Greetings everyone,

With another year without the fireworks competition, much like in 2020, I thought that it would be interesting, fun and appropriate to again prepare weather reports for each (hypothetical) fireworks day this year in an attempt to determine what prevailing conditions would have occurred. Unlike last year, however, a complete listing of fireworks dates was never released. That said, as per the preliminary information that was supplied here ( http://www.montreal-fireworks.com/forum/index.php?action=vthread&forum =4&topic=3396 ), it seems safe to assume that the 2021 edition of Montreal fireworks would have commenced Saturday, June 19th and conclude Saturday, July 24th. Therefore, based on this arrangement, and assuming a continuation of eight (8) display days, the most likely schedule would be the following:

Saturday, June 19th
Saturday, June 26th
Saturday, July 3rd
Saturday, July 10th
Wednesday, July 14th
Saturday, July 17th
Wednesday, July 21st
Saturday, July 24th


Adhering to these particular days, I will provide both preliminary and finalized weather forecasts for each. The preliminary forecasts would typically appear approximately 48 hours prior to the evenings of fireworks days, and the finalized versions of these would be provided 24 hours prior (with follow-ups on the fireworks day itself, if applicable). While it is challenging to meaningfully verify actual on-site weather conditions during these evenings, generalizations could still be made about most likely conditions present during those evenings, including during the allocated 10:00-10:30 p.m. period. Forecast reports will be presented in ways similar to previous years, with temperature/humidity, precipitation and wind speed and/or direction being the focus of the forecasts. In situations of deep convection, including thunderstorms, more details/follow-ups may be necessary, or if wind speeds are too strong or conversely too light/calm. Everyone is welcome to share updates, as well!

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For the likely opening display occupying the evening of June 19th, a very warm and humid air mass would be affecting Southern Ontario to Southern Quebec. Within this environment would be largely cloudy skies comprised of a cumulus cloud deck, including for the evening period. However, some breaks within this cloud cover would allow for some periods of sunshine. As a result of this, maximum temperatures should be 26-27 C, and 21-22 C around display time (closer to 19 C if rainfall is present during this time). The high humidity should induce a maximum humidex of 33 C, while 27 C during the evening.

Depending on the degree of sunshine, thunderstorms (a few strong) and/or convective rainfall would be possible ahead of the cold front and trough that are collectively causing these. Partly in light of limited opportunity for solar heating, convective coverage should remain scattered at best, with isolated thunderstorms among this. The thunderstorm risk appears greatest during the early- to early-evening period, though the most organized thunderstorm clusters would be capable of torrential rains, locally damaging winds and frequent lightning. The chance for precipitation would be 40% for the afternoon to early-evening period but 70% during the pre-dawn portion of June 19th.

The timing of the cold front would cast uncertainty as to convective coverage and the overall wind fields that would prevail for the evening. That said, light NW winds (7-9 km/h) appear most favorable for the early- to mid-evening, which would allow the somewhat thick accumulations of smoke to drift gently to the left of the La Ronde audience, as well as towards those on the adjacent sections of the bridge just behind. Breezier Westerly to WSW winds (18-23 km/h) would be dominant for the afternoon.

Another update to follow tomorrow late-evening to early-overnight (June 18th-June 19th).

Cheers,

Trav.

Conditions continue to be generally consistent with the information presented in the above posting. As also mentioned above, some updates for the thunderstorm risk, as well as for wind direction, will be provided below. As such, these would be the most likely conditions for Saturday, June 19th for the greater Montreal area.

Temperature/Humidity

The maximum temperature should be 27-28 C by mid-afternoon, and then 20-21 C for the mid-evening. Following pre-dawn deep convection/thunderstorms, humidity levels will favorably be high until the mid-afternoon, followed by a decline to moderate standards for the late-afternoon and onward. This would yield a maximum humidex of 31-32 C for the mid-afternoon, followed by a humidex of 24 C for the mid-evening.

Precipitation

The aforementioned cold front and mid-level trough will be the focus for rather sparsely-distributed (deep) convection this afternoon. The probability of precipitation would collectively be at 20-30% for the afternoon period. Beyond the mid-afternoon, precipitation development becomes less favorable as the front and trough advance farther downstream. For the evening, skies should be partly cloudy, consisting of mid-altitude cumulus clusters.

Wind

Wind speeds continue to be in the form of WSW throughout the day, but being quite gusty during the afternoon (especially mid-afternoon), at 38-43 km/h, and with accompanying maximum gusts of 54-58 km/h. Wind speeds do decrease considerably by mid-evening (7-9 km/h), however, and still from the WSW. This would allow the smoke to drift fairly slowly towards right-hand and partly central sections of the La Ronde audience, though very high altitude smoke would be blowing more quickly and more directly over the audience. While some accumulation at low altitudes, and during more active segments, particularly extensive smoke accumulation is not expected due to a slight drop in humidity and marginally sufficient wind speeds.

If necessary, an additional update would be provided by early this afternoon for wind direction for the evening period.

Trav.

From what I observed, it seemed that forecast details presented were largely consistent for June 19th. That said, I believe that the overall wind direction by display time was more in the form of WNW. This would have still allowed the smoke to drift slowly towards the La Ronde audience, but moving slightly more to left-hand (and still central) sections at all altitudes (still moving a little faster at very high altitude). Also, skies were mainly clear, with a few isolated cumulus clusters.

Trav.

An area of low pressure (among a family of low pressure systems) will affect Eastern Ontario to Southern Quebec for June 26th and the days beyond, towards the beginning of July. This could lead to a substantial amount of rainfall locally over the several days in which these systems have influence, especially where thunderstorms are most pronounced.

For June 26th itself, this area of low pressure will yield an environment characterized by periods of light rain and very warm conditions for the afternoon to evening. This light rainfall, combined with strong warm air circulation created by the system, would induce very high humidity by the late-afternoon. The light rain would become more persistent by late-evening and evolve more into a moderate rainfall. Beyond this, isolated non-severe thunderstorms become possible for the pre-dawn period. As such, this would more likely create rather damp conditions for this display. A maximum temperature of 24-25 C, for the greater Montreal area, is favorable once the air becomes saturated by the earlier light rain. Owing to the very high humidity, a humidex of 32-33 C is likely. In response to the near-saturated air, temperatures would not be liable to decline too much by late-evening and onward, and so a temperature of 21-22 C is likely during display time (humidex of 29 C).

Winds should be in the form of somewhat breezy Southerlies (13-16 km/h) for the evening, allowing the (rapidly) accumulating smoke to drift clear to the right of the La Ronde audience. A veered component in the wind fields near the surface would further cause SSW tendencies at higher altitudes, and so high-altitude smoke would sometimes be drifting narrowly overhead towards the extreme right-hand portion of the La Ronde audience. Periods of extensive smoke accumulation would be very likely during more active sections, and long low-altitude, especially at the display’s right-hand section.

Another update to follow by this late-evening (June 25th), or into pre-dawn June 26th.

Trav.

Conditions remain consistent with the above posting. These would be the most likely conditions for Saturday, June 26th for the greater Montreal area.

Temperature/Humidity

Despite rain-cooled and saturated air throughout the day, strong warm air advection will support warm to very warm temperatures, as well as humidification that is amplified by the moisture supplied by the actual periods of rainfall. Under these circumstances, a maximum temperature of 25 C is favored, with a humidex of about 33 C in response to the very high humidity. For the late-evening, conditions will similarly remain rather humid, and so a temperature of 22-23 C is likely (humidex of 30-31 C).

Precipitation

Periods of light rainfall (morning) to moderate-heavy (late-morning and beyond) are likely to be persistent throughout the day, not just by evening (as conversely mentioned in the assessment above). This will keep the air saturated/damp and quite humid. In light of the widespread rainfall distribution, the probability of precipitation throughout the day would be at least 90%. Isolated non-severe thunderstorms are also possible by late-evening as lift increases.

Wind

Winds would be in the form of breezy Southerlies to SSW for the day (14-18 km/h, except 28-31 km/h during the afternoon), including for the evening period. By late-evening Southerlies should be predominant. While smoke accumulations would be rather extensive, especially during more active sections of the display, and along low-level towards La Ronde’s right, the smoke would be moving fairly quickly clear to the right of the on-site audience. A slight veering wind field with height would suggest a strong SSW tendency, and so high-altitude smoke would be moving even more quickly and overhead narrowly reaching extreme right-hand sections of the La Ronde audience.

An additional update would be provided by early tomorrow afternoon (June 26th), if necessary.

Trav.

Based on what I observed yesterday evening (June 26th), during display time, rainfall persisted to about 10:21 p.m., with the heaviest rainfall occurring from 10:12 p.m. to 10:17 p.m.. Thus, it is likely that about 70% of this display would have coincided with rainfall.

Trav.

For the third display day of 2021 (Saturday, July 3rd), an area of low pressure off of the East coast will advance NE. Being situated at the back end of this system, colder than normal air will settle into Southern Quebec, keeping maximum temperatures at 21 C for the greater Montreal area. By late-evening, the air would cool to about 16-17 C, and together with 17-21 km/h NE/NNE winds, conditions would feel rather chilly at times. As a result of this flow, the (minor) accumulations of smoke would drift clear to the left of and away from the La Ronde audience but towards those on Notre-Dame Street going South of the bridge (and that adjacent portion of the bridge itself), as well as the Old Port.

In light of the cooler air, humidity would remain borderline low-moderate for the day, and a partly cloudy sky would be dominant, including for the evening period.

Another update will follow by late this evening (July 2nd) or predawn July 3rd.

Trav.

Forecast details presented above remain valid for this third display day. As such, presented here are the most likely conditions for Saturday, July 3rd for the greater Montreal area.

Temperature/Humidity

Extending the cooler air mass featured by July 2nd, July 3rd will similarly trend colder than normal. Consequently, as mentioned previously, a maximum temperature of 21 C is favorable. By late-evening, the air does cool to 16-17 C. As the humidity would largely be low, a humidex would be negligible throughout the day.

Precipitation

Being in close proximity to the aforementioned East coast low pressure system, skies should be partly cloudy, though with a concentration of cloud cover that exceeds sunny periods. Composed largely of low stratiform cloud, pPartly cloudy skies continue to be favorable for the evening.

Wind

Wind velocity would predominantly be NE, at 17-21 km/h through the afternoon-evening period. This would allow the smoke to drift clear to the left of and away from the La Ronde audience. At the same time, the smoke would be drifting towards those on the bridge over the river, as well as towards the Southern tier of Notre-Dame street (i.e. those sections South of the bridge), and towards the Old Port. This would cause the display to appear hazy from these locations, but smoke accumulation would be minor and displacing quickly enough most of the time (especially at high altitude).

If necessary, another update will follow today (July 3rd) to address wind direction.

Trav.

For July 10th, which would feature the fourth display day of 2021, conditions would be guided by an area of high pressure. This would keep the risk for rainfall development minimal and instead promote largely clear skies, with very isolated fair-weather cumulus.

In light of this system, humidity should also be predominantly low across this region, and so a humidex is negligible for July 10th. For the greater Montreal area, a maximum temperature of 27 C is likely by mid-afternoon, followed by a late-evening value of 23 C.

Winds are mostly light to calm for the day, from the NNE. Speeds continue to be rather light for the evening, at 4-7 km/h, though it is currently unclear as to a directional transition by late-evening. A change to Southerlies, however, appears possible in time for the late-evening, which would allow accumulations of smoke to drift gently clear to the right of the La Ronde audience at low- to mid-altitude. Nevertheless, periods of extensive smoke accumulation would be possible during especially more active segments, causing the display to appear hazy deeper into it. Thick accumulations, though, are not expected due to low humidity.

Another update will likely follow by late this evening into the early-overnight (July 9th-July 10th).

Trav.

The weather situation remains consistent with the above post for the fourth display day. As such, here are the most likely conditions for the greater Montreal area for Saturday, July 10th.

Temperature/Humidity

Following the cooling regime of July 7th-July 9th, including the cool conditions induced by the remnants of Tropical Cyclone Elsa on July 9th, high pressure will begin affecting the region. Under more plentiful sunshine, a maximum temperature of 27 C is favorable by mid-afternoon, decreasing to 23 C by late-evening. Borderline low-moderate humidity is likely for this day, creating a modest humidex of 30 C by mid-afternoon, and 26 C for late-evening.

Precipitation

With high pressure governing the day, skies should be mostly clear, with some isolated clusters of cirrus cumulus. This would continue for the evening period.

Wind

Wind speeds remain light throughout the day, at 4-7 km/h. Directional tendencies are largely Westerly to WSW for the afternoon, but SSW is favored for the evening as the higher pressure system drifts farther East. This would allow the smoke to move quite slowly to the right of the on-site audience, though higher altitude smoke would gently move towards far right-hand sections. While accumulations are not expected to be dense, the display would quickly take on a hazy appearance at especially low- to mid-altitude deeper into the display.

If necessary, another update will follow early this afternoon (July 10th) to address wind direction.

Trav.

Hi Trav --- I recently realized that you post weather forecast for each hypothetical fireworks nights. As I am planning to go out in town, later today, it is good to come here and to find your projection! It is only a shame that we don't have actual fireworks displays to rave about!

Fred

Hi Fred,

Yes, it would have been more than a thrill to have actual fireworks displays! Nevertheless, at the very least, we could see what kind of year that this might have been with respect to weather conditions for the fireworks days/nights.

Trav.

An area of low pressure will migrate NE in time for July 14th. As with July 13th, the warm sector of this low pressure system will continue to support very high humidity for the day, as well as enhanced instability suitable for isolated non-severe thunderstorms among scattered convective coverage.

In light of this environment, a temperature of 23 C is favored in the greater Montreal area for the late-evening, but with a humidex of 31 C. During the day, a maximum of 26 C is likely (humidex of 33 C). In a situation of rainfall during the late-evening, a temperature of 21 C would be more appropriate (humidex of 28 C).

Environmental conditions will be suitable for the development of isolated non-severe thunderstorms during the early- to mid-afternoon period (30% probability – 40% for convective rainfall collectively). In response to more limited lift into the evening period, convection should become more sparsely-distributed (30% probability).

Winds would be somewhat light during the day, at 12-15 km/h, from the SSW, including during the evening. This would be near-similar to the wind fields observed during the fourth display evening (July 10th). Due to abundant humidity, particularly significant smoke accumulation would occur during the display, especially during intense segments and segments that feature smoke-rich products. That said, the smoke would be displacing at mostly a decent pace clear to the right of the La Ronde audience (although more towards the audience in a convective rainfall/thunderstorm situation). High altitude smoke would be drifting more towards far right-hand sections of the on-site audience. Right-hand sections of the firing site would frequently appear hazy deeper into the show under the thick blanket of smoke.

Another update would follow late this evening into the early-overnight (July 13th-July 14th)

Trav.

Outlined conditions presented in the above posting continue to be largely valid. As such, provided here is the weather outlook for the greater Montreal for Wednesday, July 14th.

Temperature/Humidity

A maximum temperature of 26 C is likely by mid-afternoon, decreasing to 23 C by late-evening. Humidity remains very high within this current warm sector, and so a maximum humidex of 35 C is favored (31 C for the late-evening.

Precipitation

While instability would remain high throughout the day, lift appears best during the early part of the day. The probability of precipitation would, thus, be 40% during the morning-afternoon and 20% for the evening. Defined cumulus clusters would make up the evening sky.

Wind

Wind speeds remain fairly light for most of the day (breezier during the afternoon), from the SW. Speeds of 9-12 km/h are favored, including during the late-evening. This would allow the smoke to move gently to the right of the La Ronde audience, though also moving towards far right-hand sections, including higher-altitude smoke. Extensive smoke accumulation would be favorable during more active segments and if/when smoke-rich products are used. Still, the smoke should be displacing quickly enough most of time. The display would appear most hazy at the right

If necessary, another update will follow early this afternoon (July 14th) to address wind direction.

Trav.

For the sixth display day, featured by July 17th, an area of low pressure will be advancing into extreme Southern Quebec. In the process, the lift generated by this system will likely yield substantial cloud cover for the day, manifested as mid-level altocumulus and high-altitude cirrus. Under the influence of this system, the maximum temperature in the greater Montreal area is likely to reach 27-28 C, along with borderline moderate to high humidity. This would induce a maximum humidex of 32 C. By late-evening, the air would cool slightly to 24 C under moderate humidity (humidex of 28 C). Periods of light rain associated with this area of low pressure should occur until after display time, during the overnight, although this will continue to be monitored for the possibility of an earlier onset.

With respect to wind fields, speeds should be quite light to occasionally calm for much of the day, at 4-7 km/h. This pattern would continue into the late-evening period, but directional tendencies do begin taking on a South to SSE component. While thick accumulations of smoke are not favorable, the display could often appear hazy due to slow smoke movement. This is especially true for right-hand portions of the display (relative to the on-site audience). That said, owing to the lighter nature of the wind, the variable direction does cast uncertainty as to localized tendencies. Therefore, this will continue to be carefully monitored.

Another update to follow by either late this evening (July 16th) to early-predawn (July 17th).

Trav.