, the temperature should drop to 26-27 C. Humidity will not be particularly high, though, and so will be constrained to borderline low- moderate standards. Therefore, the humidex will be negligible, especially into the evening.

Precipitation

No rainfall is expected, as convection will remain suppressed. However, sufficient lift in the area will support a fairly uniform layer of cirrus cloud into the evening.

Wind

Winds should be in the form of light North-Northwesterlies (NNW) during the morning to early-afternoon, with speeds of 4-7 km/h favorable during this time. However, by evening, winds should shift to more of a WSW tendency with slightly stronger speeds of 11-14 km/h. This would allow the smoke to blow reasonably quickly towards central and right-hand sections of the La Ronde audience, making the display appear often murky (especially deeper into the show and following active segments). Thankfully, smoke accumulation would likely not be extensive due to the lower humidity.

If necessary, another update will follow this afternoon for evening wind direction.

Trav.

Expanding on the post above, wind speeds should continue to be light this evening (July 4th), but even lighter, at 6-8 km/h. Also, wind direction should be more in the form of WNW this evening, so the smoke would most likely move gently towards central and left-hand sections of the on-site audience (had there been a display, of course). Still, particularly excessive smoke accumulation would not be favorable in light of low humidity, but the display would become murky, largely from La Ronde's perspective, not too long after commencing.

All other details are still applicable.

Trav.

What a wonderful night it would have been... except for the wind speed and direction!

Fred

Hi Fred,

Yes, it would have definitely been another wonderful night! Although it is difficult to confirm this, at the firing site, I think the wind direction might have even been a mix between the above-specified WNW, but also NW, suggesting that the smoke would have sometimes been more directed towards left-hand sections of the audience (and towards those on the bridge watching from behind). Wind speeds also appeared a touch stronger (around 13 km/h during display time), so it seems likely that the smoke would have correspondingly been moving a little quicker, but still displacing gently, overall.

Composite radar imagery also revealed that the cloud cover was producing some local light rain just before and during display time. However, it appears that this precipitation was largely not reaching the ground/near-surface due to the dry air favorably inducing evaporation. Thus, it is likely that conditions remained dry during the 10:00-10:30 p.m. - indeed, rainfall was not reported at St-Hubert airport the entire time.

Trav.

As the very warm to hot pattern continues, conditions for the fourth scheduled display of 2020 will favorably be very warm and highly moist. Consequently, maximum temperatures of 28-29 C will be possible on Saturday, July 11th for the greater Montreal area but would feel like 37-38 C under very high humidity concentrations. Due to very high humidity, the temperature would only decline to 25-26 C, with a continued humidex of 37-38 C. With rainfall, the temperature would drop to 23 C (humidex of 32 C), since the air would already be near-saturated.

Meanwhile, July 11th presents an interesting situation in that the remnants of tropical cyclone Fay will drift North to slightly NNW and merge with another area low pressure coming from the SW. As this happens, periods of (heavy) rainfall will be favorable during the morning of Saturday. It is this rainfall that will continue to moisten the air and keep it near-saturated and buoyant. However, recent and latest analyses would suggest that breaks in the cloud deck would emerge by early-afternoon, which would effectively allow sunlight to get through regularly by this point. This would further moisten the air and cause the temperature to rise fairly close to the 30.0 C threshold. That said, due to potentially spending extensive amounts of time under cloud cover and rainfall during the morning, it seems likely that Saturday will narrowly miss reaching or exceeding 30.0 C, putting an end to what is going to be a significant heat wave by this afternoon (July 10th). That said, the periods of sunshine will encourage scattered convective rainfall and isolated thunderstorms (a few strong) by mid- to late-afternoon (60% probability of precipitation). The thunderstorm risk would continue into the evening period, but convective coverage would diminish progressively with the loss of solar heating (40% probability of precipitation by late-evening). Skies would be cloudy during the evening.

During this event, wind speed and direction would be variable. By late-evening, directional tendencies should be WSW to SW, at 11-14 km/h, suggesting that the smoke, at all altitudes, would be displacing towards right-hand sections (partly central) of the La Ronde audience. In light of such a near-saturated and highly humid environment, smoke accumulation would be rapid, especially along low-level and during more energetic segments. Still, this accumulating smoke would displace reasonably fast enough, but the display might have appeared fairly murky at right-hand sections under the thick smoke.

Another update to follow by late this evening into the early-overnight (July 10th-July 11th).

Trav.