diff --git a/client/src/services/userPreferences.test.ts b/client/src/services/userPreferences.test.ts
index 9a8b94e..a7d3949 100644
--- a/client/src/services/userPreferences.test.ts
+++ b/client/src/services/userPreferences.test.ts
@@ -2,6 +2,7 @@ import { beforeEach, describe, expect, it } from 'vitest'
 import {
   getColorSchemePreference,
   getOwmApiKey,
+  getOwmApiKeyForActiveUser,
   getThemePreference,
   setColorSchemePreference,
   setOwmApiKey,
@@ -33,6 +34,24 @@ describe('userPreferences', () => {
     expect(getOwmApiKey(USER_ID)).toBe('')
   })
 
+  it('reads namespaced OWM key via active user id', () => {
+    setOwmApiKey(USER_ID, 'namespaced-only')
+    localStorage.setItem('active_userid', USER_ID)
+    localStorage.removeItem('owm_api_key')
+
+    expect(getOwmApiKeyForActiveUser()).toBe('namespaced-only')
+    expect(getOwmApiKey()).toBe('namespaced-only')
+  })
+
+  it('does not read namespaced OWM key without active user id', () => {
+    setOwmApiKey(USER_ID, 'namespaced-only')
+    localStorage.removeItem('active_userid')
+    localStorage.removeItem('owm_api_key')
+
+    expect(getOwmApiKeyForActiveUser()).toBe('')
+    expect(getOwmApiKey()).toBe('')
+  })
+
   it('writes theme preferences to namespaced keys', () => {
     setThemePreference(USER_ID, 'ocean')
     setColorSchemePreference(USER_ID, 'light')
diff --git a/client/src/services/userPreferences.ts b/client/src/services/userPreferences.ts
index b349f10..fb6d7f3 100644
--- a/client/src/services/userPreferences.ts
+++ b/client/src/services/userPreferences.ts
@@ -35,7 +35,7 @@ function migrateLegacyPrefs(userId: string): void {
 }
 
 function resolveUserId(userId?: string | null): string | null {
-  const id = userId ?? getActiveUserId()
+  const id = (userId?.trim() || getActiveUserId()?.trim()) || null
   if (!id) return null
   migrateLegacyPrefs(id)
   return id
@@ -75,6 +75,11 @@ export function getOwmApiKey(userId?: string | null): string {
   return localStorage.getItem(LEGACY_OWM_KEY) ?? ''
 }
 
+/** OWM key for the signed-in user (`active_userid`). Prefer this over a bare `getOwmApiKey()` call. */
+export function getOwmApiKeyForActiveUser(): string {
+  return getOwmApiKey(getActiveUserId())
+}
+
 export function setOwmApiKey(userId: string, value: string): void {
   migrateLegacyPrefs(userId)
   const trimmed = value.trim()
diff --git a/client/src/services/weather.ts b/client/src/services/weather.ts
index 2dc4359..5b18016 100644
--- a/client/src/services/weather.ts
+++ b/client/src/services/weather.ts
@@ -1,5 +1,5 @@
 import { apiFetch } from './api.js'
-import { getOwmApiKey } from './userPreferences.js'
+import { getOwmApiKeyForActiveUser } from './userPreferences.js'
 
 export class WeatherApiError extends Error {
   code: 'NO_KEY' | 'REQUEST_FAILED'
@@ -27,7 +27,7 @@ export async function fetchOpenWeatherCurrent(params: {
     throw new WeatherApiError('lat/lon or location query required')
   }
 
-  const userKey = getOwmApiKey().trim()
+  const userKey = getOwmApiKeyForActiveUser().trim()
   const headers: Record<string, string> = {}
   if (userKey) headers['X-OWM-Api-Key'] = userKey