by Ruth Mottram, DMI,
April 12th 2016
An early melt event over the Greenland ice sheet occurred this week, 
smashing by a month the previous records of more than 10% of the ice 
sheet melting.
Left: Maps showing areas where melting has taken place within the last two days. Right: The percentage of the total area of the ice where the melting occurred from January 1 until 11th May (in blue). The dark grey curve represents the 1990-2013 average. The grey shaded area represents the year to year variation for each day.
Daily mean temperatures at NUK_L (near Nuuk) and KAN_U (near Kangerlussuaq) for each day in 2016 ( Click to enlarge.
Based on observation-initialized weather model runs by DMI, almost  12% of the Greenland ice sheet had more than 1mm of melt on Monday 11th April, following an early start to melting the previous day. Scientists at DMI were at first incredulous due to the early date. “We had to check that our models were still working properly” said Peter Langen, a climate scientist at DMI. “Fortunately we could see from the stations on the ice sheet that it had been well above melting, even above 10 °C. This helped to explain the results”.   The former top 3 earliest dates for a melt area larger than 10% were previously all in May (5th May 2010, 8th May 1990, 8th May 2006).

“Even weather stations quite high up on the ice sheet observed very high temperatures on Monday”, said Robert Fausto, a scientist at GEUS who 
maintains melt data. “At KAN_U for example, a site at 
1,840 m above sea level, we observed a maximum temperature of 3.1°C. 
This would be a warm day in July, never mind April”. Other PROMICE 
stations in the network at lower levels had daily average temperatures 
between 5 and 10 °C. 
Similarly, around the coast of Greenland where DMI has climate records 
dating back to 1873, Greenland came close to setting a record 
temperature for the whole of Greenland in April. Kangerlussuaq 
measured a daily maximum of 17.8°C, the previous record is 18.0 °C 
and the DMI observation station at the Summit of Greenland set a 
new “warm” April record of -6.6°C. “Averything is melting” observed 
Nuuk resident Aqqaluk Petersen.
Map showing the unusual flow pattern over Greenland on Monday, 11 April 2016, 18 UTC. Lines (isohypses) connect points of equal height of the 500 hPa pressure level, a measure of the average temperature between surface and 5-6 km height. The coloured numbers give the freezing level (i.e. below which the temperature is above zero degrees; SFC means that this level is at the surface) in kilometers.
Overflademassebalancen mandag d. 11. april viser for det meste en tilvækst fra frysende regn og sne, mens små mørkerøde områder viser afstrømning fra isen.
The melt was driven by warm air advected from the SW bringing rain along the coast, similar to an extreme melt event in 2012 when 95% of the surface of the ice sheet had melt, a situation that has been reported in detail by GEUS and DMI scientists (Fausto et al., 2016). 
Martin Stendel, a climate scientist at DMI explains “it is a very unusual situation, especially so early in the year, with very cold air and deep low pressures system to the west and east of Greenland and very warm air forming a “cap” over the island. This helped to force a frontal system with very warm air up the west coast bringing rain over the ice sheet. A freezing level of 2.4 km over Narsarsuaq is highly unusual (compare to Portugal), as is a 500-hPa height of almost 5,760 m, a value typically observed in the subtropics – in summer. The very cold weather by contrast in north eastern Greenland is exactly what we would expect with this pattern.”
Weather forecasters Marie Rasmussen and Jesper Eriksen at DMI expect the situation over Greenland to gradually cool over most of the island this week, though a new frontal system from Thursday may again cause widespread melt especially in the south.
Rainfall and meltwater on the ice sheet at this time of year mostly runs into the snow and refreezes. “Meltwater refreezing releases heat into the snow at depth, reducing the amount of heating needed for melt to start and forming ice layers that can help melt water run off the ice sheet earlier with climate warming” said Prof. Jason Box at GEUS who leads a Danish Research 
Council project with Fausto, DMI, and DTU colleagues 

As the daily surface mass balance plot shows, the blue shows a mass 
gain, most likely from freezing rainfall and perhaps some snow, as 
the small dark red areas show an overall loss of ice.