With the 2016 competition commencing fairly soon, and with this now being the mid-point of June, I thought that it would be appropriate to post this thread.

The focus here will be (in large part) on temperature, moisture/humidity, precipitation, wind speed, and wind direction. In situations where thunderstorms become more favorable, more emphasis and subsequent updates will be placed, notably if strong to severe thunderstorms are possible on fireworks days/evenings. This is especially necessary due to the constantly evolving nature of convective precipitation coverage and intensity. Similarly, more updates will be provided if wind speeds are expected to be either too weak or too strong, or when wind direction might be unfavorable.

As always, you are also more than free to share weather updates here!

For those interested in reading my projections for the Spring and Summer of 2016 (even though astronomical Spring is soon coming to an end), the outlook, which was originally released on March 17th, 2016 - St-Patrick's Day -, can be found here:

https://www.facebook.com/notes/travis-moore/winter-2015-2016-and-a-loo k-ahead-to-spring-summer-2016/10153971353701346

In general, for S. Ontario to S. Quebec, I am anticipating a more noticeably very warm to hot late-Spring and Summer period this year (so, an "overall" above to potentially well above normal temperature distribution for the mid-May to mid-September period), including more days reaching maximum temperatures of 30.0+ C (14-16 such days for the island of Montreal and closely surrounding locations, specifically), an increase in the number of days with minimum temperatures of 20.0+ C, and possibly more (severe) thunderstorm development days than normal. Note, however, that due to the nature of thunderstorms, certain areas will obviously observe more occurrences than others within the forecast regions.

I hope for ideal weather for all fireworks days, as well as for setup!

Trav.

Trav, it is great to know that you will supply forecasts this year again!

That being said, I am sure that you will be very interested by this very particular trial:
http://www.journaldemontreal.com/2016/06/21/en-cour-pour-avoir-prevu-d e-la-pluie-il-craint-un-precedent

But, as your forecast reports are remarkably accurate, you should not have any problem!



Fred

Always a pleasure, Fred. I will submit initial forecasts typically two days prior to fireworks dates, with more finalized details the day before (and on the day, as necessary).

And, wow, I have never heard of such a predicament, as presented in that article, but it is very interesting as it is frightful! I do agree with the points made by the meteorologist, though!

Thanks for sharing!

Trav.

Should we get prepared for a rainy, cold, and windy opening night as we experienced last year?

Fred

A strengthening area of low pressure will eject East and continue to produce very warm to increasingly humid conditions for S. Ontario to S. Quebec for Canada Day, followed by pronounced cooling for the forecast period (Saturday, July 2nd). Before this cooling, however, strong to severe thunderstorms will be possible for the late-afternoon to mid-evening period for E. Ontario to extreme S./SW Quebec (more on this below).

Following the cold front later tomorrow (July 1st), an upper-level trough will migrate over the region and will likely, unfortunately, lead to well below normal temperatures for the day. Instability associated with this trough will lead to generally scattered showers (40% probability) and isolated non-severe thunderstorms (30% probability), largely in areas where solar heating is most prevalent. Since precipitation is largely governed by instability on Saturday, scattered showers should progressively subside towards sunset and beyond, leaving mostly cloudy conditions with some clear breaks. Strong cold air advection, mostly cloudy conditions (some sunny periods), possible rain showers, and gusty winds will largely act together to suppress maximum temperatures throughout the day (maximums no more than 19-20 C), and late-evening temperatures of 17-18 C in the Montreal metropolitan area are likely. As a result, a light sweater and/or light jacket will likely be necessary for most people, especially considering the breezy nature of the winds and low moisture content (moisture remains low through the day). Note, though, that this cooling is very temporary, as temperatures should begin to rise fairly sharply by Sunday, July 3rd, and near- to actual heat wave status is very possible next week, beginning July 5th.

Winds need to be monitored closely. Wind speeds are expected to be gusty throughout the day and remain largely WSW to sometimes straight westerlies. Sustained speeds and gusts are shown to be 28-31 km/h and 43-47 km/h, respectively. Speeds should weaken slightly into the evening, but “occasional” gusts are remaining just slightly below the 40 km/h threshold. As such, winds should be pushing the smoke quickly towards the La Ronde audience directly. Low moisture profiles, however, will not favor rapidly accumulating smoke, but smoke blowing frequently towards the La Ronde audience could sometimes cause the display to appear murky, depending on the concentration.

Another update to follow by the end of tomorrow, or into early-Saturday, with a focus on wind speed and direction.

*So yes, Fred - there are similarities in weather for both the opening shows of 2015 and 2016, except that this year's is chilly throughout the day, but evening conditions are virtually identical.

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Your Canada Day forecast

Temperature/Humidity

Maximum temperatures in extreme S./SW Quebec should reach 27-28 C (locally 29 C is possible, especially in areas farther East, where solar heating is more prolonged) before extensive cloud coverage arrives by the mid-afternoon period because of the advancing cold front. Humidity remains low for the early part of the day but becomes moderate by mid-afternoon, and then high by early-evening. With increasingly saturated air, a humidex of 28-29 C is favorable into the early-evening (base temperature of 21-22 C).

Precipitation

Due to the sharp cold front, rainfall is likely to occur by late-afternoon into the evening. Thunderstorms could also accompany the rains, a few of which could reach strong to severe standards. Damaging winds and small hail will be the primary threats with the strongest storms, and a few storms will be capable of intense lightning, although this will be dependent on how high moisture availability actually becomes. How widespread stronger thunderstorms become, though, is questionable due to the lack of pronounced warm air advection, but, for other reasons, at least scattered coverage is expected. As mentioned, increased high- and eventually mid- to low-level cloud coverage should begin to unfold by mid-afternoon. The convective threat should begin to diminish towards 11:00 p.m. and onward, although delays will be possible with local fireworks events if thunderstorms are in the area beforehand.

Wind

Winds remain light for the first half of the day, with southerly to SSE directional tendencies (7-11 km/h). By mid-afternoon, SSE winds begin to increase to 18-22 km/h, gradually shifting to a SW flow by the mid-evening. Note, however, that if thunderstorms are directly overhead, wind speeds will be briefly strong ahead of their gust fronts and will temporarily alter the wind direction locally.

Trav.

No significant changes to the forecast details specified above. As such, here are the most likely weather conditions to affect the Montreal area for Saturday, July 2nd.

Temperature/Humidity

With the upper-trough moving over the area, temperatures will generally struggle to reach normal values due to fairly strong cold air advection, extensive cloud coverage and isolated rain showers. Latest sounding data, however, does suggest more periods for solar heating through more clear breaks in the cloud deck, so maximum temperatures could reach 20-21 C by mid-afternoon (cooler if showers do occur). This would also lead to slightly higher evening temperatures, so 19-20 C is favorable during the early-evening, but falling to 18-19 C by display time. Humidity continues to be low, so no humidex is expected. A light sweater may be necessary for some, especially due to the chilling effect of breezy westerly/WNW winds.

Precipitation

Light rain showers should become scattered (40% probability) into the afternoon hours, notably where solar heating is maximized. Very sparsely distributed non-severe thunderstorms are possible, but weak instability should keep them very isolated. Because lift is purely governed by instability, convective rain showers should gradually subside as we move closer to sunset and onward. Skies should be partly cloudy (more and larger clear breaks) during the evening, but mostly cloudy skies should occupy most of the morning to early-afternoon, with the sun making more of an appearance towards mid- to late-afternoon.

Wind

Wind speeds continue to be gusty throughout the day, but with slightly less sustained speeds and maximum gusts of 29-33 km/h and 42-46 km/h, respectively, mostly during the late-morning to late-afternoon period. By about sunset and onward, speeds should diminish further to 17-21 km/h (occasional gusts of 29-32 km/h). Winds continue to be generally westerly (sometimes WNW) throughout the day. As such, smoke from the fireworks should be moving fairly quickly towards the La Ronde audience directly (with some slight tendency towards left-hand sections of the seating area), sometimes causing the display to appear murky. However, excessive smoke buildup is not expected due to breezy winds and low humidity.

In summary, a cool evening, with low humidity, partly cloudy skies and breezy westerly/WNW winds.

Another update to follow, if necessary, by early this afternoon (July 2nd).

Trav.

A broad area of low pressure is expected to move NE in time for Wednesday, July 6th, and amplify the circulation of warm, moist air into the day Thursday (July 7th). Along the system’s warm front, however, a risk for convective rain showers and thunderstorms into the late-evening hours and overnight period could exist. The situation will need to be monitored, but if thunderstorms do occur, latest thinking is that most will remain sub-severe due to widespread cloud coverage ahead of the front during most of the day, but isolated stronger storms will still be possible for various reasons. Strong to severe thunderstorms will be possible into Thursday.

As mentioned in my third posting in this thread, temperatures are expected to be considerably warmer than they were for the opening display. Maximum temperatures during the day should reach 29-30 C, along with building humidity as the day progresses. By the mid-afternoon period, humidity should be high, continuing through the evening, so a humidex of 32-33 C is likely (base temperature of 25-26 C in the metropolitan area) during the late-evening. During the day, a maximum humidex of 35-36 C is favorable, along with mostly cloudy skies (due to the advancing warm front), but sunny breaks will be present, mostly during the morning to early-afternoon.

Winds are also important to monitor. Latest data indicates that winds could be quite light to very light (possibly near calm, at times), and from the East to ESE. Overall speeds are expected to be 7-10 km/h throughout the day. This situation would suggest that the smoke could be (very) gently blowing towards those spectators on Notre-Dame street and closely surrounding areas. That said, the smoke also could be accumulating fairly rapidly due to the light winds and high humidity, especially during more active sections of the display, and along low- to mid-levels over time, though the easterlies should “slightly” help to move the smoke directly away from the La Ronde audience.

Another update to come later tomorrow evening (July 5th) or early July 6th, with a focus on the possible risk for thunderstorms and light easterly to ESE winds.

Trav.

Forecast details specified in the above post remain mostly consistent for tomorrow, although changes to wind speed and direction are in order. As such, here are the expected weather conditions for Saturday, July 6th, for the Montreal area.

Temperature/Humidity

Maximum temperatures are expected to reach 30-31 C by the mid-afternoon period along with an increase in humidity. With high humidity, a maximum humidex of 36-37 C is likely. By late-evening, temperatures are not expected to drop excessively (especially in the metropolitan area), owing to higher humidity levels and stronger warm air advection. Temperatures should remain as high as 27-28 C by display time, with a humidex of 34-35 C is still favorable due to borderline high to very high humidity. If rain does occur persistently, then temperatures should be closer to 23-24 C. Increased cloud coverage by mid-afternoon should prevent temperatures from becoming overly high, but gradually stronger warm air advection and continued periods for solar heating should help the maximum temperature reach at least 30 C before rain showers (if any) can interfere later on.

Precipitation

The aforementioned warm front is still expected to eject NE through the day tomorrow, becoming stationary as it reaches closer to S. Quebec by late-tomorrow afternoon into the early-evening. This boundary will continue to be the focus for convective rain shower and isolated non-severe thunderstorm development through the evening hours and potentially overnight. Some thunderstorms may attain stronger levels due to the jet stream in the area and progressively higher degrees of warm and moist air circulation late-day, which is increasing instability at the time. Convective development becomes more likely by 7:00 p.m. Convective coverage, at this point, is scattered, so I would hold precipitation probabilities at 40% (30% for “strong” thunderstorms). Have an umbrella or another form of head covering at your disposal for the evening. Otherwise, skies should be mostly cloudy for the evening.

Wind

Recent and latest model guidance are in better agreement as to more SW to WSW wind tendencies throughout most of the day, and with stronger wind speeds during the afternoon period. Into the afternoon, wind speeds of 18-22 km/h are more favorable. By the evening, however, a slight directional shift and significant reduction in wind speed are expected, notably by just prior to sunset. By early-evening, speeds of 13-16 km/h are expected, but this should further be reduced to 4-7 km/h by mid- to late-evening. In addition, winds should become more westerly to eventually WNW during by mid- to late-evening. This suggests that smoke from the fireworks should be moving very slowly towards the La Ronde audience, but with more of a tendency toward left-hand sections of the seating area. Periods of extensive smoke accumulation are possible due to lighter wind speeds and higher humidity levels by late-evening, but accumulations are mostly pronounced when the display becomes more active, and along low- to mid-levels of the display. This could, again, cause the display to appear sometimes murky for those at La Ronde. *Also note that if thunderstorms do occur, the general wind flow will become altered and be more influenced by the winds produced by the thunderstorms.

In summary, a comparatively very warm to hot day, with continued very warm temperatures into the evening hours, along with high to gradually very high humidity, mostly cloudy skies (mid- to late-day), and light WNW winds. Scattered convective rain showers and thunderstorms (a few strong) are also possible along that stationary front.

*Another update will follow by late tomorrow morning to early afternoon (July 6th) to address and changes to winds, and the existing thunderstorm risk.

Trav.

No significant changes to the forecast with respect to wind speed and the convective shower/thunderstorm risk this evening (a few thunderstorms have already developed, mostly North and West of the Island). There is, however, a slight directional change during the mid- to late-evening. Instead of WNW to westerly tendencies (which should be case during the late-afternoon to early-evening), the eastward progression of the parent low pressure system should induce more NNW winds to northerly winds around display time before becoming more NNE to eventually NE near midnight and onward. This would imply that smoke should be blowing very gently to the left of the La Ronde audience (right for those on Notre-Dame) and towards adjacent sections of the bridge (and still potentially far left sections of the La Ronde audience). However, being near the center of the low pressure system will still likely lead to light wind speeds in the area for the duration of the evening to early-overnight. Periods of extensive smoke accumulation will still be favorable due to (very) light wind speeds and borderline high to very high humidity. Wind speeds should be 5-8 km/h throughout the evening. Again, if thunderstorms do occur (overhead or nearby), the general wind flow will be affected temporarily locally. Thunderstorms should remain non-severe.

Also, I am going to boost late-evening temperatures to 28-29 C (including during display time) in the metropolitan area, assuming no persistent rainfall.

All other factors hold constant.

Trav.

A broad and weakening area of low pressure is expected to affect this weekend’s weather (July 9th and 10th) across S. Ontario to S. Quebec, bringing with it a return to unseasonably cool conditions and possibly copious rainfall. This cooler and unsettled pattern, however, should be temporary and allow for a return to a very warm to hot pattern for some time (notably the July 12th-July 22nd period), within which a significant heat wave could be born (July 13th-July 16th).

As the area of low pressure advances towards S. Quebec on Saturday (July 9th), it will gradually become occluded, and ahead of the occluded front, persistent and copious rains could take place by the time the system departs. Current and recent analyses suggest that the air will likely remain very saturated over a great vertical depth through the day Saturday. As a result, not much lift will be needed in order for precipitation to develop. Because the air is saturated, however, this will keep instability minimal, and so while thunderstorms are possible, they are not expected to be severe. Thunderstorms, themselves, have the best chance of occurring during the morning hours of Saturday, with straight rain during the afternoon to evening hours (sparse embedded non-severe thunderstorms still possible) Rainfall will be enhanced where thunderstorms have the greatest influence. Rainfall, at this point, appears widespread, so precipitation probabilities of 80-90% are in order, especially for the afternoon period. Periods of steady rain will be possible, as well. There is, however, a possibility for a dry slot to emerge during the mid-evening period, but models do not fully agree on this feature. The air continues to be saturated well into the evening, though, so rainfall is still favorable to develop. This will be monitored in future data analyses.

As far as temperatures are concerned, because the air will quickly become saturated by the early-afternoon hours, the warmest temperature of the day will actually occur during the morning hours. Once saturation occurs, the temperature should fall to 17-18 C into the early-afternoon and remain steady through to the evening. Maximum moisture/humidity levels are a little restrictive because of the lower temperature distributions, but temperatures should still be high enough to allow humidity to attain high levels. Thus, though cool, the air will likely feel moist/damp.

Due to the trajectory of the parent low pressure system, it will prevent S. Quebec from entering its warm air sector directly (it will remain well South), so predominantly breezy ESE to occasionally SE winds (13-16 km/h) should take precedence through the day. As such, fairly rapidly accumulating smoke from from the fireworks (due to saturated air) should be moving at a reasonable pace, and virtually directly away from the La Ronde audience. As a consequence, the smoke should be drifting towards those on Notre-Dame Street, mostly left-hand sections (when facing the river) of the street. Directional tendencies, however, will still need to be studied, as there is some uncertainty (varies between SE to ENE – in either case, there is a strong chance for an easterly component).

Another update to follow by either late-day tomorrow (July 8th) or early-day July 9th, with subsequent updates, as needed, by the mid-afternoon of July 9th. Low attendance is possible for Saturday evening, even if rain does not occur during the evening.

Trav.

Weather conditions described in the above posting are still largely applicable for today. Therefore, here are the most favorable conditions for Saturday, July 9th, for the Montreal area (and closely surrounding locations).

Temperature/Humidity

Temperatures are still forecasted to be unseasonably cool for the day due to persistent rainfall, extensive cloud coverage and breezy easterly to ENE winds. The air will not become fully saturated until the afternoon hours, so the maximum temperature should arrive by late-morning (18-19 C), just before dropping to and remaining steady at 16-17 C during the afternoon to evening period. With near complete saturation at these afternoon-evening temperatures, humidity will be high. As a result, the air will be moist and damp. Have a light jacket/sweater with you.

Precipitation

Rainfall will be persistent through mostly the afternoon to early-overnight timeframe (generally overcast for the late-morning) ahead of the aforementioned occluded front. Latest sounding data continues to support saturated air over an extensive vertical depth, and lift along the front will likely generate ongoing rainfall. The moist air mass should persist into the evening, with continued periods of rain (at times heavy) during the time, much like the afternoon. That said, a dry slot is still possible during the late-evening and so will still need to be monitored through today. Higher degrees of instability during the early-morning hours/pre-dawn hours of today could lead to some organized thunderstorms, as well. By the afternoon into the evening, non-severe thunderstorms will still be possible, but they would be sparse and more embedded within the widespread rainfall. Precipitation probabilities are 80-90%, at this point, over the course of the afternoon and evening (except perhaps during the late-evening, if that dry slot appears to be a more dominant feature) due to widespread coverage, and the thunderstorm risk should be 30% (40% during the morning hours due to more scattered coverage). Have an umbrella at your disposal (or another form of head covering of your choice). Copious rains are likely for this weekend.

Wind

Winds are expected to be largely breezy, and from the ENE including during the evening period (sometimes straight easterlies, but consistently ENE is more likely during the evening). Speeds are likely to be 13-17 km/h throughout the day, including the evening. As such, smoke from the fireworks should be building fairly rapidly, at times, due to saturated air, but it should also be moving reasonably quickly, and directly away from the La Ronde audience. This continues to suggest that the smoke would largely be moving towards those positioned on Notre-Dame/de Lorimier street, as well as adjacent sections of the bridge bordering those streets. With the slight NE component to the winds, it would slightly help affected viewers to avoid smoke by positioning themselves farther away from the bridge, in the direction of the Olympic Stadium.

In summary, a wet and cool evening, with high humidity and breezy easterly to ENE winds. Low-attendance is likely in major vantage points. The situation is a little reminiscent of Canadian displays in the mid-90s.

*Another update to follow by early- to mid-afternoon today (July 9th) to address evening rainfall, as well as any revisions to wind speed and/or direction.

Trav.

Thank you for these forecasts and updates, Trav, they are appreciated, as always.

Do you attend the shows this year? I am surprised to not read your reports!

Fred

Forecast details specified in my previous posting are still applicable. Periods of light rain are still favorable this evening but not quite as widespread, and there, thus, remains a fair possibility for a break in the rainfall by late-evening (including display time), or a transition to lighter showers at the time, due to being positioned more in the center of the parent low pressure system. A brief and isolated non-severe thunderstorm is also possible, but the thunderstorms should largely subside by mid-evening, leaving straight rain showers. I would just boost evening temperatures slightly to 17-18 C, with continued high humidity (due to saturated air). Weather conditions are not overly terrible (despite predominantly wet conditions today) since winds should be mostly favorable for those at La Ronde (but not so much for those on Notre-Dame street and surrounding streets).

No changes necessary for wind speed and direction.

----------------------
No problem for the forecasts, Fred! I've been somewhat limited with time recently to write my reports, but I will have them ready soon! That said, my thoughts are outlined in my mind - it's just a matter of putting them together. On a side note, it has been increasingly difficult traveling from the SW West Island this Summer due to significant construction activities on the 720 and Decarie expressway (lots of traffic diversions)!

Trav.

My apologies for the delay. Due to severe thunderstorms over the St-Lazare-West Island area later yesterday evening (July 14th), we lost our power temporarily and so was unable to post.

An area of weak high pressure is expected to move SE through the day Saturday, July 16th. As it does, conditions should generally become increasingly stable and dry, mostly by late-day. However, a shortwave trough and jet stream divergence will provide some weak lift durin the afternoon hours in the general area, generating mostly cloudy skies (sunny breaks) and isolated light rain showers (30% probability), especially where solar heating is maximzed. Maximum temperatures should be 24-25 C by mid-afternoon, coupled with moderate humidity. Mid-evening temperatures of 22-23 C (humidex of 25-26 C) are largely favorable in the metropolitan area, including during display time. The probability of light rain showers, though, should remain minimal, especially just prior to sunset and beyond. Most places will more likely be under mostly to partly sunny skies, with isolated patches of cirrus and cumulus clouds remaining into the evening.

With high pressure moving in, winds should be light through the day, and from the WSW. Speeds should be 6-9 km/h during the late-morning to early-afternoon period but diminish to as low as 4-7 km/h by late-evening, although slightly higher speeds are possible for the evening, so this will continue to be monitored closely. The winds should remain westerly during the evening. This would cause the smoke to move gently and and directly towards the La Ronde audience, or potentially extreme right-hand sections of the audience directly if the tendency becomes more WSW (which is also possible). Periods of fairly large smoke accumulations could develop due to the moderate moisture and light to very light evening winds, though the smoke would be most pronounced at low- to mid-levels during active sections of the display. However, the display could appear frequently murky for those at La Ronde, but the very light nature of the winds could often times cause the smoke to appear stagnant deeper into the display.

*Another update to follow by either later today (July 15th) or early-day July 16th, with subsequent updates, as necessary, by mid-afternoon July 16th, mostly to address wind velocity.

Trav.

Forecast details specified in the above posting continue to hold constant. Therefore, here are most likely conditions to affect the Montreal area for Saturday (today), July 16th.

Temperature/Humidity

As high pressure continues to drift SE through the day, gradually more stable conditions will ensue, but mostly into very late-day. Before this system advances, however, the area will still be under the influence of borderline moderate to high humidity. Maximum mid-afternoon temperatures of 24-25 C are still expected (a little restricted due to more cloud coverage). By late-evening, including display time, temperatures of 22-23 C are still projected to occur, and with moderate humidity, and so a humidex of 27-28 C is favorable.

Precipitation

Sparsely distributed light rain showers (30% probability) and overall partly cloudy skies (sunny breaks) will still be possible during the afternoon hours due to a shortwave trough ejecting East, as well as because of the continued influence of the jet stream in the area. This will provide lift for some isolated showers, but these should largely subside near and after sunset. Skies should be partly cloudy into the evening hours (high-level cirrus and low cumulus clouds).

Wind

Wind speeds continue to be very light into the evening hours due to the influence of high pressure. By the evening hours, this general area will be near the center of this system, where winds tend to be weakest. Directional tendencies remain largely WSW to variable (due to the light nature of the winds). When winds are very light to calm, they are more subject to variable directions due to local influences becoming more dominant. That said, projections continue to support very light WSW winds (4-7 km/h) into the evening hours. This suggests that, due to continued borderline moderate-high humidity, smoke could accumulate fairly quickly and become often near-stagnant (mostly deeper into the display), especially along low- to mid-levels, and typically when the display becomes more active. The smoke should also be moving very, very gently towards the La Ronde audience directly.

In summary, a warm and fairly humid evening, with partly cloudy skies and very light WSW to westerly winds.

*Another update to follow to address wind velocity by early- to mid-afternoon today (July 16th).

Trav.

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.