Weather conditions specified in the above posting continue to hold mostly constant. As a result, here is the dominant pattern for the Montreal area for Wednesday, July 15th.

Temperature/Humidity

As compared to the last four days, maximum temperatures will be lowered to 22-23 C due to the passage of a cold front this evening (July 14th) and high pressure settling in. By late-evening, temperatures should drop to 18-19 C (a touch on the cooler side) in the metropolitan area. Humidity levels will be low, so the humidex is negligible. UV will still be high during peak hours, however, so protect yourselves accordingly if expected to be outdoors for prolonged periods.

Precipitation

No precipitation is expected across the region. With weak lift, skies should be mostly clear throughout the day, with a few isolated fair-weather cumulus. Clear skies should be present for the evening.

Wind

Winds should be light at 9-13 km/h (slightly breezier through the morning and afternoon at 16-19 km/h), and from the NNW. As such, the smoke from the fireworks should be pushing gently clear to the left of the audience at La Ronde (right for those on Notre-Dame) and towards spectators positioned on the bridge immediately adjacent to the park. Again, the display may sometimes appear murky for viewers stationed at the Old Port.

In summary, a pleasant evening (a touch cool), with light NNW winds, low humidity, and clear skies.

Trav.

An area of low pressure is slowly moving NE through the day tomorrow (July 17th) and will gradually circulate a more tropical air mass by early-July 18th. As the low’s warm front (and accompanying shortwave trough) ejects East/NE, a few showers and organized thunderstorms will be possible tomorrow evening into the early-overnight hours. Moisture levels are expected to increase to borderline high to very high levels for Saturday (July 18th), along with maximum temperatures as high as 29-30 C, and a humidex of 37-38 C. By evening, temperatures could still be as warm as 26-27 C in the metropolitan area (humidex of 33-34 C). Because instability is projected to be rather strong for the afternoon hours ahead of a weak cold front, a few thunderstorms and/or convective showers will be possible and may persist through to the early-evening (near sunset) before diminishing thereafter. Wind shear profiles are somewhat limited, however, so the risk for more scattered to ubiquitous severe weather should remain isolated. There should be a mix of sun and cloud (vertically defined cumulus) during the day, and skies should be partly cloudy for the evening.

Wind tendencies are still a little uncertain, but recent analyses indicates WSW for the afternoon (more SSE to SSW/South during the morning) but become more SW in time for the evening. However, wind speeds could be very light into the evening hours. This would favor rapidly accumulating smoke to be pushing slowly towards right-hand sections of the La Ronde audience. Periods of extensive smoke build-up are possible, especially during the more active sections, and generally along low- to mid-levels of the display. This may cause the display to sometimes appear murky, especially towards right-hand sections of the display.

Another update to follow by tomorrow evening (July 17th), mostly for precipitation threat and wind speed/direction.

Trav.

Hi Trav. The hourly forecast of MeteoMedia now predicts a change of wind direction, which would become from S to NE before the display. It would be better than SE from my viewpoint. Do you have the same forecast?

Fred

Conditions specified above continue to remain largely applicable. As such, presented below are the dominant conditions for the Montreal area for Saturday, July 18th.

Temperature/Humidity

Due to extensive cloud coverage early in the forecast period (morning), this may limit maximum temperatures to some extent, but increasing breaks in the cloud deck near noon and beyond should promote periods for adequate solar heating. As such, maximum temperatures are likely 28-29 C (30 C is still possible, depending on the onset of solar heating). Humidity increases to borderline high to very high just before noon, inducing a humidex of 36-37 C by mid-afternoon). By late-evening, temperatures are likely to remain at 26-27 C in the metropolitan area, with a humidex of 33-34 C due to very high humidity.

Precipitation

As mentioned above, a weak cold front associated with the area of low pressure and shortwave trough will be the focus for convective showers/rains and thunderstorms (some isolated strong to severe), especially into the early-afternoon hours. Towards the late-afternoon, the risk should diminish behind the front (5:30 p.m. and onwards). Skies are mostly cloudy during the morning but become more of a mix of sun and cloud (large and defined cumulus clouds) into the afternoon. By evening, skies should be partly cloudy.

Wind

Winds continue to be mostly WSW throughout the afternoon (SSW to SSE during the morning), but they appear to be remaining with the tendency into the evening hours. Speeds are breezy through the day (14-18 km/h) but diminish to 6-9 km/h by mid-evening. Due to the very high humidity and very light winds by evening, this suggests that smoke could be accumulating rather quickly (especially along low- to mid-levels of the display and when the more active sections take place). The smoke should also be blowing (very) gently and more directly towards the La Ronde audience (though still somewhat more concentrated at right-hand and central sections). This will likely cause the display to appear frequently murky.

In summary, a real July evening, with likely the warmest temperatures so far for the season. Winds will be light from the WSW and humidity should be very high. Skies should be partly cloudy.

*If necessary, I will post another update by the mid-afternoon of tomorrow (July 18th) for wind speed and direction since there remains some uncertainty with these variables.

Edit: Fred, I am still thinking roughly WSW for wind direction at this point, but I would like to verify upcoming model data to be more certain.

Trav.

Indeed, MeteoMedia has revised its forecast and now announces the same wind direction than you: west. With wind speed lower than 10 km/h, I am now very concerned by the smoke accumulation issue! It would be a shame to have the view blocked by a wall of smoke. It's rare but it already happened!

Fred

Newest analyses, like the previous runs, indicate WSW winds for this evening, with roughly identical speeds (6-9 km/h). Large amount of smoke accumulation are still likely, but I am thinking that the smoke will still be (very) gently pushing more towards right-hand sections (sometimes central) of the La Ronde audience because of the slight SW component.

Also, extensive cloud coverage ahead of the front has significantly limited thunderstorm/rain shower development, in spite of high humidity. It is also likely that convergence ahead of the frontal boundary is relatively weak to really drive more scattered precipitation. As a result, precipitation has remained quite sparse this afternoon. Had the display been tomorrow (July 19th), though, I would have been much, much more concerned about the (severe) thunderstorm risk.

To similarly account for extended cloud coverage, I am also going to decrease evening temperatures slightly to 25-26 C in the metropolitan area this evening. Humidity continues to be high but should still increase to very high standards by late this evening, so a humidex of 33-34 C is appropriate.

Trav.

An area of low pressure migrating East from Ontario will be pushing temperatures and moisture back to seasonal to above seasonal standards, as well as setting the stage for a potential heat wave into the work week next week (at this point, July 27th-31st). The system’s warm front will be ejecting East through the day Saturday (July 25th) across S. Ontario to S. Quebec and is expected to generate widespread convective showers ahead of it.

The timing of this frontal boundary still has some uncertainty, but latest and recent model data have suggested more of an impact for S. Quebec by the early-evening of Saturday. As a result, periods of rain will be possible at that time across this region, with chances increasing by 5:30 p.m. Cloud coverage (mostly high-level cirrus) should be increasing into the early-afternoon hours with more considerable cloudiness towards 4:00 p.m. (with mid- to lower-level clouds) in the wake of this boundary. Isolated non-severe thunderstorms will also be a possibility during the evening hours, but this should be mostly straight rain/light showers.

At this point, winds are ESE through the morning to early-afternoon but should transition to SSE tendencies near dinner time and onwards as the front draws closer. Speeds should also be light at 9-12 km/h during the evening (11-14 km/h during the morning-afternoon). This suggests that smoke from the fireworks should be moving gently clear to the right of the La Ronde audience (clear to the left for those on Notre-Dame). Moisture should be high (a touch lower from borderline high to very high, as was the case on July 18th to July 21st) for the evening (moderate during the afternoon), as well. This could lead to periods of occasionally brief smoke build up (typically whenever the display becomes more active), mostly due to the light winds and with possible rainfall further moistening the air at the time. Mid-afternoon temperatures should be 25-26 C, and late-evening values in the metropolitan area will likely remain at 21-22 C (gradually closer to 19-20 C if periods of rain occur). A humidex of 26-27 C is applicable.

*Another update to follow by tomorrow evening (July 24th).

Trav.

What was described in the above posting continues to remain applicable for the day tomorrow. As such, here are the dominant weather conditions for Saturday, July 25th, for the Montreal area:

Temperature/Humidity

With a returning SSE to Southerly flow regime, temperatures will begin to rise to seasonal standards by tomorrow. Maximum temperatures by mid-afternoon should be 26-27 C (humidex of 31-32 C), and by late-evening, values should still be as warm as 22-23 C in the metropolitan area. However, note that if fairly persistent light showers occur during the evening in the area, temperatures could cool to 20-21 C. Moisture levels become borderline moderate to high near noon and increase to borderline high to very high standards (similar to those humidity levels during Hong Kong/China’s display on July 18th). A humidex of 30-31 C is likely during the late-evening.

Precipitation

As mentioned above, the associated low pressure system’s warm front will be ejecting East through the day. This will cause an increase in high-level cirrus clouds just before lunch time, and more considerable cloudiness by the early-afternoon (accompanying low- to mid-level clouds). At this point, scattered light rain showers (40% probability) are favorable in the area by the early-evening hours, with chances increasing toward 11:00 p.m. (60% probability), and especially after midnight (90% probability). Isolated non-severe thunderstorms (30% probability) are also possible during the evening, though the chance of thunderstorms increases near and after midnight due to more vigorous lift associated with the frontal boundary at the time. An umbrella, or some form of head covering, may be necessary.

Wind

Winds continue to be SSE to even straight southerlies (SE during the late-morning to early-afternoon) by the late-afternoon and evening. Speeds also continue to be light but should be adequate enough to move accumulating smoke gently. Speeds of 9-12 km/h are expected, so the smoke should be, again, pushing gently clear to the right of the La Ronde audience (clear to the left for those on Notre-Dame). Some brief periods of smoke accumulation may be possible (mostly to La Ronde’s right during more active sections of the display, and mostly along low to mid-levels of the display) due to the borderline high to very high humidity (enhanced by possible further moistening from light rain showers) and light winds. Note also that if thunderstorms do occur, local wind direction could become disrupted from the overall wind pattern.

In summary, a warm and quite humid evening, with light SSE to Southerly winds and cloudy skies. Scattered light rain showers will be possible throughout the evening before becoming more widespread near and especially after midnight. Have an umbrella and/or head covering handy.

*If necessary, I will post another update by tomorrow mid-afternoon (July 25th) addressing mostly the precipitation/thunderstorm risk.

Trav.

Conditions specified above still hold largely constant. However, I am going to increase wind speeds slightly to 11-15 km/h (occasional gusts of 19-22 km/h) to account for a somewhat more robust circulation into this evening. Directional tendencies remain unchanged, so smoke accumulations should be moving reasonably quick clear to the right of the La Ronde audience. Temperatures should also be 23-24 C (21-22 C if persistent showers occur). Humidity is identical to what was specified previously.

The risk for scattered light rain showers and isolated non-severe thunderstorms (40% probability collectively) still continues for this evening, more so towards 8:30 p.m. (near sunset) and onwards, but especially by 10:30 p.m. and beyond, when more widespread (deep) convection is more favorable. The thunderstorm risk should similarly become higher until late this evening and after midnight. Distant lightning is also possible. Again, have an umbrella (or some form of head covering) handy, especially for the later evening hours.

Trav.

The risk for scattered light rain showers and isolated non-severe thunderstorms (40% probability collectively) still continues for this evening, more so towards 8:30 p.m. (near sunset) and onwards, but especially by 10:30 p.m. and beyond, when more widespread (deep) convection is more favorable. The thunderstorm risk should similarly become higher until late this evening and after midnight. Distant lightning is also possible. Again, have an umbrella (or some form of head covering) handy, especially for the later evening hours.

Well, you called it. As usual.



Bring a hat, folks.

Thanks for sharing that radar image, Duncan_S. As that band of light rain showers advanced towards the island near sunset, it began to exhibit some discontinuities, leading to patches of dry slots, but re-intensification behind it led to some very heavy rains just after midnight. Convective precipitation, in particular, is always changing in spatial coverage and intensity (often spontaneously), so it's always good to have the latest imageries when monitoring it.
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As mentioned four posts above, a potential heat wave has begun to establish itself yesterday (July 27th) across S. Ontario to S. Quebec, along with severe weather occurring late yesterday afternoon through to the mid-evening. As another area of low pressure advances, its circulation will further amplify temperatures and humidity into the day Wednesday (July 29th), easily leading to the warmest conditions of the year (so far), and this could be one of the warmest/hottest fireworks days in recent years.

Indeed, temperatures are expected to reach to as much as 33-34 C across the island of Montreal (especially the metropolitan area), and humidity is projected to be very high (mostly by the evening hours). By late-evening, temperatures may still be as warm as 28-29 C in the metropolitan area, and considering the very high humidity, a humidex of 35-36 C (38-39 C during the afternoon) is sufficient. Convective rain showers and thunderstorms (some possibly severe) are not expected until Thursday, July 30th due to a passing cold front.

Winds will likely be light at 9-12 km/h, and wind direction should be WSW throughout the day but becomes more SW by evening to SSW by late-evening. This would favor rapidly building smoke accumulations to be blowing gently to the right of the La Ronde audience (left for those on Notre-Dame), though there is a possibility that the smoke could be moving towards extreme right-hand sections of the audience (notably smoke associated with high-level shells). This will be monitored in future runs. Periods of large smoke accumulations will be possible when the display becomes more active (and at low- to mid-altitudes of the display) due to the light winds and very high atmospheric moisture, but build-up should be especially towards La Ronde’s right.

*Another update to follow later this evening (July 28th).

Trav.

What was specified in the above posting still holds mostly constant. As such, here are the dominant conditions for Wednesday, July 29th for the Montreal area:

Temperature/Humidity

Temperatures continue to be hot for the day, with a daily maximum of 33-34 C, while late-evening temperatures in the metropolitan area should still be as high as 28-29 C. Atmospheric moisture continues to be very high, so a humidex of 41-42 C is likely during the mid-afternoon and 38-39 C during the late-evening.

Precipitation

Due to strong instability, very sparse air mass showers and non-severe thunderstorms may occur during the afternoon hours but will quickly subside toward sunset. Skies should be mostly clear during the evening, with a few isolated clusters of cumulus clouds due to some lift.

Wind

Winds continue to be light during the evening, at 8-11 km/h. Directional tendencies should be SW throughout the day (with similar speeds as the evening) but should transition to more SSW by late-evening. As a result, smoke accumulations should be moving gently and mostly clear to the right of the La Ronde audience (left for those on Notre-Dame). However, smoke associated with high-level effects may sometimes be pushing towards extreme right-hand sections of the La Ronde audience. Periods of large smoke accumulation are possible due to the light winds and very high humidity (mostly during active sections of the display, and sometimes along low- to mid-levels), though mostly to La Ronde’s right.

In summary, a very warm to hot evening (one of the warmest fireworks nights in recent history), with very high humidity, light SW to eventually SSW winds, and a few isolated clusters of cumulus clouds. A real July evening on the way.

*If necessary, I will provide another update by mid-afternoon tomorrow (July 29th) concerning wind direction for the late-evening.

Trav.

A broad area of low pressure will continue to circulate warm and fairly moist air to S. Ontario to S. Quebec into this weekend (August 1st-2nd). A secondary cold front associated with this system is expected to also produce some afternoon to early-evening convective rain showers and isolated, mostly non-severe thunderstorms. Precipitation coverage should be scattered along the front, and extensive cloud coverage is likely throughout the day into the evening hours.

Temperatures will remain seasonably warm across S. Quebec on Saturday (August 1st), including here, on the island of Montreal, along with borderline moderate to high humidity throughout the day. Late-evening temperatures in the greater Montreal area should be as warm as 20-21 C (humidex of 24-25 C), and daytime highs should be 24-25 C (humidex of 28-29 C). In the case of persistent rain showers during the evening hours, temperatures should be closer to 18-19 C.

Winds are projected to be WSW throughout the day and breezy at 19-22 km/h (occasional gusts of 27-31 km/h) during the afternoon hours. By evening, directional tendencies should remain identical, but speeds become light, at 9-12 km/h. As such, smoke should be moving gently towards the La Ronde audience directly, with more concentration at right-hand and central sections of the La Ronde audience. Smoke accumulations are not expected to be overly large due to lesser humidity levels, but the display will likely appear somewhat murky. Note, however, that there is a chance that winds could become SW by the late-evening, which would allow the smoke to move towards right-hand sections of the La Ronde audience. This will have to be monitored in upcoming runs.

Another update to follow by tomorrow evening (July 31st).

Trav.

Weather conditions specified above continue to remain mostly identical to what was described above, though there are some minor modifications. As such, here are the dominant conditions for the Montreal area for Saturday, August 1st.

Temperature/Humidity

Temperatures continue to be warm during the afternoon hours, with maximum highs of 25-26 C. By late-evening, in the metropolitan area, temperatures should decline to 21-22 C. Humidity is moderate through the day, generating a mild humidex of 27-28 C, and by late-evening, humidity should increase to borderline moderate to high levels, inducing a humidex of 24-25 C.

Precipitation

An upper-level trough has settled over S. Ontario to S. Quebec and will be the focus for (deep) convection into the afternoon to early-evening hours. Scattered thunderstorms/convective rain showers (40% probability) will likely develop into the afternoon due to enhanced instability supplied by the trough. Given periods for solar heating and strengthening wind shear profiles, a few organized multi-cell thunderstorms may attain severe limits. Because thunderstorms and rain showers are largely driven by instability, convection should gradually diminish towards sunset and beyond (8:30 p.m. and onwards). Skies should be partly cloudy by late-evening (low-, mid-, and high-level clouds).

Wind

Winds continue to be breezy through most of the day, and from the WSW. Speeds during the afternoon are sustained at 19-23 km/h, with gusts of 28-33 km/h. By evening, however, winds become light (9-12 km/h) and should shift to more SW tendencies. As a result, smoke accumulations should be pushing at a reasonable speed towards right-hand sections of the La Ronde audience, notably smoke associated with high-level activity.

In summary, a warm evening, with temperatures in the lower 20s C, borderline moderate to high humidity, light SW winds, and partly cloudy skies.

*If necessary, another update will be provided by mid-afternoon today (August 1st) that will address largely wind velocity and thunderstorms/rain showers.

Trav.

Wind tendencies remain virtually identical to what was specified previously. However, I am going to increase wind speeds to 13-17 km/h, given a continued fairly strong circulation. Directional tendencies should remain mostly as WSW through to early this evening and gradually shift to the SW near display time and onwards. This means smoke should be moving relatively quickly towards right-hand sections (sometimes central) of the La Ronde audience, especially smoke associated with high-level activity.

Thunderstorms/rain showers should gradually subside near sunset and beyond (risk should run up to 8:30-9:00 p.m.).

And so concludes the weather reports for 2015!

Trav.