Customize your own hourly forecast!

Did you know that you can use digital forecast data provided by the National Weather Service (NWS) to create your own customized forecast? Our web interface allows users to choose up to 12 weather elements, such as temperature and chance of precipitation, and displays an hourly forecast for each element in either graphical or tabular format. Forecasts utilize up-to-the-minute data and have a spatial resolution of 5 square km (3.1 square miles). This resolution will be increased to 2.5 km (1.5 miles) for all NWS offices in the near-future. Users can generate forecasts for any location within the Continental U.S., Hawaii, Guam, Puerto Rico, and the U.S. Virgin Islands. So whether you are planning a quiet day at the lake or want to hike to the top of a mountain, a detailed site-specific weather forecast from the National Weather Service is always available!

 

How do I generate a forecast?

To generate a forecast, first start at our website, http://www.weather.gov/detroit.

Forecasts for Southeast Michigan:

From our home page, either enter your city and state or zip code in the white box on the top left of the page, or click your approximate location on the map in the center of the screen. A page displaying the text forecast and current conditions will then come up. The exact place the forecast is valid for will be displayed at the top of the page. If you would like to pinpoint a more exact location, scroll down and click a point on the more detailed map on the right side of the screen. Once you have the location you want, scroll down to the Additional Forecasts & Information table on the bottom right of the screen. To generate an hourly forecast for your location, click either Hourly Weather Graph or Tabular Forecast, depending on the format you prefer.

Forecasts outside of Southeast Michigan:

Either enter your city and state or zip code in the white box on the top left of the Detroit/Pontiac homepage, or start at http://www.weather.gov and click on your area of interest. If you click on the national map, the local NWS office that forecasts for that part of the country will come up, and you can then use the regional map in the center of the page to choose a more specific area you are interested in. When the page displaying the text forecast and current conditions comes up, follow the directions in the section above to generate an hour-by-hour forecast.

 

Where does the data come from?

The data comes from a digital data base maintained and distributed by the National Weather Service. Forecast grids are produced locally and are kept up-to-date 24 hours a day, seven days a week. Meteorologists at each NWS office first import analyzed or digital computer model data into a graphical forecast editor. Then, using a combination of smart tools, computer algorithms, and editing techniques common to most graphical software, the data is manipulated to create a graphical representation of expected weather for the next seven days. Using these tools, forecasters can take advantage of the high spatial resolution of the grids and account for local effects such as lake breezes, temperature variations near large lakes, terrain, and urban heat island effects. Forecasters create one digital grid for each separate weather element (temperature, sky cover, etc.), and for each time period in the forecast. The valid time period for each grid typically varies between one hour and twelve hours depending on the element and the weather situation. Each 5 km point is assigned it's own unique value for every grid. The result is an extremely detailed, and very large, digital forecast database!

National Weather Service offices around the country individually produce a digital database of forecast grids for their area of responsibility. Each local office's set of grids is then collected and merged into one seamless National Digital Forecast Database (NDFD), which is also available to the public. Forecasts for Southeast Michigan are made at the forecast office in White Lake, MI (NWS Detroit/Pontiac).

Example of a minimum temperature grid from the NWS Detroit/Pontiac gridded database. Each pixel represents an area of 5 square km (3.1 miles).

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