There are a number of ways to define the informal beginning of Winter. Previous posts have looked at the date of the first freeze and the first measurable snowfall. In this post, I look at the first day where the high temperature is at or below freezing. For Fairbanks, the average date for the first sub-freezing high is October 9th. So far their coldest max temperature has been 34 on 9/22. For Anchorage the average date is October 27th. On the map, only stations with at least 15 years were used and the years were not required to be consecutive nor contemporary. The earliest average date for any station is for Barrow (September 2nd) and the latest average date belongs to Craig (December 24th).
As for coming up with a proxy measure for the beginning of Winter in Alaska, any thoughts on the different criteria are welcome. Here are some thoughts. 1) First snow, 2) First low temperature below 20, 3) Seven or more days with 1"+ snow on the ground, 4) First day with high temp below freezing, 5) Seven or more days with low temperature below freezing, 6) ..... I intend to write a paper on the relative dates of the seasons for Alaska.
Very little research has been done on the subject.
I consider Spring to be when daily temps no longer dip below freezing. That's when serious melting begins in Alaska's lakes and rivers. If it were my choice I'd apply that criteria in reverse to the end of Fall and the beginning of Winter. Frozen water means Winter to me, and when it gets to freezing Fall's over.
ReplyDeleteNot sure how many days in a row is best then back it up to the first day providing it's in the chosen series. Chinooks in Winter don't count as Spring's arrival.
It can snow anytime within reason depending on location and elevation.
Gary the Limnologist
PS: Solar angle could be another criteria. When it's high enough to melt snow it's Spring. Use the same angle to denote Fall.
I might add, given the above, how do we denote Summer? From an arborist's perspective of course! When the leaves sprout it's now Summer. When they turn yellow it's Fall. Simple.
DeleteGary makes a good point that out-of-season snow can occur quite readily, so it may not be a good marker for seasonal boundaries.
ReplyDeletePresumably you recall Rick's posts on this from January? I found his descriptions very illuminating and interesting:
http://ak-wx.blogspot.com/2013/01/one-more-round-of-interior-alaska.html
http://ak-wx.blogspot.com/2013/01/seasonal-defintions-in-interior-alaska.html
I had not seen Rick's earlier post from January. In general I like the definitions from his post. However, the river ice metrics lose applicability once you drop south of 60° latitude. Also, the green-up and fall leaves definitions are good markers but next to impossible to estimate based on the climatological record. Plus, there are no trees in tundra areas and no deciduous trees in much of Southeast Alaska. Ideally, any formula would cover the entire state. What I am zeroing in on is a definition for Winter and Summer and the time in-between would be Fall or Spring.
ReplyDeleteGeeze, in a sense I was having some anthropological fun above.
ReplyDeleteThere are tundra biome plants that express seasonality, as well as trees in SE Alaska that have leaves (like Alder and Willow: http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/stelprdb5320147.pdf), but that begs the question IF all Alaska is to be included with a single seasonal criteria. Especially if WX data are to be accessed and manipulated.
Rick has two good Blogs above, and I'll have to stand by my comments therein. Especially now that it's winter because I can't ride my Harley.
Gary
Didn't mean to ignore your earlier posts Gary. I have no quibbles with your suggestions. Since you brought up the arborist point of view, how do we distinguish between the relative weighting of species? The birches lost their leaves about 5-7 days before the aspens (here in Anchorage). Should the aspens be given less weight than the birches? I don't know the answer to all those questions. The cop out is to go only by what is included in the climatological record. I have no shame when it comes to taking the easiest solution. :)
DeleteHi Brian. No quibble complaints from here. Your skills and efforts are appreciated and far exceed my analytical ability. For the reason given (species specific behavior) employing the floral realm would be problematic. Same for faunal, including Harley riders.
DeleteIf it were my task I'd take the voice of experience (Rick's Blogs) and maybe develop one or more "seasonal definition" scenarios. See if they differ or overlap, and if so, why. Numerics are critical, as that's the basis for comparison.The exact WX values will vary by location around the State of course, but maybe there's a discernible trend or breaking phenomenon that characterizes seasonality by common WX zones.
That's why I like photoperiod, or better yet solar angle and insolation. All definable by location and repeatable across periods weather and climate variability. It may take zonal blocs by latitude (or even longitude...Attu vs Ketchikan) to group the seasons.
Unfortunately what's now called Summer and Winter in Barrow, would be considered something else again elsewhere. Maybe Shulski and Wendler's recent book has some insights: http://climate.gi.alaska.edu/book
Gary
I gave this a bit of thought and my suggestion would be to try the 5 or 7-day mean temperature going below freezing, as suggested by Rick - but add a criterion that the winter threshold (e.g. 32 F) cannot be above the 70th percentile or below the 10th percentile of the annual range in mean temperature. In other words, winter can't occupy more than 70% or less than 10% of the yearly cycle; it wouldn't make sense otherwise.
ReplyDeleteIn Barrow this would work out to a winter threshold of 24.4 F which on average encompasses Oct 4 to May 21. In Craig the threshold would be 39.3 F which goes from late Nov to mid March. In Fairbanks it would be 32 F and Oct 7 to April 14.
With some experimentation you might be able to come up with something quite satisfactory.
Not sure yet what to say about a definition for summer.
I propose the following to aid in developing a proxy measure for Winter, the original topic. Get rid of some noise and deal with developing a criteria for Winter (X).
ReplyDeleteAs suggested, that may be below freezing temps for some defined period with a beginning and an end. Then treat the rest of the year as 1-X.
Forget Spring and Fall for now. They're too tied to human emotion, latitude, elevation, and perceived changes in our natural world. Call 1-X what you want...I suppose Summer is ok. Non-Winter would work as well.
On a worldwide view, many places never see Summer for any length, and many never see Winter, so to have any basis in reality, a location would require at least two "seasons" to be included in the analysis.
Gary