As the true "dog days of summer" get underway, AccuWeather forecasters say Mother Nature is poised to crank up the thermostat across the northwestern United States and portions of southwestern Canada. Record-challenging heat is set to arrive just as many Americans prepare to celebrate Independence Day with a wide variety of outdoor activities. High temperatures will soar to levels well above the historical average during the holiday and beyond. Intense summer heat will elevate the risk for heat-