Over the previous few days, the forecast for Fairbanks had been calling for snow between 1 and 2 inches with temperatures in the teens below zero. The old adage that it is too cold to snow is not exactly accurate. However, it can be too cold to snow a whole lot. That is why Barrow has the lowest annual snowfall of all first-order stations in Alaska.
On Saturday (11/14/2013), Fairbanks received 1.7" of snow with a daily average temperature of 0°F. Looking at the chart below, that is only a few degrees colder than a typical 1"-2" snowfall day during the winter months. On Sunday (11/15/2013), Fairbanks received 0.9" of snow with a daily average temperature of -7°F. That is about 5° colder than a typical snow under 1". Some of the minimum temperature vs. snow amounts are remarkable. The 'Trace' amounts may consist of ice crystals in many instances. Still it is difficult to fathom receiving 1"-2" of snow with a daily average under -35°F!
For how rare -60 is I find it hard to believe that we have more than a trace. I don't think I have ever seen a noticable accumulation at even -40. Perhaps a moose kicked snow unto the measuring apparatus.ReplyDelete
Do you think you could list the dates of the minimums? And how extreme are the next highest values? Can we rule out faulty data?
Brian, thanks, I was actually curious as to the lowest temperatures with measurable snow, so this answers that question. The reports at very low temperatures do seem a bit suspect, though. All five occasions with mean temperature of -40 or lower and 0.5" of snow or more occurred prior to 1918.ReplyDelete
Thanks for digging that information up Richard. I committed the Fairbanks data sin of using data prior to 1920. The chart has been updated to reflect only those years from 1920 onward and dates have been added to the minimum values.ReplyDelete
I see that Fairbanks ended up with 1.0" yesterday and a daily average temperature of -15°F. That is under the 10th percentile for that category.
One observation about frozen precip during extreme cold...it can come in the form of ice crystals from the major local power plants...Ft. Wainwright, the one downtown, and at the University. And it can come from other sources...heating and car exhaust, ice fog, and I suppose other natural processes.ReplyDelete
I've been outdoors and in the falling plume's debris path. How much falls is minimal in a short time, but if the wind direction remains steady, it can accumulate trace amounts. Years ago it would be accompanied by coal dust, but less so now it seems.
The power plant plumes rise through the inversion, then can get flat topped and driven sideways, presumably by air flow above the cold surface layer. Settling of the crystals then can occur.
Look at this pic to see the process on cold days:
It looks like the coldest temperature ever with 1"+ of snow was 1.5" of snow in Allakaket on 12/22/1911. The high temperature that day was -53°F and the low was -59°F. Here is the observation form.ReplyDelete
I think I will do a blog post on the coldest snow events tomorrow.
Interesting post. Before I moved to Alaska I never realized it could snow at such cold temperatures. I have heard that in Feb 1999 around midday it was -40, cloudy and snowing (from an observer). Not sure if there was accumulation or not. One thing to be cautious about, using the average temperature may get some biased results as the snow may have fallen during the high of the and temperatures fell once it cleared out. Matthew K.ReplyDelete
Like many northern inhabitants I've witnessed snow and cold combos. And while atypical and somewhat rare, I've never considered it a short lived phenomenon.ReplyDelete
What's not to expect when warm moist air advects over a thick layer of cold surface air? Until the surface layer warms, or the upper air drys or clears away, it'll precipitate if the conditions are right for the formation of snow or ice crystals.
The point about the asymetric timing of the precip and temp obs is a good one. Believe what you see, not what you later read.
Matthew and Gary. I definitely agree with the limitation of using the daily average temperature. Unfortunately, there is probably not a better alternative unless there is a lot of time to delve into hourly observations. With a large sample size, most of the differences should be ironed out. For the low snowfall totals, there are probably many instances where clear and very cold temperatures were recorded at one time of the day before clouds and moisture advected in and dumped some light snow snow. Days with 2"+ probably do not have that issue. Maybe I can look at the daily temperature range as a proxy measure for intraday variability.ReplyDelete
Please don't go to extra work. Perhaps if one wanted to better define daily temps, a measure of variability (V, SD, ?) could be used as a qualifier for the daily average. It's simple enough to say that it doesn't snow much when it's real cold. We could also agree to say it can both be warm, snow, then turn cold (or the reverse) in a daily period.ReplyDelete
The times it's synchronously snowed when really cold for me are rare. It's more likely to do one or both over a period of time.
The day before we got 1" at -15 it was about -30. The day after it is about -10. I suspect unless you have an extreme inversion where snow forms above the inversion, like Gary suggested, that you should have a warming. For those cold, snowy days, what is the temp difference the day before or the next day?ReplyDelete
I added a couple of charts to the post. One of the additional charts (at the bottom) is a chart of Anchorage that displays the same information as the original chart in this posting. Interestingly, some of the record minimum dates are the same for both cities. The other chart shows the average high and average low temperatures for Fairbanks (the chart in the middle) for each of the snow categories. Interestingly, the average temperature range is nearly identical for every category. That really surprised me.ReplyDelete