As we are now just under two weeks away from the commencing of the 2018 edition of Montreal fireworks, I thought that this would be an appropriate time to introduce this thread.

Here, I will provide descriptive weather reports for each fireworks display. These reports will first be given as preliminaries by about two days in advance of actual fireworks display dates, followed by finalized forecasts approximately the late-evening on the day prior to a show, or early into the fireworks day itself. The reports will contain outlooks on temperature, humidity, precipitation likelihoods, and wind speed/direction. In cases where strong to severe thunderstorms are possible, or if wind speeds are expected to be either very light or very strong, more details will be supplied, as well as more updated brief postings following finalized forecasts (note that these updates may sometimes be released fairly late on fireworks days, depending on the situation).

As always, you are also more than free to share any weather information that you may have, or ask about anything that may be unclear.

Also, for those interested, my late-Spring and Summer 2018 outlook (and review of this past late-Fall and Winter 2017-2018) can be accessed using the following link. This outlook was released on March 17th, 2018 but was largely reproduced from the preliminary details specified in the September 22nd, 2017 release:

https://www.linkedin.com/pulse/fall-winter-2017-2018-look-ahead-spring -summer-2018-travis-moore/?published=t

In general, I am expecting a slightly above average temperature distribution to govern this May-September period, along with above average precipitation. Thunderstorm frequency should correspondingly be above normal though more tamed than last year and 2016. The Summer of 2018 should further be more of a humid than hot one, suggesting that the number of days with 30.0 C or higher should be limited (but slightly more than last year). However, the number of days with high to very high humidity should be higher than normal.

I hope for ideal weather conditions for all of the displays, as well as during their respective setup periods.

Trav.

After a 7-day heat wave across much of extreme S./SW Quebec, which was one of the most enduring heat waves in recorded history for the island of Montreal (and the longest since the August 2001 heat wave event), considerably cooler and less humid conditions are expected for the first display of the 2018 edition of the Montreal fireworks competition. This is due to a sharp cold front and pre-frontal trough advancing East late this evening into overnight tonight (pre-dawn July 6th). Very shortly, the heat wave will conclude, and the high heat and humidity warnings will be terminated.

For Saturday, July 7th, conditions should continue to build on the cooler, less humid atmosphere initiated by July 6th as a broad anti-cyclone (i.e. high pressure) further settles over S. Ontario to S. Quebec. This should also feature a cool start to the day (12 C). Under the influence of this system, instability will be suppressed, and so the risk for any precipitation development should be kept at a minimum. Maximum temperatures of about 24-25 C are expected, with reasonably warm late-evening temperatures of 22-23 C for the greater Montreal area. Due to a somewhat more prominent SW/SSW wind flow regime unfolding late-day, humidity will increase to borderline low-moderate standards by late-afternoon, so humidex values are relatively meager (humidex of 24-25 C for the late-evening).

As the high pressure system undergoes eastward progression through the day, the surface and near-surface wind fields should correspondingly adjust through the day, beginning as Westerlies/WSW early in the day and afternoon and transitioning to SW/SSW by late-afternoon. Speeds should be somewhat breezy during the afternoon, at 17-24 km/h, but this should also diminish slightly by late-afternoon and onwards, to 13-17 km/h (somewhat breezy). As a result, the smoke from the fireworks should be moving at a reasonable pace mostly to the right of the La Ronde audience (left for those on Notre-Dame/de Lorimier streets), though extreme right-hand sections of the audience could sometimes receive smoke. However, because of a continued Westerly/WSW flow above the surface, smoke from very high-altitude shells, such as 10- to particularly 12-inch shells (if they exist in this display) should advance fairly quickly towards the La Ronde audience more directly, notably right-hand sections. Moderate humidity, at best, would also suggest that smoke will not have much opportunity to build. Some accumulation could occur during more active sections along low- to mid-level, but this should be rather temporary. The change to SSW tendencies will also eventually encourage the warmer and more humid conditions to resume by the afternoon of Sunday, July 8th.

Another update to follow below this posting by tomorrow evening (July 6th).

Trav.

What had been specified in the above posting still largely holds for this opening display. As such, here are the predominant weather conditions for the greater Montreal area for Saturday, July 7th.

Temperature/Humidity

Temperatures are mostly likely to reach 26-27 C by the mid-afternoon period. By late-evening, including over the course of display time, a temperature of 22-23 C is applicable. Humidity should rise to moderate standards by the afternoon hours but should decrease slightly to borderline low-moderate levels by mid-evening. This will create a slight humidex of 24-25 C during the late-evening.

Precipitation

Under the influence of high pressure, precipitation development will be minimal. Skies should be mostly clear through the day, with a few high-level cirrus cloud clusters and isolated fair-weather cumulus. Mostly clear skies should occupy the evening, with a few isolated cirrus clouds.

Wind

Winds continue to be in the form of WSW to begin the day, but as the area of high pressure shifts eastward, the surface wind flow will correspondingly transition to SW/SSW tendencies towards sunset. Wind speeds are still expected to be breezy from the WSW during the afternoon, at 17-24 km/h (occasional gusts of 33-36 km/h). A slight reduction in speeds, however, should unfold by late-afternoon, though still remaining somewhat breezy, at 13-17 km/h. As such, smoke accumulation from the fireworks should not be excessive and should be moving at a reasonable pace to the right of the La Ronde audience (left for those on Notre-Dame/de Lorimier), though the smoke could occasionally reach extreme right-hand sections of the audience. Also, because wind direction veers with height within the boundary layer, smoke from very high-altitude shells (if they exist in this display) will more likely move relatively quickly towards the La Ronde audience overhead (mostly right-hand sections). The combination of borderline low-moderate humidity and somewhat breezy winds should keep smoke accumulations minimal.

If necessary, another update will follow by the mid-afternoon tomorrow (July 7th) to address wind velocity.

Trav.

I am happy that you still provide your detailed weather forecast this year, Trav. Thank you!

Fred

You're very welcome, Fred, and it is always a pleasure!

No real change to the details presented previously, though I would just boost late-evening temperatures slightly, to 23-24 C. Humidity should remain steady at where it is now (low), so the humidex is negligible.

Trav.

As was the case for the opening display, an area of high pressure will be moving into S. Quebec for the day Wednesday (July 11th). As a result, this will be the dominant system affecting the Austrian display.

With high pressure guiding weather conditions for Wednesday, precipitation development should, once again, be restricted. This would leave mostly sunny skies, with isolated fair-weather cumulus and a few clusters of cirrus clouds. Humidity should also be limited to low standards, at best, during the day, including into the evening hours, making the humidex negligible. Late-evening temperatures, for the greater Montreal area, are most likely to be 22-23 C (maximum temperatures of 25-26 C during the mid-afternoon). Due to some lift occurring during the evening period, a few clusters of cumulus should be present, with some residual cirrus clusters. Thus, a mild increase in cloudiness is expected for the evening, but with still large clear breaks.

Unlike the opening display, however, wind speeds should be fairly light during the evening but enough to mostly displace the smoke adequately outside of more active segments. This is owing to a weaker pressure gradient between the aforementioned high pressure system and surrounding areas of low pressure, including the remnants of Tropical Storm Chris in the Atlantic. Speeds of 9-12 km/h are favored for the afternoon, with a very slight weakening to 8-11 km/h for the evening. Wind direction should also be in the form of Northerlies/NNW/NNE, though they could transition temporarily to light SW winds into the evening period. This would allow the smoke to move gently to the right of the La Ronde audience (left for those on Notre-Dame/de Lorimier), though also to far right-hand sections. It is currently unclear, however, as to whether the transition to SW tendencies for the evening will occur, in part because of some challenges in the models’ ability to resolve the interaction between the high pressure system’s wind fields with the remnants of Tropical Storm Chris, casting some degree of uncertainty. Some periods of heavier smoke accumulation will be favorable (notably during more active segments, and depending on dominant products used at low-level), mostly along low- to mid-levels, which could sometimes cause the display to appear murky to the right. Also, much like during the opening display, winds should exhibit a veering component with height, and so smoke from higher-altitude activity could again be drifting towards the La Ronde audience more directly, just a little more slowly than during the opening. Opportunities for particularly extensive smoke buildup, though, should be limited due to lower humidity.

Another update to follow by either later tomorrow evening (July 10th) into pre-dawn July 11th.

Trav.

Forecast details presented in the above posting are still largely applicable for the day tomorrow (July 11th). As such, here are the most likely weather conditions for Wednesday, July 11th, for the greater Montreal area.

Temperature/Humidity

A maximum temperature of 25-26 C is expected, with a drop to 22-23 C by late-evening. Because of the aforementioned area of high pressure throughout the day, humidity will trace low standards, so the humidex will, once again, be negligible.

Precipitation

Also due to high pressure, precipitation development should be kept at a minimum. Instead, a few isolated fair-weather cumulus and clusters of cirrus cloud will more favorably be present. Some weak lift by late-afternoon should continue to support sparsely distributed clusters of cumulus/cirrus, but skies will be mostly clear throughout the evening, despite these patches of cloud.

Wind

Some degree of uncertainty remains with dominant wind direction into the evening period, mostly because of the light speeds at that time. When wind speeds are light, local influences become more important in controlling direction.

Winds should still be in the form of light NNE to straight Northerlies through the day, with a temporary transition to SW to WSW still appearing favorable by near sunset. However, although wind speeds are somewhat breezy earlier in the day (12-16 km/h), speeds do diminish to very light standards by the late-afternoon and onwards, to 4-7 km/h, and persist for the evening. This suggests that the smoke from the fireworks should be moving gently towards principally right-hand sections of the La Ronde audience, causing the display to sometimes appear murky at low- to mid-levels, mostly deeper into the show. Fortunately, humidity will remain low, so particularly thick smoke accumulation should not be too much of an issue, but smoke could still sometimes build quickly. Winds also continue to veer with height, and these speeds are similarly expected to be fairly light and more Westerly. Thus, smoke from higher-level activity should be moving fairly gently overhead towards the La Ronde audience more directly.

If necessary, another update will follow by this mid-afternoon (July 11th) to address wind velocity.

Trav.

Surface winds are shown to still have a Southerly component for this evening (July 11th), but instead of SW to WSW, winds should be blowing rather lightly from more the South to SSE. Thus, the smoke should still be moving very gently (sometimes appearing near-stationary) but more distinctly to the right of the La Ronde audience. Maximum wind speeds of 5-8 km/h are likely. Also, smoke at mid- to high-levels of the display should still be moving towards the La Ronde audience more directly, but notably to right-hand and partially central sections. Periods of heavier smoke accumulation still appear possible, but mostly deeper into the show, during and following more active segments, and along low- to mid-levels, but especially thick smoke buildup is not favorable due to continued low humidity.

For all other details, please refer to the above post, as they remain valid.

And just to correct a small detail two posts above - it should read "Hurricane Chris", not Tropical Storm Chris.

Trav.

Quick update to state (although too late) that smoke from higher-level activity should be moving slowly more to the left of the La Ronde audience.

EDIT at 11:44 p.m. July 11th: Consistent with the above postings, smoke was moving to the right at low-levels, but it turned out that, fortunately, the smoke was pushing gently to the right at all altitudes, and at a marginally sufficient pace.

Trav.

The warmest and most humid fireworks evening so far this year is expected for July 14th, which will affect the Chinese display.

A strengthening circulation of very warm and moist air will advect into S. Ontario and S. Quebec through the day Saturday (July 14th), which should eventually result in at least near-heat wave status over the July 14th-July 17th period . In the process, early-day convection (mostly late-pre-dawn July 14th) associated with a stationary frontal boundary and shortwave troughs will encourage convective rains and embedded isolated non-severe thunderstorms. Behind these features, instability will be enhanced as the day progresses, so clusters of large, defined cumulus clouds will be present through most of the day, leaving partly cloud skies. Late-evening temperatures, for the greater Montreal area, should be 26-27 C, with a humidex of 33-34 C due to borderline high to very high humidity.

Into the late-evening, moderate instability is likely to continue, persisting into the overnight hours. As another shortwave trough ejects SE through the evening farther West, there is reason to believe that an isolated non-severe thunderstorm risk will re-introduce itself by late-evening across S. Quebec. As such, I would assign a 30% probability at this point (possibly a later upgrade to 40%, depending on the nature of lift at the time in newer model data output) to account for sparsely-distributed convection by late-evening. Apart from this, defined clusters of cumulus clouds should be present throughout the evening, generating partly cloudy skies.

Winds are also expected to be light during the evening period, which could carry more significance because of considerably higher humidity levels at the time. However, speeds should be marginally sufficient (7-10 km/h) to displace the (gradually thick) smoke to the right of the La Ronde audience (left for those on Notre-Dame and de Lorimier) due to Southerlies to SSE. Higher-altitude smoke should be moving somewhat more quickly, though a little more towards extreme right-hand sections of the La Ronde audience overhead. Depending on how numerous energetic segments are, and depending on dominant pyrotechnic material at low-level, though, periods of thick smoke accumulation will be possible before the smoke can move off sufficiently to the right. This would also cause far right-hand sections of the display to appear sometimes either murky or partially covered at low- to mid-level.

Another update to follow by either late tomorrow evening (July 13th) or pre-dawn Saturday (July 14th), with a focus on thunderstorm risk and wind speed/direction.

Trav.

Details presented in the above posting are still largely valid, though some revisions were made to wind speed and direction. As such, here are the dominant weather conditions for the greater Montreal area, for Saturday, July 14th.

Temperature/Humidity

A maximum temperature of 28-29 C is expected during the mid-afternoon. By late-evening, because of borderline high to very high humidity levels, temperatures are less liable to fall quickly and, thus, should drop only slightly, to 25-26 C. Higher humidity levels should also feature a humidex of 32-33 C for the late-evening. *Note, however, that if rainfall does occur, temperatures could fall to as low as 21-22 C, depending on the persistence of the rainfall.

Precipitation

As a shortwave trough and stationary warm front affect the region during the late-pre-dawn period to just after sunrise, convective rain showers and embedded isolated non-severe thunderstorms should occur. Beyond this, atmospheric instability will strengthen into the afternoon as periods for solar heating emerge, in addition to increased humidification. Thus, large clusters of defined cumulus cloud cover (with eventual clear breaks between them) should be present through the afternoon and into the evening period, leaving partly cloudy to broken skies at that time. Due to instability continuing to be moderate for the evening, and with some lift supplied by a trough advancing from the West, non-severe thunderstorms and convective rain showers will become possible by late-afternoon and onwards. However, these are likely to be sparse in coverage for the late-evening, so a 30% probability of precipitation is still appropriate before increasing to 40% overnight. At the very least, it will be possible to see occasional lightning flickering in the distance.

Wind

Winds are expected to be more in the form of Southwesterlies (SW) for most of the day (SSW early), including the evening. Speeds of 11-14 km/h are favored for the late-evening, diminishing slightly from breezier speeds (14-18 km/h) during the afternoon period. This would typically be enough to displace the (gradually thicker) smoke accumulation, including mid- to high-altitude smoke, adequately to the right of the La Ronde audience (left for those on Notre-Dame/de Lorimier), though the smoke should also sometimes be moving towards extreme right-hand sections. Also, the smoke at higher altitudes should be moving at a somewhat faster pace than at lower levels but, again, in the same direction. A few periods of larger smoke accumulation will still be possible, depending on dominant pyrotechnic material at low-levels and the frequency of energetic segments. This could sometimes cause far right-hand sections of the display (from La Ronde’s perspective) to appear murky or partially covered deeper into the display. *Note that if a moderate-heavy rainfall or a thunderstorm does occur over the area, the local wind flow will likely temporarily be disrupted and transition to Westerlies, causing the smoke to correspondingly turn towards the La Ronde audience more directly.

If necessary, another update will follow by the mid-afternoon of today (July 14th), mostly to address any potential changes in wind direction and/or speed, as well as convective coverage.

Trav.

A few minor revisions to details presented above.

First, wind direction should continue to retain SSW status through the evening, with speeds of 9-12 km/h (a very slight decline from 11-14 km/h). As such, as specified in the above post, smoke from the fireworks should be moving usually adequately to the right of the La Ronde audience, though more clear to the right. Higher-altitude smoke should also principally be moving to the right, and at a slightly faster pace, but could also sometimes reach extreme right-hand sections of the audience, as mentioned above. Periods of larger smoke accumulation will be possible at mostly the right of the display deeper into the show, but this will be contingent on the factors outlined previously.

Convective coverage continues to be sparse this evening, and I suspect that will continue into the early-overnight period. Thus, a 30% probability of precipitation should continue until then (rather than 40% overnight). This is due to the most prominent lift remaining to our North.

Finally, I would boost slightly late-evening temperatures to the original 26-27 C (humidex of 33-34 C).

For all other information, please refer to the above posting.

Trav.

Cooler and considerably less humid conditions are expected for Wednesday, July 18th and, therefore, will be present for the Canadian display.

Behind a strengthening cold front and broad mid- to upper-trough that may induce (strong) thunderstorms this pre-dawn period (July 17th), strong high pressure will advance into S. Ontario to S. Quebec for July 18th, which will yield cooler and drier morning and late-evening conditions for the greater Montreal area. Consequently, maximum temperatures of 23-24 C are expected for the mid-afternoon and should fall to 20-21 C by late-evening. Of all fireworks nights thus far, humidity levels should be at their lowest (contrasting sharply to the very humid conditions during the Chinese display), and so humidex values will be negligible.

With high pressure in the area, precipitation development should also be minimal, as will cloud development. A few isolated fair-weather cumulus and cirrus clusters should instead be present, but skies will remain largely clear for the day, especially for the evening and onwards.

Finally, being located on the Eastern periphery of the high pressure system Wednesday, winds should be predominantly out from the NW (NNW early), with speeds of 13-17 km/h. However, by early-evening, Westerlies to WSW become more favored, along with weakening speeds to light standards (to 6-9 km/h). This would guide the smoke gently towards the La Ronde audience directly. Higher-altitude smoke should be moving at a somewhat faster rate but will be moving mostly towards central and left-hand sections of the audience. Fortunately, extensive smoke accumulation is not likely as humidity is low, but the display could still appear murky as we progress deeper into it.

Another update to follow later this evening (July 17th) into pre-dawn July 18th.

Trav.

Details presented in the above posting continue to largely hold for the Canadian display. As such, here are the primary conditions expected for Wednesday, July 18th, for the greater Montreal area:

Temperature/Humidity

Temperatures are expected to drop to 20-21 C by late-evening (24-25 C for the mid-afternoon), so a touch cool, especially amplified by the fairly gentle breezes from the WNW. Humidity levels continue to be low for the day, and so the humidex should be negligible.

Precipitation

Rainfall development will be restricted under the influence of high pressure. At the most, isolated clusters of cirrus cloud and fair-weather cumulus will be present. Skies should be predominantly clear, especially beyond sunset.

Wind

Winds continue to be from the NW through the afternoon (NNW early) before transitioning to more WNW into the early-evening. Speeds of 13-17 km/h are favored for the day, but this diminishes to 9-12 km/h for the late-evening period. As such, the smoke should be displacing reasonably quickly but towards the La Ronde audience directly, mostly focused on central and left-hand sections and eventually to sections of the bridge behind the park. This will also be applicable for upper-level smoke, which should be moving at a slightly faster pace. Overtime, this will likely cause the display to sometimes appear murky, but particularly extensive smoke accumulation is not expected due to low humidity.

If necessary, another update will follow by later this mid-afternoon (July 18th) to address any changes to wind direction and/or speed.

Trav.

An area of double-barrelled low pressure (i.e. an area of low pressure with a double center) will be intensifying to the South on Saturday (July 21st) and will have some influence on weather conditions throughout the day for extreme S./SW Quebec, including the island of Montreal. This system will also signal the beginning of a transition to a gradually wetter and stormier pattern, beginning on July 22nd.

Temperatures for July 21st will continue to be hot and may feature the last 30.0+ C occurrence for a while, though the coming week will often remain very warm, accompanied by rich surface moisture/humidity. By the late-evening period, values drop to about 25-26 C, so still very warm, which is a contrast to July 18th. Humidity should be typically moderate for the day, except borderline moderate-high for the late-afternoon before dropping to moderate for the mid- to late-evening. Thus, a maximum humidex of 34-35 C is favored for the mid-afternoon, along with a humidex of 28-29 C for the late-evening.

Although the low pressure system will be evolving to our South, into New York State, precipitation development should remain minimal until July 22nd. However, high-level cirrus cloud coverage should increase (accompanied by a few clusters of fair-weather cumulus) into especially the mid- to late-afternoon due to the northward approach of that area of low pressure and weak lift overspreading the region. This cloud coverage should persist for the evening.

As the system ejects farther North, the wind fields at and near the surface will also undergo slight but important changes through the day. Although there remains some uncertainty in how quickly wind direction will transition from the early-day SE winds, it appears likely that light SSE winds (9-12 km/h) will take place for the evening period (dropping from the more SE tendencies of 14-18 km/h from the afternoon). As such, the smoke should be drifting reasonably quickly clear to the right of the La Ronde audience (left for those on Notre-Dame/de Lorimier). This will also apply for higher-altitude smoke, just that the smoke accumulation will be moving slightly faster than at lower level. Some periods of larger smoke accumulation will be possible during more active sections of the display, especially at the far right of the display (La Ronde’s right) due to moderate humidity and light winds, but this should only be temporary as the winds will usually be sufficient to clear the smoke at a reasonable rate.

Another update to follow by late-day July 20th into pre-dawn July 21st.

Trav.