Massive water accumulations with these thunderstorm families, and multiple reports of funnel clouds in the general area!

Trav.

Just another (late) update to acknowledge that the smoke, at all altitudes of the display would move more towards right-hand to partially central sections of the La Ronde audience due to a faster shift in wind direction behind the cold front/shortwave trough. Also, convection would remain suppressed for this evening due to the rapid evacuation of the cold front and shortwave trough to the East, leaving partly cloudy skies in the form cirrus clusters. Wind speeds would also be a littler breezier from the SW (23-26 km/h), with occasional gusts nearing 40 km/h. This may prompt slight delays, given a slight change in direction that favors blowing somewhat more towards the on-site audience.

Trav.

The Belgian display, on July 20th, will face a return flow of moist air infiltrating this region, causing the humidity to achieve high status. As such, a maximum temperature of 27 C is favorable by mid-afternoon, accompanied by a maximum humidex of 32 C. Then by late-evening, this should decrease to 26 C (humidex of 31 C).

While lift would be limited enough to suppress particularly deep convection, there would, nevertheless, be some high-altitude cirrus interspersed with clusters of moderately-defined cumulus clusters, especially during the afternoon to evening, in the wake of an upcoming area of low pressure. This would create partly cloudy sky conditions during the late-evening. A shortwave trough would also eject East during the predawn period, making the thunderstorm risk more important on July 21st.

Winds would largely be in the form light SSW to even straight Southerlies but backing to SE tendencies by around sunset and going forward (8-11 km/h). Therefore, at all altitudes of the display, the smoke should be displacing slowly clear to the right of and slightly away from the La Ronde audience, though some periods of larger smoke accumulation will be favorable at the far right portions of the display along low- to mid-levels. Such extensive accumulations would, however, only be temporary and present mostly during active portions of the display. This wind regime would also continue to keep forest fire smoke concentrations farther North, some patchy hazy skies are favorable due to light winds and progressively high humidity.

Another update to follow by late tomorrow evening (July 19th) to early-predawn July 20th.

Trav.

Conditions described in the above post continue to be valid for the Belgian display, and July 20th collectively. As such, here are the expected weather conditions for Thursday, July 20th for the greater Montreal area.

Temperature/Humidity

A return flow of moister air would circulate into Southern/SW Quebec and would send humidity to high status by mid-afternoon. In response to this pattern, a maximum temperature of 27 C is favorable by mid-afternoon, which would be accompanied by a maximum humidex of 32 C. With respect to late-evening, including display time, this should decrease slightly to 26 C (humidex of 30 C).

Precipitation

Lift in the region continues to be limited. However, sufficient solar heating and progressive moistening would contribute to some moderate instability by late-afternoon into the evening. This would encourage some window of opportunity for slow-moving sparsely-distributed convective rain showers and isolated non-severe thunderstorms (collectively 30% probability during the mid-afternoon to end-evening period. Otherwise, modest overall lift would generally favor some high-altitude cirrus blended with defined cumulus clusters, especially during the afternoon to evening in response to the aforementioned upcoming area of low pressure that is more important for July 21st. Thus, partly cloudy skies are likely for the late-evening.

Wind

The overall synoptic-scale wind velocity would largely be in the form of light SSW to straight Southerlies. However, some backing would occur by around sunset to allow for SE winds by around sunset to ESE tendencies deeper into the evening (8-11 km/h throughout the day). As such, smoke accumulations should be displacing slowly clear to the right of and almost directly away from the La Ronde audience, though some periods of larger accumulation will be favorable at the far right portions of the display along low- to mid-portions during more energetic moments. Again, this overall wind regime would help to direct forest fire smoke concentrations farther North, but some haze is favorable as a result of light winds and high humidity by mid-afternoon. EDIT: For those on Notre-Dame Street, this more likely to be a hazy display, especially for those viewing farther away from the bridge. As such, it is best to be positioned closer to the bridge in order to avoid smoke interception and, thus, improve viewing clarity.

If necessary, another update will follow by this mid-afternoon (July 20th).

Trav.

The day of the Canadian display (July 27th) would be influenced by a cut-off area of low pressure. As this system ejects NE, it would sustain humidity levels into very high status as a result of the convective rainfall that would occupy principally the late-morning to mid-afternoon period. Thereafter, a gradual clearing would occur, leaving behind a few clusters of cumulus with large clear breaks between these, including during the evening and display time. Along with a display time temperature of 22 C in the greater Montreal area, the continued very high humidity would also support a humidex of 30 C at the time (32 C during the afternoon with a maximum temperature of 23 C).

Due to persistent cloud coverage during most of the early- to mid-sections of the day, the thunderstorm risk would be minimal, though periods of moderate to heavy rainfall are possible during the late-morning to mid-afternoon. This would keep the air saturated for the remainder of the day.

Winds would be light to calm throughout the day as a result of this system, and wind direction would appear in a variety. Early in the day through to the mid-afternoon, wind velocity would be in the form of light SSW to Southerlies, but at the back end of this system late-day, NW wind fields during the early evening followed by a fairly quick transition to straight light Westerlies (7-9 km/h) by display time appears favorable. This would allow the smoke, which could be extensive at times in response to the very high humidity and saturated air, to drift slowly towards the on-site audience. Smoke at the highest altitudes would be moving more quickly, and towards left-hand and partially central sections of the La Ronde audience overhead. Thus, a hazy display is possible, but this will continue to be monitored.

Another update to follow by later today (July 26th) to early-predawn July 27th.

Trav.

Weather conditions described in the above posting continue to be largely valid for the day today (July 27th). As such, presented here are the dominant patterns for the greater Montreal area.

Temperature/Humidity

As mentioned, July 27th would be under the influence of a cut-off area of low pressure. Within its warm sector would be a slight amplification of humidity and warming through the day. The latest thinking is that the sun would penetrate the low-cloud deck by early-afternoon, allowing for more time spent with solar heating. As such, a maximum temperature of 26-27 C is favorable by mid-afternoon. Very high humidity would further send the humidex value to 34-35 C during that time. By display time, a temperature of 24-25 C is favored under continued very high humidity (humidex of 32 C). As such, this would represent the most humid conditions during a fireworks display so far this year.

Precipitation

As this system ejects NE, convective rainfall would favorably occupy principally the morning to early-afternoon period (90% probability) downstream of the associated warm front. Thereafter, the risk for convective rainfall becomes sparse for the remainder of the afternoon as lift weakens (30% probability). A gradual clearing would generally follow the early-afternoon, but the near-saturated air and modest lift would leave behind clusters of cumulus with large clear breaks between them – this would persist during the evening and display time, though with larger clear breaks present. The thunderstorm risk continues to be limited for the day, including the morning, but periods of moderate to heavy rainfall locally remain very possible for the morning.

Wind

Winds would be light to occasionally calm throughout the day. During the morning, wind velocity would be in the form of light Easterlies to ESE (7-9 km/h), but at the back end of this system late-day, Northerlies to NW wind fields for the afternoon would transition swiftly to SW by late-afternoon to early-evening, followed by light WSW tendencies deeper into the evening towards display time (7-9 km/h). This would allow the often thick smoke accumulations (especially along low- to mid-altitudes of the display) to drift fairly gently towards right-hand and central sections of the on-site audience. Smoke at the highest altitudes would be moving somewhat more quickly, but more directly towards the La Ronde audience overhead, collectively creating a potentially hazy display at large. That said, it would help that the winds would be marginally strong enough to help displace the smoke.

Another update to follow by this mid- to late-afternoon to address wind direction/speed, if necessary.

Trav.

To provide an update as to wind direction, tendencies appear more so SW by display time (under the same speeds mentioned previously, at 7-9 km/h). This would allow the smoke to focus more towards right-hand sections of the La Ronde audience, though higher-altitude smoke would be moving towards there and partially central sections from overhead. Smoke accumulations would still appear thick along principally low- to mid-altitude in response to very high humidity, but most especially when the display is more energetic.

Trav.

For the American display on Sunday (July 30th), much cooler and less humid conditions would be favorable. To that end, the humidity would be borderline low to moderate, and so a humidex would be negligible under a 22 C display time temperature (25 C maximum for the day).

One aspect to monitor is a cold front advancing South during the day, having some influence in the area for the mid- to late-evening period. Some convective showers and isolated non-severe thunderstorms (30% probability) could initiate along this boundary at the time, so this will have to be examined.

Winds are generally following a pattern similar to the Canadian display, though extensive smoke accumulations would be limited during the American show as a result of much lower humidity. Wind speeds would be 9-12 km/h, from the SW, for the evening period, allowing the smoke to drift at a reasonable speed towards far-right hand sections of the La Ronde audience, though smoke at the highest altitudes would be advancing more quickly towards right-hand sections and partially central from overhead.

Another update to follow this late-evening (July 29th) to early-predawn July 30th.

Trav.

Conditions specified in the above posting continue to be valid for the American display. Adhering to these previously-presented details, here are the dominant patterns for the greater Montreal area for the day today (July 30th).

Temperature/Humidity

Under the influence of high atmospheric pressure, and as part of a cooler-than-normal pattern that would be persistent for potentially nearly two weeks, much cooler and less humid conditions would be favorable for this display. As such, these would represent the coolest and least humid conditions to appear during a fireworks evening so far this year. The humidity would be at the lower end of moderate, and so a modest humidex of 21-22 C is applicable during display time under a temperature of 20-21 C (a 24 C maximum during mid-afternoon – maximum humidex of 25-26 C). Note that if convective rainfall (40% probability – please see more details in the next section), this would cool the air temperature to 17-18 C (humidex of 20 C).

Precipitation

While the day itself is largely pleasant outside the chillier morning and evening, the aforementioned cold front (and shortwave trough) would continue to be prominent features for the evening and overnight period. Fortunately, the extent of lift downstream of these would not be particularly aggressive, though it would be sufficient for scattered convective coverage. As such, some convective showers (40% probability) would be possible in the area during the mid- to late-evening, and some modest instability partly gathered from earlier in the day would provide some window of opportunity for a few isolated slow-moving and briefly-sustained non-severe thunderstorms (30% probability). Following what would be a day spent with plentiful sunshine, extensive cloud coverage would gradually overspread the region by evening in response to the previously-mentioned features, with some small patches of clear breaks between this cumulus to cirrus cloud deck.

Wind


Winds are would remain light (9-12 km/h) for most of the day, interchanging between SW and WSW. During the afternoon, wind speeds, however, would adopt a breezier pattern (18-22 km/h from the same directions) before becoming light for the late-evening (9-12 km/h). By display time, however, wind fields would tend to be more in the form of WSW. This would allow the smoke to eject at a reasonable speed towards right-hand and partially central sections of the on-site audience from all altitudes of the display. Faster displacement of smoke at the highest altitudes of the show is also favored, though this smoke would be moving more directly towards the La Ronde audience overhead. No extensive smoke accumulations are expected, but the display would often appear hazy from principally the right-hand portion of the display (at mostly low- to mid-level) relative to the La Ronde audience.

If necessary, another update will appear here this mid- to late-afternoon (July 30th) to address wind direction and convective rainfall character.

Trav.

Fairly strong and slow-moving thunderstorm family over the West Island-Vaudreuil corridor this early-evening, along with convective rainfall farther East over greater Montreal and the fireworks site. Scattered convective rain showers and isolated non-severe thunderstorms remain possible for the evening, as described above, though improving conditions are favorable in time for the duration of the display.

Edit: Temperature, indeed, cooled to 17-18 C in response to the rainfall.

Trav.

though improving conditions are favorable in time for the duration of the display.

Yes, the conditions have improved shortly before the display, while we had a light rain for a couple of minutes at one moment during the show (just before Purple Rain).

(I even saw a very famous pyro without shoes in the grandstands!)

But what about the after-show! There was a thunderstorm and heavy rainfall when I had to leave the Salon des artificiers and have a walk across La Ronde to exit at the front, then doing the usual circumvolution on the right side (when we exit), before going toward the left side to get the bus, because the left path is always blocked by the countless fences! What a water ride!

Fred

An area of low pressure will advance East in time for the day tomorrow (August 3rd). As it does, a re-introduction of warm and very humid air will circulate into these regions. Discontinuities in the cloud deck during the afternoon would allow for a maximum of 24-25 C (humidex of 31 C in response to high humidity) in the greater Montreal area. By evening, the temperature would be 22 C under nearly saturated air. This would yield a humidex of 28-29 C.

Accompanying the aforementioned low pressure system would be a series of shortwave troughs ejecting SE throughout much of the day. The enhanced lift induced by these features does bring concern that several rounds of strong to severe thunderstorms could appear throughout much of the day, with the first of these appearing during the early- to mid-morning period. The primary hazards with these would be local flash-flooding, damaging winds and in some cases, intense lightning where instability can be maximized. Furthermore, prior to thunderstorm consolidations, some window of opportunity exists for an isolated weak tornado during the mid-afternoon. There are some indications, though, that the last of the shortwaves could affect the area just prior to display time, which would begin suppressing further developments thereafter. This would be by quite a narrow margin, but it will continue to be monitored.

Winds would be generally in the form of breezy SW (17-21 km/h, with occasional gusts of 29-33 km/h) during the morning to afternoon period, and undergoing a transition to light (SSW) tendencies by late-evening (8-11 km/h). This would allow the often rather thick smoke accumulations to slowly drift to the right of the on-site audience (much like during the American display, but with slightly slower displacement at low- to mid-altitude). This could sometimes create a hazy display at the right-hand portion of the display for La Ronde, enhanced by any smoke-rich products that may be used at low- to mid-level. If thunderstorms and/or convective rainfall are in the area, however, then the smoke would suddenly advance more towards the La Ronde audience.

Another update to follow late this evening (August 2nd) into early-predawn August 3rd.

Fred: Yes, that was quite a deluge of rainfall tied to that isolated thunderstorm family after the display! The one over the West Island-Vaudreuil corridor during the early-evening also led to large amounts of water accumulation there!

Trav.

Weather conditions specified in the above-posting for today (August 3rd) remain largely applicable. As such, here are the dominant conditions for the greater Montreal area for August 3rd.

Temperature/Humidity

The aforementioned area of low pressure will advance East and re-introduce a (very) humid air mass into this general area. With continued broken skies for the afternoon, sufficient solar heating would help to guide a maximum temperature of 24-25 C by mid-afternoon (humidex of 31 C as a result of high humidity) in the greater Montreal area. By evening, the temperature would be 21 C under nearly saturated air, correspondingly generating a humidex of 27-28 C.

Precipitation

A series of vigorous shortwave troughs would advance SE throughout much of the day ahead/downstream of the low pressure system’s cold front. The enhanced lift would favor widespread convective rainfall and scattered thunderstorms, some of which would continue to prove to reach strong to severe status during the afternoon period. As such, a Severe Thunderstorm Watch could appear early today. The risk for rainfall collectively would be 90% for the morning to afternoon period, and dropping to 60% for the duration of the evening as a result of slightly reduced lift that would otherwise prompt lesser coverage of convective rainfall, especially deeper into the evening. The sun should make some appearance during the afternoon, however, which would partly provoke a few organized multi-cell thunderstorm formations locally. The primary hazards with these continue to be local flash-flooding, small hail, damaging straight-line winds and potentially intense lightning where instability is at a maximum. The previously-mentioned isolated weak tornado risk, while still existent, should remain minimal within this environment. Sky conditions would be overcast with a low cumulus cloud deck for the evening. There remains some opportunity for lift to reduce just enough around display time, however, to allow for a brief dry slot for the display to be fired safely, so this will continue to be checked. Nevertheless, there is potential for the rounds of heavy rainfall to cause some technical issues for the display.

Wind

Winds remain in the form of breezy SW for much of the day, reaching speeds of up to 23-27 km/h, with occasional gusts of 37-41 km/h during the early- to mid-afternoon. Directional tendencies still show a transition to light Southerlies by late-evening (9-12 km/h). As such, the often thick smoke accumulations would fairly slowly drift clear to the right of the on-site audience, almost similar to what was observed during the American display but with slightly slower displacement at low- to mid-altitude. This would, thus, create a hazy display at its right-hand portions relative to La Ronde, enhanced by any smoke-rich products that may be used at low- to mid-levels of the display space. Note, however, that if thunderstorms and/or convective rainfall are in the area directly, then the smoke would suddenly turn towards the La Ronde audience before the synoptic-scale flow can be restored, but the latest thinking that the thunderstorms would be most prominent up to the early-evening.

Updates to follow this early- to late-afternoon (August 3rd) to address wind direction and notably convective rainfall.

Trav.

Lift associated with upcoming shortwave troughs continues to be rather aggressive for not only this early-evening but throughout the evening (August 3rd), and so the latest thinking is that the thunderstorm risk, including for strong/severe multi-cell thunderstorms, will favorably persist. Caution should, thus, be exercised in case of severe weather.

Synoptic-scale wind fields would still be in the form of light SSW this mid- to late-evening (easing from their breezy/gusty nature this afternoon), which would displace the smoke clear to the right of the on-site audience. Speeds would be a little stronger than what was previously specified, however, at 12-16 km/h, allowing for quicker displacement at all altitudes. Again, if thunderstorms do interfere, this would cause the smoke to rapidly turn towards the audience (notably left and centralized sections), especially since strong downbursts and very torrential rainfall remain primary hazards with these thunderstorms.

The sun has been out in the West Island-Vaudreuil area and closely surrounding areas for the last 83 minutes, which has partly caused a few briefly-sustained isolated thunderstorms/convective showers to recently appear, around Lachute and Chambly, as well as one this morning over Eastern greater Montreal and the East End previously this morning. At the very least, earlier cloud cover limited thunderstorm potential for earlier in the afternoon, keeping conditions dry and overcast with local light rain beyond this morning's steadier rainfall.

Trav.

Glued to the radar again this week Trav! Let's hope that, whatever precipitation there is, we have wind to move the smoke!