The last few days have been relatively cool in Denver. 60s and 70s for the most part and more of the same for the next few days. The great thing about growing a pumpkin in a hoop house is lower temperatures really don't matter. It is 11:00 right now and it is a perfect 84 degrees in my hoop house with an outside temperature of 66 degrees. Windy days are also not a problem for plants growing in hoop houses. The wind goes sailing by with just a gentle breeze coming through the hoop house. Colorado growers have talked about the challenges of growing in our enviroment for years. I believe the three main things that cause us trouble is lack of humidity, big and quick temperature changes, hail storms and high UV light. The hoop house kind of evens things out in many ways. In my hoop house, with a 75 watt bulb in it at nigth (with the light shielded from the plant), the temperature usually doesn't get lower than 53 degrees at night, the humidity is higher because the plastic holds the moisture in, the plastic cover protects the plants from smaller hail and I would believe at least some UV rays would be filtered out by the plastic. The biggest challenge with hoop houses is not letting it get to hot. On a cloudy day where the sun breaks through the clouds the temperature can easily rise 10 degrees in 15 minutes. In an hour or so the temperature in the hoop house can easily get over 100 degrees. I have a wireless thermometer in my hoop house and I work from home so I can easily watch the temperature all day and modify how much I open the hoop house to control the temperature.
Update (2:00pm): Pea sized hail just hit and the hoop houses held strong so no damage to the plants at all. At least one item on my least has held true to this point. Almost a year ago my plant got hit by hail and I lost about a foot of the main vine. Mitigating risk is a big part of growing big pumpkins.