diff --git a/lib/microwaveprop/propagation.ex b/lib/microwaveprop/propagation.ex
index ecd446d0..6c8ba3da 100644
--- a/lib/microwaveprop/propagation.ex
+++ b/lib/microwaveprop/propagation.ex
@@ -246,9 +246,7 @@ defmodule Microwaveprop.Propagation do
 
   @spec available_valid_times(non_neg_integer()) :: [DateTime.t()]
   def available_valid_times(band_mhz) do
-    now = DateTime.utc_now()
-    past_cutoff = DateTime.add(now, -3600, :second)
-    future_cutoff = DateTime.add(now, @hrrr_forecast_horizon_hours * 3600, :second)
+    {past_cutoff, future_cutoff} = hot_cache_window()
 
     case ScoresFile.list_valid_times(band_mhz) do
       [] -> []
@@ -256,6 +254,21 @@ defmodule Microwaveprop.Propagation do
     end
   end
 
+  @doc """
+  The active forecast window for the `/map` UI: one hour in the past
+  through HRRR's 18-hour forecast horizon. Used by `ScoreCacheReconciler`
+  and `NotifyListener` to bound ETS growth — long-horizon GEFS `.prop`
+  files on disk must not balloon `propagation_score_cache` past the
+  memory the UI actually reads.
+  """
+  @spec hot_cache_window() :: {DateTime.t(), DateTime.t()}
+  def hot_cache_window do
+    now = DateTime.utc_now()
+    past = DateTime.add(now, -3600, :second)
+    future = DateTime.add(now, @hrrr_forecast_horizon_hours * 3600, :second)
+    {past, future}
+  end
+
   defp filter_or_latest(times, past_cutoff, future_cutoff) do
     fresh =
       Enum.filter(times, fn t ->
diff --git a/lib/microwaveprop/propagation/notify_listener.ex b/lib/microwaveprop/propagation/notify_listener.ex
index dfcf1608..1aab8975 100644
--- a/lib/microwaveprop/propagation/notify_listener.ex
+++ b/lib/microwaveprop/propagation/notify_listener.ex
@@ -106,9 +106,13 @@ defmodule Microwaveprop.Propagation.NotifyListener do
       %{valid_time: valid_time}
     )
 
-    # Prune anything older than 2 hours so the cache doesn't grow
-    # unbounded when Rust covers many forecast hours back-to-back.
-    ScoreCache.prune_older_than(DateTime.add(DateTime.utc_now(), -2, :hour))
+    # Prune anything outside the active map window. Old entries (>1h
+    # past) and long-horizon GEFS entries (>18h future) would otherwise
+    # accumulate and push the `propagation_score_cache` ETS table past
+    # 2 GiB — scheduler starvation from the GC sweeps tripped the
+    # /live probe and cycled the pods every ~25 min.
+    {past, future} = Propagation.hot_cache_window()
+    ScoreCache.prune_outside_window(past, future)
 
     _ = Phoenix.PubSub.broadcast(@pubsub, @topic, {:propagation_updated, [valid_time]})
 
diff --git a/lib/microwaveprop/propagation/score_cache.ex b/lib/microwaveprop/propagation/score_cache.ex
index 58ac8f9f..b0294223 100644
--- a/lib/microwaveprop/propagation/score_cache.ex
+++ b/lib/microwaveprop/propagation/score_cache.ex
@@ -106,6 +106,24 @@ defmodule Microwaveprop.Propagation.ScoreCache do
     :ets.select_delete(@table, match_spec)
   end
 
+  @doc """
+  Delete every entry whose `valid_time` falls outside the inclusive
+  window `[past_cutoff, future_cutoff]`. Used to bound the cache to
+  the active forecast horizon (past ~1 h + HRRR's 18 h forward) so
+  long-horizon GEFS valid_times never accumulate in ETS.
+  """
+  @spec prune_outside_window(DateTime.t(), DateTime.t()) :: non_neg_integer()
+  def prune_outside_window(past_cutoff, future_cutoff) do
+    match_spec = [
+      {{{:_, :"$1"}, :_},
+       [
+         {:orelse, {:<, :"$1", {:const, past_cutoff}}, {:>, :"$1", {:const, future_cutoff}}}
+       ], [true]}
+    ]
+
+    :ets.select_delete(@table, match_spec)
+  end
+
   @spec clear() :: :ok
   def clear do
     :ets.delete_all_objects(@table)
diff --git a/lib/microwaveprop/propagation/score_cache_reconciler.ex b/lib/microwaveprop/propagation/score_cache_reconciler.ex
index 04016291..b54fe790 100644
--- a/lib/microwaveprop/propagation/score_cache_reconciler.ex
+++ b/lib/microwaveprop/propagation/score_cache_reconciler.ex
@@ -24,6 +24,7 @@ defmodule Microwaveprop.Propagation.ScoreCacheReconciler do
   """
   use GenServer
 
+  alias Microwaveprop.Propagation
   alias Microwaveprop.Propagation.BandConfig
   alias Microwaveprop.Propagation.ScoreCache
   alias Microwaveprop.Propagation.ScoresFile
@@ -99,7 +100,17 @@ defmodule Microwaveprop.Propagation.ScoreCacheReconciler do
   def handle_info(_msg, state), do: {:noreply, state}
 
   defp warm_missing_for_band(band_mhz) do
-    on_disk = MapSet.new(ScoresFile.list_valid_times(band_mhz))
+    {past_cutoff, future_cutoff} = Propagation.hot_cache_window()
+
+    on_disk =
+      band_mhz
+      |> ScoresFile.list_valid_times()
+      |> Enum.filter(fn vt ->
+        DateTime.compare(vt, past_cutoff) != :lt and
+          DateTime.compare(vt, future_cutoff) != :gt
+      end)
+      |> MapSet.new()
+
     in_cache = MapSet.new(ScoreCache.valid_times(band_mhz))
     missing = MapSet.difference(on_disk, in_cache)
 
diff --git a/test/microwaveprop/propagation/score_cache_reconciler_test.exs b/test/microwaveprop/propagation/score_cache_reconciler_test.exs
index 8f31233e..f575061c 100644
--- a/test/microwaveprop/propagation/score_cache_reconciler_test.exs
+++ b/test/microwaveprop/propagation/score_cache_reconciler_test.exs
@@ -47,6 +47,18 @@ defmodule Microwaveprop.Propagation.ScoreCacheReconcilerTest do
     ]
   end
 
+  # In-window timestamps for reconciler tests — the reconciler now
+  # filters valid_times to `[now-1h, now+18h]`, so hardcoded fixtures
+  # in the past drift out of scope as time passes. `current_hour/1`
+  # returns an hour-aligned DateTime offset by N hours from now.
+  defp current_hour(offset_hours \\ 0) do
+    DateTime.utc_now()
+    |> Map.put(:minute, 0)
+    |> Map.put(:second, 0)
+    |> Map.put(:microsecond, {0, 0})
+    |> DateTime.add(offset_hours * 3600, :second)
+  end
+
   describe "next_sweep_interval/0" do
     test "returns a value in [base + 1, base + jitter_max] with defaults" do
       # Exercise the randomized default many times; each draw must land
@@ -75,7 +87,7 @@ defmodule Microwaveprop.Propagation.ScoreCacheReconcilerTest do
   describe "sweep_once/0" do
     test "warms ScoreCache for every {band, valid_time} on disk and missing from cache",
          %{band_mhz: band_mhz} do
-      valid_time = ~U[2026-04-21 12:00:00Z]
+      valid_time = current_hour(1)
       ScoresFile.write!(band_mhz, valid_time, sample_scores())
 
       assert :miss = ScoreCache.fetch(band_mhz, valid_time)
@@ -88,7 +100,7 @@ defmodule Microwaveprop.Propagation.ScoreCacheReconcilerTest do
 
     test "is a no-op when cache is already in sync with disk",
          %{band_mhz: band_mhz} do
-      valid_time = ~U[2026-04-21 13:00:00Z]
+      valid_time = current_hour(2)
       ScoresFile.write!(band_mhz, valid_time, sample_scores())
 
       # Prime the cache manually
@@ -100,6 +112,32 @@ defmodule Microwaveprop.Propagation.ScoreCacheReconcilerTest do
     test "returns 0 when the scores directory is empty" do
       assert 0 = ScoreCacheReconciler.sweep_once()
     end
+
+    test "skips valid_times outside the hot-cache window (now-1h..now+18h)",
+         %{band_mhz: band_mhz} do
+      # Three on-disk files: one way in the past, one in the window,
+      # one far in the future (simulating GEFS Day 2-7). Only the
+      # middle one should make it into ETS.
+      now =
+        DateTime.utc_now()
+        |> Map.put(:minute, 0)
+        |> Map.put(:second, 0)
+        |> Map.put(:microsecond, {0, 0})
+
+      stale_past = DateTime.add(now, -6 * 3600, :second)
+      in_window = now
+      far_future = DateTime.add(now, 72 * 3600, :second)
+
+      ScoresFile.write!(band_mhz, stale_past, sample_scores())
+      ScoresFile.write!(band_mhz, in_window, sample_scores())
+      ScoresFile.write!(band_mhz, far_future, sample_scores())
+
+      _ = ScoreCacheReconciler.sweep_once()
+
+      assert ScoreCache.fetch(band_mhz, stale_past) == :miss
+      assert {:ok, _} = ScoreCache.fetch(band_mhz, in_window)
+      assert ScoreCache.fetch(band_mhz, far_future) == :miss
+    end
   end
 
   describe "GenServer lifecycle" do
@@ -138,7 +176,7 @@ defmodule Microwaveprop.Propagation.ScoreCacheReconcilerTest do
 
     test "run_on_start: true warms cache from disk via handle_info(:sweep)",
          %{band_mhz: band_mhz} do
-      valid_time = ~U[2026-04-21 14:00:00Z]
+      valid_time = current_hour(3)
       ScoresFile.write!(band_mhz, valid_time, sample_scores())
 
       assert :miss = ScoreCache.fetch(band_mhz, valid_time)
@@ -153,7 +191,7 @@ defmodule Microwaveprop.Propagation.ScoreCacheReconcilerTest do
 
     test "run_on_start: false does not sweep within the wait window",
          %{band_mhz: band_mhz} do
-      valid_time = ~U[2026-04-21 15:00:00Z]
+      valid_time = current_hour(4)
       ScoresFile.write!(band_mhz, valid_time, sample_scores())
 
       start_supervised!({ScoreCacheReconciler, run_on_start: false, interval_ms: 100})
@@ -166,8 +204,8 @@ defmodule Microwaveprop.Propagation.ScoreCacheReconcilerTest do
 
     test "interval_ms rescheduling picks up files written after the first sweep",
          %{band_mhz: band_mhz} do
-      first = ~U[2026-04-21 16:00:00Z]
-      second = ~U[2026-04-21 17:00:00Z]
+      first = current_hour(5)
+      second = current_hour(6)
 
       ScoresFile.write!(band_mhz, first, sample_scores())
 
@@ -186,7 +224,7 @@ defmodule Microwaveprop.Propagation.ScoreCacheReconcilerTest do
     end
 
     test "logs an info line when warmed > 0", %{band_mhz: band_mhz} do
-      valid_time = ~U[2026-04-21 18:00:00Z]
+      valid_time = current_hour(7)
       ScoresFile.write!(band_mhz, valid_time, sample_scores())
 
       # config/test.exs pins the global logger to :warning, which drops the
diff --git a/test/microwaveprop/propagation/score_cache_test.exs b/test/microwaveprop/propagation/score_cache_test.exs
index 93c527af..ed635498 100644
--- a/test/microwaveprop/propagation/score_cache_test.exs
+++ b/test/microwaveprop/propagation/score_cache_test.exs
@@ -96,6 +96,34 @@ defmodule Microwaveprop.Propagation.ScoreCacheTest do
     end
   end
 
+  describe "prune_outside_window/2" do
+    test "removes entries strictly outside [past_cutoff, future_cutoff]" do
+      ScoreCache.put(10_000, ~U[2026-04-12 08:00:00Z], [%{lat: 1.0, lon: 1.0, score: 1}])
+      ScoreCache.put(10_000, ~U[2026-04-12 12:00:00Z], [%{lat: 2.0, lon: 2.0, score: 2}])
+      ScoreCache.put(10_000, ~U[2026-04-12 20:00:00Z], [%{lat: 3.0, lon: 3.0, score: 3}])
+
+      removed =
+        ScoreCache.prune_outside_window(~U[2026-04-12 10:00:00Z], ~U[2026-04-12 18:00:00Z])
+
+      assert removed == 2
+      assert ScoreCache.fetch(10_000, ~U[2026-04-12 08:00:00Z]) == :miss
+      assert {:ok, [%{score: 2}]} = ScoreCache.fetch(10_000, ~U[2026-04-12 12:00:00Z])
+      assert ScoreCache.fetch(10_000, ~U[2026-04-12 20:00:00Z]) == :miss
+    end
+
+    test "keeps entries equal to either cutoff (inclusive bounds)" do
+      ScoreCache.put(10_000, ~U[2026-04-12 10:00:00Z], [%{lat: 1.0, lon: 1.0, score: 1}])
+      ScoreCache.put(10_000, ~U[2026-04-12 18:00:00Z], [%{lat: 2.0, lon: 2.0, score: 2}])
+
+      removed =
+        ScoreCache.prune_outside_window(~U[2026-04-12 10:00:00Z], ~U[2026-04-12 18:00:00Z])
+
+      assert removed == 0
+      assert {:ok, _} = ScoreCache.fetch(10_000, ~U[2026-04-12 10:00:00Z])
+      assert {:ok, _} = ScoreCache.fetch(10_000, ~U[2026-04-12 18:00:00Z])
+    end
+  end
+
   describe "fetch_point/4" do
     test "returns :miss when nothing cached" do
       assert ScoreCache.fetch_point(10_000, ~U[2026-04-12 12:00:00Z], 32.0, -97.0) == :miss