July 2011 has been stunning, as far as temperature is concerned, across many regions of North America, including with the U.S currently facing one of its most severe heat waves in recorded history. Much of central and eastern Canada, too, has experienced well above seasonal temperatures so far this month, which, with the potential of an upcoming defined heat wave, could lead to final average monthly daytime highs that are above seasonal, perhaps on par with values seen in July 2010, which was one of the warmest Julys on record.

In any event, although still remaining very warm for today, we will be seeing a break in the high to very high humidity due to an area of high pressure moving into Ontario and Quebec, providing mainly sunny and dry conditions. However, through the day Wednesday (July 20th), I am expecting a returning flow from the SW to SSW (because of a series of low pressure systems - one coming in from the West, while the other stationed to the North), which will, once again, boost temperature and humidity values back up to values similar to what they previously were before today. As such, expect temperatures to reach near or at 30 C later Wednesday (locally as much as 32 C), with high humidity levels, making it feel in the mid 30s C (very high 20s C by late evening). Temperatures on July 21st in Montreal could reach a very hot value of 35 C, with humidity values well exceeding 40 C (this will likely prompt high heat and humidity advisories across Ontario and Quebec).

I am still keeping an eye on the potential development for precipitation later in the day Wednesday, in accordance with the advancing low to the West, though I believe that instability is more prevalent on July 21st, when more oppressive heat and humidity will endure. Severe weather is possible by the late evening to overnight period of July 21st.

As for the winds on Wednesday evening, they seem to be cooperative in both direction in speed - however, I am still monitoring speeds, as the models are indicating breezy conditions, likely because of a steepening pressure gradient. The winds themselves are sustained between 21-25 km/h for the day and associated gusts could, on occasion, reach 34 km/h. Wind speeds should diminish slightly by evening but are still remaining breezy (they will quickly pick up again on July 21st). Smoke from the display, then, will likely push the smoke quickly to the right of the audience at La Ronde.

I will post a final update later today or early tomorrow to confirm these conditions after evaluating wind tendencies and precipitation in the newer model runs.

Trav.

The weather forecast for today (July 20th) still follows closely along the lines of the above post. As such, here is a summary of the details in what to expect for the day:

Temperature/Humidity

Two low pressure systems, one situated to the North (heading northeast), and the other approaching from the West, are responsible for the returning circulation of a hot and, at times, oppressively humid airmass. Moreover, a third area of low pressure, in association with the low from the West, will form by early Thursday (July 21st), enhancing the circulation. As this defined heat wave is governing much of central and eastern North America, temperatures are expected to be reaching hot standards, causing the mercury to rise to roughly 32-33 Celsius for maximum daytime highs today, here in Montreal. In such cases, evening to late-evening temperatures are, naturally, expected to remain very warm at 27-28 C (possibly 29 C in the metropolitan area). Humidity is forecasted to be high across southern Quebec today, so assuming that daytime highs reach 31-33 C, humidex readings should be attaining 38 to as much as 40 C (late evening values at 34-35 C, including in the metropolitan area). Note that humidex values on July 21st are not far from 50 C, with actual maximum temperatures at 35-36 C. High heat and humidity, as well as smog advisories are likely.

Precipitation

With this hot and humid airmass, the air is becoming quite unstable, especially as we approach the overnight hours into Thursday, July 21st, where thunderstorms and potentially severe thunderstorms are possible, mostly late in the day, as the cold front from the system out West advances in this direction. Available convective energy is also quite high to support their development. For today, because the air is also unstable, some defined clusters of cumulus clouds will develop, especially for the afternoon period - later in the day, you will notice an increase in cloud cover due to the combined effect of a cold front to our North and the warm front associated with the system approaching from the West. However, I am, again, not anticipating precipitation until the later overnight hours and onwards, but, that being said, I still would not rule out the chance for isolated storms during the late evening (30% probability), given the available convective energy present at the time - otherwise, expect partly cloudy skies.

Wind

Wind speeds are still something to keep an eye on. The newer models are currently indicating winds to firstly be light during the early morning hours but then gradually increasing by late morning. Speeds will likely be at their highest during the mid-afternoon period, being sustained between 31-34 km/h and accompanied by gusts occasionally attaining 43-45 km/h. By evening, I am still detecting a weakening, where speeds are settling more within the range of 21-24 km/h, with gusts, at times, closer to 34-36 km/h. I understand from the past that the cut-off point for safe firing is approximately 40 km/h (regardless of direction), but sustained speeds, and occasional gusts, should be hovering below this level for the evening hours. Nevertheless, as we are dealing with values not too far away from this threshold, I would still like to review the newer model runs through today to get an even better sense of the dominant speeds for the evening. Regardless, though, it will be a breezy evening. Directional tendencies themselves begin as southerlies for the morning hours, but they do shift to more southwesterlies to South-southwesterlies (SSW) by the afternoon and evening, so the smoke, again, should be moving quickly to the right of the audience at La Ronde (to the left of those on Notre-Dame), although there may be points where the smoke could be blowing towards the extreme right end of the seating area. For those who are not comfortable with the combination of a very warm and humid atmosphere, the breezy winds will provide you with some relief for both today and tomorrow.

That’s the way the weather should behave for today. To summarize, the day will be a hot and humid one, setting the stage for a heat wave. Humidity levels are high, so temperatures will feel much warmer (near 40 C during the day and 34-35 C by late evening, especially in the metropolitan area). There is a slight risk for isolated thunderstorms by late evening (30%), but the risk is more prevalent for the overnight hours into Thursday, July 21st. Severe weather is possible late Thursday. I would still like to revise the newer model outputs for wind speed, but the day will largely be breezy, especially for the mid-afternoon. Winds first come out from the South, and then progressively from the southwest by afternoon-evening. It is very important to stay well hydrated during this kind of weather, and please protect yourselves accordingly from the high to very high UV, if you plan to be outdoors for whatever reason.

***If I detect higher wind speeds in the model data today, I will post an additional update covering only this - if not, then what is stated in the wind section still holds true.

Trav.

I suspect that the winds will be a relief tonight, with such warm and humid air. But I am concern with the speed of them. Hopefully, they are not going to exceed the 40 km/h limit. Is your model accurate enough to estimate when the winds should reach their highest speed?

I remember the Hong Kong display in 2009, which started at 9:55pm to avoid more powerful winds expected at 10:30pm. The pyro crew got these information at 9:45 and decision was made to begin the show five minutes early, to minimize the risk to stop the show just before the finale. It was incredible how accurate this information was, since the wind speed actually increased at 10:30!

Fred

Hi Fred,

The newer model simulations, like the previous runs, continue to predict that the highest sustained winds and associated gusts will occur during the mid-afternoon hours today, which has been the case, so far. The top gust that I had previously been estimating for the day was no more than 45 km/h, and that was the highest hourly speed recorded just before 4:00 p.m. today, with a sustained speed of 35 km/h. The last hourly gust was measured at 41 km/h, with a sustained speed between 30-32 km/h.

I am still expecting the winds to weaken slightly by this evening, likely just beyond 9:00 p.m. The wind range for the early evening is mostly between 23-27 km/h, with occasional gusts reaching 36-38 km/h. From 9:00-9:30 p.m, we should see a further decrease to a range of 20-23 km/h, with associated gusts, at times, between 30-34 km/h, which would be suffucient but still a little marginal. Directional tendencies still remain the same, as mentioned above, so the smoke should be, again, moving quickly to the right of the audience at La Ronde, although, at some points, it could be pushing towards the extreme right end of the seating area because of possible changes to southwesterly winds in between.

I do, indeed, recall the precision of that provided information - it is usually quite rare to predict a distinctive change in any meteorological paramater (wind, temperature, moisture, precipitation, etc.) right on a given target time, but sometimes the atmosphere just behaves that way. We do, however, strive to do that more consistently for the future.

Trav.

This heat wave continues to remain in effect for southern Ontario, as well as western and southern Quebec into today, July 22nd, as hot and humid temperatures still dominate these regions, prompting high heat and humidity advisories. The humidity was so high in southern Ontario that the original humidex advisory had become a weather warning. Here in Montreal, the dewpoint reached an impressive maximum of 25 C, generating humidex readings into the high 40s C. For those who are unfamiliar with the "dewpoint" concept, it is simply a measure of atmospheric moisture, as well as indicating at what approximate altitude saturation is taking place. Dewpoints are usually expressed as a temperature (usually Celsius or Fahrenheit), but the larger they are in value, the higher the moisture/humidity - during the mid-late Spring/Summer, dewpoints at roughly 16-19 C are regarded as high, while a dewpoint of 20 C or more is deemed very high. I want to emphasize that dewpoints of 25 C or more are exceedingly rare in southern Quebec, and such values are categorized as extreme.

For those of you who are finding it difficult to cope with this weather, relief is on the way for the weekend, particularly on Sunday, as an area of high pressure slowly migrates from the northwest. This system will also be partly responsible for the weather conditions for the Canadian display for tomorrow.

With this high pressure system advancing, we can expect mainly clear skies for the entire day (some scattered cumulus and cirrus clouds, especially for the late-morning to afternoon period), along with daytime highs at roughly 29 C (late-evening temperatures roughly at 24 C), although the humidity will be much less oppressive as it will be today, and especially yesterday (July 21st). Winds are, again, something to watch in terms of speed, as they may be generally around the same range as what we had seen during the day this past Saturday - the difference, however, is that the model simulations are detecting speeds to be rapidly diminishing by evening, but, of course, I would still like to monitor this. Directional tendencies are currently in the form of northwesterlies to North-northwesterlies, so smoke could be blowing to the left of the audience at La Ronde, but heading to those on the bridge, just adjacent to the firing site.

As always, I will provide a final report later today or early tomorrow to confirm these conditions.
---------------------------------------------------------------------- ---------
As I had anticipated, severe weather did erupt across many parts of southern Quebec on the evening of July 21st, including here in Montreal. Doppler radar did a fantastic job in picking up the thunderstorms during the late afternoon-evening period - some rotation was even detected within some of these storms, indicating potential active mesocyclones - no confirmed tornado touchdowns, however. The reason as to why these storms fired up was partly because of the oppressively high humidity, which contributed to massive amounts of available convective energy at the surface (in excess of 3000 Joules/kg) and mid levels of the atmosphere. When I was evaluating the potential for severe weather through the day, doppler radar also revealed good windshear at various depths above the surface. Adiabatic lapse rates (the rate at which the temperature of a given air parcel decreases with increasing altitude relative to the temperature of the ambient air with height) was also high, especially at mid level. The breezy conditions during the day also facilitated the mixing of air between low and high level, destabilizing the atmosphere, and, of course, there was plenty of daytime heating. There were other supportive factors as well, but it was the moderately strong cold front which descended from the northwest that acted as the necessary catalyst. A few of these storms were quite powerful and were particularly recognized for their strong straight-line winds and frequent to continuous lightning. Here are some of the videos that I'd like to share of the late-afternoon and evening storms on July 21st:

Late-afternoon:

http://www.youtube.com/watch?v=Q5CVn5jOoAk

Evening:

http://www.youtube.com/watch?v=x48MWNXGS3U

http://www.youtube.com/watch?v=_ggLuYdzgNE

Trav.

Lightning were spectacular last night. I thought that we would have experienced a situation similar to the Hong Kong in 2009 whether a fireworks was scheduled, with many lightning in the background at the time of the display.

Fred

Virtually everything that was mentioned previously still stands firmly, but I will add some details to the wind section. Also note that the "Saturday" mentioned in the previous post was meant to be "Wednesday".

Temperature/Humidity

I am going to raise the maximum temperature for the day to 31 C, along with late evening temperatures at roughly 26-27 C (metropolitan area included). Notice that humidity levels have dropped to "high" standards yesterday from the extreme levels witnessed on July 21st - this decrease was related to the passage of the cold front on the evening of July 21st. Expect borderline moderate-high humidity for the day today into this evening, so humidex values should read at, assuming a temperature range of 29-31 C, 34-36 C (evening to late-evening values at 29 C to 30 C).

Precipitation

No precipitation is forecasted for the day, as an area of high pressure is slowly advancing from the West. Some scattered fair-weather cirrus and cumulus clouds may be present during the day, however, but it will be mainly clear.

Wind

Winds, once again, are expected to be, at times, gusty, with the highest sustained speeds and associated gusts likely to occur during the mid-afternoon hours, roughly at 27-31 km/h (gusts at 39-42 km/h). Wind speeds should diminish slightly by evening but remain breezy at 19-22 km/h (occasional gusts between 30-33 km/h). Directional tendencies are firstly from the SW early in the day but then gradually shift to the WSW to even straight westerlies by the afternoon. However, I am still detecting a shift to the WNW to NW by the mid-evening hours. As such, smoke should be blowing to the left of the audience at La Ronde, although possibly affecting, at times, the left extremities of the seating area there, as well as those on the bridge viewing near the castle structure. The reason behind this overall wind pattern is simply because we are going to be situated between the advancing area of high pressure to the West, as the well the departing area of low pressure stationed over the Maritimes, and the winds are breezy because of the pressure gradient building between these systems.

That's the way the weather should behave for today. In summary, continuing very warm to hot conditions, but with lower humidity at borderline moderate-high levels, so the day should be mostly comfortable, especially near dusk and onwards. No precipitation is expected, but there may be some scattered cirrus and cumulus cloud clusters present, especially for the afternoon period. Winds are breezy, but, at times, gusty for the mid-afternoon hours. Speeds should decrease somewhat by the evening but still remaining breezy, and wind direction should be coming from the NW by the mid-evening. *I would like to, however, continue to monitor the winds through today and analyze the latest model runs for directional tendencies - I will post a brief update today covering this, regardless if there aren't any significant changes.

I thought that we would have experienced a situation similar to the Hong Kong in 2009 whether a fireworks was scheduled, with many lightning in the background at the time of the display.

That crossed my mind at the time as well, Fred! The lightning was certainly stunning that evening, especially because of its continuous nature.

Trav.

For the wind update, I am still detecting that directional shift to the WNW to eventually NW later this evening, and there are indications that this change is taking place just after 8:00 p.m. EDT in the models, which remains unchanged from the previous prognostics. Speeds are still the same for this afternoon (as expected, the winds are, at times, quite gusty and are WSW to westerly), but, again, they should be diminishing late this afternoon and into the evening. I'm just going to reduce the occasional gust values for the evening from the above post from 30-33 km/h to 25-28 km/h km/h, and the sustained winds between 16-19 km/h (from the 19-22 km/h specified above). With potentially straight northwesterlies in place, as mentioned above, the smoke will likely be moving mostly to the left of the audience at La Ronde, although, again, there may be times where it affects the left end of the seating area there (especially if WNW tendencies take place in between), as well as for those on the bridge overlooking the firing site at sections near the castle structure.

For everything else, please refer to the above post, as it still holds true. As expected, humidity values have been very slowly decreasing through the day and are now at borderline moderate-high humidity, which recently prompted the cancellation of the high heat and humidity advisory that had been in place since July 20th through Quebec.

Edit as of 5:41 p.m. EDT: NNW winds are also possible by 10:00 p.m - if such is the case, then the smoke should be heading mostly clear to the left of the audience at La Ronde and towards those on the bridge adjacent to the firing site (near the river). This also means that those at the Old Port may also, at times, be obscured by smoke

Trav.

The radar is showing a very small area of precipitations, moving from north to south. It's currently on the north shore of Montreal and should hit La Ronde between 7:00pm and 8:00pm. Hopefully, it is the one and only episode of rain for tonight!

Fred

Hi Fred,

The isolated pockets of precipitation moving from the NW to SE in southern Ontario and Quebec are associated with a weak passing cold front (hence the drop in humidity through today). I apologize for neglecting to mention this instability earlier, but the atmosphere should stabilize in these regions beyond 8:00 p.m tonight.

Edit: Also, that band of precipitation that you were detecting is weakening rapidly as it heads SE (indicating that the air is progressively stabilizing), so it should dissipate by the time it arrives.

Trav.

As we advance into a short term, unsettled weather pattern for both today and tomorrow, another area of high pressure is expected to follow and slowly make its way eastward by this Wednesday (July 27th), eventually providing Ontario and Quebec with largely fair weather while assisting to gradually heat the air back up to very warm temperature values and eventually boosting temperatures even further by the end of the week as it moves East, with the aid of a low pressure area moving in from the West. Conditions should also be dry, along with borderline low-moderate humidity. Temperatures by late-evening should be around a comfortable 24-25 Celsius (especially in the metropolitan area). Breezy/gusty winds are not an issue for the French display - in fact, wind speeds may be more at the opposite end of the extreme, with very light to, occasionally, near-calm speeds - such is the case when in close proximity to high pressure centers.

I will provide a final update later tomorrow to confirm these conditions, but as far as I can tell, the overall light nature of the winds is the factor for consideration. Additionally, current model simulations are showing WNW to westerly winds, so this is also something to watch, as, in this situation, the smoke would gently head towards the audience at La Ronde. Although the day should remain largely dry, I would still like to keep an eye on the aforementioned low pressure system advancing from the West, as a couple of weather progs are indicating it to be traveling faster eastward than others, and so arriving earlier - I do not believe that such will be the case, but it is good to continue to monitor this and see if the newer simulations become more in agreement amongst the models.

In the meantime, isolated thunderstorms and convective rains are possible through tomorrow (July 26th) due to an upper level trough, especially during the afternoon. A few of the thunderstorms may reach severe criteria.

Trav.

Most of what was stated in the above post still holds true, but there are some additional details that I'd like to add. Here is the forecast for Wednesday, July 27th.

Temperature/Humidity

Temperatures are expected to climb into the mid 20s C for today at roughly 26-27 C, with late-evening temperatures around 24-25 C (especially in the metropolitan area). I'm going to shift humidity levels from borderline low-moderate to moderate-high, so it will feel near 30-31 C for the afternoon.

Precipitation

The newest model runs are more in agreement, and so they are showing that low pressure system to the West arriving more for Thursday into Friday. Consequently, we should see mostly sunny conditions for today, but there will be an increase in cloud cover by the evening hours and into the overnight, so partly cloudy skies for this evening. Convective showers and thunderstorms (some potentially severe) are possible for Thursday into Friday. Temperatures also return to very warm to hot standards for Thursday into Friday, along with a boost in humidity.

Wind

This is where it becomes a little tricky. With an area of high pressure in place, most of today is expected to experience generally light winds. Winds should be coming mostly out from the NW to NNW through the afternoon, with speeds between 11-14 km/h, although slightly breezier during the mid-afternoon at 15-18 km/h. However, the models are still showing speeds to rapidly diminish by the evening hours to as little as 4-7 km/h interspersed with calm conditions. The directional tendencies are usually difficult to predict when winds are this light, but they appear to be withholding NNW tendencies for the early evening, but then later shift to southerlies - if southerlies dominate, smoke would VERY slowly be moving to the right of the audience at La Ronde - if from the NNW, then to the left. Directional variability is also possible during the evening, but with the light nature of the winds, smoke buildup may be problematic for most spectators. I will continue to monitor this and post an update, if necessary.

That's the way the weather should behave for the day. In summary, pleasant temperatures coupled with borderline moderate-high humidity. An increase in cloud cover takes place towards the end of the day. Winds are slightly breezy during the day (especially for the mid-afternoon) but become very light to, occasionally, calm by the evening. Severe weather is possible later Thursday into Friday.

Trav.

Just a quick update about the winds. The newer models from this morning are showing signs of winds taking a WSW to SW tendency by this evening, so the smoke may be, at times, blowing slowly towards the audience at La Ronde, most notably for right sections to extreme right sections of the seating area. Speeds are still within the same range, although, at times, slightly higher at 7-10 km/h. If SSW winds dominate, then the smoke will move clear to the right of the audience. Those are the possibilities by 10:00 p.m.

Also, there will also be a few scattered cloudy periods this afternoon, as the system from the West advances, but increasing cloud cover is more prominent for the evening and onwards. UV is high today.

Trav.

Well, I suppose that these are the last set of weather reports for the season!

Conditions are looking mostly good for the closing display tomorrow night. Following this upcoming area of low pressure from the West, which will further boost humidity levels today to boderline high-very high standards, as well as progressively de-stabilize the atmosphere, an area of high pressure will slowly descend from the NNW, gradually clearing skies out for Saturday. I do not anticipate precipitation for Saturday evening, but a secondary cold front coming from the NNW may provide some lingering scattered showers for the morning hours into lunch time. There will still be a few clusters of cumulus clouds for the afternoon and evening period, but, again, I am expecting precipitation development should subside. Temperatures should be around similar values to what we had seen during the French display (23-25 C, mostly applicable to the metropolitan area) for the late-evening, and humidity should be reduced to moderate levels.

I am still keeping an eye on wind tendencies. Current models are showing breezy conditions for the majority of Saturday, but the speeds diminish quickly by evening. Wind direction should be in the form of northwesterlies for most of the day, but there are indications of a shift to WNW patterns by evening, which would push the smoke to left sections of the audience at La Ronde. I will continue to monitor this.

As mentioned in the second to last above post, we may see a little of nature's fireworks for today due to this upcoming low pressure system, and some storms may be reaching severe criteria, especially for the late-afternoon to early evening period. Things should gradually improve beyond the evening hours.

I will provide an update later today to confirm these conditions, but it is mostly the wind direction that is still in question for the evening Saturday.

Trav.

It looks that we will enjoy perfect weather conditions for the ultimate show of the year. On the weather side, it was a great fireworks season since no display has been disturbed by Mother Nature (no rain, thunderstorm, lack of winds, etc.).

Fred