Thunderstorm activity Thursday was much more isolated than that of Wednesday evening. For the most part, storms developed and tracked through northern California and the Klamath Basin. That doesn’t mean that yesterday’s storms, and subsequent lightning strikes, are done wreaking havoc. The Oregon Gulch Fire is believed to have been sparked by Wednesday evening’s lightning strikes. Thursday evening, the fire southeast of Ashland, grew 100 times it’s size in three hours. At approximately 3:30 PM, it was reported to be 300 acres, but by 7:00 PM, it had grown to more than 3000 acres.
A combination of very low relative humidity and gusty afternoon winds aided in the expansion of the Oregon Gulch Fire. As the smoke plume billowed into the sky, what is known as a “pyrocumulonimbus” cloud formed. This occurs when the heat from the fire expands and rises to a considerable height in the atmosphere, which is similar to that of a strong thunderstorm. As the pyrocumulonimbus cloud increases in height, it may even produce lightning and rainfall. Many times, this rain falls as “virga,” which evaporates before it reaches the ground. The smoke plume from the fire was visible on both satellite and radar reflectivity, and the cloud was so expansive, that it actually produced lightning strikes. This photo of the Oregon Gulch pyrocumulonimbus cloud was taken by K.C. Walden:
There is little relief in terms of rainfall for the fire fighting efforts in southern Oregon and northern California. Unfortunately, the thunderstorm threat in ongoing. While the Rogue Valley and northern California as expected to remain dry Friday, isolated storms are still in the forecast along and east of the Cascades. Through the weekend, thunderstorms are back in the forecast for most locations. The heat doesn’t leave either…in fact, Thursday was the thirteenth triple digit day in Medford, and this July looks to go down as the hottest on record. Near triple digit temperatures remain in the forecast for northern California and the Rogue Valley into next week.
Chief Meteorologist Kate McKenna