diff --git a/core/modules/config/config.routing.yml b/core/modules/config/config.routing.yml
index f2a944a..36e6f89 100644
--- a/core/modules/config/config.routing.yml
+++ b/core/modules/config/config.routing.yml
@@ -54,3 +54,10 @@ config.export_single:
     config_name: NULL
   requirements:
     _permission: 'export configuration'
+
+config.snapshot_diff:
+  path: '/admin/config/development/configuration/sync/snapshot-diff/{storage}'
+  defaults:
+    _content: '\Drupal\config\Controller\ConfigController::snapshotDiff'
+  requirements:
+    _permission: 'import configuration'
diff --git a/core/modules/config/lib/Drupal/config/Controller/ConfigController.php b/core/modules/config/lib/Drupal/config/Controller/ConfigController.php
index 88cdeab..abb6cc2 100644
--- a/core/modules/config/lib/Drupal/config/Controller/ConfigController.php
+++ b/core/modules/config/lib/Drupal/config/Controller/ConfigController.php
@@ -11,15 +11,16 @@
 use Drupal\Component\Serialization\Yaml;
 use Drupal\Core\Config\ConfigManagerInterface;
 use Drupal\Core\Config\StorageInterface;
-use Drupal\Core\DependencyInjection\ContainerInjectionInterface;
 use Drupal\system\FileDownloadController;
 use Symfony\Component\DependencyInjection\ContainerInterface;
 use Symfony\Component\HttpFoundation\Request;
+use Drupal\Core\Config\StorageComparer;
+use Drupal\Core\Controller\ControllerBase;
 
 /**
  * Returns responses for config module routes.
  */
-class ConfigController implements ContainerInjectionInterface {
+class ConfigController extends ControllerBase {
 
   /**
    * The target storage.
@@ -36,6 +37,13 @@ class ConfigController implements ContainerInjectionInterface {
   protected $sourceStorage;
 
   /**
+   * The snapshot.
+   *
+   * @var \Drupal\Core\Config\StorageInterface
+   */
+  protected $snapshotStorage;
+
+  /**
    * The configuration manager.
    *
    * @var \Drupal\Core\Config\ConfigManagerInterface
@@ -56,6 +64,7 @@ public static function create(ContainerInterface $container) {
     return new static(
       $container->get('config.storage'),
       $container->get('config.storage.staging'),
+      $container->get('config.storage.snapshot'),
       $container->get('config.manager'),
       new FileDownloadController()
     );
@@ -71,9 +80,10 @@ public static function create(ContainerInterface $container) {
    * @param \Drupal\system\FileDownloadController $file_download_controller
    *   The file download controller.
    */
-  public function __construct(StorageInterface $target_storage, StorageInterface $source_storage, ConfigManagerInterface $config_manager, FileDownloadController $file_download_controller) {
+  public function __construct(StorageInterface $target_storage, StorageInterface $source_storage, StorageInterface $snapshot_storage, ConfigManagerInterface $config_manager, FileDownloadController $file_download_controller) {
     $this->targetStorage = $target_storage;
     $this->sourceStorage = $source_storage;
+    $this->snapshotStorage = $snapshot_storage;
     $this->configManager = $config_manager;
     $this->fileDownloadController = $file_download_controller;
   }
@@ -110,15 +120,15 @@ public function diff($source_name, $target_name = NULL) {
 
     $build = array();
 
-    $build['#title'] = t('View changes of @config_file', array('@config_file' => $source_name));
+    $build['#title'] = $this->t('View changes of @config_file', array('@config_file' => $source_name));
     // Add the CSS for the inline diff.
     $build['#attached']['css'][] = drupal_get_path('module', 'system') . '/css/system.diff.css';
 
     $build['diff'] = array(
       '#type' => 'table',
       '#header' => array(
-        array('data' => t('Old'), 'colspan' => '2'),
-        array('data' => t('New'), 'colspan' => '2'),
+        array('data' => $this->t('Old'), 'colspan' => '2'),
+        array('data' => $this->t('New'), 'colspan' => '2'),
       ),
       '#rows' => $formatter->format($diff),
     );
@@ -131,9 +141,66 @@ public function diff($source_name, $target_name = NULL) {
         ),
       ),
       '#title' => "Back to 'Synchronize configuration' page.",
-      '#href' => 'admin/config/development/configuration',
+      '#route_name' => 'config.sync',
     );
 
     return $build;
   }
+
+  /**
+   * Show diff of snapshot and active/staging storage.
+   *
+   * @return string
+   *   Table showing a two-way diff between the snapshot and
+   *   active/staged configuration.
+   */
+  public function snapshotDiff($storage = 'active') {
+    $build = array();
+
+    // Add the CSS for the inline diff.
+    $build['#attached']['css'][] = drupal_get_path('module', 'system') . '/css/system.diff.css';
+
+    if ($storage == 'active') {
+      $build['#title'] = $this->t('View changes between snapshot and active configuration.');
+      $used_storage = $this->targetStorage;
+      $compare_button = $this->l($this->t('Compare snapshot with staging storage'), 'config.snapshot_diff', array('storage' => 'staging'), array('attributes' => array('class' => array('button'))));
+    }
+    else {
+      $build['#title'] = $this->t('View changes between snapshot and staging configuration.');
+      $used_storage = $this->sourceStorage;
+      $compare_button = $this->l($this->t('Compare snapshot with active storage'), 'config.snapshot_diff', array('storage' => 'active'), array('attributes' => array('class' => array('button'))));
+    }
+
+    $build['compare']['#markup'] = $compare_button;
+
+    $storage_snapshot_comparer = new StorageComparer($used_storage, $this->snapshotStorage);
+
+    // Collect changes.
+    $storage_snapshot_comparer->createChangelist();
+    $changelist = $storage_snapshot_comparer->getChangelist();
+
+    // Verify that we have an initial snapshot that matches the active/staging
+    // configuration.
+    if ($storage_snapshot_comparer->createChangelist()->hasChanges()) {
+      // Show changes for each configuration object.
+      foreach ($changelist as $op) {
+        foreach ($op as $name) {
+          $diff = $this->configManager->diff($this->snapshotStorage, $used_storage, $name);
+          $formatter = new \DrupalDiffFormatter();
+          $formatter->show_header = FALSE;
+          $build[$name] = array(
+            '#prefix' => '<h3>' . $name . '</h3>',
+            '#type' => 'table',
+            '#header' => array(
+              array('data' => $this->t('Snapshot'), 'colspan' => '2'),
+              array('data' => ($storage == 'active') ? $this->t('Active storage') : $this->t('Staging storage'), 'colspan' => '2'),
+            ),
+            '#rows' => $formatter->format($diff),
+          );
+        }
+      }
+    }
+
+    return $build;
+  }
 }
diff --git a/core/modules/config/lib/Drupal/config/Form/ConfigSync.php b/core/modules/config/lib/Drupal/config/Form/ConfigSync.php
index 19f417f..f70e4f5 100644
--- a/core/modules/config/lib/Drupal/config/Form/ConfigSync.php
+++ b/core/modules/config/lib/Drupal/config/Form/ConfigSync.php
@@ -92,12 +92,21 @@ class ConfigSync extends FormBase {
   protected $themeHandler;
 
   /**
+   * The snapshot configuration object.
+   *
+   * @var \Drupal\Core\Config\StorageInterface
+   */
+  protected $snapshotStorage;
+
+  /**
    * Constructs the object.
    *
    * @param \Drupal\Core\Config\StorageInterface $sourceStorage
    *   The source storage object.
    * @param \Drupal\Core\Config\StorageInterface $targetStorage
    *   The target storage manager.
+   * @param \Drupal\Core\Config\StorageInterface $snapshotStorage
+   *   The snapshot storage object.
    * @param \Drupal\Core\Lock\LockBackendInterface $lock
    *   The lock object.
    * @param \Symfony\Component\EventDispatcher\EventDispatcherInterface $event_dispatcher
@@ -113,9 +122,10 @@ class ConfigSync extends FormBase {
    * @param \Drupal\Core\Extension\ThemeHandlerInterface $theme_handler
    *   The theme handler
    */
-  public function __construct(StorageInterface $sourceStorage, StorageInterface $targetStorage, LockBackendInterface $lock, EventDispatcherInterface $event_dispatcher, ConfigManagerInterface $config_manager, UrlGeneratorInterface $url_generator, TypedConfigManager $typed_config, ModuleHandlerInterface $module_handler, ThemeHandlerInterface $theme_handler) {
+  public function __construct(StorageInterface $sourceStorage, StorageInterface $targetStorage, StorageInterface $snapshotStorage, LockBackendInterface $lock, EventDispatcherInterface $event_dispatcher, ConfigManagerInterface $config_manager, UrlGeneratorInterface $url_generator, TypedConfigManager $typed_config, ModuleHandlerInterface $module_handler, ThemeHandlerInterface $theme_handler) {
     $this->sourceStorage = $sourceStorage;
     $this->targetStorage = $targetStorage;
+    $this->snapshotStorage = $snapshotStorage;
     $this->lock = $lock;
     $this->eventDispatcher = $event_dispatcher;
     $this->configManager = $config_manager;
@@ -132,6 +142,7 @@ public static function create(ContainerInterface $container) {
     return new static(
       $container->get('config.storage.staging'),
       $container->get('config.storage'),
+      $container->get('config.storage.snapshot'),
       $container->get('lock'),
       $container->get('event_dispatcher'),
       $container->get('config.manager'),
@@ -153,6 +164,16 @@ public function getFormId() {
    * {@inheritdoc}
    */
   public function buildForm(array $form, array &$form_state) {
+    $active_snapshot_comparer = new StorageComparer($this->targetStorage, $this->snapshotStorage);
+
+    // Verify that we have an initial snapshot that matches the active
+    // configuration.
+    if (empty($form_state['input']) && $active_snapshot_comparer->createChangelist()->hasChanges()) {
+      drupal_set_message($this->t('Changes have been made to your active configuration, which might be lost on the next import attempt. You can find and review the differences between snapshot and active/staging storage here: <a href="@link">Compare snapshot and active/staging storage</a>.', array(
+        '@link' => $this->url('config.snapshot_diff', array('storage' => 'active')))), 'warning');
+
+    }
+
     $form['actions'] = array('#type' => 'actions');
     $form['actions']['submit'] = array(
       '#type' => 'submit',
diff --git a/core/modules/config/lib/Drupal/config/Tests/ConfigExportImportUITest.php b/core/modules/config/lib/Drupal/config/Tests/ConfigExportImportUITest.php
index 0a01bd1..3d218b2 100644
--- a/core/modules/config/lib/Drupal/config/Tests/ConfigExportImportUITest.php
+++ b/core/modules/config/lib/Drupal/config/Tests/ConfigExportImportUITest.php
@@ -130,4 +130,24 @@ public function testExportImport() {
     $this->drupalGet('node/add');
     $this->assertFieldByName("{$this->field->name}[0][value]", '', 'Widget is displayed');
   }
+
+  /**
+   * Tests that a warning appears when unsynchronized changes exist.
+   */
+  public function testImportWarning() {
+    $new_slogan = $this->randomName(16);
+    \Drupal::config('system.site')
+      ->set('slogan', $new_slogan)
+      ->save();
+
+    $this->drupalGet('admin/config/development/configuration');
+    $this->assertText('Changes have been made to your active configuration, which might be lost on the next import attempt. You can find and review the differences between snapshot and active/staging storage here');
+    $this->clickLink('Compare snapshot and active/staging storage');
+    $this->assertText('View changes between snapshot and active configuration');
+    $this->assertText('system.site');
+    $this->assertText('Active storage');
+    $this->assertText($new_slogan, "New slogan $new_slogan found when viewing changes.");
+    $this->clickLink('Compare snapshot with staging storage');
+    $this->assertText('View changes between snapshot and staging configuration');
+  }
 }