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+# Weather Nearby API Endpoint Design
+
+**Date:** 2026-03-22
+**Status:** Approved
+
+## Overview
+
+API endpoint to find weather stations within a specified radius of a geographic point, returning stations with recent weather data.
+
+## Specification
+
+**Endpoint:** `GET /api/v1/weather/nearby`
+
+**Purpose:** Find weather stations within a specified radius of a geographic point.
+
+**Query Parameters:**
+- `lat` (required) - Latitude (-90 to 90)
+- `lon` (required) - Longitude (-180 to 180)
+- `radius` (required) - Search radius in miles (> 0, max 1000)
+- `hours` (optional) - Time window for "recent" weather data in hours (default: 6, max: 168 for 7 days)
+- `limit` (optional) - Maximum number of results (default: 50, max: 100)
+
+**Example Request:**
+```
+GET /api/v1/weather/nearby?lat=37.7749&lon=-122.4194&radius=25&hours=6&limit=50
+```
+
+## Implementation Details
+
+### Database Query Strategy
+
+Use PostGIS geography type with `ST_DWithin` for efficient spatial filtering:
+
+```sql
+-- Conceptual query structure
+SELECT DISTINCT ON (base_callsign) *
+FROM packets
+WHERE has_weather = true
+  AND received_at >= (NOW() - interval '6 hours')
+  AND ST_DWithin(
+    location::geography,
+    ST_SetSRID(ST_MakePoint(lon, lat), 4326)::geography,
+    radius_meters
+  )
+ORDER BY base_callsign, received_at DESC
+LIMIT 50
+```
+
+Then order the results by distance using `ST_Distance` in a subquery.
+
+**Performance Notes:**
+- Leverages existing spatial index on `location` column
+- `has_weather` boolean index for fast filtering
+- `DISTINCT ON` prevents duplicate SSIDs
+- Subquery pattern keeps distance calculation efficient
+- Miles converted to meters internally (1 mile = 1609.34 meters)
+
+### Code Structure
+
+1. **Controller:** `lib/aprsme_web/controllers/api/v1/weather_controller.ex`
+   - Parameter validation (lat/lon ranges, radius > 0, etc.)
+   - Call context function
+   - Render JSON response
+
+2. **Context Function:** Add to `lib/aprsme/packets/prepared_queries.ex`
+   - `get_nearby_weather_stations(lat, lon, radius_miles, opts)`
+   - Uses prepared query pattern like existing `get_nearby_stations_knn`
+   - Converts miles to meters for PostGIS
+
+3. **JSON View:** `lib/aprsme_web/controllers/api/v1/weather_json.ex`
+   - Format response structure
+   - Handle null weather fields
+   - Include metadata
+
+4. **Router:** Add route to `/api/v1` scope in `router.ex`
+
+## Response Format
+
+### Success Response (200 OK)
+
+```json
+{
+  "data": [
+    {
+      "callsign": "N0CALL-13",
+      "base_callsign": "N0CALL",
+      "position": {
+        "lat": 37.7849,
+        "lon": -122.4094
+      },
+      "distance_miles": 0.87,
+      "weather": {
+        "temperature": 72.5,
+        "humidity": 65.0,
+        "pressure": 1013.2,
+        "wind_speed": 8.5,
+        "wind_direction": 270,
+        "wind_gust": 12.0,
+        "rain_1h": 0.0,
+        "rain_24h": 0.5,
+        "rain_since_midnight": 0.3
+      },
+      "symbol": {
+        "table_id": "/",
+        "code": "_"
+      },
+      "comment": "Davis Vantage Pro2",
+      "last_report": "2026-03-22T15:30:00Z"
+    }
+  ],
+  "meta": {
+    "count": 12,
+    "params": {
+      "lat": 37.7749,
+      "lon": -122.4194,
+      "radius_miles": 25,
+      "hours": 6,
+      "limit": 50
+    }
+  }
+}
+```
+
+**Notes:**
+- Weather fields are `null` if not reported by the station
+- Distance calculated as straight-line (great circle) distance
+- Times in ISO 8601 UTC format
+
+### Error Responses
+
+- `400 Bad Request` - Invalid/missing parameters
+- `422 Unprocessable Entity` - Parameters out of valid range
+- `500 Internal Server Error` - Database/server error
+
+## Error Handling & Validation
+
+### Parameter Validation
+
+```elixir
+# Latitude: -90 to 90
+validate_lat(lat) when lat >= -90 and lat <= 90
+
+# Longitude: -180 to 180
+validate_lon(lon) when lon >= -180 and lon <= 180
+
+# Radius: > 0, reasonable max (e.g., 1000 miles)
+validate_radius(radius) when radius > 0 and radius <= 1000
+
+# Hours: 1 to 168 (7 days max)
+validate_hours(hours) when hours >= 1 and hours <= 168
+
+# Limit: 1 to 100
+validate_limit(limit) when limit >= 1 and limit <= 100
+```
+
+### Error Messages
+
+- Missing required param: `"Missing required parameter: lat"`
+- Invalid format: `"Invalid latitude: must be a number between -90 and 90"`
+- Out of range: `"Radius must be between 0 and 1000 miles"`
+
+### Fallback Controller
+
+Uses existing `AprsmeWeb.Api.V1.FallbackController` to handle:
+- Validation errors → 400/422 responses
+- Database errors → 500 with generic message (details logged)
+- Rate limiting handled by existing `RateLimiter` plug
+
+### Edge Cases
+
+- No weather stations found → Return empty array with 200 OK
+- Antimeridian crossing (longitude wrap) → PostGIS geography handles automatically
+- Invalid callsign characters → Sanitized by database layer
+- Timeout on large queries → Database query timeout (existing)
+
+## Testing Strategy
+
+### Unit Tests (Controller)
+- Valid parameters return 200 with correct structure
+- Missing required params return 400
+- Out-of-range params return 422
+- Parameter type coercion (string to float/int)
+- Default values applied correctly
+
+### Integration Tests (Database)
+- Find stations within radius (seed test data with known positions)
+- Exclude stations outside radius
+- Exclude stations without recent weather data
+- Exclude stations without `has_weather == true`
+- Respect time window (hours parameter)
+- Respect result limit
+- Order by distance (closest first)
+- Handle antimeridian crossing
+- DISTINCT ON base_callsign (no duplicate SSIDs)
+
+### Test Data Setup
+```elixir
+# Center point: 37.7749, -122.4194 (San Francisco)
+# Station A: 0.5 miles away, weather 1 hour ago ✓
+# Station B: 10 miles away, weather 2 hours ago ✓
+# Station C: 50 miles away, weather 1 hour ago ✗ (outside radius)
+# Station D: 5 miles away, weather 8 hours ago ✗ (outside time window)
+# Station E: 5 miles away, no weather data ✗ (has_weather == false)
+```
+
+### Performance Tests
+- Query execution time < 100ms for typical queries
+- Index usage verified with EXPLAIN ANALYZE
+- Large radius (1000 miles, dense area) completes reasonably
+
+### Test File Location
+- `test/aprsme_web/controllers/api/v1/weather_controller_test.exs`
+
+## Implementation Files
+
+1. `lib/aprsme_web/controllers/api/v1/weather_controller.ex` (new)
+2. `lib/aprsme_web/controllers/api/v1/weather_json.ex` (new)
+3. `lib/aprsme/packets/prepared_queries.ex` (add function)
+4. `lib/aprsme_web/router.ex` (add route)
+5. `test/aprsme_web/controllers/api/v1/weather_controller_test.exs` (new)