Forecast details specified in the previous posting continue to remain largely applicable. However, though wind speeds remain mostly unchanged (3-6 km/h), directional tendencies are projected to be more SW to SSW by mid- to late-evening, suggesting that while the smoke will likely sometimes remain stagnant, it could be more directed to the right of the La Ronde audience, or extreme right-hand sections of the audience. That said, the smoke should be moving very slowly (at times, potentially near-still), and periods of extensive smoke accumulations will be possible (and depending on the overall pyrotechnic material used in the display). Humidity also continues be on the border between moderate and high (more so moderate), so smoke build up is favorable. All other factors remain constant.

I also hope that the severe thunderstorms that affected the island over the last two days (July 14th and July 15th, but notably July 14th) did not affect the setup process too much.

Trav.

Another area of high pressure is expected to move SE through today (July 19th) and continue to affect tomorrow (July 20th). In the wake of this system, humidity will transition to lower standards, and the air will stabilize significantly, as compared to what was observed on July 18th, when strong to severe thunderstorms affected much of S. Quebec.

Unlike the previous high pressure system that affected Switzerland’s presentation day (July 16th), this system is broader and more significant. Consequently, humidity will more likely be on the border between low and moderate standards by mid- to late-evening Wednesday. In addition, this general area will eventually be located more on the western end of this system as the day progresses, allowing for a return to gradually very warm to hot weather by July 21st, possibly establishing another (near) heat wave event (July 21st-July 23rd). July 20th will also return to very warm standards, but humidity levels should remain borderline low to moderate through the day, including into the evening hours. As such, maximum temperatures should reach 27-28 C by the mid-afternoon hours, and drop to 22-23 C by the late-evening (negligible humidex). A stronger pressure gradient developing will also likely lead to stronger wind flow on the western fringe of the system, and so directional tendencies will mostly be from the WSW through the day but becoming more SW by late-afternoon to evening. Speeds should be breezy during the afternoon, at 19-23 km/h but falling to 13-16 km/h by mid- to late-evening. As a result, smoke from the fireworks should not be building quickly and should be moving to the right of the La Ronde audience (possibly extreme right-hand sections of the audience).

Conditions should be remaining stable under the influence of high pressure, so severe thunderstorms (or convection/precipitation altogether) are not expected, as compared to what occurred for the American team on July 17th, 2010 - that was also the same late-afternoon when an elderly couple was struck by lightning while waiting for the fireworks. Skies should be mostly clear during the evening (mostly sunny during the afternoon) with a few patches of cirrus clouds.

Another update to follow late today or early tomorrow (July 19th to July 20th).

Trav.

Forecasted conditions specified in the above posting continue to apply. As such, here are the predominant weather patterns for the Montreal area for Saturday, July 20th.

Temperature/Humidity

As the aforementioned current area of high pressure drifts farther SE through the day tomorrow, maximum/overall temperatures are expected to re-establish above normal tendencies. A maximum temperature of 27-28 C will be favorable by the mid-afternoon of Wednesday. As the system continues to eject SE, it will also gradually help to boost humidity levels to moderate standards by late-day because of increasing warm air advection. As a result, moderate humidity levels should develop into the late-evening period, and temperatures at the time, in the metropolitan area, should be 22-23 C, including during the display. With moderate humidity, a humidex of 26-27 C is likely.

Precipitation

With the surface high pressure system, coupled with a building upper-level ridge, overall atmospheric stability will be favored, keeping rainfall/convective probabilities minimal. Skies should remain mainly clear throughout the day and into the evening. Some weak lift in the area should support a few isolated patches of cirrus clouds. Thunderstorms will become increasingly favorable by late-day July 21st, and potentially strong to severe thunderstorms during the July 22nd to July 24th period (mostly July 22nd).

Wind

Winds are expected to be in the form of breezy West-Southwesterlies (WSW) through most of the day. Speeds of 19-23 km/h are favorable during the late-morning to mid-afternoon period. As we will be more on the western fringe of the area of high pressure by largely late-day, however, winds should gradually transition to SW tendencies by about sunset and onward, becoming potentially even SSW by late-evening. Speeds also decrease to 11-14 km/h. As a result, the smoke from the fireworks should be moving generally to the right of the La Ronde audience (although there is a possibility for smoke to sometimes affect extreme right-hand sections of the audience), and reasonably quickly, even though speeds are diminishing from what they will likely be during the afternoon period. Moderate humidity should also not promote too much smoke buildup.

In summary, a warm and moderately humid mid- to late-evening, with light SW winds and mostly clear skies.

*Another update to come by mid-afternoon tomorrow (July 20th), if necessary, to address evening wind direction.

Trav.

As per the previous two postings, SW winds continue to be favored by mid- to late-evening, so the smoke should be blowing largely to the right of the La Ronde audience, though right-hand sections of the audience could often receive the smoke directly, mostly smoke associated with higher-level shells.

Humidity should also be more on the border between low and moderate, so a humidex of 27 C is favorable by mid-evening.

All other factors remain constant.

Trav.

A broad area of low pressure and attendant mid- to upper-level trough are expected to affect S. Ontario to S. Quebec through most of the day Saturday (July 23rd). The strong SW/SSW circulation of warm, moist air has begun to circulate into these regions today (July 21st), with a return to hotter and more humid conditions.

A pair of cold fronts associated with this area of low pressure will be the focus for possible scattered non-severe thunderstorms (isolated strong to severe thunderstorms possible) and convective rains through the day Saturday. Latest model guidance suggests that most of the instability on Saturday will be more focused through the morning to mid-afternoon period, with gradual stability by late-afternoon, leaving partly cloudy skies by mid- to late-evening. Note, however, that there remains uncertainty as to the overall timing of the secondary cold front and accompanying trough, so this will have be monitored and studied in coming model data to see if there is any possible extension of instability into the evening hours. Late-evening temperatures of 22-23 C are favorable in the metropolitan area, and under continued high humidity (humidex of 28-29 C).

Because of uncertainties in the timing of the cold front, the timing of the associated wind shift is subsequently uncertain. Winds through most of the morning to afternoon are likely in the form of westerlies (occasionally WNW), but once the secondary cold front moves through, a shift to northwesterlies (NW) should develop. Wind speeds similar to what had been observed during the American display should be present for the Spanish display (11-14 km/h). As such, smoke from the fireworks, assuming a directional shift to NW by early-evening, should be pushing the smoke reasonably quickly towards far left-hand sections of the La Ronde audience, as well as spectators positioned on the bridge behind the park.

*Another update to follow by the end of tomorrow (July 22nd) into early-July 23rd.

Trav.

Most of what was stated in the above post still holds generally constant, but more clarifications will be given below concerning the thunderstorm/convective rainfall probabilities and wind direction. As such, here are the forecast details for the Montreal area for Saturday, July 23rd.

Temperature/Humidity

Temperatures continue to be very warm into the day Saturday. Maximum temperatures of 28-29 C are favored by mid-afternoon (if thunderstorms/rain showers occur persistently, then temperatures will temporarily fall to 21-22 C at that time, along with moistening) , and humidity, though a decline from today’s (July 22nd) very high concentration, should still remain on the border between moderate and high, despite the passage of the secondary cold front by late-afternoon. With this humidity, a humidex of 32 to 33 C is likely into the mid-afternoon. By evening, temperatures should fall to 23-24 C in the metropolitan area, and with continued high humidity, a humidex of 29-30 C should occur.

Precipitation

Mostly scattered non-severe thunderstorms/convective rains will be possible tomorrow ahead of the secondary cold front. With scattered coverage by late-morning, a 40% probability is warranted. Other dynamics (including moderate instability) coming together will also favor an isolated strong to severe thunderstorm threat (30% probability) into the late-morning to early-afternoon, although the greatest likelihood for severe weather will remain South of the border, where wind shear is maximized and juxtaposed with moderate instability. Instability/convection should subside significantly towards traditional dinner time and onward, leaving partly cloudy skies for the duration of the evening.

Wind

With the timing of the cold front being clearer, the onset of a directional shift to northwesterlies (NW) should take place by about sunset. Directional tendencies prior to frontal passage are still in the form of WNW, but this should undergo a transition to a more consistent NW flow by sunset and onward. Speeds are also expected to be breezy during the day, at 17-21 km/h (occasional gusts of 29-32 km/h), but this diminishes to 11-14 km/h by the very late-afternoon. As a result, the smoke from the fireworks should be moving reasonably quickly, and mostly to the EDIT:***left*** of the La Ronde audience (notably smoke from high to very high-level shells), with lower-level smoke moving sometimes towards far left-hand sections of the audience. Smoke should also be moving towards spectators on sections of the bridge immediately located behind La Ronde. Periods of moderate smoke accumulations will likely occur (largely during more energetic sections of the display) due to fairly high humidty, but these should be clearing at a reasonable pace.

In summary, another warm and fairly humid evening, with light NW winds and partly cloudy skies.

*Another update to follow, if necessary, to address convective rainfall and/or wind velocity by mid-afternoon tomorrow (July 23rd).

****EDIT: I just corrected an error in the wind section - it should read "to the left of the La Ronde audience". My apologies.

Trav.

Isolated clusters of strong to severe thunderstorms are in the area, largely with torrential rains and locally strong winds.

Trav.

Isolated clusters of strong to severe thunderstorms are in the area, largely with torrential rains and locally strong winds.

Presumably these will subside soon. What time will things start to clear up? Will it be dry this evening? Breezy? (I hope!)

Paul.

Hi Paul,

Yes, things should significantly improve as we move closer to dinner time and onwards, leaving partly cloudy skies, and light NW winds. There is one more round to come through shortly, mostly for the West Island and Vaudreuil.

Another update to come for wind speed and direction by mid-afternoon!

Trav.

Trav, thank you for all these updates, they are very important today.

I am confident that we will have good weather conditions tonight, but I am concerned with the delay in the setup due to thunderstorm alerts in the area.

However, RICASA just posted a picture taken inside the control room, above the grandstands. Tests are apparently underway! I am not sure it means that all the setup is completed, though.

Fred

However, RICASA just posted a picture taken inside the control room, above the grandstands. Tests are apparently underway! I am not sure it means that all the setup is completed, though.

They may as well spend the time they have testing what is completed. They are using 15 field controllers (these are the computers that control the firing modules) so there's plenty to do - especially as any faults will have to be corrected. That they're ready to test now is a good sign!

Paul.

No problem for the updates, Fred.

Light NW winds are favorable early this evening, but a slight shift to NNW tendencies is possible by late-evening. However, speeds are expected to be a little lighter, at 8-11 km/h this evening. Since the thunderstorms did moisten the air to higher humidity levels, this may favor more periods of extensive smoke accumulation during active parts of the display (mostly along low- to mid-level), but the smoke should still be moving adequately enough to the left of the La Ronde audience (at times, towards far left-hand sections of the audience), and to those on adjacent sections of the bridge just slightly behind La Ronde.

Temperatures should rebound to 22-23 C into this evening, with a humidex of 28 C.

The severe thunderstorm watch should soon be lifted, but a few convective rain showers will still be possible until about (traditional) dinner time. Partly cloudy skies are favored this evening (low-level cumulus and high-level cirrus clouds).

Trav.

I realize that I am very late with this update, but the newest data that I have been analyzing suggests the wind direction (identical speeds specified above) will more likely remain WSW this evening before the arrival of the NW tendencies mentioned previously, so the smoke should be moving more directly towards the La Ronde audience.

My apologies for this late update. All other information remains constant.

Trav.

Hi Trav,

Hum… Let's say that this late post secured your faultless reputation!

I have been surprised by the freshness of the air last night, a feeling stressed by the level of humidity. In addition to that, we realized from the clusters of smoke produced by protocolar salutes that we were going to endure some pyros-related precipitations. And we had!

Early in the evening, a shower began as I arrived at La Ronde. I was fortunate to be at the entrance, where there's a large location to protect ourselves from the rain.



Fred

Just to add to Fred's post, once the shower ended, it produced one of the best rainbows I've seen in a very long time.