Tuesday, December 18, 2012

A Tanana Valley Jet and other Exicting Developments

Valley temperatures have moderated a bit around Fairbanks, though hill temperatures have leveled out. To the left is a plot of the temperature in the lowest kilometer from the past three soundings (nominal times 3AM Monday, 3PM Monday and 3AM Tuesday). The warming as continued on the valleys since early this morning. Almost everywhere is now up to -30F or warmer.

The core of the cold air has moved into the eastern Interior, with lows this morning of 51 below at Northway and 48 below (thru 8am) at Chicken. Meanwhile, our friends in the Delta Junction are being buffeted by 15 to 40 mph and temperatures in the teens below in a classic "Tanana Valley Jet". This happens when cold air in the Upper Tanana Valley moves downriver (in response to lower pressure to the west) and is squeezed through the constriction in the valley near Cathedral Rapids. Since air is a fluid, the velocity has to increase to move through the constriction. The result: strong down-valley winds from about Dot Lake westward across the Delta Junction area and the Tanana Flats south of Fairbanks. On occasion the jet makes it all the way to Nenana, which it did in this case (temperatures was still -41F at 11pm but has been as around 6 below for some hours down with a gusty east wind).

The NOAA-18 1km resolution infrared image from 630am Tuesday shows this in detail.

The cold air pooled in the Upper Tanana is evident (along with the cold valleys of the Fortymile County and the Yukon Flats). The Tanana Valley Jet shows up as the streaky looking of darker color (warmer temperatures) west of the Tetlin Flats.  


  1. I have lived with this Jet for years at my cabin 43 miles south of Manley Hot Springs. It sources in the upper Tanana, as well as Hess Creek and Livengood-Tolovana River.

    It can be generated in winter as noted, or on a somewhat daily basis, primarily during equinoctal periods, when solar heating (?) causes differential temps E-W along the north face of the Alaska Range.

    It's like a clock from 10AM to about 7PM when active. It can be heard while developing as an air noise increase...sounds like a train when approaching.


    1. Gary, Probably what you get most of the time in winter is the Minto Flats outflow that originates Livengood/Hess Creek area, though of course occasionally the upper Tanana valley outflow makes it as far west as your area of interest.

  2. Hi Rick. I fly to and from Fairbanks to access the cabin, as does Doyle a neighbor and one of your seasonal weather observers. It's rare in winter to experience the Minto outflow without the adjoining Tanana Jet. What I've noted over the last 30 years is that the Tanana Jet usually precedes the Minto winds. Once the Tanana Jet is established, the air from Minto will begin to fill the pressure differential.

    I suppose a look at the Blair Lakes, Livengood, and Wien Lake RAWS data might show this winter pattern. In March and September, the daily flow regime appears to mainly be via the Tanana Jet in my experience flying through both.