Below are the rankings for 925hPa air temperatures north of 72.5N, based on the ncep reanalysis for since 1948.
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Extremely interesting statistics!!
Compare 2011 and 2015
Year May..June...July.Aug.MJJA
2011 7.......5.....1.....2.....1
2015 27....11.....2....26....13
These years shared similarities since the beginning of the season (remember Vid?). Even the shape of the final pack has a lot in common. And July month.
However see August 26th position! And yet the huge wreck that three weak cold storms caused over the already broken MYI Beaufort ice, and the compaction from the relatively cold Laptev area. Then the final storm.
And May in 27th position, which saw a warmth wave in Alaska and Canada, with South winds that opened up the Beaufort sea and Chukchi kicking in albedo effect, a preconditioning element that, in absence of it, melting would have been delayed.
Then snow cover preconditioning due to Winter weather. Not accounted for in these statistics.
Overall averaged temperatures are extremely misleading.
Local temperatures 850hpa-925hpa and land surface temps can be significant though, especially in Peripheral areas during May-June.
This year we also had the out-of-mind hot Pacific and the few systems it brought to the Arctic, sometimes via North America, sometimes warm advection, other times not-so-warm systems like the big Chukchi August storm. You can have more and more heat being transported to the Arctic Ocean, under what seems overall cool temperatures. Then the ocean stores heat and releases it later in the season.
As discussed recently in this forum, the pulses of heat expansion in the Equator due to El Niño directly translate to pulses of inflow at the Bering Strait. No need for an ocean current requiring years to reach the Arctic. Any small element of expansion due to temperature increase at the Equator creates a sound wave (1NM/s) which reaches and funnels in Bering in 2 hours and immediately generates a flow pulse into the Arctic due to the difference of pressure. But more importantly, it creates slower gravitational waves (same kind as the tsunami waves) that travel to Bering in a matter of one day and contribute to sea level increase. Therefore, sea level at Bering would increase at the same pace as El Niño temperatures increase. However, water spills into the Arctic moderating sea level increase but leading to enhanced currents into the coasts of Alaska and Siberia. IIRC very early bottom melting was observed near the coasts. And East Siberian Coast opened up very quickly even when it was late and cold. Temperatures at Chukchi and Beaufort are, no doubt, really warm for the year. So although this effect may be small, it may have helped trigger the retreat of ice, so important for albedo amplification, and contributed to bottom melting in key areas.PS. I have been convinced this is not correct :--)
The rest are observations about facts happening during this melting season