Rick T. here with a short post for future reference. Here's an annotated plot of the most extreme cold snaps during the Weather Bureau/NWS era (since late 1929) in Fairbanks, from downtown, Weeks Field, International Airport, wherever the observations were being made. Here we're looking at all the cold snaps with a 7-day average temperature of 40 below or lower. Note: average temperature, not average low temperature. The dramatic dropoff in frequency and intensity of cold snaps post-1975 is partly PDO shift, partly trend and partly urban growth and the attendant ice fog, which serves as something of a "blanket" for the valley floor.
For those in Fairbanks in 1989: yes, the lowest weekly mean temperature reported from the Airport was -43.0F, and I agree, I think there was a problem with the temperature sensor on at least a few days. But based on the Ft. Wainwright observations, such as there were, it was not greatly lower than that.
Thanks Rick, nice chart. Three years ago I tried to look at the hypothesis that increased ice fog could help explain the decline of very cold temperatures, but the data suggested that ice fog is less common now than it used to be - presumably because it's not as cold. Do you know if anyone has looked at this to quantify the potential warming effect of fog? I still think it's an interesting question.
ReplyDeletehttp://ak-wx.blogspot.com/2014/01/cold-and-visibility-trends.html
I suggest ice fog has been increasingly less prevalent because of reduced vehicle and heating appliance/power plant emissions despite the cold. And yes it's not been since the last mid-Century for cold weather.
DeleteThat's not to suggest the ice fog element decreases radiation at the surface and increases potential winter temperatures (an interesting theory), but in the '60's to later '70's we had ice fog at a Class #1 and accompanying real long cold spells. Now it's (so far this winter for example) not been as bad as I recall.
So where's the measurement of fog? Typically at the airport. It's a clear open area adjacent to the lower Chena River air drainage subject to frequent turbine aircraft emissions and the collection of fog from residential Fairbanks uphill.
Surely there's been low level temp measurements with and w/o ice fog present? There's WX balloons every day plus several pollution studies regarding temperature inversion.
Gary
Normally during inversions, Ft. Wainwright is colder than the airport. So if the Airport temp is significantly colder, then the possibility of an instrument error increases. Eielson AFB is even colder than the other two. So there's another check.
ReplyDeleteSomeday Richard will visit during a cold event and we can drive about and observe the temps, visibility, and depth of ice fog.
ReplyDeletehttps://www.youtube.com/watch?v=bF4FxCz2IY8
https://www.youtube.com/watch?v=Olbo4Am4U44
Gary