diff --git a/src/data_collection/amsc_awos_sources.py b/src/data_collection/amsc_awos_sources.py
index 5d203a05..1f159d6f 100644
--- a/src/data_collection/amsc_awos_sources.py
+++ b/src/data_collection/amsc_awos_sources.py
@@ -335,11 +335,11 @@ class AmscAwosSourceMixin:
         }
         cookie = get_runtime_secret("POLYWEATHER_AMSC_COOKIE")
         session_id = get_runtime_secret("POLYWEATHER_AMSC_SESSION_ID")
-        if cookie:
-            headers["Cookie"] = cookie
-        elif session_id:
+        if session_id:
             headers["sessionId"] = session_id
             headers["app"] = "AMS"
+        elif cookie:
+            headers["Cookie"] = cookie
         return headers
 
     def _amsc_http_get_json(self, url: str, *, headers: Optional[Dict[str, str]] = None) -> Optional[Dict[str, Any]]:
diff --git a/tests/test_ops_amsc_health.py b/tests/test_ops_amsc_health.py
index ff043d1b..0261b167 100644
--- a/tests/test_ops_amsc_health.py
+++ b/tests/test_ops_amsc_health.py
@@ -45,6 +45,25 @@ def test_amsc_headers_prefer_runtime_secret_over_env(monkeypatch, tmp_path):
     assert headers["app"] == "AMS"
 
 
+def test_amsc_headers_prefer_rotated_session_id_over_stale_cookie(monkeypatch, tmp_path):
+    monkeypatch.setenv("POLYWEATHER_DB_PATH", str(tmp_path / "polyweather.db"))
+    monkeypatch.setenv("POLYWEATHER_AMSC_COOKIE", "stale-cookie")
+    DBManager().set_runtime_secret(
+        "POLYWEATHER_AMSC_SESSION_ID",
+        "fresh-session-1234",
+        updated_by="ops@example.com",
+    )
+
+    class FakeSource(AmscAwosSourceMixin):
+        timeout = 1.0
+
+    headers = FakeSource()._amsc_headers()
+
+    assert headers["sessionId"] == "fresh-session-1234"
+    assert headers["app"] == "AMS"
+    assert "Cookie" not in headers
+
+
 def test_ops_sensitive_config_update_rotates_session_without_echoing_secret(
     monkeypatch,
     tmp_path,
@@ -145,6 +164,46 @@ def test_ops_amsc_health_uses_configured_session_header(monkeypatch):
     assert captured["headers"]["app"] == "AMS"
 
 
+def test_ops_amsc_health_prefers_session_id_over_cookie(monkeypatch):
+    captured = {}
+
+    payload = {
+        "code": 200,
+        "data": {
+            "35R/17L": {
+                "RNO": "35R/17L",
+                "OTIME": "2026-05-30 20:03:00",
+                "TDZ_TEMP": "23.6",
+                "END_TEMP": "23.4",
+            }
+        },
+    }
+
+    class FakeResponse:
+        ok = True
+        status_code = 200
+        content = b"{}"
+
+        def json(self):
+            return payload
+
+    def fake_get(_url, **kwargs):
+        captured["headers"] = kwargs.get("headers") or {}
+        return FakeResponse()
+
+    monkeypatch.setenv("AMSC_AWOS_BASE_URL", "https://example.test/getWindPlate")
+    monkeypatch.setenv("POLYWEATHER_AMSC_SESSION_ID", "fresh-session")
+    monkeypatch.setenv("POLYWEATHER_AMSC_COOKIE", "stale-cookie")
+    monkeypatch.setattr(ops_api._requests, "get", fake_get)
+
+    result = ops_api._check_amsc_awos_health(timeout=1)
+
+    assert result["ok"] is True
+    assert captured["headers"]["sessionId"] == "fresh-session"
+    assert captured["headers"]["app"] == "AMS"
+    assert "Cookie" not in captured["headers"]
+
+
 def test_ops_amsc_health_rejects_empty_success_response(monkeypatch):
     class FakeResponse:
         ok = True
diff --git a/web/services/ops_api.py b/web/services/ops_api.py
index f625e56c..edf3e0f7 100644
--- a/web/services/ops_api.py
+++ b/web/services/ops_api.py
@@ -1400,11 +1400,11 @@ def _build_amsc_awos_headers() -> dict[str, str]:
     }
     cookie = get_runtime_secret("POLYWEATHER_AMSC_COOKIE")
     session_id = get_runtime_secret("POLYWEATHER_AMSC_SESSION_ID")
-    if cookie:
-        headers["Cookie"] = cookie
-    elif session_id:
+    if session_id:
         headers["sessionId"] = session_id
         headers["app"] = "AMS"
+    elif cookie:
+        headers["Cookie"] = cookie
     return headers