Details described in the above posting continue to be applicable for the display presented by the Philippines. As such, here are predominant weather conditions for Saturday, July 21st, for the greater Montreal area:

Temperature/Humidity

Like July 20th, hot and moderately humid conditions are expected for July 21st. Maximum temperatures should be 29-30 C by mid-afternoon and will then fall to 25-26 C for the late-evening. Humidity should be largely moderate for the day, including into the evening period. This will generate a maximum humidex of 33-34 C for the mid-afternoon, and then 27-28 C for the late-evening.

Precipitation

As per the posting above, precipitation development associated with the double-barrelled low-pressure system continues to be restricted to the day Sunday (July 22nd). However, introductory cloud coverage will be present by the middle of July 21st, mostly by the early-afternoon, as weak lift begins to overspread the region. This will largely include an increase in cirrus cloud coverage, with isolated clusters of fair-weather cumulus. The cloud coverage will increase somewhat more into the evening but still with a few large clear breaks. Thus, broken skies are favored for late-evening. Beyond July 21st, a (very) wet pattern is expected to develop, as mentioned above.

Wind

Winds continue to be in the form of Southeasterlies (SE) and ESE for the day, and this would appear to persist through the evening (as opposed to the previously mentioned SSE tendencies). Speeds remain rather breezy for the afternoon period, at 14-18 km/h but then weaken slightly to 12-15 km/h by about sunset (so, a touch breezy). Therefore, the smoke should be moving adequately clear to the right of the La Ronde audience but also somewhat directly away while moving to the right, drifitng towards far left-hand sections of Notre-Dame Street. Higher-altitude smoke should also be drifting in a similar manner and somewhat more quickly relative to lower-level smoke accumulation. Periods of larger smoke accumulation should be mostly small for the La Ronde audience, despite moderate humidity. *For those on Notre-Dame street, the closer you are positioned to the bridge would be most ideal to avoid smoke interception.

If necessary, another update will follow by this mid-afternoon (July 21st) to address mostly wind direction and speed.

Trav.

As mentioned in the above two postings, a (very) wet pattern had, indeed, unfolded over particularly the last week for much of E. Ontario to S. Quebec. Despite the dry first half of July, some locations, such as Ottawa, are observing one of their wettest Julys on record because of principally the last week (mostly following July 21st). The overall wet pattern is expected to persevere over these regions, especially where thunderstorms and convective rain showers are most dominant.

In the case of the American display this Saturday (July 28th), a mid-/upper-level trough that will be centered over Northern Ontario/central Quebec should keep conditions unsettled for most of the day. This same trough, coupled with a surface cold front, could also yield isolated to eventually scattered thunderstorms (some strong to severe) this morning through to the early-afternoon period (July 27th). Severe thunderstorm watches will be possible. With sufficient lift and instability, this should yield partly cloudy skies, mostly in the form of defined clusters of large cumulus and high-level cirrus. This will also include scattered convective showers (40% probability for rainfall) and isolated non-severe thunderstorms (30% for these). This instability should continue towards the late-afternoon to as late as the early-evening. That said, less favorable lift does appear likely beyond sunset, and with solar heating diminishing, convective coverage should be reduced to sparser distributions, leaving partly cloudy skies (the same cloud types overspreading the area) and some clear breaks.

Winds are expected to be breezy for the day Saturday and should remain in a similar manner for the evening. Directional tendencies are mostly in the form of SSW early in the day before becoming more Southwesterly (SW) into the afternoon. By the evening period, it is currently unclear whether the former SW winds will transition to WSW by late-evening, but somewhat breezy SW winds appear, so far, reasonable for the evening. As a result, the smoke should be moving relatively quickly to the right of the La Ronde audience, though drifting to extreme right-hand sections, especially higher-altitude smoke. If winds do become more WSW for the evening, then the smoke would move directly towards the La Ronde audience, mostly right-hand sections and partially central, causing the display to appear murky deeper into it. Some periods of larger smoke accumulation will be possible, depending on dominant material used in the display, but this should displace reasonably quickly. Wind direction will continue to be monitored.

Maximum temperatures of 26-27 C are expected by the mid-afternoon of July 28th and should fall to 23-24 C by late-evening. If rainfall does occur in the area earlier in the evening/late-afternoon, temperatures would cool to 20-21 C. Humidity will be borderline moderate to high (high earlier in the day) but would increase to higher standards in a situation where rainfall occurs previously. A maximum humidex of 31-32 C is favorable for the mid-afternoon and 27-28 C for the late-evening.

Another update to follow either late this evening (July 27th) or pre-dawn July 28th.

Trav.

The above-mentioned details continue to be largely valid for the day today (July 28th). As a result, presented here are the most likely weather conditions for Saturday, July 28th, including for the American display.

Temperature/Humidity

Temperatures should reach a maximum of 26-27 C during the mid-afternoon period, with generally high humidity (not very high, like the last several days). This will generate a maximum humidex of 31-32 C. By late-evening, values decline to 24-25 C, and with constant humidity, a humidex of 28-29 C is applicable. However, as mentioned in the above posting, if rainfall does occur during the early-evening, temperatures will likely cool briefly to 20-21 C.

Precipitation

The aforementioned broad mid-/upper-level trough will continue circulating to the NW through today. Coupled with sufficient solar heating, this feature will enhance instability and lift through principally the mid- to late-afternoon period. As instability strengthens, scattered convective rain showers and isolated non-severe thunderstorms are very likely to develop. Given the distribution of the convective rain showers and thunderstorms, a 40% and 30% probability, respectively, will apply. Note that some thunderstorms will be capable of torrential rains due to the fairly humid/moist environment. As solar heating diminishes beyond sunset, convective coverage should correspondingly also be reduced and so rainfall should remain at a 30% probability. Thunderstorms should also weaken quickly not too long after sunset. Skies should remain partly cloudy (still with large clear breaks) for the late-evening, consisting of patchy high-level cirrus and residual clusters of cumulus.

Wind

Winds continue to be breezy (occasionally gusty) through the day, especially for the afternoon period, and mostly in the form of a SW direction (SSW early in the day). Speeds of 17-22 km/h are favorable for the mid-afternoon period (with occasional gusts of 28-32 km/h). By near sunset and onwards, speeds weaken to 12-15 km/h, so somewhat breezy. That said, the SW tendencies in the afternoon do appear to transition to WSW for the evening. As such, the smoke should be moving reasonably quickly, but mostly towards right-hand sections of the La Ronde audience (partially central). This also applies to higher-altitude smoke, except that this smoke would be moving at a slightly faster pace. This could make the display appear sometimes hazy to La Ronde’s right deeper into it, and during times of higher activity. Borderline moderate to high humidity could also briefly encourage periods of larger smoke accumulation (depending on the extent of smoke-rich products), but, again, this should be displacing quickly.

If necessary, another update will follow by this mid-afternoon (July 28th) to mostly address wind speed and direction for the late-evening period.

Trav.

Hopefully, an early night thunderstorm or shower won't cause the closure of the Ferris Wheel, as they are a lot of things to photograph today!

Fred

Hi Fred,

The risk for precipitation altogether will continue through to just slightly after sunset, but the coverage of convective rain showers and mostly non-severe thunderstorms will diminish quickly not long after sunset. As a result, there will be a narrow window of opportunity for a rain shower early this evening, as well as brief distant lightning before convective coverage decreases completely. The stronger thunderstorms, as they exist sparsely this afternoon in the area, will be secluded to the afternoon period, and so the current severe thunderstorm watch should come to a close by late this afternoon into early this evening.

No real change to the wind speed and direction, so the smoke should mostly be directed at right-hand sections (partially central occasionally) of the La Ronde audience (especially higher-altitude smoke). I would diminish speeds just slightly, however, to 9-12 km/h (from the 12-15 km/h specified above), so still reasonable speeds at the surface.

All other information is still valid.

Trav.

I just saw Travis' video of the thunderstorm which occurred in Montreal on July 28, about two hours before the American display:

https://www.youtube.com/watch?v=PjgmznOl97A

To complement this video, I should have taken a picture of Paul when he arrived to the Salon des artificiers : I do believe that he walked from his car to the Salon between 13:00 and 17:00 in this above linked video!!

Trav, we may experience bad weather conditions the day of the Italian show. I think your detailed forecast will be very useful, once again.

Fred

Hi Fred,

Thank you for sharing that. That thunder crash was also very loud at about 12:30 in the video link!

Indeed, that was a ferocious rainfall from the very late-afternoon to early-evening thunderstorm of July 28th. The formation of this very isolated thunderstorm event is consistent with my reasoning behind finding it necessary to keep the risk for rainfall and isolated thunderstorms active until just slightly after sunset, as mentioned in my previous three postings. In addition, I stressed that some of the thunderstorms that do develop in Saturday’s environment would be capable of torrential rains (see the “Precipitation” section above), owing to the high humidity concentration in the air. Indeed, Paul did mention previously how soaked he was after/during that torrential rain!

The historical radar imagery supplied (6:14 to 6:30 in the video) also highlights well the timing, how isolated the thunderstorm realistically was, and the narrow trajectory it followed. It was really the only thunderstorm in the general area at the time, which justifies the 30% probability assigned for any given location, just that the island, and areas to the SW and immediately East, happened to fall in the 30%!
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A broad area of low pressure and series of embedded shortwave troughs will be advancing into S. Ontario to S. Quebec for the day Wednesday, August 1st. These systems will progressively allow for tropical air to return to the regions, circulating warm and very moist conditions and, for the greater Montreal area, creating potentially the highest humidity levels of all fireworks days so far this year. At first, the system’s warm front and the first of several shortwave troughs will yield sufficient lift for increased cloudiness, isolated pre-dawn to lunch time convective rain showers, and sparsely-distributed non-severe thunderstorms. As the day progresses, the low’s cold front will become more important for the afternoon to evening period.

While thunderstorms and/or (heavy) convective rainfall are favorable to develop in this very humid environment, notably by the mid-afternoon, the extensive cloud coverage early in the day does cast some uncertainty as to how particularly severe thunderstorms may become later in the day (especially close to 9:00 p.m.). That being said, latest data does support breaks in the cloud deck by late-morning that would allow for some brief sunny periods into principally the early-afternoon, enhancing instability. Depending on how much solar heating unfolds, the risk for stronger thunderstorms will increase into the late-afternoon to evening period and so will need to be carefully monitored. The potential for a line of thunderstorms will be possible in a worst-case situation, which will increase the damaging wind threat locally. Note that thunderstorms, regardless of their severity, will, like on July 28th, likely be capable of torrential rains in this environment, and so local flooding will also be hazard with some thunderstorms later in the day. The stronger thunderstorms will also generate intense lightning. Mid- to late-afternoon and evening convective coverage, collectively, is expected to be widespread in this situation, so “at least” a 60% probability is favored (this may be upgraded to 80% for late-afternoon to evening period). The probability for strong to severe thunderstorms should be 40% at this point, but an increased probability will be contingent on the degree of solar heating. For these reasons, I suspect that severe thunderstorm watches will be re-introduced at some point on August 1st.

Another area of concern would be the richness of the humidity into the late-afternoon to evening period as the aforementioned warm front lifts North. At the same time, because of the dampness of the air, the air itself is expected to be almost completely saturated over a great tropospheric depth. This is likely to encourage thicker smoke build up from the fireworks and also reduce color richness/vibrancy. Wind speeds are shown to be somewhat light (9-12 km/h), and mostly from the SSW, although higher altitude smoke should move a little faster, but still gently, in the same direction. The wind direction and speed, thus, should help a little, but it seems that smoke accumulation could, at times, be accumulating faster than displacing clear to the right of the La Ronde audience. At the very least, the hazy display appearance should not be as extensive as it was during the American show. ***Note, however, that if thunderstorms or a strong convective rainfall does occur during and/or slightly before display time, then the local wind fields will likely become more Westerly, causing the smoke to move towards the La Ronde audience directly, and quickly due to the potentially strong downbursts of wind.

It is also uncertain to what extent smoke-rich products will be used in the Italian display, or how numerous active segments might be. I suspect this will be lesser in extent than in the American display, which could allow the smoke the time to clear sufficiently during times of lighter activity, but periods of extensive smoke accumulation will still be favored.

Since the air is virtually saturated, temperatures will not be liable to drop much into the evening. Depending on how much solar heating occurs, maximum temperatures of 29-30 C are favorable by mid-afternoon, with a humidex of 35-36 C. Late-evening values should be closer to 24-25 C (humidex of 33-34 C).

Another update to follow by either late-evening July 31st into pre-dawn August 1st.

Trav.

Weather information presented in the above post continues to be largely applicable, but some revisions have been made in the update below for convective coverage and wind speed. As such, here are the most dominant conditions for Wednesday, August 1st for the greater Montreal area.

Temperature/Humidity

Maximum temperatures of 27-28 C (a slight reduction from the 29-30 C in the above post) are favorable for the mid-afternoon due to a strong circulation of warm, moist air, and some solar heating making an appearance during the late-morning to mid-afternoon. By late-evening, values decline only slightly, to 24-25 C, owing to near-saturated air. Humidity increases to borderline high to very high standards by the mid-afternoon and continues into the evening, so a maximum humidex of 35-36 C is possible for the mid-afternoon. A humidex of 32-33 C is likely for the late-evening. ***Note that if rainfall/thunderstorms occur during the evening at any point, temperatures will drop to 21-22 C***.

Precipitation

The aforementioned broad area of low pressure will first induce isolated convective rainfall and sparsely-distributed thunderstorms during the morning period, as well as an increase in cloudiness consisting of stratus and cumulus, via the warm front. Near lunch time, there continues to be some breaks favored in the original continuous cloud deck, which should invite at least some periods for solar heating, especially into the early-afternoon. Together with progressively very high humidity, this should yield typically moderate instability and will likely encourage thunderstorm and convective rainfall development deeper into the afternoon and onwards ahead of the quasi-stationary cold front. However, the degree of lift does appear to be somewhat limited, so convective coverage, collectively, during the mid-afternoon to mid-evening period should be kept at a 60% probability (30% for the morning period). Strong to severe thunderstorms will also be favorable in this environment, especially during the mid-afternoon to mid-evening period, but given that these storms will be mostly scattered in coverage in this general area, the probability for these, specifically, will be 40%. The thunderstorms will be capable of torrential rains, intense lightning and locally strong downbursts of wind. Again, severe thunderstorm watches will be possible at some point today. The “best” chance for these storm types, however, will be closely NW of the island, where lift and instability will be greatest. Mostly cloudy skies, with a few clear breaks, are favorable for the late-evening, but the risk for rainfall will continue, and into the overnight period, although convective coverage begins to diminish slightly by late-evening.

Wind

The predominant wind direction remains in the form of SSW to straight Southerlies. However, since the circulation has recently increased in association with the low pressure system, this should generate slightly faster wind speeds for the evening period, allowing for somewhat breezy evening conditions (12-16 km/h – 19-24 km/h for the afternoon). This would be ideal to combat rapidly developing smoke accumulation, especially if there are many smoke-rich products and/or numerous active sections in the Italian display, though I suspect a lesser extent than in the American and Philippines displays. The wind direction should further displace the smoke clear to the right of the La Ronde audience, as specified previously. Higher-altitude smoke should be moving a little faster than that at lower-altitude. ***That said, note that if a strong convective rainfall or thunderstorm occurs, the local wind flow will temporarily be disrupted, causing a sudden transition to Westerlies and, thus, allowing the smoke to move towards the La Ronde audience more directly***. The humidity enrichment for the evening will still, overall, likely affect the vibrancy of some of the fireworks colors, but at least the smoke should be clearing usually adequately (at all altitudes).

*If necessary, I will post another update by the mid-afternoon today (August 1st) to address convective development for the evening and any changes to wind speed.

Trav.

The thunderstorms will be capable of torrential rains, intense lightning and locally strong downbursts of wind. Again, severe thunderstorm watches will be possible at some point today. The “best” chance for these storm types, however, will be closely NW of the island, where lift and instability will be greatest.

Some weather reports currently state that Outaouais, Laurentides, Lanaudière, Mauricie and Lac-Saint-Jean are the most likely to be hit by thunderstorms. How likely is it that we will avoid them? I cross my fingers to get a dry fireworks, but I feel more optimistic than last evening!

Fred

Hi Fred,

Yes, I still strongly support the idea that most severe thunderstorms will continue to develop mostly NW of the island, so the risk would continue to be greater there this afternoon-evening (August 1st), as compared to here. Indeed, severe thunderstorm watches are currently enforced in those areas, including towards Mirabel and Lachute. Because lift is limited farther South, including here, thunderstorm coverage should continue to be mostly scattered for the evening for this general area. Scattered to widespread convective rain showers will still be favorable between now and throughout the evening, since the air is still near-saturated, with scattered thunderstorm coverage. As such, I would keep the thunderstorm risk at 40%, since solar heating did, indeed, materialize sufficiently, but rainfall, collectively, should be retained at a 60% probability over the same time frame. We are currently experiencing some light rain out here, in the SW West Island.

Also, I would increase wind speeds slightly for the evening period, to 14-18 km/h (occasional gusts of 28-32 km/h), and from the same direction specified above. As such, the smoke should be moving rather quickly (at all altitudes), still clear to the right of the La Ronde audience (assuming no interference from thunderstorms). This is important due to the current very rich moisture concentration, although color vibrancy could sometimes still be affected in this environment.

If we remain thunderstorm-free (with distant lightning to the NW, at the very most), and it does remain dry, then we should not have too much problem, since wind speeds will act to battle rapidly building smoke associated with the current very high humidity. The wind direction will also be very suitable, unlike during the American display, so the result should be very different for viewing (again, assuming no interference from thunderstorms). It is also quite possible that the (strong) thunderstorms/moderate-heavier rainfall may not arrive until not long after the display and beyond, which would be ideal, but they will continue to be possible, in a scattered fashion, for the evening.

*All other presented details in my previous posting remain valid.

Trav.

Building on the previous days of unstable weather conditions, a series of shortwave troughs will be ejecting NE through the day Wednesday, August 8th. These features should provide sufficient lift for sporadic convective rainfall and thunderstorm development across E. Ontario to S. Quebec. Tropospheric profiles continue to remain near-saturated over a great vertical depth, so this will, in combination with some lift from the troughs, encourage extensive cloud cover, but with some breaks in the cloud deck to encourage some sunny breaks. These sunny breaks, however, will contribute to enhanced local destabilization wherever the sun is able to get through. At this point, I would keep convective coverage scattered for the day (so, a 40% probability), especially by the late-morning. Isolated thunderstorms (a few strong) will also be possible (30% probability for these), notably if periods of solar heating are extensive. This convective distribution should extend into the evening period, as well, though the thunderstorm risk will begin to subside as diurnal heating weakens. There will exist a narrow window of opportunity for thunderstorm development, though, during the early-evening. The main hazard with thunderstorms will be torrential rains, but the more organized thunderstorms, especially earlier in the day, will be capable of intense lightning and locally damaging downbursts of wind.

Maximum temperatures will also be very warm (28-29 C by mid-afternoon), and because of a continuation of very high humidity, maximum humidex values of 36-37 C are expected. For the late-evening period, temperatures should drop to 23-24 C, and with persistent very high humidity, the humidex should be 31-32 C at the time. If light rainfall occurs, temperatures should drop slightly, to 21 C.

Winds speed and direction will have to be monitored, but at this point, light SSW tendencies (8-11 km/h) are favored for the day, even at higher altitudes. This should extend into the evening. As a result, smoke accumulations should be drifting gently to the right of the La Ronde audience (left for those on Notre-Dame Street). However, if SW winds prevail, then the smoke could sometimes be moving closer to far right-hand sections of the on-site audience. Note that because of the light winds, near-saturated air and very high humidity at the surface, periods of extensive smoke accumulation will be possible deeper into the display, especially following moments of higher activity, and if smoke-rich products are extensively used at low-level.

Another update to follow by late this evening (August 7th) into pre-dawn August 8th.

Trav.

Forecast information presented in the above posting still remains generally valid. However, some revisions have been made for rainfall coverage and wind speed/direction. As such, here are the conditions most likely to govern today (August 8th) for the greater Montreal area, and for the final display of 2018.

Temperature/Humidity

Maximum temperatures of 28-29 C are expected by the mid-afternoon, owing to at least some periods for solar heating developing by late-morning. By late-evening, temperatures should fall to 21-22 C due to some rainfall expected later in the day, eventually causing the air to be virtually saturated. Due to sufficiently high temperatures and a near-saturated lower atmosphere, humidity should be very high, especially later in the day. Thus, a maximum humidex of 36 C is favored by mid-afternoon, and then 28-29 C for the late-evening.

Precipitation

As mentioned in the above posting, a series of troughs will be ejecting NE through the day today, especially influential by the mid-afternoon to the evening period. As stronger lift associated with these features strengthens and overspreads the region, convective rainfall and isolated to eventually scattered thunderstorm development should occur. As such, by the afternoon, a 40% probability is still favored for convective rainfall, and a 30% probability for thunderstorms due to their mostly isolated nature early in the forecast period. ***Note that some thunderstorms could achieve strong to severe standards as instability in this environment increases into the afternoon to the early-evening, and so it is possible to again see severe thunderstorm watches eventually introduced in parts of the general area, including the island of Montreal***. As lift remains high into the evening, and given the near-saturated profiles, convective rainfall should become widespread, so in this particular situation, the probability for rainfall should be at least 60% for the late-afternoon period and onwards. Locally moderate to heavy rainfall will be possible in this environment, even if not accompanied by thunder/lightning. The thunderstorm risk itself will also continue, and though thunderstorm intensity should diminish by not long beyond sunset, the dominant hazard that will remain with them will be torrential rains. This attribute can still make thunderstorms classified as severe, as the potential for locally high water accumulation over a short period of time exists. Cloud coverage is expected to be considerable, including numerous clusters of low cloud.

Wind

Some uncertainty remains with respect to wind direction due to the generally weaker wind speeds that are dominant for the day. With weaker wind fields, local factors become more important in affecting actual wind direction. At this point, speeds of 4-7 km/h are favored through the day, including the evening period. Wind direction should be mostly in the form of SW to SSW for the afternoon, but these could transition to more WSW for the evening before turning WNW to NW near midnight. Due to the saturated/damp air, low cloud, very high humidity and light wind fields, significant smoke accumulation is very likely, and so a smoky/hazy display is quite possible deeper into the show. This could be amplified if the show contains numerous pieces of high activity (which is reasonable to assume), and if smoke-rich products are used often. Furthermore, the smoke may be moving (very) gently towards central and right-hand sections of the La Ronde audience. This would especially be true if thunderstorms are in the area.

*Another update to follow by the mid-afternoon of today (August 8th) to address wind speed/direction and rainfall potential.

Trav.

Lift ahead of a rapidly-moving shortwave trough will continue to affect this region into the late-afternoon to evening. With near-saturated to eventually saturated air, convective rainfall will likely be ubiquitous this evening, in particular, given the timing of the trough. As described previously, significant rainfall (and water accumulation) will be possible locally in this environment, especially if it is accompanied by thunderstorms.

Wind direction should follow NE tendencies for the evening, though actual speeds will be light, at 5-8 km/h, so the smoke should be moving fairly gently towards sections of the bridge nearest to the park and river, and for sections of Notre-Dame street nearest to the bridge. It is also possible that, at times, the smoke may not have near-stationary motion. Significant smoke accumulations continue to be favored due to the factors previously outlined in the above posting. Again, if thunderstorms and/or heavy rainfall do occur, the wind flow will likely temporarily shift to westerlies, causing the smoke to turn more towards the La Ronde audience.

For all other information, please refer to the above posting, as specified details are still applicable.

Trav.

I was this close to preparing a preliminary weather forecast for Saturday, August 11th!

In any case, it was quite an interesting season, weather-wise, too, for this year's fireworks season, especially with respect to precipitation. Indeed, the first five displays were rain-free, while the last three all had rainfall, with the last two featuring rainfall during show time. The most dramatic situation was the strong isolated thunderstorm that occurred just under two hours before the commencing of the American show.

And so concludes the weather reports for 2018! I continue to be actively on Facebook providing weather forecasts for this general area during mostly times of severe weather.

Before resuming my PhD research more extensively, I will also be teaching meteorology and climate science at Concordia University this Fall semester, so feel free to drop by for a chat during my office hours, or somewhere on campus!

Cheers,

Trav.