Weather conditions mentioned in the previous posting remain mostly valid, but some revisions were made to convective rainfall coverage and wind velocity. As such, presented here are the dominant patterns favored for the greater Montreal area for July 10th.

Temperature/Humidity

As mentioned previously (post #15), a maximum temperature of 27-28 C would be present for the mid- to late-afternoon (Humidex of 35 C) for the greater Montreal area under borderline high to very high humidity. By mid-evening, this decreases to 23-24 C (Humidex of 30-31 C due to very high humidity). Under a rain-cooled situation, though less favorable, a late-evening temperature of 21 C (Humidex 28-29 C) would be likely.

Precipitation

Despite high available instability, lift remains too conservative through most of the day to drastically make efficient use of this environment, though with the predawn/early-morning period featuring some opportunity for isolated convective rainfall/non-severe thunderstorms (30% probability at the time, and then some scattered coverage later in the morning inducing a 40% probability). Beyond this, partly cloudy conditions should prevail, consisting of clusters of towering cumulus. That said, a secondary shortwave trough and a surface warm front would begin to offer improved ascent by mid-afternoon and moving forward into the mid-evening. During this timeframe, scattered thunderstorm/convective rainfall coverage would be favored (40% probability). Given the environment, some opportunity for at least few strong to severe thunderstorms would still be present. The latest thinking, though, is that these would be sparse and likely focused to near the New York and Vermont borders and North of the island of Montreal, where lift is maximized. As previously mentioned, these more organized thunderstorm families would be capable of locally strong downbursts, intense lightning, significant rainfall rates, and small- to medium-sized hail. Meanwhile, mostly cloudy skies (comprised of towering cumulus) would be present for the (late-)evening, with larger clear breaks between them.

Wind

Winds follow a SE flow for the day, resolutely holding light speeds (9-12 km/h). By mid- to late-evening, there are indications that the wind field would transition to SSW, though with slightly lighter speeds (6-8 km/h). Consequently, smoke accumulations, at all altitudes of the display, would be moving fairly slowly clear to the right of the La Ronde audience. That said, some periods of extensive smoke accumulation would be possible at low- to mid-altitudes of the display because of high to even very high humidity and light wind flow, notably during more energetic moments of the display. If smoke-rich products are further regularly used, this would amplify smoke accumulation. Therefore, right-hand sections of the display (La Ronde's right) at low- to mid-altitude would sometimes appear hazy/hidden. Once again, the laser segments would be beneficial in this case.

*If necessary, another update will appear here this afternoon (July 10th) for wind direction/speed, and convective rainfall coverage.

Trav.

Just to quickly update, wind fields should be more ENE to NNE (still light speeds, at 4-7 km/h), and so this would allow the (dense) accumulations of smoke to move more directly away from the on-site audience and to their left, and slowly towards those closest to the bridge near the river and closely adjacent portions of Notre-Dame Street. All other details presented in the above post (post #16) still apply. Thankfully, thunderstorm behavior/initiating zones aligned well with the expectations described above.

Trav.

For July 17th, a maximum temperature of 30 C (Humidex of 38 C) is possible for the greater Montreal area if convective rainfall/thunderstorms do not significantly affect the island. 23-24 C would be favorable during display time and still narrowly holding onto very high humidity (Humidex of 31 C). Beyond this, the temperature and humidity decrease quickly. If the cooler air mass ejects SE quicker, then cooler/less humid conditions would be more favored during the display.

For the fourth consecutive time, representing a record-streak in this competition's history, strong to severe thunderstorms could affect this general area for a fireworks day. As such, a Severe Thunderstorm Watch could again be enforced. That being said, it is also quite possible that actual display time will also avoid such events for a fourth straight time. A strong cold front and accompanying potent shortwave trough would be advancing SE through the day and would be the focus for scattered thunderstorm coverage, especially during the late-afternoon towards sunset when ascent becomes more aggressive. The primary hazards would be locally damaging straight-line winds with some of these thunderstorm families due to mostly their fast movement. The latest thinking, though, is that complete frontal passage would take place by around sunset, and so the greatest risk for thunderstorms would occupy the morning (30% probability) to notably mid- to late-afternoon (60%). Nevertheless, let's hope that thunderstorms again avoid the firing site collectively throughout the morning-afternoon to keep the risk for technical problems minimal.

At the same time, due to a sharp temperature gradient taking place behind the cold front, a fairly strong WSW to Westerly wind field could develop during the mid- to late-evening to early-predawn period. Winds would be mostly in the form of gusty Southwesterlies/SSW for the day, at 27-31 km/h (occasional gusts reaching 41-44 km/h). As the winds become more WSW to Westerly later in the evening, sustained speeds of 28-33 km/h would occur (occasional gusts reaching 43-47 km/h). This may, therefore, induce a delayed start to the display if air mass transition is allowed to occur sooner than later. Rapid smoke displacement would be present at all altitudes of the display, though the show would appear hazy for the on-site audience outside of laser segments, and especially if very high humidity is able to hold.

*Another update to follow this late-evening (July 16th) to early-predawn July 17th, notably for thunderstorms/thunderstorm character and evening wind speed.

Trav.

Weather conditions described in the above-posting (post #18) are still generally applicable. As such, here are the conditions for the greater Montreal area for July 17th.

Temperature/Humidity

29-30 C would still be within reach for a maximum temperature (Humidex of 38-39 C) if convective rainfall/thunderstorms hold off long enough before affecting the island. Due to the earlier onset of the cooler, drier air mass, one revision would be a cooler display temperature of 19-20 C under moderate humidity (Humidex of 23 C) as the air rapidly cools and dehumidifies during the evening.

Precipitation

A cold front and shortwave trough will migrate SE through the day. The nature of the environment would offer some opportunity for organized thunderstorms during principally the mid- to late-afternoon period among the scattered thunderstorms/convective rainfall that develop (60% probability collectively and 40% for thunderstorms). The predawn period of July 17th would feature sparse thunderstorms/convective rainfall (30%). As mentioned previously, this could invite another Severe Thunderstorm Watch for a fourth consecutive display day. The primary hazards with the most organized thunderstorms would be locally damaging straight-line winds, torrential rainfall, as well as an isolated weak tornado earlier in the afternoon. Lightning frequency would be somewhat more reserved, though moderate frequency would still be achievable. Fortunately, consistent with the last post, thunderstorms/convective rainfall should still evacuate the area completely by late-afternoon, just a little after traditional dinner time and before sunset. Following this, large clusters of less defined cumulus cloud would govern the skies, with sizeable clear breaks between them. Hopefully, the firing site avoids thunderstorms to keep the risk for technical problems minimal.

Wind

Winds would be in the form of breezy Southerlies to SW for the morning to afternoon, with sustained speeds and gusts of 24-28 km/h and 39-44 km/h, respectively. Just before sunset, the tendency would become SW to eventually gusty WSW to straight Westerlies just before and during display time. By display time, these do show signs of becoming breezy/gusty WNW, when speeds would be 29-33 km/h (occasional gusts of 43-47 km/h). This would allow the light smoke accumulation to drift very quickly towards central and left-hand sections of the La Ronde audience – particularly quick displacement is expected at higher altitudes of the display. This would cause the show to appear hazy at La Ronde outside of laser segments, even though thick smoke accumulation is not favored. Due to the gusty nature of the winds, it remains possible for this show to experience starting delays. Wind speeds generally weaken closer to midnight and beyond.

If necessary, another update will appear here this afternoon (July 17th) to address wind speed for the evening period.

Trav.