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MailTribune.com
  • Did you get warm quickly? It was no illusion

    End of inversion, plus Siskiyous effect made for 20-degree Medford increase in 12 minutes
  • If there were a few moments Wednesday morning when you thought the temperature outside suddenly seemed a lot warmer, you weren't crazy.
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  • If there were a few moments Wednesday morning when you thought the temperature outside suddenly seemed a lot warmer, you weren't crazy.
    Between 8 and 8:12 a.m., the temperature in Medford shot up from 36 to 56 degrees as winds pushed out a lingering temperature inversion and warmer air spilled down from nearby mountains, the National Weather Service reported.
    "It's pretty unique," said meteorologist Mike Ottenweller. "We (usually) might see 10 degrees in an hour or something like that."
    The sudden 20-degree rise in temperature signaled the end of an 11-day inversion of stagnant air that kept the average high temperature at 34 degrees, 5 degrees below average for January.
    "The inversion we had over the top of us for the last week or so was rather strong," Ottenweller said.
    A cold front helped mix some of the warmer air originally trapped at higher elevations because of the inversion.
    A weather balloon released at 3 a.m. Wednesday documented 55-degree air at 800 feet above the ground, with 33-degree air on the surface.
    In addition, air from the nearby Siskiyou Mountains is compressed and becomes warmer as it spills into the Rogue Valley. Ottenweller compared the action to the way a bicycle pump is hot to the touch after several pumps compress and release air. It's called adiabatic warming.
    "I think it was both of those things working together," Ottenweller said, adding that the quick increase was the result of perfect timing. "The spike was really highlighted because we were already basically at our coldest point of the morning."
    It didn't happen Wednesday, but such a rapid shift can mean quick ice- and snowmelt, resulting in flooding and landslides.
    "That can be a hazard of these types of winds and this type of warming," Ottenweller said.
    He added that when he lived in Alaska, he saw temperatures shift from minus 2 degrees to 50 or 60 degrees in an hour.
    The record for a similar phenomenon occurred Jan. 22, 1943, in South Dakota, weather service officials said. In that case, temperatures shot from 2 below zero to 45 degrees in about two minutes.
    Reach reporter Ryan Pfeil at 541-776-4468 or by email at rpfeil@mailtribune.com.
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