1 5 Greenland Ice Sheet late-season melt: Investigating multi-scale drivers of K-transect events Thomas J. Ballinger 1 , Thomas L. Mote 2 , Kyle Mattingly 2 , Angela C. Bliss 3 , Edward Hanna 4 , Dirk van As 5 , Melissa 10 Prieto 1 , Saeideh Gharehchahi 1 , Xavier Fettweis 6 , Brice Noël 7 , Paul C.J.P. Smeets 7 , Mads H. Ribergaard 8 , and John Cappelen 8 Correspondence to: Thomas J. Ballinger (tballinger@txstate.edu) 15 1 Department of Geography, Texas State University, San Marcos, TX, USA 2 Department of Geography, University of Georgia, Athens, GA, USA 3 College of Earth, Ocean, and Atmospheric Sciences, Oregon State University, Corvallis, OR, USA 4 School of Geography and Lincoln Centre for Water and Planetary Health, University of Lincoln, Lincoln, UK 5 Geological Survey of Denmark and Greenland, Copenhagen, Denmark 20 6 Laboratory of Climatology, Department of Geography, University of Liège, Liège, Belgium 7 Institute for Marine and Atmospheric Research, Utrecht University, Utrecht, the Netherlands 8 Danish Meteorological Institute, Copenhagen, Denmark Manuscript submitted to The Cryosphere Discussions on 19 December 2018 25 Abstract. One consequence of recent Arctic warming is an increased occurrence and longer seasonality of above- freezing air temperature episodes. There is significant disagreement in the literature concerning potential physical connectivity between high-latitude open water duration proximate to the Greenland Ice Sheet (GrIS) and unseasonal (i.e. late summer and autumn) GrIS melt events. Here, a new date of sea ice advance (DOA) product is used to 30 determine the occurrence of Baffin Bay sea ice growth along Greenland’s west coast for the 2011–2015 period. For the unseasonal melt period preceding the DOA, northwest Atlantic Ocean and atmospheric conditions are analyzed and linked to unseasonal melt events observed at a series of on-ice automatic weather stations (AWS) along the K- transect in southwest Greenland. Mesoscale and synoptic influences on the above and below freezing surface air temperature events are assessed through analyses of AWS wind, pressure, and humidity observations. These surface 35 observations are further compared against Modèle Atmosphérique Régional (MAR), Regional Atmospheric Climate Model (RACMO2), and ERA-Interim reanalysis fields to understand the airmass origins and (thermo)dynamic drivers of the melt events. Results suggest that the K-transect late season, ablation zone melt events are strongly affected by ridging atmospheric circulation patterns that transport warm, moist air from the sub-polar North Atlantic toward west Greenland. While thermal conduction and advection off south Baffin Bay open waters impact coastal air temperatures, 40 consistent with previous studies, marine air incursions from Baffin Bay onto the ice sheet are obstructed by barrier flows and the pressure gradient-driven katabatic regime along the western GrIS margin. The Cryosphere Discuss., https://doi.org/10.5194/tc-2018-285 Manuscript under review for journal The Cryosphere Discussion started: 2 January 2019 c  Author(s) 2019. CC BY 4.0 License.