diff --git a/src/app/__tests__/unit/weatherService.test.ts b/src/app/__tests__/unit/weatherService.test.ts
index b692f539..74ea1a60 100644
--- a/src/app/__tests__/unit/weatherService.test.ts
+++ b/src/app/__tests__/unit/weatherService.test.ts
@@ -76,3 +76,88 @@ describe('weatherService negative cache helpers', () => {
     }, now)).toBe(false);
   });
 });
+
+describe('weatherService legacy cache normalization', () => {
+  const legacyDay = (date: string) => ({
+    id: `weather-${date}`,
+    date,
+    coordinates: [47.5, 19] as [number, number],
+    temperature: { min: 10, max: 20, average: 15 },
+    precipitation: { total: 0, probability: null },
+    wind: { speed: null, direction: null },
+    conditions: { description: 'Clear', icon: 'sun', code: 0, cloudCover: null, humidity: null },
+    fetchedAt: '2026-06-01T00:00:00.000Z'
+  });
+
+  it('marks all-future legacy cache entries as historical averages', () => {
+    const normalized = weatherServiceTestUtils.normalizeCachedWeatherSummary({
+      ...emptySummary,
+      startDate: '2027-06-01',
+      endDate: '2027-06-02',
+      dailyWeather: [
+        legacyDay('2027-06-01'),
+        legacyDay('2027-06-02')
+      ] as WeatherSummary['dailyWeather']
+    }, new Date('2026-06-01T12:00:00.000Z'));
+
+    expect(normalized.dailyWeather).toEqual(expect.arrayContaining([
+      expect.objectContaining({
+        date: '2027-06-01',
+        dataSource: 'historical-average',
+        isHistorical: true,
+        isForecast: false
+      }),
+      expect.objectContaining({
+        date: '2027-06-02',
+        dataSource: 'historical-average',
+        isHistorical: true,
+        isForecast: false
+      })
+    ]));
+  });
+
+  it('infers recorded open-meteo data for legacy cache entries that include past days', () => {
+    const normalized = weatherServiceTestUtils.normalizeCachedWeatherSummary({
+      ...emptySummary,
+      startDate: '2026-05-30',
+      endDate: '2026-06-01',
+      dailyWeather: [
+        legacyDay('2026-05-30'),
+        legacyDay('2026-06-01')
+      ] as WeatherSummary['dailyWeather']
+    }, new Date('2026-06-01T12:00:00.000Z'));
+
+    expect(normalized.dailyWeather).toEqual(expect.arrayContaining([
+      expect.objectContaining({
+        date: '2026-05-30',
+        dataSource: 'open-meteo',
+        isHistorical: true,
+        isForecast: false
+      }),
+      expect.objectContaining({
+        date: '2026-06-01',
+        dataSource: 'open-meteo',
+        isHistorical: true,
+        isForecast: false
+      })
+    ]));
+  });
+
+  it('fills missing forecast and historical flags when cached data has a source', () => {
+    const normalized = weatherServiceTestUtils.normalizeCachedWeatherSummary({
+      ...emptySummary,
+      startDate: '2026-06-01',
+      endDate: '2026-06-02',
+      dailyWeather: [
+        { ...legacyDay('2026-06-02'), dataSource: 'open-meteo' }
+      ] as WeatherSummary['dailyWeather']
+    }, new Date('2026-06-01T12:00:00.000Z'));
+
+    expect(normalized.dailyWeather[0]).toEqual(expect.objectContaining({
+      date: '2026-06-02',
+      dataSource: 'open-meteo',
+      isHistorical: false,
+      isForecast: true
+    }));
+  });
+});
diff --git a/src/app/components/Weather/WeatherSummary.tsx b/src/app/components/Weather/WeatherSummary.tsx
index c776a1b5..1f964f1b 100644
--- a/src/app/components/Weather/WeatherSummary.tsx
+++ b/src/app/components/Weather/WeatherSummary.tsx
@@ -26,6 +26,13 @@ export default function WeatherSummary({ summary }: Props) {
     const hasHistAvg = sourceDays.some(d => d.dataSource === 'historical-average');
     const hasForecast = sourceDays.some(d => d.isForecast);
     const hasRecorded = sourceDays.some(d => d.isHistorical && d.dataSource !== 'historical-average');
+    const hasExplicitSourceMetadata = sourceDays.some(d =>
+      d.dataSource === 'historical-average' ||
+      d.dataSource === 'open-meteo' ||
+      d.dataSource === 'cache' ||
+      typeof d.isForecast === 'boolean' ||
+      typeof d.isHistorical === 'boolean'
+    );
 
     if (hasHistAvg && hasForecast && hasRecorded) return 'Recorded + Forecast + Hist. avg.';
     if (hasHistAvg && hasForecast) return 'Forecast + Hist. avg.';
@@ -34,6 +41,9 @@ export default function WeatherSummary({ summary }: Props) {
     if (hasHistAvg) return 'Hist. avg.';
     if (hasForecast) return 'Forecast';
     if (hasRecorded) return 'Recorded';
+    if (!hasExplicitSourceMetadata) {
+      return sourceDays.every(d => d.date > todayISO) ? 'Hist. avg.' : 'Recorded';
+    }
     return '';
   })();
   return (
diff --git a/src/app/components/Weather/__tests__/WeatherSummary.test.tsx b/src/app/components/Weather/__tests__/WeatherSummary.test.tsx
new file mode 100644
index 00000000..4f87e8be
--- /dev/null
+++ b/src/app/components/Weather/__tests__/WeatherSummary.test.tsx
@@ -0,0 +1,54 @@
+/**
+ * @jest-environment jsdom
+ */
+
+import { render, screen } from '@testing-library/react';
+import '@testing-library/jest-dom';
+
+import WeatherSummary from '@/app/components/Weather/WeatherSummary';
+import type { WeatherSummary as WeatherSummaryType } from '@/app/types/weather';
+
+const buildLegacySummary = (dates: string[]): WeatherSummaryType => ({
+  locationId: 'location-1',
+  startDate: dates[0],
+  endDate: dates[dates.length - 1],
+  dailyWeather: dates.map(date => ({
+    id: `weather-${date}`,
+    date,
+    coordinates: [47.5, 19] as [number, number],
+    temperature: { min: 10, max: 20, average: 15 },
+    precipitation: { total: 0, probability: null },
+    wind: { speed: null, direction: null },
+    conditions: { description: 'Clear', icon: 'sun', code: 0, cloudCover: null, humidity: null },
+    fetchedAt: '2026-06-01T00:00:00.000Z',
+  })) as WeatherSummaryType['dailyWeather'],
+  summary: {
+    averageTemp: 15,
+    totalPrecipitation: 0,
+    predominantCondition: 'Clear',
+  },
+});
+
+describe('WeatherSummary', () => {
+  afterEach(() => {
+    jest.useRealTimers();
+  });
+
+  it('labels all-future legacy cached weather as historical averages', () => {
+    jest.useFakeTimers();
+    jest.setSystemTime(new Date('2026-06-01T12:00:00.000Z'));
+
+    render(<WeatherSummary summary={buildLegacySummary(['2027-06-01', '2027-06-02'])} />);
+
+    expect(screen.getByText('Weather · Hist. avg.')).toBeInTheDocument();
+  });
+
+  it('labels past legacy cached weather as recorded instead of rendering a blank source label', () => {
+    jest.useFakeTimers();
+    jest.setSystemTime(new Date('2026-06-01T12:00:00.000Z'));
+
+    render(<WeatherSummary summary={buildLegacySummary(['2026-05-31', '2026-06-01'])} />);
+
+    expect(screen.getByText('Weather · Recorded')).toBeInTheDocument();
+  });
+});
diff --git a/src/app/services/weatherService.ts b/src/app/services/weatherService.ts
index eff6e802..262f98ee 100644
--- a/src/app/services/weatherService.ts
+++ b/src/app/services/weatherService.ts
@@ -282,7 +282,7 @@ async function readCache(key: string): Promise<CacheEntry | null> {
       const exp = parseISO(d.expiresAt);
       return isValid(exp) && isAfter(exp, today);
     });
-    const summary: WeatherSummary = { ...parsed.summary, dailyWeather: filtered };
+    const summary = normalizeCachedWeatherSummary({ ...parsed.summary, dailyWeather: filtered });
     const fetchedAt = typeof parsed.fetchedAt === 'string' ? parsed.fetchedAt : LEGACY_FETCHED_AT;
     const entry: CacheEntry = {
       key: parsed.key || key,
@@ -346,6 +346,48 @@ function computeSources(daily: WeatherData[]): CacheSources {
   return result;
 }
 
+function isKnownWeatherDataSource(value: unknown): value is WeatherData['dataSource'] {
+  return value === 'open-meteo' || value === 'cache' || value === 'historical-average';
+}
+
+function normalizeCachedWeatherSummary(summary: WeatherSummary, today: Date = new Date()): WeatherSummary {
+  const todayISO = toISODate(today);
+  const hasExplicitSourceMetadata = summary.dailyWeather.some(day => {
+    const rawDay = day as Partial<WeatherData>;
+    return (
+      isKnownWeatherDataSource(rawDay.dataSource) ||
+      typeof rawDay.isForecast === 'boolean' ||
+      typeof rawDay.isHistorical === 'boolean'
+    );
+  });
+  const legacyAllFuture = !hasExplicitSourceMetadata && summary.dailyWeather.every(day => day.date > todayISO);
+
+  return {
+    ...summary,
+    dailyWeather: summary.dailyWeather.map(day => {
+      const rawDay = day as Partial<WeatherData>;
+      const dataSource = isKnownWeatherDataSource(rawDay.dataSource)
+        ? rawDay.dataSource
+        : legacyAllFuture
+          ? 'historical-average'
+          : 'open-meteo';
+      const isHistorical = typeof rawDay.isHistorical === 'boolean'
+        ? rawDay.isHistorical
+        : dataSource === 'historical-average' || day.date <= todayISO;
+      const isForecast = typeof rawDay.isForecast === 'boolean'
+        ? rawDay.isForecast
+        : dataSource === 'open-meteo' && !isHistorical;
+
+      return {
+        ...day,
+        dataSource,
+        isHistorical,
+        isForecast,
+      };
+    }),
+  };
+}
+
 function enumerateDateStrings(startISO: string, endISO: string): string[] {
   const start = parseISO(startISO);
   const end = parseISO(endISO);
@@ -844,6 +886,7 @@ export const weatherServiceTestUtils = {
   getRateLimitHeaderDelayMs,
   needsForecastRefresh,
   isFreshEmptyCacheEntry,
+  normalizeCachedWeatherSummary,
   resetRateLimitStateForTests
 };