diff --git a/src/main.ts b/src/main.ts
index 65ea711..01d8808 100644
--- a/src/main.ts
+++ b/src/main.ts
@@ -2465,8 +2465,39 @@ function activateBoard(record: MountedBoard): void {
   // are: one honest station cannot describe a 600 km corridor. California uses
   // the local climatology model; the detailed SF and SoCal boards keep their
   // live observations.
+  //
+  /*
+   * And the merged board uses climatology too, which took a 400 in production
+   * to notice.
+   *
+   * `carriesMetroDetail` is true of it — it carries both metros' districts —
+   * so it asked, at `entry.city.center`, which is the middle of the *state*:
+   * `GET /api/v1/weather?lat=37.30&lng=-119.25` → `400 bad_request, "Nothing
+   * this deployment serves is near 37.3,-119.25"`. The API is right. What it
+   * serves is San Francisco and the Southland, five hundred and sixty
+   * kilometres apart, and the point midway between them is farm country in the
+   * Sierra foothills that no station on this deployment describes.
+   *
+   * The sky already had this problem and solved it by asking per source
+   * (`skyRegions`, above). Weather does not get the same answer, because the
+   * two feeds are not the same shape: aircraft from two regions *merge* — they
+   * are disjoint sets of objects in one sky — and two observations do not. One
+   * board cannot be simultaneously foggy at the Golden Gate and clear over
+   * Riverside, and picking either one and applying it statewide is a worse lie
+   * than the climatology model, which at least varies with latitude and season.
+   *
+   * So this follows the rule the comment above already states rather than
+   * inventing an exception to it: a board that spans more than one served
+   * region takes the model. The metros keep their live observations on their
+   * own boards, and the day the atmosphere is regional rather than per board,
+   * this is the line that changes.
+   */
+  const spansManyWeatherRegions = ONE_CALIFORNIA && id === "california";
   weatherWatch =
-    carriesMetroDetail(entry.city) && access.can.liveEnvironment && access.feeds?.weather
+    carriesMetroDetail(entry.city) &&
+    !spansManyWeatherRegions &&
+    access.can.liveEnvironment &&
+    access.feeds?.weather
       ? tera.watchWeather(entry.city.center, () => {
           updateSun();
           renderChrome();