When I wrote my previous post May temperature data wasn't fully available from NCEP/NCAR, now it is.
At -6.05degC May 2015 surface temperature north of 70degN is one of the coldest May average temperatures, May 2001 average was -7.25, May 2000 was -6.80degC, making this May the third coldest since 2000. Yet May 2015 still shows the start of a spring volume loss anomaly.
The PIOMAS grid box effective thickness is seen in the following map plot.
The somewhat thicker ice towards Siberia may be indicative of the winter export of thick ice from the Central Arctic, but it also largely falls under the region of cool temperatures over May and that may account for some April to May thickening.
The following plot shows 1981 to 2010 average volume loss between April and May 2015. Red shows the 1981 to 2010 average loss, blue shows the loss this year, a positive loss is a gain in volume.
The gain in volume in the East Siberian Sea and Laptev sea is greater than normal, much greater in the case of Laptev. While on average the Central Arctic would show a small loss between April and May, this year it has shown a gain. I suspect that the cold May is playing a key role here, as these regions are under the band of May cold see in May's data.
Turning once again to differences I have plotted the regional differences from May 2013, after the 2012 record, but before the last two summers of poor melt weather. Yet again the Central Arctic holds the increased volume, while the bulk of the Arctic Ocean has lower volume than at the same time in 2013.
By the end of June we will know how large the drop in area and extent has been over June, how low the drop in compactness will have gone in June, and how low the PIOMAS Spring volume anomaly will go.