ONTARIO Itâs still 20 days until summer officially starts, but citizens throughout the area will want to prepare like itâs already here, as an excessive heat watch has been issued for the Western Treasure Valley. The National Weather Serve watch comes with a triple digit forecast for Wednesday and Thursday, but it is the latter of these that carries the urgent weather message. From Thursday morning through Thursday evening, temperatures are expected to peak at about 103 degrees Fahrenheit in the upper and lower Treasure Valley areas, and are expected to stretch all the way to southern Idaho. These dry and warm conditions are expected to be about 10 to 15 degrees above normal, according to information from the Weather Service.