Rain with above-freezing temperatures is obviously unusual at this time of year in Nome, but it has happened many times before in the climate record. The first chart below shows the number of January days with plain rain reported in the hourly observations since 1936 (red columns); note that there is a big gap in the data from 1947 to 1972. Also, a number of years have incomplete or missing data in the early years (marked with asterisks). The blue columns show the frequency of above-freezing temperatures (with or without rain) in the hourly data. The second chart shows the same information for the December-February period each year.
The climate shift in 1976 with the change to a positive Pacific Decadal Oscillation stands out very clearly, as the frequency of warm and warm-rainy days appears to have increased dramatically. For the winter as a whole, above-freezing and plain rain events have been less common in the past decade than in the first decade of the positive PDO regime; this reflects the shift back towards the negative PDO phase (see the PDO time series chart below; image credit: http://en.wikipedia.org/wiki/File:PDO.svg). However, in January plain rain has now occurred in 9 of the past 13 years, which is a higher annual rate of recurrence than earlier in the climate record.
Is there an opportunity for learning here? I've often wondered what atmospheric mechanisms the positive PDO created that increased warmth and moisture in Alaska?
ReplyDeleteI've read some of the published papers on the recent + PDO (mainly for a fisheries perspective), but still come away lacking a good appreciation of the associated weather and climate changes. Maybe there's a good link or two available.
Gary
Gary,
DeleteHartmann and Wendler 2005 may be helpful, if you haven't seen it before:
http://journals.ametsoc.org/doi/abs/10.1175/JCLI3532.1
It's interesting that January showed the greatest warming from negative to positive PDO regimes... the present pattern across Alaska seems very positive-PDO-like, but in fact the PDO is near neutral and has been generally negative since summer. However, there is a very anomalous warm pool in the North Pacific that has been maintained for months and seems to be helping to drive the pattern:
http://www1.ncdc.noaa.gov/pub/data/oisst/navy-anom-bb.gif
Excellent James, thanks for both links. Bingo on the current warm pool in the NP.
DeleteThe first source led me to this almost hidden link. Why do they put the good stuff at the bottom of the cover page where only the resolved might note it? Lots to learn here:
http://akclimate.org/research
The Accuweather guy was on the radio today. Says the ridge over NA driving cold south to you folks might break down by Feb. Does that mean we (and the groundhog on his special forecast day 2/2/14) will see more winter? Bet it's so, says he.
Gary
Gary, I did a quick plot at ESRL looking at temperatures in Alaska following a January with a PDO value greater than 1.0 (6 out of 60 years and all very warm) and they showed pretty average temperatures during the month of February – even below average in the NW portion of the state.
ReplyDeleteThanks Brian for the quick outlook and reanalysis. Apologies Richard for using your surname in my comment above, I'll blame my fingers and tired brain for the lack of proper behavior.
DeleteIt's raining now in Fairbanks. What next, falling Pineapples?
Gary