Medford soared into the triple digits at 1:53 p.m. Tuesday, the National Weather Service reported.
It's the first time the heat has climbed above 99 degrees this year.
The last time temperatures broke the 100-degree mark was July 26, 2013, weather officials said.
The temperature continued to climb until it hit 105 degrees at the Medford airport — where temperature readings are taken for the city — at 4:22 p.m.
A building high pressure system is responsible for the temperature spike.
Weather officials have said they expect a slight cooldown starting today, when the forecast calls for a high of 93. Officials say the high temperatures will stay in the mid- to low 90s for the rest of the week.