diff --git a/components/layout/app-shell.tsx b/components/layout/app-shell.tsx
index 775d1c4..fc32072 100644
--- a/components/layout/app-shell.tsx
+++ b/components/layout/app-shell.tsx
@@ -2,7 +2,8 @@
 
 import Link from "next/link";
 import { usePathname } from "next/navigation";
-import { CloudSun, Droplets, Settings, TriangleAlert } from "lucide-react";
+import { useEffect, useState } from "react";
+import { CloudSun, Droplets, Settings, TriangleAlert, WifiOff } from "lucide-react";
 import type { LucideIcon } from "lucide-react";
 import { isAppNavItemVisible } from "@/lib/app-sections";
 import { NAV_ITEMS } from "@/lib/constants";
@@ -23,6 +24,18 @@ export function AppShell({ children }: { children: React.ReactNode }) {
   const { t } = useI18n();
   const appSections = useWeatherStore((state) => state.appSections);
   const visibleNavItems = NAV_ITEMS.filter((item) => isAppNavItemVisible(item.href, appSections));
+  const [isOffline, setIsOffline] = useState(false);
+
+  useEffect(() => {
+    const updateConnectionStatus = () => setIsOffline(!navigator.onLine);
+    updateConnectionStatus();
+    window.addEventListener("online", updateConnectionStatus);
+    window.addEventListener("offline", updateConnectionStatus);
+    return () => {
+      window.removeEventListener("online", updateConnectionStatus);
+      window.removeEventListener("offline", updateConnectionStatus);
+    };
+  }, []);
 
   return (
     <div className="min-h-screen overflow-x-hidden bg-background">
@@ -56,6 +69,14 @@ export function AppShell({ children }: { children: React.ReactNode }) {
           </div>
         </div>
       </header>
+      {isOffline && (
+        <div className="border-b border-warning/25 bg-warning/10 px-4 py-2 text-sm font-medium text-warning sm:px-6 lg:px-8">
+          <div className="mx-auto flex max-w-7xl items-center gap-2">
+            <WifiOff className="size-4 shrink-0" aria-hidden="true" />
+            <span>{t("offline.banner")}</span>
+          </div>
+        </div>
+      )}
       <main className="app-main-safe mx-auto max-w-7xl px-4 pt-5 sm:px-6 sm:pt-8 lg:px-8">{children}</main>
       <nav
         aria-label={t("nav.mobile")}
diff --git a/lib/i18n.tsx b/lib/i18n.tsx
index 1361166..05f8644 100644
--- a/lib/i18n.tsx
+++ b/lib/i18n.tsx
@@ -327,6 +327,7 @@ const translations = {
     "offline.description":
       "wtr. nie może teraz pobrać aktualnych danych IMGW. Ostatnio odwiedzone widoki mogą być dostępne z pamięci urządzenia.",
     "offline.back": "Wróć do aplikacji",
+    "offline.banner": "Brak połączenia · dane mogą być nieaktualne",
   },
   en: {
     "nav.weather": "Weather",
@@ -647,6 +648,7 @@ const translations = {
     "offline.description":
       "wtr. cannot fetch current IMGW data right now. Recently visited views may still be available from your device cache.",
     "offline.back": "Back to the app",
+    "offline.banner": "Offline · data may be out of date",
   },
 } as const;
 
diff --git a/public/sw.js b/public/sw.js
index 11be1d1..0d74542 100644
--- a/public/sw.js
+++ b/public/sw.js
@@ -7,6 +7,8 @@ const ACTIVE_CACHES = new Set([SHELL_CACHE, RUNTIME_CACHE, API_CACHE]);
 
 const SHELL = [
   "/",
+  "/warnings",
+  "/hydro",
   "/settings",
   "/offline",
   "/manifest.json",