get-forecast

Instructions

Implementation Reference

• src/index.ts:119-163 (handler)

  The async handler function for the 'get-forecast' tool. It fetches the weather points URL from NWS API using lat/long, then retrieves and formats the forecast periods including temperature, wind, and short forecast.

  async ({ latitude, longitude }) => {
      const pointsUrl = `${NWS_API_BASE}/points/${latitude.toFixed(4)},${longitude.toFixed(4)}`;
      const pointsData = await fetchJson<PointsResponse>(pointsUrl, {
          Accept: "application/geo+json",
      });
  
      if (!pointsData || !pointsData.properties?.forecast) {
          return {
              content: [
                  {
                      type: "text",
                      text: `Failed to get forecast data for coordinates: ${latitude}, ${longitude}`,
                  },
              ],
          };
      }
  
      const forecastData = await fetchJson<ForecastResponse>(pointsData.properties.forecast);
      if (!forecastData) {
          return {
              content: [{ type: "text", text: "Failed to retrieve forecast data" }],
          };
      }
  
      const periods = forecastData.properties?.periods || [];
      if (periods.length === 0) {
          return {
              content: [{ type: "text", text: "No forecast periods available" }],
          };
      }
  
      const formattedForecast = periods.map((period) =>
          [
              `${period.name || "Unknown"}:`,
              `Temperature: ${period.temperature || "Unknown"}°${period.temperatureUnit || "F"}`,
              `Wind: ${period.windSpeed || "Unknown"} ${period.windDirection || ""}`,
              `${period.shortForecast || "No forecast available"}`,
              "---",
          ].join("\n")
      );
  
      return {
          content: [{ type: "text", text: `Forecast for ${latitude}, ${longitude}:\n\n${formattedForecast.join("\n")}` }],
      };
  }

• src/index.ts:115-118 (schema)

  Input schema defined with Zod for latitude and longitude parameters.

  {
      latitude: z.number().min(-90).max(90).describe("Latitude of the location"),
      longitude: z.number().min(-180).max(180).describe("Longitude of the location"),
  },

• src/index.ts:112-164 (registration)

  Registration of the 'get-forecast' tool on the MCP server, specifying name, description, input schema, and handler function.

  server.tool(
      "get-forecast",
      "Get weather forecast for a location",
      {
          latitude: z.number().min(-90).max(90).describe("Latitude of the location"),
          longitude: z.number().min(-180).max(180).describe("Longitude of the location"),
      },
      async ({ latitude, longitude }) => {
          const pointsUrl = `${NWS_API_BASE}/points/${latitude.toFixed(4)},${longitude.toFixed(4)}`;
          const pointsData = await fetchJson<PointsResponse>(pointsUrl, {
              Accept: "application/geo+json",
          });
  
          if (!pointsData || !pointsData.properties?.forecast) {
              return {
                  content: [
                      {
                          type: "text",
                          text: `Failed to get forecast data for coordinates: ${latitude}, ${longitude}`,
                      },
                  ],
              };
          }
  
          const forecastData = await fetchJson<ForecastResponse>(pointsData.properties.forecast);
          if (!forecastData) {
              return {
                  content: [{ type: "text", text: "Failed to retrieve forecast data" }],
              };
          }
  
          const periods = forecastData.properties?.periods || [];
          if (periods.length === 0) {
              return {
                  content: [{ type: "text", text: "No forecast periods available" }],
              };
          }
  
          const formattedForecast = periods.map((period) =>
              [
                  `${period.name || "Unknown"}:`,
                  `Temperature: ${period.temperature || "Unknown"}°${period.temperatureUnit || "F"}`,
                  `Wind: ${period.windSpeed || "Unknown"} ${period.windDirection || ""}`,
                  `${period.shortForecast || "No forecast available"}`,
                  "---",
              ].join("\n")
          );
  
          return {
              content: [{ type: "text", text: `Forecast for ${latitude}, ${longitude}:\n\n${formattedForecast.join("\n")}` }],
          };
      }
  );

• src/index.ts:54-77 (schema)

  TypeScript interfaces for NWS API responses: ForecastPeriod, PointsResponse, ForecastResponse (AlertsResponse is for another tool but in block). Used in get-forecast.

  interface ForecastPeriod {
      name?: string;
      temperature?: number;
      temperatureUnit?: string;
      windSpeed?: string;
      windDirection?: string;
      shortForecast?: string;
  }
  
  interface AlertsResponse {
      features: AlertFeature[];
  }
  
  interface PointsResponse {
      properties: {
          forecast?: string;
      };
  }
  
  interface ForecastResponse {
      properties: {
          periods: ForecastPeriod[];
      };
  }

• src/index.ts:20-29 (helper)

  Shared fetchJson utility function used to make API requests in the get-forecast handler.

  async function fetchJson<T>(url: string, headers: Record<string, string> = {}): Promise<T | null> {
      try {
          const response = await fetch(url, { headers: { "User-Agent": USER_AGENT, ...headers } });
          if (!response.ok) throw new Error(`HTTP error ${response.status}`);
          return (await response.json()) as T;
      } catch (err) {
          console.error("Fetch error:", err);
          return null;
      }
  }