diff --git a/installer/build.py b/installer/build.py
index 91fbcb20..db3291e7 100644
--- a/installer/build.py
+++ b/installer/build.py
@@ -405,6 +405,40 @@ def run_dev() -> int:
     ).returncode
 
 
+def generate_build_metadata(args: argparse.Namespace) -> None:
+    """Generate version and build info files (mirrors CI steps)."""
+    print("\n" + "=" * 60)
+    print("Generating build metadata...")
+    print("=" * 60 + "\n")
+
+    # Generate version file
+    version_script = ROOT / "scripts" / "generate_version.py"
+    if version_script.exists():
+        run_command([sys.executable, str(version_script)], cwd=ROOT)
+    else:
+        print(f"Warning: {version_script} not found, skipping version generation")
+
+    # Generate build info (_build_info.py with BUILD_TAG)
+    build_info_script = ROOT / "scripts" / "generate_build_info.py"
+    if build_info_script.exists():
+        tag = args.tag
+        if not tag and args.nightly:
+            from datetime import datetime, timezone
+
+            tag = f"nightly-{datetime.now(timezone.utc).strftime('%Y%m%d')}"
+
+        cmd = [sys.executable, str(build_info_script)]
+        if tag:
+            cmd.append(tag)
+            print(f"  Build tag: {tag}")
+        else:
+            print("  Build tag: None (stable)")
+
+        run_command(cmd, cwd=ROOT)
+    else:
+        print(f"Warning: {build_info_script} not found, skipping build info generation")
+
+
 def main() -> int:
     """Run the build process."""
     parser = argparse.ArgumentParser(
@@ -441,6 +475,17 @@ def main() -> int:
         action="store_true",
         help="Skip portable ZIP creation",
     )
+    parser.add_argument(
+        "--nightly",
+        action="store_true",
+        help="Build as nightly (generates nightly-YYYYMMDD build tag)",
+    )
+    parser.add_argument(
+        "--tag",
+        type=str,
+        default=None,
+        help="Custom build tag (e.g. nightly-20260208). Overrides --nightly.",
+    )
 
     args = parser.parse_args()
 
@@ -471,6 +516,9 @@ def main() -> int:
     if not args.skip_icons:
         check_icons()
 
+    # Generate version and build info (same as CI)
+    generate_build_metadata(args)
+
     # Build with PyInstaller
     if not build_pyinstaller():
         return 1
diff --git a/src/accessiweather/app.py b/src/accessiweather/app.py
index 1afee0e3..869488e5 100644
--- a/src/accessiweather/app.py
+++ b/src/accessiweather/app.py
@@ -377,6 +377,16 @@ def do_check():
                     current_version = getattr(self, "version", "0.0.0")
                     build_tag = getattr(self, "build_tag", None)
                     current_nightly_date = parse_nightly_date(build_tag) if build_tag else None
+                    display_version = current_nightly_date if current_nightly_date else current_version
+
+                    # Safety: if frozen but no build_tag and checking nightly channel,
+                    # skip auto-prompt to avoid infinite update loops
+                    if not build_tag and channel == "nightly":
+                        logger.warning(
+                            "Skipping startup nightly update check: no build_tag available. "
+                            "Use Help > Check for Updates to check manually."
+                        )
+                        return
 
                     async def check():
                         service = UpdateService("AccessiWeather")
@@ -399,7 +409,7 @@ async def check():
                         def show_update_notification():
                             result = wx.MessageBox(
                                 f"A new {channel_label} update is available!\n\n"
-                                f"Current: {current_version}\n"
+                                f"Current: {display_version}\n"
                                 f"Latest: {update_info.version}\n\n"
                                 "Download now?",
                                 "Update Available",
diff --git a/src/accessiweather/config_utils.py b/src/accessiweather/config_utils.py
index 585b1ceb..94947a2a 100644
--- a/src/accessiweather/config_utils.py
+++ b/src/accessiweather/config_utils.py
@@ -52,6 +52,20 @@ def is_portable_mode() -> bool:
 
         logger.debug(f"Checking portable mode for executable directory: {app_dir}")
 
+        # Check for uninstaller (Inno Setup leaves unins*.exe in app directory)
+        # This reliably detects installed copies regardless of install location
+        app_dir_path = os.path.dirname(sys.executable)
+        uninstaller_exists = any(
+            f.startswith("unins") and f.endswith(".exe")
+            for f in os.listdir(app_dir_path)
+            if os.path.isfile(os.path.join(app_dir_path, f))
+        )
+        if uninstaller_exists:
+            logger.debug(
+                f"Not in portable mode: uninstaller found in {app_dir_path}"
+            )
+            return False
+
         # Check if we're running from Program Files (standard installation)
         program_files = os.environ.get("PROGRAMFILES", "")
         program_files_x86 = os.environ.get("PROGRAMFILES(X86)", "")
diff --git a/src/accessiweather/ui/main_window.py b/src/accessiweather/ui/main_window.py
index 43b10c09..930ebfe4 100644
--- a/src/accessiweather/ui/main_window.py
+++ b/src/accessiweather/ui/main_window.py
@@ -429,6 +429,8 @@ def _on_check_updates(self) -> None:
         current_version = getattr(self.app, "version", "0.0.0")
         build_tag = getattr(self.app, "build_tag", None)
         current_nightly_date = parse_nightly_date(build_tag) if build_tag else None
+        # Show nightly date as the display version when running a nightly build
+        display_version = current_nightly_date if current_nightly_date else current_version
 
         # Show checking status
         wx.BeginBusyCursor()
@@ -460,7 +462,7 @@ async def check():
                     elif current_nightly_date:
                         msg = f"You're on the latest nightly ({current_nightly_date})."
                     else:
-                        msg = f"You're up to date ({current_version})."
+                        msg = f"You're up to date ({display_version})."
 
                     wx.CallAfter(
                         wx.MessageBox,
@@ -475,7 +477,7 @@ async def check():
                     def prompt():
                         result = wx.MessageBox(
                             f"A new {channel_label} update is available!\n\n"
-                            f"Current: {current_version}\n"
+                            f"Current: {display_version}\n"
                             f"Latest: {update_info.version}\n\n"
                             "Download now?",
                             "Update Available",