src/lib/components/charts/ChartToolbar.svelte

@@ -2,10 +2,12 @@
   ChartToolbar.svelte — Chart action bar with download and display controls
 
   Provides a toolbar row with:
-  - Download as PNG button
-  - Download as SVG button
-  - Download all charts button (when multiple charts exist)
-  - Slot for additional custom controls (e.g. legend toggle, average toggle)
+  - Download full meteogram as PNG button
+  - Download full meteogram as SVG button
+  - Slot for additional custom controls (e.g. legend toggle)
+
+  When multiple charts are provided, they are stitched into a single
+  combined image on download.
 
   Usage:
     <ChartToolbar
@@ -18,10 +20,11 @@
     </ChartToolbar>
 -->
 <script lang="ts">
+	import { downloadMeteogram } from '$lib/utils/echarts/download';
+
+	import type { ExportFormat } from '$lib/utils/echarts/download';
 	import type * as echarts from 'echarts';
 	import type { Snippet } from 'svelte';
-	import { downloadChart, downloadAllCharts } from '$lib/utils/echarts/download';
-	import type { ExportFormat } from '$lib/utils/echarts/download';
 
 	// ─── Props ──────────────────────────────────────────────────────────────────
 
@@ -32,8 +35,6 @@
 		fileName?: string;
 		/** Pixel ratio for PNG exports (default: 2) */
 		pixelRatio?: number;
-		/** Whether to show the "Download All" button when multiple charts exist */
-		showDownloadAll?: boolean;
 		/** Optional CSS class for the outer container */
 		class?: string;
 		/** Slot for additional controls (switches, checkboxes, etc.) */
@@ -44,19 +45,17 @@
 		charts = [],
 		fileName = 'open-meteo-chart',
 		pixelRatio = 2,
-		showDownloadAll = true,
 		class: className = '',
 		controls
 	}: Props = $props();
 
 	// ─── State ──────────────────────────────────────────────────────────────────
 
-	let downloadingFormat: ExportFormat | 'all' | null = $state(null);
+	let downloadingFormat: ExportFormat | null = $state(null);
 
 	// ─── Computed ───────────────────────────────────────────────────────────────
 
 	let hasCharts = $derived(charts.length > 0);
-	let hasMultipleCharts = $derived(charts.length > 1);
 
 	// ─── Handlers ───────────────────────────────────────────────────────────────
 
@@ -66,30 +65,8 @@
 		downloadingFormat = format;
 
 		try {
-			// Small delay to let the UI update to show the loading state
 			await new Promise((resolve) => setTimeout(resolve, 50));
-
-			if (charts.length === 1) {
-				downloadChart(charts[0], { fileName, format, pixelRatio });
-			} else {
-				downloadAllCharts(charts, { fileName, format, pixelRatio });
-			}
-		} finally {
-			// Reset state after a brief moment
-			setTimeout(() => {
-				downloadingFormat = null;
-			}, 500);
-		}
-	}
-
-	async function handleDownloadAll(format: ExportFormat = 'png'): Promise<void> {
-		if (!hasCharts || downloadingFormat) return;
-
-		downloadingFormat = 'all';
-
-		try {
-			await new Promise((resolve) => setTimeout(resolve, 50));
-			downloadAllCharts(charts, { fileName, format, pixelRatio });
+			downloadMeteogram(charts, { fileName, format, pixelRatio });
 		} finally {
 			setTimeout(() => {
 				downloadingFormat = null;
@@ -98,7 +75,9 @@
 	}
 </script>
 
-<div class="chart-toolbar flex flex-col items-center gap-4 md:flex-row md:justify-between {className}">
+<div
+	class="chart-toolbar flex flex-col items-center gap-4 md:flex-row md:justify-between {className}"
+>
 	<!-- Left side: Custom controls slot -->
 	<div class="flex flex-wrap items-center gap-4 md:gap-6">
 		{#if controls}
@@ -114,7 +93,7 @@
 			class="toolbar-btn"
 			disabled={!hasCharts || downloadingFormat !== null}
 			onclick={() => handleDownload('png')}
-			title="Download chart as PNG image"
+			title="Download meteogram as PNG image"
 		>
 			{#if downloadingFormat === 'png'}
 				<svg
@@ -154,7 +133,7 @@
 			class="toolbar-btn"
 			disabled={!hasCharts || downloadingFormat !== null}
 			onclick={() => handleDownload('svg')}
-			title="Download chart as SVG vector image"
+			title="Download meteogram as SVG vector image"
 		>
 			{#if downloadingFormat === 'svg'}
 				<svg
@@ -187,49 +166,6 @@
 			{/if}
 			<span>SVG</span>
 		</button>
-
-		<!-- Download All (only shown when there are multiple charts) -->
-		{#if showDownloadAll && hasMultipleCharts}
-			<div class="mx-1 hidden h-5 w-px bg-border md:block" aria-hidden="true"></div>
-			<button
-				type="button"
-				class="toolbar-btn"
-				disabled={!hasCharts || downloadingFormat !== null}
-				onclick={() => handleDownloadAll('png')}
-				title="Download all charts as separate PNG images"
-			>
-				{#if downloadingFormat === 'all'}
-					<svg
-						class="h-4 w-4 animate-spin"
-						xmlns="http://www.w3.org/2000/svg"
-						viewBox="0 0 24 24"
-						fill="none"
-						stroke="currentColor"
-						stroke-width="2"
-						aria-hidden="true"
-					>
-						<path d="M21 12a9 9 0 1 1-6.219-8.56" />
-					</svg>
-				{:else}
-					<svg
-						class="h-4 w-4"
-						xmlns="http://www.w3.org/2000/svg"
-						viewBox="0 0 24 24"
-						fill="none"
-						stroke="currentColor"
-						stroke-width="2"
-						stroke-linecap="round"
-						stroke-linejoin="round"
-						aria-hidden="true"
-					>
-						<path d="M21 15v4a2 2 0 0 1-2 2H5a2 2 0 0 1-2-2v-4" />
-						<polyline points="7 10 12 15 17 10" />
-						<line x1="12" y1="15" x2="12" y2="3" />
-					</svg>
-				{/if}
-				<span>All ({charts.length})</span>
-			</button>
-		{/if}
 	</div>
 </div>
 

src/lib/utils/echarts/download.ts

@@ -2,10 +2,9 @@
  * ECharts Download Utilities
  *
  * Provides programmatic chart export functionality for downloading
- * charts as PNG or SVG images. These utilities wrap ECharts' built-in
- * export capabilities with a convenient API and sensible defaults.
+ * charts as PNG or SVG images. Supports stitching multiple chart
+ * instances into a single combined meteogram image.
  */
-
 import type * as echarts from 'echarts';
 
 // ─── Types ───────────────────────────────────────────────────────────────────
@@ -49,7 +48,6 @@ export function downloadChart(chart: echarts.ECharts, options: DownloadOptions =
 
 	const resolvedBg = backgroundColor ?? (format === 'svg' ? 'none' : '#ffffff');
 
-	// Use ECharts' getDataURL for PNG, getConnectedDataURL for SVG
 	const dataUrl = chart.getDataURL({
 		type: format === 'svg' ? 'svg' : 'png',
 		pixelRatio: format === 'png' ? pixelRatio : 1,
@@ -61,25 +59,47 @@ export function downloadChart(chart: echarts.ECharts, options: DownloadOptions =
 }
 
 /**
- * Downloads all provided ECharts instances as separate image files.
- * Each file is named with an incrementing suffix (e.g. chart-1.png, chart-2.png).
+ * Downloads multiple ECharts instances stitched into a single combined
+ * meteogram image. Charts are stacked vertically in the order provided.
  *
- * @param charts  - Array of ECharts instances to export
- * @param options - Download configuration options (fileName is used as prefix)
+ * For a single chart, delegates to `downloadChart`.
+ *
+ * @param charts  - Array of ECharts instances to combine
+ * @param options - Download configuration options
  */
-export function downloadAllCharts(
-	charts: echarts.ECharts[],
-	options: DownloadOptions = {}
-): void {
-	const { fileName = DEFAULT_FILE_NAME, ...rest } = options;
+export function downloadMeteogram(charts: echarts.ECharts[], options: DownloadOptions = {}): void {
+	const validCharts = charts.filter((c) => c && !c.isDisposed());
+	if (validCharts.length === 0) return;
 
-	charts.forEach((chart, index) => {
-		if (chart && !chart.isDisposed()) {
-			downloadChart(chart, {
-				...rest,
-				fileName: charts.length === 1 ? fileName : `${fileName}-${index + 1}`
-			});
-		}
+	if (validCharts.length === 1) {
+		downloadChart(validCharts[0], options);
+		return;
+	}
+
+	const {
+		fileName = DEFAULT_FILE_NAME,
+		format = 'png',
+		pixelRatio = DEFAULT_PIXEL_RATIO,
+		backgroundColor,
+		excludeComponents = ['toolbox']
+	} = options;
+
+	const resolvedBg = backgroundColor ?? (format === 'svg' ? 'none' : '#ffffff');
+
+	if (format === 'svg') {
+		downloadMeteogramSvg(validCharts, {
+			fileName,
+			backgroundColor: resolvedBg,
+			excludeComponents
+		});
+		return;
+	}
+
+	downloadMeteogramPng(validCharts, {
+		fileName,
+		pixelRatio,
+		backgroundColor: resolvedBg,
+		excludeComponents
 	});
 }
 
@@ -91,10 +111,7 @@ export function downloadAllCharts(
  * @param options - Export configuration options
  * @returns A base64-encoded data URL string
  */
-export function getChartDataUrl(
-	chart: echarts.ECharts,
-	options: DownloadOptions = {}
-): string {
+export function getChartDataUrl(chart: echarts.ECharts, options: DownloadOptions = {}): string {
 	const {
 		format = 'png',
 		pixelRatio = DEFAULT_PIXEL_RATIO,
@@ -112,22 +129,192 @@ export function getChartDataUrl(
 	});
 }
 
+// ─── Internal: PNG Meteogram ─────────────────────────────────────────────────
+
+interface PngStitchOptions {
+	fileName: string;
+	pixelRatio: number;
+	backgroundColor: string;
+	excludeComponents: string[];
+}
+
+/**
+ * Stitches multiple charts into a single PNG by rendering each chart's
+ * data URL onto an off-screen canvas, stacked vertically.
+ */
+function downloadMeteogramPng(charts: echarts.ECharts[], opts: PngStitchOptions): void {
+	const { fileName, pixelRatio, backgroundColor, excludeComponents } = opts;
+
+	const dataUrls = charts.map((chart) =>
+		chart.getDataURL({
+			type: 'png',
+			pixelRatio,
+			backgroundColor: 'transparent',
+			excludeComponents
+		})
+	);
+
+	const images: HTMLImageElement[] = [];
+	let loadedCount = 0;
+
+	dataUrls.forEach((url, index) => {
+		const img = new Image();
+		images[index] = img;
+
+		img.onload = () => {
+			loadedCount++;
+			if (loadedCount === dataUrls.length) {
+				composePngAndDownload(images, fileName, backgroundColor);
+			}
+		};
+
+		img.onerror = () => {
+			loadedCount++;
+			if (loadedCount === dataUrls.length) {
+				composePngAndDownload(images, fileName, backgroundColor);
+			}
+		};
+
+		img.src = url;
+	});
+}
+
+function composePngAndDownload(
+	images: HTMLImageElement[],
+	fileName: string,
+	backgroundColor: string
+): void {
+	const validImages = images.filter((img) => img.naturalWidth > 0);
+	if (validImages.length === 0) return;
+
+	const maxWidth = Math.max(...validImages.map((img) => img.naturalWidth));
+	const totalHeight = validImages.reduce((sum, img) => sum + img.naturalHeight, 0);
+
+	const canvas = document.createElement('canvas');
+	canvas.width = maxWidth;
+	canvas.height = totalHeight;
+
+	const ctx = canvas.getContext('2d');
+	if (!ctx) return;
+
+	if (backgroundColor && backgroundColor !== 'transparent' && backgroundColor !== 'none') {
+		ctx.fillStyle = backgroundColor;
+		ctx.fillRect(0, 0, maxWidth, totalHeight);
+	}
+
+	let y = 0;
+	for (const img of validImages) {
+		ctx.drawImage(img, 0, y);
+		y += img.naturalHeight;
+	}
+
+	const dataUrl = canvas.toDataURL('image/png');
+	triggerDownload(dataUrl, `${fileName}.png`);
+}
+
+// ─── Internal: SVG Meteogram ─────────────────────────────────────────────────
+
+interface SvgStitchOptions {
+	fileName: string;
+	backgroundColor: string;
+	excludeComponents: string[];
+}
+
+/**
+ * Stitches multiple charts into a single SVG by extracting each chart's
+ * SVG markup and embedding them as nested groups with vertical offsets.
+ */
+function downloadMeteogramSvg(charts: echarts.ECharts[], opts: SvgStitchOptions): void {
+	const { fileName, backgroundColor, excludeComponents } = opts;
+
+	const svgStrings = charts.map((chart) =>
+		chart.getDataURL({
+			type: 'svg',
+			pixelRatio: 1,
+			backgroundColor: 'transparent',
+			excludeComponents
+		})
+	);
+
+	const parser = new DOMParser();
+	const fragments: { svg: SVGSVGElement; width: number; height: number }[] = [];
+
+	for (const svgDataUrl of svgStrings) {
+		const svgContent = decodeSvgDataUrl(svgDataUrl);
+		if (!svgContent) continue;
+
+		const doc = parser.parseFromString(svgContent, 'image/svg+xml');
+		const svg = doc.querySelector('svg');
+		if (!svg) continue;
+
+		const width = parseFloat(svg.getAttribute('width') || '0');
+		const height = parseFloat(svg.getAttribute('height') || '0');
+
+		if (width > 0 && height > 0) {
+			fragments.push({ svg, width, height });
+		}
+	}
+
+	if (fragments.length === 0) return;
+
+	const maxWidth = Math.max(...fragments.map((f) => f.width));
+	const totalHeight = fragments.reduce((sum, f) => sum + f.height, 0);
+
+	let combinedSvg = `<svg xmlns="http://www.w3.org/2000/svg" width="${maxWidth}" height="${totalHeight}" viewBox="0 0 ${maxWidth} ${totalHeight}">`;
+
+	if (backgroundColor && backgroundColor !== 'none' && backgroundColor !== 'transparent') {
+		combinedSvg += `<rect width="${maxWidth}" height="${totalHeight}" fill="${backgroundColor}"/>`;
+	}
+
+	let yOffset = 0;
+	for (const fragment of fragments) {
+		combinedSvg += `<g transform="translate(0,${yOffset})">`;
+		combinedSvg += fragment.svg.innerHTML;
+		combinedSvg += `</g>`;
+		yOffset += fragment.height;
+	}
+
+	combinedSvg += `</svg>`;
+
+	const blob = new Blob([combinedSvg], { type: 'image/svg+xml;charset=utf-8' });
+	const url = URL.createObjectURL(blob);
+	triggerDownload(url, `${fileName}.svg`);
+
+	setTimeout(() => URL.revokeObjectURL(url), 10000);
+}
+
+function decodeSvgDataUrl(dataUrl: string): string | null {
+	try {
+		if (dataUrl.startsWith('data:image/svg+xml;charset=UTF-8,')) {
+			return decodeURIComponent(dataUrl.slice('data:image/svg+xml;charset=UTF-8,'.length));
+		}
+		if (dataUrl.startsWith('data:image/svg+xml;base64,')) {
+			return atob(dataUrl.slice('data:image/svg+xml;base64,'.length));
+		}
+		if (dataUrl.startsWith('data:image/svg+xml,')) {
+			return decodeURIComponent(dataUrl.slice('data:image/svg+xml,'.length));
+		}
+		return null;
+	} catch {
+		return null;
+	}
+}
+
 // ─── Internal Helpers ────────────────────────────────────────────────────────
 
 /**
- * Triggers a browser file download from a data URL.
+ * Triggers a browser file download from a data URL or object URL.
  * Creates a temporary anchor element, clicks it, and removes it.
  */
-function triggerDownload(dataUrl: string, fileName: string): void {
+function triggerDownload(url: string, fileName: string): void {
 	const link = document.createElement('a');
-	link.href = dataUrl;
+	link.href = url;
 	link.download = fileName;
 	link.style.display = 'none';
 
 	document.body.appendChild(link);
 	link.click();
 
-	// Clean up the DOM after a brief delay to ensure the download starts
 	requestAnimationFrame(() => {
 		document.body.removeChild(link);
 	});

src/lib/utils/echarts/index.ts

@@ -68,5 +68,5 @@ export type {
 } from './series';
 
 // Download: export charts as PNG or SVG
-export { downloadChart, downloadAllCharts, getChartDataUrl } from './download';
+export { downloadChart, downloadMeteogram, getChartDataUrl } from './download';
 export type { ExportFormat, DownloadOptions } from './download';

src/routes/weather/14-day/+page.svelte

@@ -27,7 +27,11 @@
 
 	import type * as echarts from 'echarts';
 
-	// ─── State ──────────────────────────────────────────────────────────────────
+	// ─── Display State (does NOT trigger data re-fetch) ─────────────────────────
+
+	let showLegend = $state(false);
+
+	// ─── Data Fetch State ───────────────────────────────────────────────────────
 
 	let chartComponents: EChart[] = $state([]);
 	let chartInstances: echarts.ECharts[] = $state([]);
@@ -35,12 +39,8 @@
 	let mounted = $state(false);
 	let loading = $state(true);
 
-	let showLegend = $state(false);
-	let averageOnly = $state(false);
-
 	const location = get(storedLocation);
 
-	// Local component state for chart configuration
 	let params = $state({
 		latitude: [52.52],
 		longitude: [13.41],
@@ -49,6 +49,18 @@
 		models: ['gfs_seamless']
 	});
 
+	// ─── Cached API Response ────────────────────────────────────────────────────
+
+	interface FetchedData {
+		hourly: Record<string, unknown>;
+		hourly_units: Record<string, string>;
+		utc_offset_seconds: number;
+		markAreas: Array<[{ xAxis: number; itemStyle: { color: string } }, { xAxis: number }]>;
+		timestamps: number[];
+	}
+
+	let fetchedData: FetchedData | null = $state(null);
+
 	// ─── Lifecycle ──────────────────────────────────────────────────────────────
 
 	onMount(() => {
@@ -67,32 +79,31 @@
 		chartInstances = [...chartInstances, chart];
 	}
 
-	// ─── Data Loading & Chart Building ──────────────────────────────────────────
+	// ─── Data Fetching (only when params.hourly or params.models change) ───────
 
 	$effect(() => {
-		const loadData = async () => {
-			if (!mounted) return;
+		const hourlyVars = params.hourly;
+		const modelList = params.models;
 
+		if (!mounted || !hourlyVars?.length || !modelList?.length) return;
+
+		const loadData = async () => {
 			loading = true;
 			chartInstances = [];
 			chartComponents = [];
 
-			// Fetch sunrise/sunset from the standard forecast API
-			const dataDaily = await fetch(
-				`https://api.open-meteo.com/v1/forecast?latitude=${location.latitude}&longitude=${location.longitude}&timeformat=unixtime&daily=sunset,sunrise&forecast_days=14`
-			);
-			const wd = await dataDaily.json();
+			const [dataDaily, dataReq] = await Promise.all([
+				fetch(
+					`https://api.open-meteo.com/v1/forecast?latitude=${location.latitude}&longitude=${location.longitude}&timeformat=unixtime&daily=sunset,sunrise&forecast_days=14`
+				),
+				fetch(
+					`https://ensemble-api.open-meteo.com/v1/ensemble?latitude=${location.latitude}&longitude=${location.longitude}&hourly=${hourlyVars.join(',')}&models=${modelList.join(',')}&timeformat=unixtime&forecast_days=14`
+				)
+			]);
 
-			// Fetch ensemble data
-			const dataReq = await fetch(
-				`https://ensemble-api.open-meteo.com/v1/ensemble?latitude=${location.latitude}&longitude=${location.longitude}&hourly=${params.hourly?.join(',') || ''}&models=${params.models?.join(',') || ''}&timeformat=unixtime&forecast_days=14`
-			);
-			const data = await dataReq.json();
+			const [wd, data] = await Promise.all([dataDaily.json(), dataReq.json()]);
 
-			// ─── Compute daylight bands ─────────────────────────────────────
-
-			let markAreas: Array<[{ xAxis: number; itemStyle: { color: string } }, { xAxis: number }]> =
-				[];
+			let markAreas: FetchedData['markAreas'] = [];
 
 			if ('daily' in wd && 'sunrise' in wd.daily && 'sunset' in wd.daily) {
 				markAreas = buildDaylightMarkAreas(
@@ -102,90 +113,99 @@
 				);
 			}
 
-			// ─── Build chart options for each variable ──────────────────────
-
-			const colors = getThemeColors();
 			const timestamps = convertTimestamps(data.hourly.time, data.utc_offset_seconds);
-			const variableCount = params.hourly?.length || 0;
-			const newOptions: Array<Record<string, unknown>> = [];
 
-			for (let vi = 0; vi < variableCount; vi++) {
-				const variable = params.hourly![vi];
-				const unit = findUnit(data.hourly_units, data.hourly, variable);
-				const timeLength = data.hourly.time.length;
+			fetchedData = {
+				hourly: data.hourly,
+				hourly_units: data.hourly_units,
+				utc_offset_seconds: data.utc_offset_seconds,
+				markAreas,
+				timestamps
+			};
 
-				// ─── Calculate average and spread ───────────────────────────
-
-				const { average } = calculateAverage(data.hourly, variable, timeLength);
-				const { minValues, maxValues } = calculateSpread(data.hourly, variable, timeLength);
-
-				// ─── Build series ───────────────────────────────────────────
-
-				const series: Array<Record<string, unknown>> = [];
-
-				// Ensemble spread (min/max area)
-				const spreadData: Array<[number, number, number]> = minValues.map(
-					(min, index) =>
-						[timestamps[index], min ?? 0, maxValues[index] ?? 0] as [number, number, number]
-				);
-
-				series.push(...buildSpreadSeries({ variable, spreadData }));
-
-				// Average line
-				const averageData = average.map((val, idx) => [timestamps[idx], val] as [number, number]);
-				series.push(buildAverageSeries({ variable, data: averageData, unit }));
-
-				// Current time marker
-				series.push(buildCurrentTimeSeries({ utcOffsetSeconds: data.utc_offset_seconds }));
-
-				// Daylight bands
-				const daylightSeries = buildDaylightSeries({ markAreas });
-				if (daylightSeries) {
-					series.push(daylightSeries);
-				}
-
-				// ─── Compose final option ───────────────────────────────────
-
-				const isFirst = vi === 0;
-				const isLast = vi === variableCount - 1;
-
-				const option = composeChartOption({
-					title: isFirst
-						? {
-								text: 'Model Spread',
-								subtext: `Compare ${params.hourly?.join(', ') || ''} in models: ${params.models?.join(', ') || ''}`
-							}
-						: null,
-					tooltip: { unit },
-					legend: {
-						show: showLegend,
-						data: [variable + '_average']
-					},
-					grid: {
-						hasTitle: isFirst,
-						hasSubtitle: isFirst,
-						showLegend
-					},
-					yAxis: { unit },
-					series,
-					toolbox: {
-						saveAsImage: true,
-						fileName: `14-day-forecast-${variable}`,
-						format: 'png'
-					},
-					showCredit: isLast,
-					colors
-				});
-
-				newOptions.push(option);
-			}
-
-			chartOptions = newOptions;
 			loading = false;
 		};
 
 		loadData();
 	});
+
+	// ─── Chart Option Building (runs when fetchedData OR display toggles change) ─
+
+	$effect(() => {
+		if (!fetchedData) return;
+
+		const {
+			hourly: hourlyData,
+			hourly_units,
+			utc_offset_seconds,
+			markAreas,
+			timestamps
+		} = fetchedData;
+		const _showLegend = showLegend;
+
+		const colors = getThemeColors();
+		const variableCount = params.hourly?.length || 0;
+		const timeLength = (hourlyData.time as number[]).length;
+		const newOptions: Array<Record<string, unknown>> = [];
+
+		for (let vi = 0; vi < variableCount; vi++) {
+			const variable = params.hourly![vi];
+			const unit = findUnit(hourly_units, hourlyData, variable);
+
+			const { average } = calculateAverage(hourlyData, variable, timeLength);
+			const { minValues, maxValues } = calculateSpread(hourlyData, variable, timeLength);
+
+			const series: Array<Record<string, unknown>> = [];
+
+			const spreadData: Array<[number, number, number]> = minValues.map(
+				(min, index) =>
+					[timestamps[index], min ?? 0, maxValues[index] ?? 0] as [number, number, number]
+			);
+
+			series.push(...buildSpreadSeries({ variable, spreadData }));
+
+			const averageData = average.map((val, idx) => [timestamps[idx], val] as [number, number]);
+			series.push(buildAverageSeries({ variable, data: averageData, unit }));
+
+			series.push(buildCurrentTimeSeries({ utcOffsetSeconds: utc_offset_seconds }));
+
+			const daylightSeries = buildDaylightSeries({ markAreas });
+			if (daylightSeries) {
+				series.push(daylightSeries);
+			}
+
+			const isFirst = vi === 0;
+			const isLast = vi === variableCount - 1;
+
+			const option = composeChartOption({
+				title: isFirst
+					? {
+							text: 'Model Spread',
+							subtext: `Compare ${params.hourly?.join(', ') || ''} in models: ${params.models?.join(', ') || ''}`
+						}
+					: null,
+				tooltip: { unit },
+				legend: {
+					show: _showLegend,
+					data: [variable + '_average']
+				},
+				grid: {
+					hasTitle: isFirst,
+					hasSubtitle: isFirst,
+					showLegend: _showLegend
+				},
+				yAxis: { unit },
+				series,
+				toolbox: false,
+				showCredit: isLast,
+				colors
+			});
+
+			newOptions.push(option);
+		}
+
+		chartOptions = newOptions;
+	});
 </script>
 
 <!-- ─── Chart Area ─────────────────────────────────────────────────────────── -->
@@ -211,27 +231,9 @@
 	<ChartToolbar charts={chartInstances} fileName="14-day-forecast">
 		{#snippet controls()}
 			<div class="flex gap-2">
-				<Switch
-					id="show_legend"
-					name="Show legend"
-					bind:checked={showLegend}
-					onCheckedChange={() => {
-						params.hourly = params.hourly;
-					}}
-				/>
+				<Switch id="show_legend" name="Show legend" bind:checked={showLegend} />
 				<Label for="show_legend" class="mb-0.5 cursor-pointer text-lg">Show legend</Label>
 			</div>
-			<div class="flex gap-2">
-				<Switch
-					id="average_only"
-					name="Average only"
-					bind:checked={averageOnly}
-					onCheckedChange={() => {
-						params.hourly = params.hourly;
-					}}
-				/>
-				<Label for="average_only" class="mb-0.5 cursor-pointer text-lg">Average only</Label>
-			</div>
 		{/snippet}
 	</ChartToolbar>
 </div>

src/routes/weather/compare/+page.svelte

@@ -29,10 +29,13 @@
 
 	import type * as echarts from 'echarts';
 
-	// Wrap models in array to match template expectation of nested arrays like hourly
 	const models = [modelsFlat];
 
-	// ─── State ──────────────────────────────────────────────────────────────────
+	// ─── Display State (does NOT trigger data re-fetch) ─────────────────────────
+
+	let showLegend = $state(false);
+
+	// ─── Data Fetch State ───────────────────────────────────────────────────────
 
 	let chartComponents: EChart[] = $state([]);
 	let chartInstances: echarts.ECharts[] = $state([]);
@@ -40,9 +43,6 @@
 	let mounted = $state(false);
 	let loading = $state(true);
 
-	let showLegend = $state(false);
-	let averageOnly = $state(false);
-
 	const location = get(storedLocation);
 
 	let params = $state({
@@ -59,6 +59,18 @@
 		]
 	});
 
+	// ─── Cached API Response ────────────────────────────────────────────────────
+
+	interface FetchedData {
+		hourly: Record<string, unknown>;
+		hourly_units: Record<string, string>;
+		utc_offset_seconds: number;
+		markAreas: Array<[{ xAxis: number; itemStyle: { color: string } }, { xAxis: number }]>;
+		timestamps: number[];
+	}
+
+	let fetchedData: FetchedData | null = $state(null);
+
 	// ─── Lifecycle ──────────────────────────────────────────────────────────────
 
 	onMount(() => {
@@ -77,28 +89,27 @@
 		chartInstances = [...chartInstances, chart];
 	}
 
-	// ─── Data Loading & Chart Building ──────────────────────────────────────────
+	// ─── Data Fetching (only when params.hourly or params.models change) ───────
 
 	$effect(() => {
-		const loadData = async () => {
-			if (!mounted) return;
+		const hourlyVars = params.hourly;
+		const modelList = params.models;
 
+		if (!mounted || !hourlyVars?.length || !modelList?.length) return;
+
+		const loadData = async () => {
 			loading = true;
 			chartInstances = [];
 			chartComponents = [];
 
 			const dataReq = await fetch(
-				`https://api.open-meteo.com/v1/forecast?latitude=${location.latitude}&longitude=${location.longitude}&hourly=${params.hourly?.join(',') || ''}&models=${params.models?.join(',') || ''}&timeformat=unixtime&daily=sunset,sunrise`
+				`https://api.open-meteo.com/v1/forecast?latitude=${location.latitude}&longitude=${location.longitude}&hourly=${hourlyVars.join(',')}&models=${modelList.join(',')}&timeformat=unixtime&daily=sunset,sunrise`
 			);
 			const data = await dataReq.json();
 
-			// ─── Compute daylight bands ─────────────────────────────────────
-
-			let markAreas: Array<[{ xAxis: number; itemStyle: { color: string } }, { xAxis: number }]> =
-				[];
+			let markAreas: FetchedData['markAreas'] = [];
 
 			if ('daily' in data) {
-				// Find the first model-suffixed key for sunrise/sunset
 				let dailyFirstModelKey: string[] | string = Object.keys(data.daily)[1].split('_');
 				dailyFirstModelKey.shift();
 				dailyFirstModelKey = dailyFirstModelKey.join('_');
@@ -115,96 +126,104 @@
 				}
 			}
 
-			// ─── Build chart options for each variable ──────────────────────
-
-			const colors = getThemeColors();
 			const timestamps = convertTimestamps(data.hourly.time, data.utc_offset_seconds);
-			const variableCount = params.hourly?.length || 0;
-			const newOptions: Array<Record<string, unknown>> = [];
 
-			for (let vi = 0; vi < variableCount; vi++) {
-				const variable = params.hourly![vi];
-				const unit = findUnit(data.hourly_units, data.hourly, variable);
-				const timeLength = data.hourly.time.length;
+			fetchedData = {
+				hourly: data.hourly,
+				hourly_units: data.hourly_units,
+				utc_offset_seconds: data.utc_offset_seconds,
+				markAreas,
+				timestamps
+			};
 
-				// ─── Build individual model series ───────────────────────────
-
-				const series: Array<Record<string, unknown>> = [];
-
-				if (!averageOnly) {
-					for (const [model, values] of Object.entries(data.hourly)) {
-						if (model === 'time') continue;
-						if (!model.startsWith(variable)) continue;
-
-						const seriesData = (values as (number | null)[]).map(
-							(val, idx) => [timestamps[idx], val] as [number, number | null]
-						);
-
-						series.push(
-							buildModelSeries({
-								name: model,
-								data: seriesData,
-								unit
-							})
-						);
-					}
-				}
-
-				// ─── Average series ─────────────────────────────────────────
-
-				const { average } = calculateAverage(data.hourly, variable, timeLength);
-				const averageData = average.map((val, idx) => [timestamps[idx], val] as [number, number]);
-
-				series.push(buildAverageSeries({ variable, data: averageData, unit }));
-
-				// ─── Annotation series ───────────────────────────────────────
-
-				series.push(buildCurrentTimeSeries({ utcOffsetSeconds: data.utc_offset_seconds }));
-
-				const daylightSeries = buildDaylightSeries({ markAreas });
-				if (daylightSeries) {
-					series.push(daylightSeries);
-				}
-
-				// ─── Compose final option ───────────────────────────────────
-
-				const isFirst = vi === 0;
-				const isLast = vi === variableCount - 1;
-
-				const option = composeChartOption({
-					title: isFirst
-						? {
-								text: 'Model Compare',
-								subtext: `Compare ${params.hourly?.join(', ') || ''} in models: ${params.models?.join(', ') || ''}`
-							}
-						: null,
-					tooltip: { unit },
-					legend: { show: showLegend },
-					grid: {
-						hasTitle: isFirst,
-						hasSubtitle: isFirst,
-						showLegend
-					},
-					yAxis: { unit },
-					series,
-					toolbox: {
-						saveAsImage: true,
-						fileName: `model-compare-${variable}`,
-						format: 'png'
-					},
-					showCredit: isLast,
-					colors
-				});
-
-				newOptions.push(option);
-			}
-
-			chartOptions = newOptions;
 			loading = false;
 		};
 
 		loadData();
 	});
+
+	// ─── Chart Option Building (runs when fetchedData OR display toggles change) ─
+
+	$effect(() => {
+		if (!fetchedData) return;
+
+		const {
+			hourly: hourlyData,
+			hourly_units,
+			utc_offset_seconds,
+			markAreas,
+			timestamps
+		} = fetchedData;
+		const _showLegend = showLegend;
+
+		const colors = getThemeColors();
+		const variableCount = params.hourly?.length || 0;
+		const timeLength = (hourlyData.time as number[]).length;
+		const newOptions: Array<Record<string, unknown>> = [];
+
+		for (let vi = 0; vi < variableCount; vi++) {
+			const variable = params.hourly![vi];
+			const unit = findUnit(hourly_units, hourlyData, variable);
+
+			const series: Array<Record<string, unknown>> = [];
+
+			for (const [model, values] of Object.entries(hourlyData)) {
+				if (model === 'time') continue;
+				if (!model.startsWith(variable)) continue;
+
+				const seriesData = (values as (number | null)[]).map(
+					(val, idx) => [timestamps[idx], val] as [number, number | null]
+				);
+
+				series.push(
+					buildModelSeries({
+						name: model,
+						data: seriesData,
+						unit
+					})
+				);
+			}
+
+			const { average } = calculateAverage(hourlyData, variable, timeLength);
+			const averageData = average.map((val, idx) => [timestamps[idx], val] as [number, number]);
+			series.push(buildAverageSeries({ variable, data: averageData, unit }));
+
+			series.push(buildCurrentTimeSeries({ utcOffsetSeconds: utc_offset_seconds }));
+
+			const daylightSeries = buildDaylightSeries({ markAreas });
+			if (daylightSeries) {
+				series.push(daylightSeries);
+			}
+
+			const isFirst = vi === 0;
+			const isLast = vi === variableCount - 1;
+
+			const option = composeChartOption({
+				title: isFirst
+					? {
+							text: 'Model Compare',
+							subtext: `Compare ${params.hourly?.join(', ') || ''} in models: ${params.models?.join(', ') || ''}`
+						}
+					: null,
+				tooltip: { unit },
+				legend: { show: _showLegend },
+				grid: {
+					hasTitle: isFirst,
+					hasSubtitle: isFirst,
+					showLegend: _showLegend
+				},
+				yAxis: { unit },
+				series,
+				toolbox: false,
+				showCredit: isLast,
+				colors
+			});
+
+			newOptions.push(option);
+		}
+
+		chartOptions = newOptions;
+	});
 </script>
 
 <!-- ─── Chart Area ─────────────────────────────────────────────────────────── -->
@@ -230,27 +249,9 @@
 	<ChartToolbar charts={chartInstances} fileName="model-comparison">
 		{#snippet controls()}
 			<div class="flex gap-2">
-				<Switch
-					id="show_legend"
-					name="Show legend"
-					bind:checked={showLegend}
-					onCheckedChange={() => {
-						params.hourly = params.hourly;
-					}}
-				/>
+				<Switch id="show_legend" name="Show legend" bind:checked={showLegend} />
 				<Label for="show_legend" class="mb-0.5 cursor-pointer text-lg">Show legend</Label>
 			</div>
-			<div class="flex gap-2">
-				<Switch
-					id="average_only"
-					name="Average only"
-					bind:checked={averageOnly}
-					onCheckedChange={() => {
-						params.hourly = params.hourly;
-					}}
-				/>
-				<Label for="average_only" class="mb-0.5 cursor-pointer text-lg">Average only</Label>
-			</div>
 		{/snippet}
 	</ChartToolbar>
 </div>
@@ -289,8 +290,7 @@
 										return item !== value;
 									});
 								} else if (params.models) {
-									params.models.push(value);
-									params.models = params.models;
+									params.models = [...params.models, value];
 								}
 							}}
 						/>
@@ -344,8 +344,7 @@
 											return item !== value;
 										});
 									} else if (params.hourly) {
-										params.hourly.push(value);
-										params.hourly = params.hourly;
+										params.hourly = [...params.hourly, value];
 									}
 								}}
 							/>