diff --git a/vendor/clouds3d.js b/vendor/clouds3d.js
index 0e89814..7f76261 100644
--- a/vendor/clouds3d.js
+++ b/vendor/clouds3d.js
@@ -397,7 +397,8 @@ function drawTileAt(lng, perp, dx, dz, centerTileX, centerTileY) {
         mirrorLabel('x=' + tileX, canvasX + GROUND_TILE_SIZE - 12, canvasY + GROUND_TILE_SIZE - 12, 'left');
 
         return true;
-    }).catch(function() {
+    }).catch(function(err) {
+        console.warn('[clouds3d] tile fetch failed', tileX, tileY, err && err.message);
         // On failure draw a neutral gray so the gap is at least
         // not the bright fog colour
         groundCtx.fillStyle = '#3a4458';
@@ -449,6 +450,7 @@ function rebuildGroundMosaic(centerTileX, centerTileY) {
 // smooth parallax within the loaded content.
 function refreshGroundMosaic() {
     if (!groundCtx) return;
+    console.log('[clouds3d] refreshGroundMosaic center', groundCenterTile);
     var fdx = (window.__flightDir && window.__flightDir.dx) || 0;
     var fdz = (window.__flightDir && window.__flightDir.dz) || 1;
     var camX = (fdx !== 0) ? groundCameraX * fdx : 0;