Hi everyone,

As we are now within a week of starting the 2025 Montreal Fireworks Competition, I thought that it would be appropriate to release this thread in preparation for that.

As always, preliminary and finalized weather forecasts will be provided here prior to each display. Preliminary details will typically appear approximately two days before display times, followed by finalized forecasts by about a day before actual displays. These forecasts will include information pertaining to temperature, humidity, rainfall opportunities, as well as wind speed and wind direction. In situations where (severe) thunderstorms or rainfall altogether become important, or in cases of weak/strong wind fields (or precarious wind direction), additional brief updates will be provided. As with 2023, where applicable, air quality will also be included in forecasts due to the ongoing wildfire situation in the Canadian West.

Let's hope for ideal weather conditions for all displays, and for each setup period!

Trav.

Thanks Trav! Looking forward to your forecasts again!

All the best,

Paul.

No problem, Paul! Always a pleasure! It could prove to be an interesting Summer with respect to the weather!

Cheers,

Trav.

Being situated North of a stationary (warm) front, and under the influence of a shortwave trough, largely cloudy conditions are favored for the opening display day (June 26th). At the same time, periods of scattered light rainfall during the afternoon (a 60% probability so far for this situation) and stretching to potentially the late-evening will act to keep conditions cool and nearly saturated as the shortwave overspreads this region. As such, a maximum temperature of 21-22 C is favored for the greater Montreal area, which would be achieved during the late-morning to early-afternoon before rain-cooled air takes place principally by the mid-afternoon. At maximum cooling during the mid-afternoon period, a temperature of 14-15 C would unfold and be sustained going forward. With saturation, moderate humidity would be achieved. Under these conditions, a light jacket and/or thick sweater would be necessary with prolonged exposure outdoors.

Winds should be in the form of light ENE to NE (7-9 km/h), including for the evening. This would allow smoke accumulation, at all altitudes to evacuate slowly and directly away from and slightly to the left of the La Ronde audience. However, those watching from Notre-Dame and De Lorimer Streets should try to displace away from the bridge (i.e. in the direction of the Olympic Stadium) to avoid viewing obstructions from smoke accumulation. Although smoke density shouldn't be particularly high, damp and saturated air would sometimes encourage sizeable accumulation at low-altitude, and/or during more energetic segments. The lower cloud ceiling would also sometimes hide portions of upper-level shells, and nearly saturated air would occasionally cause colors to appear somewhat faded.

Another update to follow this late-evening into predawn (June 25th-June 26th) to confirm or revise these details, especially in terms of rainfall persistence beyond the afternoon.

Trav.

Details described in the post above remain largely applicable for today (June 26th), though with some revisions. As such, presented here are the weather conditions for the greater Montreal area.

Temperature/Humidity

A maximum temperature of 21 C is likely, achieved by mid-afternoon, making this one of the coolest daytime highs/maximum temperatures to appear this month. Humidity would be low, and so a Humidex would not be applicable. By late-evening, around display time, the air cools to 17 C under continued low humidity. A light sweater or light jacket could be useful for the evening, though the light winds would thankfully not amplify the chill in the air greatly.

Precipitation

The aforementioned shortwave trough continues to have some influence on the region for principally the early-afternoon. This would induce significant cloud coverage, as well as scattered periods of light rainfall (60% probability at the time). Rainfall quantity itself would be limited due to generally lower intensity and duration. Following the early-afternoon, skies should be remain cloudy under mid- to high-altitude cloud cover. However, one revision here is that the light rainfall would not persist beyond this period, as the trough would send this farther South of the region. As such, mostly high-altitude cloud coverage would persist for the remainder of the afternoon through to the evening, along with some clear breaks that may very well offer some window of opportunity to briefly reveal the sunset as a high pressure zone temporarily slides South. Under this revision, cloud ceiling should ultimately be higher (mid- to high-altitude cloud) than what was previously suggested in the above posting.

Wind

Wind fields continue to be quite light from the East to ENE (4-7 km/h) for the late-afternoon to evening North of that stationary (warm) front, though the winds would be breezier from the NE (17-21 km/h) for the early- to mid-afternoon. This would allow for smoke accumulation, at all altitudes, to move gently towards the Notre-Dame audience (and correspondingly very slowly away from the La Ronde audience). Thankfully, as mentioned, humidity would be low, so larger smoke density is not favored. However, the display would often still appear hazy/foggy from Notre-Dame/De Lorimier Streets and adjacent sections of the bridge, especially venturing deeper in the display and at low-altitudes when the display grows more active (and if/when more smoke-rich products are used at times).

*Another update will appear here, if necessary, for evening wind speed/direction.

Trav.

Latest data reveals similar wind velocities for this evening. In addition, the clear breaks expected for this late-afternoon to evening would stretch to capture this mid-afternoon with an earlier Southward ejection of the aforementioned high pressure zone. It should already be sunny downtown and Eastward/NE, with this soon reaching the West Island and West. As such, a clearer mid-afternoon to evening is favored with patches of cirrus, but still with a somewhat cool late-evening temperature (17-18 C).

Trav.

Indeed now the sky has cleared and it's beautifully sunny downtown. Looks like it will be the perfect evening, even if it's not so hot as we've had recently!

Paul

Hi Paul — Yes! The clearing has just also recently reached out here in the West Island-Vaudreuil corridor! We had some light rain earlier this afternoon that came in from Ottawa, but I believe that it stayed dry farther East over greater Montreal and East/NE/SE of there. Looks like we'll, indeed, be able to take advantage of this clearing, and so it will capture more than just around sunset!

Trav.

The situation for July 3rd will support a continuation of the air mass featured by this past week, including a highly humid environment. However, a more conservative maximum temperature will take place because of potentially more interference from thunderstorms/convective rainfall and increased cloud cover. As such, a maximum temperature of 25-26 C is favorable for the greater Montreal area, and with high humidity, a Humidex of 30-31 C is likely. By late-evening, including display time, the temperature cools to 19-20 C (more comfortable than during the opening show) with a Humidex of 24 C.

Thunderstorms/convective rainfall would firstly be associated with a cold front during the morning period, followed by a pair of shortwave troughs for the afternoon. Moderate instability for the morning to mid-afternoon would encourage scattered convective rainfall coverage, prompting a 60% probability of precipitation for that time. Guided mostly by a locally strong straight-line wind hazard, there is a window of opportunity for some thunderstorms to achieve strong to severe status during the afternoon. A Severe Thunderstorm Watch would be released if this continues to be favored. Fortunately, latest thinking is that the lifting features provoking this situation would more likely evacuate to the SE in time for the late-afternoon and beyond, allowing for a gradual clearing deeper in the evening, as well as decreasing humidity levels (to moderate).

Winds should generally be light for most of the day, but they turn NW by early-afternoon under breezy speeds (17-21 km/h). By late-evening, it remains unclear whether these wind fields will hold as NW or turn more Northerly, or even WNW. At this point, a light NW wind flow is favored, with speeds of 9-12 km/h. This would allow the smoke to displace sufficiently (notably mid- to upper-level smoke) towards left-hand sections of the La Ronde audience, and for those on the bridge located behind the grandstands. Significant smoke accumulation is not favored under lesser humidity, and the laser segments should allow for additional clearing.

*Another update will appear here to confirm these details late this evening (July 2nd) into early-predawn July 3rd.

Trav.

Conditions described in the above posting remain largely valid for today (July 3rd) for the greater Montreal area:

Temperature/Humidity

As cooler and drier air quickly settle in by mid-afternoon, in addition to early-day rainfall limiting the extent of warming, a somewhat more reserved maximum temperature is favorable. However, sufficient breaks in the cloud deck to permit for sizeable sunny periods during the mid-morning to afternoon should permit a maximum of up to 26-27 C, with a reachable Humidex of 31-32 C. By late-evening, a temperature of 19-20 C would appear, with a negligible Humidex due to borderline low-moderate humidity.

Precipitation

As mentioned in the above-posting, convective rainfall and thunderstorms remain favorable for mid-morning to mid-afternoon. First, a cold front will aid in the development of scattered convective rainfall during the mid- to late-morning. Following this, a potent shortwave trough will eject SE and will begin introducing a thunderstorm risk for the late-morning to mid-afternoon period. Due to sufficient solar heating and high humidity early-day, destabilization would be moderate and would therefore offer a window of opportunity for the development of some organized thunderstorm families. Since some of these thunderstorms would be capable of locally damaging winds along their gust fronts, a Severe Thunderstorm Watch may appear to account for this. The probability of rainfall, in general, would be 70% during the morning period, and 40% for thunderstorms due to some reductions in lift supplied by the trough. Following the mid-afternoon, conditions drastically improve, and a clearing would ensue. As such, mostly clear skies are favored for the late-afternoon to evening, with isolated patches of cirrus and fair-weather cumulus.

Wind

Winds continue to be largely in the form of breezy Northwesterlies following frontal and troughing passage. During the morning, SW winds will be predominant as the warmer and more humid air mass remains in place. Latest and recent guidance points towards a stronger NW flow, with gusts sometimes reaching up to 44-48 km/h during mid-afternoon. These remain breezy into the late-afternoon to early-evening (17-21 km/h) but quickly lighten to 9-12 km/h by mid- to late-evening. As mentioned in the above posting, the generally light smoke accumulation would be moving towards left-hand sections of the La Ronde audience at a sufficient pace (faster displacement in that direction at the highest altitudes of the display), and towards those spectators on the bridge immediately behind the on-site audience.

Trav.

An update that I would like to present is a small adjustment to wind direction, as there would be an interplay between NW and WNW winds throughout the evening (July 3rd) at and near the surface (under the same range of speeds mentioned previously). This would help to still guide the smoke towards principally left-hand sections of the on-site audience, but also sometimes partially towards central sections. Mid- to upper-level smoke would still more distinctly push towards left-hand sections overhead.

The thunderstorms themselves were mostly focused to the West, affecting the West Island to the Ontario border (and NE of the island) — we received quite a rainfall out here at the West end of the West Island-Vaudreuil corridor during the mid-afternoon thunderstorm series (3:45-4:30 p.m.), but it appeared to stay dry farther East towards greater Montreal, thankfully (apart from the light rain earlier this afternoon). This morning's thunderstorms were quite lightning-abundant through Lachute towards Mirabel.

Trav.

In light of strong warm air advection, July 6th would re-establish a hot and very humid air mass in what would be one of the hottest days so far this year. Indeed, a relatively strong SW flow will allow humidity to reach very high status, accompanied by a maximum temperature of 30-31 C in the greater Montreal area (possibly 32 C if cloud cover isn't overly intrusive). A maximum Humidex of 39-40 C is also attainable. With increased cloud coverage and such humidification, this would make the Japanese display a contender for the warmest/most humid display temperature this year (23-24 C – Humidex of 31 C), and in sharp contrast with the previous two fireworks evenings. If under rain-cooled air, the late-evening temperature would be 21 C (Humidex 29-30 C).

A cold front and shortwave trough ejecting SE will also prompt an increase in cloud coverage through the day (including the morning). The lift associated with these features would be high and so would encourage widespread convective rainfall, as well as sparsely-distributed non-severe thunderstorms, for the late-afternoon to evening, notably farther North/NW of the island. However, there are indications that these lifting features could stall (narrowly) long enough for the associated convective rainfall to hold off affecting the Montreal area until the predawn period of July 7th, leaving behind mostly cloudy conditions with some clear breaks for the evening. As such, this will have to be monitored.

The speed at which the cold front and shortwave trough advances SE will determine the wind direction for the late-afternoon to evening period. Nevertheless, winds remain as breezy Southwesterlies throughout most of the day, at 19-23 km/h (occasional gusts reaching 31-35 km/h). If these lifting features are permitted to advance SE quickly enough, the SW wind field would turn into a NNE one by late-evening, while also drastically increasing the likelihood for convective rainfall and isolated thunderstorms into the late-afternoon and evening. If so, this would permit winds to turn Northerly/NNE, causing the smoke accumulation to slowly drift towards sections of the bridge immediately left of the firing site (and to La Ronde's left). If not, then the SW tendency would survive through to the evening and so would guide the smoke instead towards right-hand sections of the La Ronde audience (La Ronde's right). The very high humidity, potentially damper air and lighter wind fields during the evening would encourage periods of significant smoke accumulation, notably during more active sections of the display along its low- to mid-altitudes. The laser segments in this display would, therefore, be beneficial for this situation.

*Another update will appear here later this evening (July 5th) to predawn July 6th to review these described conditions.

Trav.

The environment described above for the Japanese display day remains applicable with respect to overall wind flow and temperature/humidity character. A revised outlook of wind and convective rainfall appears below. As such, here are the weather conditions for July 6th for the greater Montreal area:

Temperature/Humidity

A maximum temperature of 31-32 C is likely, making this easily the warmest/hottest fireworks display day this year so far (in contention for the hottest/most humid fireworks day altogether). A display temperature of 23-24 C is favorable (22-23 C after mid- to late-afternoon/early-evening rain-cooled air — Humidex of 30 C). Humidity would be very high, sending the Humidex into the 40s C (40-41 C) for the third time this year. Humidity remains borderline high to very high for the evening, inducing a Humidex of 31-32 C in time for the display.

Precipitation

The above posting describes the influence of a cold front and attendant shortwave trough. These features will advance SE through the day, prompting widespread convective rainfall development notably farther North/NW of the island. That said, latest indications have these lifting agents ejecting farther SE to begin having some impact in and around the Montreal area by mid-afternoon. Although the extent of instability would still be limited to moderate status, this would be enough to favor scattered thunderstorm coverage, including some organized thunderstorm families that would be capable of principally significant rainfall rates and potentially moderate lightning frequency. Some brief opportunity also exists for isolated supercells during the mid- to late-afternoon/sunset before thunderstorms begin to coalesce with SE progression. For these reasons, a Severe Thunderstorm Watch could again appear at some point today to account for some of these hazards. However, beyond the early-evening, consistent with the suspicions mentioned previously in the above post, the extent of lift still shows signs of retreating farther North, and so it remains favorable for convective rainfall to correspondingly shift Northward and stall to the North for the mid- to late-evening. As such, it is likely to leave behind mostly cloudy conditions under a low cloud ceiling.

Wind

As mentioned in the above posting, winds are largely in the form of breezy Southwesterlies to SSW for most of the day (19-23 km/h, with gusts of 31-35 km/h), from the later morning to late-afternoon. The closer proximity of the cold front would then allow the wind direction to adopt a more NNE to NE pattern in time for around sunset and going forward, at 11-14 km/h. This would favor the denser smoke accumulation to drift at a decent pace towards adjacent sections of the bridge nearest to the river (also to La Ronde's left and away), and towards the Old Port. Faster displacement would occur at the highest portions of the display. Laser segments would also help to clear thick smoke accumulations at notably low- to mid-altitudes of the display. Due to the damper to near-saturated air under very high humidity, and low cloud ceiling, the brightness/vividness of colors may appear dimmer than usual.

*More updates to follow today, if necessary, for evening wind flow and rainfall/thunderstorms.

Trav.

No significant changes to make to the previous posting. One attribute about thunderstorm character is that lightning production would be somewhat more reserved, though moderate frequency at best is still achievable with some of these thunderstorms as mentioned. The primary hazard remains with high short-duration rainfall rates, so let's hope that this does not cause any issue at the firing site before conditions start to improve towards mid-evening and going forward.

Trav.

A warm front and attendant shortwave troughs will affect this region through July 10th (the Canadian display day). North of these features would be a strengthening warm/moist air mass which, with suitable periods spent with sunshine, would induce moderate to potentially high instability by afternoon. A maximum temperature of 27-28 C would be present for the mid- to late-afternoon (Humidex of 33 C) for the greater Montreal area if little to no rain-cooled air appears. By mid-evening, this decreases to 23-24 C (Humidex of 30-31 C), and if under a rain-cooled environment, a late-evening temperature of 21 C (Humidex 28-29 C) would be favored.

Although lift would not be particularly significant to dramatically take advantage of this growingly humid/very warm atmosphere, it would nevertheless be sufficient for scattered convective rainfall and thunderstorms (several strong to severe). The primary hazards with the most organized thunderstorm families would be high sub-hourly rainfall rates, intense lightning, small- to medium-sized hail, and locally strong downbursts. As such, as a reflection of this environment, a Severe Thunderstorm Watch could yet again appear for a third consecutive display day, something that has likely never happened previously in the history of this competition. Rainfall probability would be 70% due to the scattered nature of the convection (especially mid-afternoon), along with a 40% probability assigned to thunderstorms specifically, including for the evening. The extent of lift does appear to weaken somewhat for late-evening, so that could offer a more limited chance for rainfall altogether. The evening itself would be overspread by mostly cloudy conditions (composed of defined towering cumulus) with sizeable clear breaks.

Winds would be largely from the ESE to SE for the day downstream of the aforementioned warm front, and blowing at light speeds (9-12 km/h — becoming breezier by mid-afternoon, at 17-21 km/h). As such, smoke accumulations, at all altitudes of the display, would be moving to the right of and away from the La Ronde audience. Some periods of extensive smoke accumulation would be possible during this show along notably low- to mid-altitudes of the display due to high humidity, and when the display becomes more active (or if/when it begins relying on smoke-rich products). However, the wind direction would benefit on-site viewing due to its easterly component.

*Another update to follow later tomorrow evening (July 9th) into predawn July 10th.

Trav.