diff --git a/CHANGELOG.md b/CHANGELOG.md
index 1f6fdcf..49a4813 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -4,6 +4,9 @@ All notable changes to this project will be documented in this file.
 
 ## [v0.13.0] unreleased
 
+- **CHANGED** Refresh the default CelesTrak space-weather cache only when a
+  requested time is outside the available data range. Custom space-weather
+  files are never refreshed automatically.
 - **FIXED** MSIS 2.0 and 2.1 support parameter directories longer than 128
   characters, avoiding premature process termination in deeply nested installs.
 - **ADDED** `interpolate_indices` option.
diff --git a/pymsis/utils.py b/pymsis/utils.py
index 88541b1..9e6b7ee 100644
--- a/pymsis/utils.py
+++ b/pymsis/utils.py
@@ -306,6 +306,23 @@ def get_f107_ap(
             _SPACE_WEATHER.data = _load_f107_ap_data()
         data = _SPACE_WEATHER.data
 
+        # Each ap value covers the three-hour interval beginning at its
+        # timestamp. Refresh only when the requested data is outside the file.
+        data_end = data["dates"][-1] + np.timedelta64(3, "h")
+        needs_refresh = _SPACE_WEATHER.path == _F107_AP_DEFAULT_FILE and np.any(
+            dates >= data_end
+        )
+        if needs_refresh:
+            try:
+                download_f107_ap()
+            except OSError:
+                # Leave the old file and cache intact. The range check below
+                # reports the normal unavailable-data error for the request.
+                pass
+            if _SPACE_WEATHER.data is None:
+                _SPACE_WEATHER.data = _load_f107_ap_data()
+            data = _SPACE_WEATHER.data
+
     data_start = data["dates"][0]
     data_end = data["dates"][-1]
     # atleast_1d keeps output shapes consistent for scalar and array inputs
diff --git a/pyproject.toml b/pyproject.toml
index 202e615..e33ff99 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -74,6 +74,10 @@ testpaths = [
 addopts = [
     "--import-mode=importlib",
 ]
+filterwarnings = [
+# Ignore warnings loading from file specifically
+    'ignore:Downloading ap and F10.7 data from file:UserWarning',
+]
 
 [tool.cibuildwheel]
 environment.PIP_ONLY_BINARY = "numpy"
diff --git a/tests/test_utils.py b/tests/test_utils.py
index 980cebd..bf1a45c 100644
--- a/tests/test_utils.py
+++ b/tests/test_utils.py
@@ -154,6 +154,68 @@ def test_download_refreshes_cache(monkeypatch, tmp_path, local_path):
     assert_array_equal(utils.get_f107_ap("2000-07-01T12:00")[0], [159.6])
 
 
+def test_historical_request_does_not_refresh(monkeypatch, tmp_path, local_path):
+    target = tmp_path / "weather.csv"
+    target.write_text(local_path.read_text().replace("159.6", "199.6"))
+    monkeypatch.setattr(utils._SPACE_WEATHER, "path", target)
+    monkeypatch.setattr(utils, "_F107_AP_DEFAULT_FILE", target)
+
+    with patch.object(utils, "download_f107_ap") as download:
+        assert_array_equal(utils.get_f107_ap("2000-07-01T12:00")[0], [199.6])
+    download.assert_not_called()
+
+
+def test_out_of_range_request_refreshes(monkeypatch, tmp_path, local_path):
+    target = tmp_path / "weather.csv"
+    lines = local_path.read_text().splitlines()
+    target.write_text("\n".join(lines[:100]) + "\n")
+    monkeypatch.setattr(utils._SPACE_WEATHER, "path", target)
+    monkeypatch.setattr(utils, "_F107_AP_DEFAULT_FILE", target)
+
+    def refresh_from_fixture():
+        target.write_bytes(local_path.read_bytes())
+        utils._SPACE_WEATHER.data = None
+
+    with patch.object(
+        utils, "download_f107_ap", side_effect=refresh_from_fixture
+    ) as download:
+        assert_array_equal(utils.get_f107_ap("2000-07-01T12:00")[0], [159.6])
+    download.assert_called_once_with()
+
+
+def test_custom_file_is_not_refreshed(monkeypatch, tmp_path, local_path):
+    target = tmp_path / "weather.csv"
+    lines = local_path.read_text().splitlines()
+    target.write_text("\n".join(lines[:100]) + "\n")
+    utils.use_space_weather_file(target)
+
+    with (
+        patch.object(utils, "download_f107_ap") as download,
+        pytest.raises(ValueError, match="not available"),
+    ):
+        utils.get_f107_ap("2000-07-01T12:00")
+    download.assert_not_called()
+
+
+def test_out_of_range_request_raises_when_refresh_fails(
+    monkeypatch, tmp_path, local_path
+):
+    target = tmp_path / "weather.csv"
+    lines = local_path.read_text().splitlines()
+    target.write_text("\n".join(lines[:100]) + "\n")
+    monkeypatch.setattr(utils._SPACE_WEATHER, "path", target)
+    monkeypatch.setattr(utils, "_F107_AP_DEFAULT_FILE", target)
+
+    with (
+        patch.object(
+            utils, "download_f107_ap", side_effect=OSError("offline")
+        ) as download,
+        pytest.raises(ValueError, match="not available"),
+    ):
+        utils.get_f107_ap("2000-07-01T12:00")
+    download.assert_called_once_with()
+
+
 @pytest.mark.parametrize(
     ("dates", "expected_f107", "expected_f107a", "expected_ap"),
     [