I anticipate your updates tomorrow about the risk of late thunderstorms. Hopefully, we will not have to deal with precipitations in addition to the very high humidity.

Thank you very much for your forecast reports. They are very appreciated.

Fred

Recent prognostics continue to reveal near-identical patterns to what had been described in the above posting. There are some adjustments, however, that will be outlined in the following analysis. Here are the most probable weather conditions for today (July 17th) for the Montreal area:

Temperature/Humidity

Temperatures continue to remain very warm to hot through the afternoon hours, with highs reaching around 30-31 C across much of S. Quebec, and as hot as the mid 30s C through to E./S./SW Ontario. Humidity levels also continue to remain borderline high to very high, pushing maximum humidex readings as high as 39-40 C. By the late-evening period, as newer model simulations indicate, temperatures should fall toward the 25-26 C range (as much as 27 C in the metropolitan area), consistent with the near-complete passage of the cold front at that time. This is also further suggested by humidity declines closer within the “high” range, making it feel like 32 C. Note, however, that if thunderstorms (or convective rains) do occur, temperatures will rapidly decrease and limit the maximum forecasted temperature from taking place.

Precipitation

With the atmospheric setup, this is a great day to be storm chasing across E. Ontario and S. Quebec.

As mentioned in the above posts, a cold frontal wave associated with a secondary area of low pressure is quickly descending from the NW this afternoon into the early-evening. Ahead of the front, surface and near-surface moisture/dewpoint levels are high to very high, and sufficient surface heating through the early part of the day will likely enhance low-level instability, together yielding a moderately unstable atmosphere during the afternoon hours. In addition, deep-layer speed and directional wind shear are enhanced, largely owing to the upper-level Westerlies associated with the jet stream flowing over the area. Consequently, the risk for widespread convective rains and thunderstorms exists across mostly E. Ontario, S. Quebec and Northern New England throughout the afternoon. Also note that some thunderstorms may be reaching severe criteria over these regions, and the environmental conditions are favorable for producing a few rotating thunderstorms, so this needs to be carefully monitored through the day. It is interesting that the potential for severe weather occurred for three years consecutively on July 17th (2010, 2011, and now possibly for 2012).

Some good news, however, is that yesterday’s model runs showed indications that the area of low pressure is speeding up in its eastward propagation. This suggests that the cold front should pass through S. Quebec by the late-afternoon to early-evening period (rather than early-overnight), leaving partly cloudy skies into the late-evening time frame. The passage of the front is further supported by decreasing mid-level relative humidities, slightly decreasing dewpoints, shifting winds to the NNW to NW (see next section), and the highest convective available potential energy pushing into New York.

Wind

Winds continue to show similar transitions explained in the previous posting. However, the timing of the directional changes has shifted a little in recent projections. Winds are shown to be first from the South to SSE by morning, becoming breezy at 15-19 km/h by the late-morning to early-afternoon. By the early to mid-afternoon period, winds shift to Southwesterlies at 24-27 km/h (occasional gusts of 33-37 km/h), and into the late-afternoon period, winds change to Northwesterlies and become lighter at 15-19 km/h, and eventually to 11-15 km/h towards the early-evening. By late-evening, winds are shown to further decrease to light/very light standards at 4-8 km/h, mostly from the NNW to NW. As such, the winds should be blowing very slowly to the left of the audience at La Ronde (right for those on Notre-Dame), although the extreme left-hand section of the grandstands could occasionally be affected, but those on the adjacent bridge just overlooking the park will likely be most influence by smoke. Also note that extensive smoke build-up towards the left of the audience at La Ronde may be possible, especially during more active sections of the display, due to the combination of light/very light winds and high humidity.

That’s the way the weather should generally behave. In summary, expect light to very light winds during the late-evening period, mostly coming out from the NNW to gradually NW. Temperatures remain warm to very warm (especially in the metropolitan area) through the evening, and humidity levels are high but decline somewhat by late-evening. Strong, scattered convective activity is greatest during the mid to late-afternoon period, potentially stretching into the early-evening.

It may be required to provide an additional update by early this afternoon in terms of wind tendencies, as well as any changes in atmospheric instability.

Apologies for the lengthy analysis!

Edit: No problem, Fred - always a pleasure.

Trav.

Severe thunderstorms and heavy rain are expected by MétéoMédia. I'm really afraid the pyro material may be flooded for tonight... That would be dramatic.

Fred

Winds continue to exhibit directional tendencies similar to what had been specified previously. As such, smoke from the fireworks should be moving mostly to the left of the audience at La Ronde, although extreme left-hand sections may occasionally be influenced. Those on adjacent parts of the bridge, however, will likely be most affected by smoke, and for viewers at the Old Port, smoke may, at times, obscure the view. I'm only going to increase the wind speed slightly to 8-12 km/h (from the NNW to NW) for the late-evening. Also, humidity levels will still remain quite high into the evening, even when the cold front has gone through - the gradual decline should occur during the overnight.

As for the thunderstorms, indeed, as expected, many severe thunderstorm cells have developed along a squall line over East Ontario, one storm of which recently affected areas near Cornwall. Additional storms have been forming near the island of Montreal and North of Ottawa, and these storms could have some influence very shortly, or passing closely near the island. One storm is currently affecting extreme SW sections of the West Island at this time.

Again, instability should gradually subside by the early-evening, but I would recommend having an umbrella handy for the hours "waiting" for the fireworks.

Trav.

The good news is that, once the current line of storms has passed, it looks like we'll be in the clear. Hopefully setup is complete and everything well protected.

Paul.

I'd still give a few more hours (until the early-evening) for that front to completely pass through S. Quebec and E. Ontario, before partly cloudy conditions prevail.

Trav.

As the cold front that went through and brought widespread severe weather to both E. Ontario and S. Quebec on July 17th, high pressure has now settled in, bringing with it pleasant weather conditions as of July 18th, though overnight lows are cool. This area of high pressure will gradually migrate East towards the Atlantic in time for this weekend (July 21st and 22nd), allowing for a nice Southwest (SW) to South-Southwest (SSW) circulation to influence both S. Ontario and S. Quebec. As a result of this pattern, temperatures will likely return to the higher 20s C, along with a boost in humidity to moderate levels, making it feel into the low 30s C. Maximum temperatures, here in Montreal, could reach 29 C for tomorrow, while late-evening temperatures should stay steady into the mid 20s C.

In terms of wind, as mentioned, they should be in the form of SW to SSW, but they seem to be showing signs of coming out from the SSW throughout the duration of the evening. Winds are also expected to be light at 7-11 km/h during the late-evening period. As such, the smoke from the fireworks should be gently blowing mostly to the right of the audience at La Ronde, although extreme right-hand sections of the grandstands could occasionally be affected.

The only thing that I am watching for now is an approaching cold front from the NW in today’s model projections, but this front should only have an impact by mid-Sunday into Monday, setting off a few isolated convective showers and thunderstorms.

Providing that the cold front maintains its current speed, this should be a very nice Summer-like evening for France.

Trav.

The newest model output remains about identical to what had been described in the previous posting. As such, here are the weather conditions for Saturday, July 21st - the last Saturday of this year’s competition.

Temperature/Humidity

As this current area of high pressure pushes farther East, along with an area of low pressure moving in from the West as the day progresses, a nice circulation of SW to SSW winds will circulate a warmer and progressively more humid air mass into S. Ontario and S. Quebec for this weekend. As a result, temperatures on Saturday could reach as high as 29-30 C (mostly for the metropolitan area), along with late-evening values around 24-25 C (25-26 C in the metropolitan area). Humidity is building to borderline moderate-high levels for tomorrow afternoon into the evening, and so this will be enough to generate humidex readings at about 32 C during the mid to late-afternoon (28-29 C by late-evening).

Precipitation

Precipitation is not expected through the day Saturday. Newer projections are keeping the aforementioned cold front just East of central Ontario into the evening hours of Saturday. As a result, expect mostly clear conditions for the day, along with a few clouds. An increase in cloudiness to partly cloudy skies is possible by the early-evening hours, however, as the cold front advances, which will enhance convection into Sunday. By later Monday, severe weather may be possible with a secondary cold front advancing from the NW, cooling temperatures through Tuesday.

Wind

Winds are likely coming out from the SSW through most of the day (South for the early-morning to early-afternoon, and perhaps again by the late-evening), with speeds steady between 8-12 km/h, including for the late-evening period. I am thinking now that the smoke should stay clear of La Ronde spectators as it slowly passes to their right (left of those on Notre-Dame).

In summary, a beautiful (and arguably perfect) Summer evening for the French display (conditions were also very pleasant for the setup period), with partly cloudy skies, borderline moderate-high humidity, and temperatures into the mid 20s C. Winds should be light from the SSW.

Trav.

Just to provide an update, but newer projections indicate that there is a slight possibility for a few scattered showers late this evening ahead of the cold frontal wave. Conditions should remain generally partly cloudy (as mentioned above), but newer runs show an increase in relative humidity at mid-levels of the atmosphere, so I just wanted to outline this risk.

I apologize for the late notification to this.

Trav.

Just to provide an update, but newer projections indicate that there is a slight possibility for a few scattered showers late this evening ahead of the cold frontal wave.

Trav, some of us praised the incredible accuracy of your forecast, once again, tonight, as a light rain started around 9:00pm, as I moved in the grandstands with Simon. Fortunately, it stopped about 30 minutes later...

Many thanks for this update and always appreciated contribution to this forum!

Fred

As the upcoming area of low pressure advances from the West, a continued surge of hot and humid air will circulate into S./E. Ontario and S. Quebec for today, allowing temperatures to locally reach the mid 30s C, along with humidex values attaining near or above 40 C. However, the passing secondary cold front later in the day (mentioned three posts above) could set off widespread convective showers and thunderstorms, several of which could be reaching severe standards. Here, in S. Quebec, the better chance for severe weather is during the late-afternoon to evening/early-overnight hours. Note also that some of these thunderstorms could also become supercell thunderstorms (thunderstorms with a persistently rotating updraft) due to enhanced deep layer shear/directional shear, so, much like on July 17th, this needs to be monitored through today due to the elevated possibility of isolated tornadoes.

As the cold front passes through later tonight, a gradual cooling will take place into tomorrow (Tuesday), along with a sharp cut in the humidity level. Behind the front, gusty NW winds will also likely occur by the later-morning hours towards the afternoon and evening period. Consequently, Portugual’s display likely could be dealing with breezy conditions, coupled with cooler temperatures (late-evening temperatures around 18-19 C) and low humidity. No precipitation is expected.

At this point, winds for the late-morning throughout the afternoon period should be sustained between 27-31 km/h (occasional gusts of 41-44 km/h). Winds continue to be breezy during the evening hours, but I believe that they will diminish to more suitable speeds at 23-26 km/h (occasional gusts between 32-35 km/h), and further down to 15-19 km/h by late-evening. As such, the smoke should be blowing quickly to the left of spectators at La Ronde, although occasionally influencing those stationed at left-hand sections of the grandstands, and more so for those on the adjacent bridge.

This is somewhat of a tricky forecast, but I will provide an update later today. I will also be occasionally following up with the severe weather potential for today on Facebook.
-------------------------------------------------------------
Fred, indeed, once the newer model projections were released Saturday afternoon, I noticed the slightly increased instability and higher mid-level relative humidities, prompting me to issue the risk for scattered light showers during the later-evening hours, even though those showers were not expected to be significant. My only worry was that I released the information too late, but I’m glad that wasn’t totally the case! The change also eliminated the “perfect” weather conditions that I had previously envisioned, and I was awaiting slightly stronger wind speeds to clear away the smoke a little faster - this was somewhat frustrating, as the wind patterns were ideal up to 9:32 p.m. I suppose that such is the complex reality of weather!

As always, it is no problem for the weather updates.

Trav.

Once again, my apologies for the delay - I've been rather busy with yesterday's severe weather! I kept thinking to myself last night that Portugual was fortunate in not being scheduled to present yesterday, although I sincerely hope that the weather did not inferfere with the setup process.

Today's weather conditions remain largely similar to what had been described in the above posting. As such, here are the conditions that are most probable for this evening (July 24th).

Temperature/Humidity

After the severe thunderstorms passed through yesterday afternoon into the evening (July 23rd) ahead of the sharp cold front mentioned previously, both mean temperature and humidity values have progressively been declining into today. As the late-evening approaches, temperatures should drop to 19-20 C (as much as 20-21 C in the metropolitan area), and the humidity should also be reduced to borderline light-moderate standards (no humidex). You may, however, feel the occasional slight chill with the somewhat breezy winds this evening.

Precipitation

Instability associated with the current upper-level trough should weaken by later this afternoon. Cloudy periods (less defined cumulus cloud clusters) will contine into the early-evening time frame in association with this trough but will be gradually clearing later in the evening to the early overnight.

Wind

As the cold front has now passed pushed East to ESE and SE for today, a fairly strong NW flow has quickly followed behind it. As a result, winds, as mentioned previously, will often be gusty though this afternoon from the NW to NNW, with sustained speeds between 23-27 km/h (gusts from 32-36 km/h - slightly reduced from the previous post). Again, by this evening, winds should diminish to average sustained speeds of 15-19 km/h, which will likely persist into the late-evening hours (closer to 14-17 km/h) but diminishing further to 12-15 km/h during the overnight. Winds should remain Northwesterly this evening, so smoke should be blowing relatively quickly to the "left" of the audience at La Ronde ("right" for those on Notre-Dame), though left-hand sections could occasionally be affected, and more so those on the adjacent sections of the bridge overlooking the park.

In summary, pleasant conditions for today and this evening, though a touch cool late this evening, along with borderline light-moderate humidity, a few clusters of cumulus clouds, and somewhat breezy NW winds.

Trav.

I am currently monitoring an area of low pressure passing closely to our South through the day tomorrow (July 27th). However, models aren't quite in agreement just yet as to how far to the South this system will remain. Still, mostly cloudy (a few sunny breaks) skies should take place for the day, and temperatures should reach as high as 26-27 C, along with moderate humidity levels, generating humidex values of about 30-31 C for the mid to late-afternoon. Humidity levels decrease slightly through the late-evening to overnight period (due to approaching high pressure to the NW), so humidex readings should be into the mid 20s C, at the very highest. Temperatures by the late-evening period should be around 22-23 C for the metropolitan area.

As for the winds, given the area low pressure to the South, and the approaching high pressure system from the NW, they should generally be out from the NNE for the day, including the evening. Speeds should be greatest during the morning hours at 23-27 km/h (gusts of up to 32-35 km/h) but will gradually subside by mid-afternoon. By the evening, speeds become light at 7-11 km/h. As such, winds should be slowly blowing the smoke to the left of the audience at La Ronde, although the NNE to NE winds could occasionally push it toward Southern sections of Notre-Dame street (going past the bridge to the South).

We'll continue to monitor the track of this system in the model runs from today, and I will provide an update once simulations display more of a consensus.

Trav.

Newer model runs seem to be more in agreement with respect to the area of low pressure that I had been monitoring to our South. As such, here are the expected weather conditions for today (July 27th) in the Montreal area.

Temperature/Humidity

Temperatures should continue to remain in the range specified above, where daily maximums should attain 26-27 C and late-evening temperatures around 21-22 C (as much as 22-23 C in the metropolitan area). Humidity should remain largely borderline moderate to high for this afternoon, generating humidex values as high as 30-31 C. Again, humidity will gradually decrease later in the day to more borderline low to moderate levels, as an area of high pressure to the NW slowly settles in.

Precipitation

As the area of low pressure (now a series of lows) is now shown to stay to our South, we should see mostly sunny conditions, along with a few clusters of cumulus clouds developing through the atmosphere. As such, the most active weather should remain over SW Ontario, S. New York and southward this afternoon into the evening. Skies clear further into this evening for S. Quebec, as high pressure slides to the SE.

Wind

Winds continue to exhibit tendencies similar to what had been described previously. Winds were breezy earlier this morning but will subside to a range of 12-15 km/h through this afternoon, and even further down to 7-11 km/h by the late-evening period. In terms of the overall direction, they are maintaining largely North-Northeasterlies (NNE) for this afternoon, but I am detecting a slight shift toward more Northeasterlies late this evening. As such, the smoke should, once again, be blowing gently to the left of the audience at La Ronde (right for those on Notre-Dame), although those on Notre-Dame street near the bridge and heading South could be receiving smoke, at times. Those on the bridge near Notre-Dame could also be similarly affected, as well as those over the river.

That's the way the weather should work for the Italian display. In summary, pleasant conditions for this evening, with borderline low to moderate humidity and warm temperatures. This will be accompanied by light winds this afternoon into the evening from the NNE, but winds could become closer to Northeasterlies late this evening, along with slightly lighter wind speeds from what they will likely be this afternoon. Skies should remain generally clear this evening, with a few isolated cumulus clouds.

Trav.

Over the last number of days, I have been watching an area of low pressure out West that has been responsible for severe weather (severe thunderstorms and tornadoes) across much of the Southern tier of the Prairie provinces. This area of low pressure is now migrating East towards central Ontario, and eventually reaching S. Ontario and S. Quebec. As current prognostics indicate, this low could have some impact as early as late Tuesday afternoon (July 31st) for S. Quebec. Consequently, convective showers and thunderstorms are possible at this time.

It's still obviously somewhat of a challenge to assess the timing of this system, as well as how strong thunderstorms might become over the region if the low maintains its current speed in future simulations. However, given the potential for a moderately unstable atmosphere over S. Quebec (again, if the low maintains its speed), coupled with enhanced vertical shear, I am convinced that a few isolated severe cells are possible, not just for late Tuesday, but into Wednesday, as well (for different reasons). The potential for thunderstorms is ongoing from July 31st to August 5th, though not necessarily occurring on each of these days.

Temperatures are expected to return to hot standards into tomorrow (July 30th), which should persist into Tuesday. Humidity levels will likely maintain borderline high to very high values, so humidex readings could surge into the high 30s C (locally very low 40s C). Tuesday's maximum, here in Montreal, could reach as high as 32 C (locally 33 C), depending on how much sunshine is received at the surface. By late-evening, temperatures should remain at 26-27 C, mostly for the metropolitan area.

As for the winds, they should be largely coming out from the South to SSW (in accordance with the positioning of that low), with somewhat breezy speeds at 14-18 km/h for the late-evening. Note that speeds are higher during the day at 24-27 km/h (occasional gusts of 33-36 km/h). As a result, smoke from the fireworks should be moving clear to the right of the audience at La Ronde.

We'll continue to monitor the weather situation for Tuesday, and I'll try to provide an update later tomorrow.

Trav.