diff --git a/lib/microwaveprop/propagation.ex b/lib/microwaveprop/propagation.ex
index 3e910f7d..08c7e827 100644
--- a/lib/microwaveprop/propagation.ex
+++ b/lib/microwaveprop/propagation.ex
@@ -198,12 +198,18 @@ defmodule Microwaveprop.Propagation do
   end
 
   @doc """
-  Remove score files with valid_times older than 2 hours. Called on
+  Remove score files with valid_times older than 3 hours. Called on
   a cron by `Microwaveprop.Workers.PropagationPruneWorker`.
+
+  The cutoff sits one hour beyond HRRR's ~2h publish lag: the hourly
+  seeder picks `run_time = now - 2h`, so the f00 analysis file is
+  written at valid_time = now - 2h. A 2h cutoff deletes it within
+  minutes; a 3h cutoff keeps it alive until the next hourly run
+  supersedes it.
   """
   @spec prune_old_scores() :: :ok
   def prune_old_scores do
-    cutoff = DateTime.add(DateTime.utc_now(), -2, :hour)
+    cutoff = DateTime.add(DateTime.utc_now(), -3, :hour)
     file_deleted = ScoresFile.prune_older_than(cutoff)
     profiles_deleted = ProfilesFile.prune_older_than(cutoff)