diff --git a/fowd/processing.py b/fowd/processing.py
index d5cad1e..72894eb 100644
--- a/fowd/processing.py
+++ b/fowd/processing.py
@@ -213,8 +213,13 @@ def handle_output(wave_records, wave_params_history, num_flags_fired):
                 wave_records_np[key] = np.asarray(val)
 
         # dump results to files
-        with open(outfile, 'ab') as f:
-            pickle.dump(wave_records_np, f)
+        if not os.path.exists(outfile):
+            with open(outfile, 'wb'):
+                pass
+
+        if wave_records_np:
+            with open(outfile, 'ab') as f:
+                pickle.dump(wave_records_np, f)
 
         with open(statefile, 'wb') as f:
             pickle.dump({
@@ -255,6 +260,9 @@ def handle_output(wave_records, wave_params_history, num_flags_fired):
     )
 
     with strict_filelock(outfile), tqdm.tqdm(**pbar_kwargs) as pbar:
+        # initialize output files
+        handle_output(wave_records, wave_params_history, num_flags_fired)
+
         for wave_start, wave_stop in find_wave_indices(elevation_normalized, start_idx=start_idx):
             pbar.update(wave_stop - last_wave_stop)
             last_wave_stop = wave_stop