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Grid point - 7 Day Forecast Help
Table of Contents


General Overview


Of the many forecast products meteorologists at the Weather Forecast Office (WFO) in Reno, NV produce, one type is Grid point forecasts. These forecasts are plotted on maps divided into 2.5 kilometer per side grid squares. Each grid square contains 6.25 square km, which equates to roughly 2.5 square miles. The point at the center of a grid square becomes the square's Grid point, whose latitude and longitude are used to identify the grid square.

WFO Reno forecasters predict such weather elements as temperature, wind speed, chance of precipitation, etc for each grid square out seven days into the future. Take one weather element prediction for one time period and plot it on the map of grid squares; we call such a plot a grid.

You can see these grids on our Cartographic Forecast pages. If you are curious, jump to these, take a look, then press your browser's Back button until you return to this page to read on.

There are hundreds of these grids, since there are dozens of weather elements and scores of time periods which make up the 7-day forecast. Viewing and understanding these hundreds of grids to form an overall weather forecast would be a difficult and time consuming process. That's where our point and click, Grid point forecasts come in!

You simply choose a forecast format, then select a Grid point by clicking on the desired location on a map of our area. That specific 2.5 square mile grid square is analyzed across all of the hundreds of grids, formatted as requested, and presented as a modern web graphic.

There are several forecast formats to choose from, the most common is the 7-day forecast when you click on the map off the main page. The 7-day format will be the focus of this document. Other types include the cartographic pages referenced above, as well as the hourly forecast graphs and tabular forecasts. The hourly graphs and tabular forecasts are explained in other documents.

The analysis is dynamic. It happens every time you click, to ensure that your forecast reflects any changes we may have made to the grids.

 
7-Day Forecast

The 7-Day Forecast is our most web-suited prognosis. It conveys information in both pictures and text, and it is interactive, with links to other sources of weather information. To get to the 7-Day Forecast, click on any point on the map off the main WFO Reno web page. The 7-Day Forecast for that point will come up. In this document, we have clicked on a point for Susanville, CA.

sample NWS Reno Webpage


The 7-Day Forecast looks like this:

Example Susanville Forecast

We will now cover the various parts of this document so you can get the maximum benefit from the forecast.

At the very top of your browser's window is its title bar, in which appears the web page's title. With one of our 7-Day Forecasts displayed in the browser window, this title bar includes the latitude and longitude of the Grid point on which you clicked as well as the average elevation of the grid square the forecast is derived from:

Title bar graphic. Shows title referencing a point with a latitude of 40.41 North and a longitude of 120.64 West.

If you intend to frequently read forecasts for this location, as you might for your home, farm, or place of business, you will want to bookmark the page or make it one of your favorites. Once you do, this title becomes the identifier of the bookmark/favorite. You may prefer a different id, in order to make your bookmark/favorite more easily recognizable. For example: you might prefer Forecast for Jones' Farm to your Grid point's default title of, let's say, 7-Day Forecast for Latitude 40.41N and Longitude 120.64 W (Elev. 4198 ft) . If so, simply use your browser's bookmark management capability to rename the link.

More information about the Grid point appears at the top of the page. If cities or towns exist in the grid square, the one closest to the Grid point clicked will be shown between the NOAA and NWS logos indicated in the image below:

Closest town/city graphic.

This point will be the location you clicked on, and it is not necessarily the town or city with the largest population. In this case, Susanville, CA was clicked. Now, if you did not click directly on a city or town, you will get a distance and direction from the nearest town or city. For example, you may see 10 NW Susanville, CA if you clicked on a point northwest of Susanville. Please note that for some larger towns and cities, you may click within the city limits but find a distance and direction to the city. For example, the Reno-Sparks area, you may see 3 NW Reno, NV even though you clicked within the city limits of Reno. This is because only one grid point is referenced as Reno, the city center, and every other grid point nearby is referenced from there.

Directly below the location identifier, you will find several informational items. They are referenced by number below:

Important informational items, referenced by the number that appears.

1. The first item identifies the WFO that produced the forecast displayed on the page. We will assume you clicked on a spot in WFO Reno's area of responsibility and that this reads "NWS Reno, NV." You may also have clicked outside our area of responsibility, which will read differently, "WFO Sacramento, CA" for instance. This text also links to that offices homepage. In this example, it will be linked to our homepage.

2. The second item repeats the closest city or town name, unless one does not exist, then it will identify the spot you picked with a phrase like "3 Miles NW Reno, NV " meaning that your point was 3 miles northwest of the center of Reno, NV.

3. The last item on the left hand side displays the latitude, longitude and elevation of the selected grid point.

4. At the top of the right hand side there are two links. The first, "Mobile Weather Information" will take you to a web page to obtain weather information on your wireless device, such as a cell phone. The second link will give you the 7-day Forecast page in Spanish.

5. Next on the right hand side is an item labeled "Last Update". This will tell you the time the forecast grids were modified. Forecasts are routinely modified at least twice per day.

6. The last item is a time range labeled Forecast Valid. This range describes the 7 days which the forecast covers. The first time of this range is important. As you read the textual Detailed 7-Day Forecast section below, the beginning time tells you when the forecast starts, either Today or Tonight.

Now, for the forecast! The next section, extending across the whole of the near-top of the page, is the Forecast at a Glance:

Picture of the Forecast at a Glance Graphic. Shows the whole Forcast at a Glance section.

It is an iconic and textual summary of the weather for the next few days. Reading from left to right, It covers at least the next 9 day and night periods, or 4 and one half days. The image above has been snipped to the first six periods.

1. The forecast period is described above each icon.

2. The weather icons. Icons show weather during each period and convey, at a glance, concepts such as bright and sunny, partly cloudy, snowy, foggy, windy, day, night, etc. The icons above vary for partly cloudy at night, to the chance of rain or showers. If a major shift in the weather is predicted or the weather could be variable during that period then the picture is split diagonally, and two weather patterns are depicted in one icon. Keep in mind that these icons are a simplified forecast and may not take into account all the weather expected during that period. For example, if snow and high winds are expected, the icon will only show snow.

3. The probability of precipitation is shown textually within the icon, if equal to or greater than 20%. The probability of precipitation is the chance of receiving measurable precipitation, defined as 0.01 inches liquid. The probability of precipitation for the Friday period in the image above is 40%, meaning there is a 40% chance it will rain and a 60% chance it will not rain.

4. Beneath each icon a very brief description of the weather appears. The circled example above (Wednesday Night) reads Chance Snow. Similar to the icons described above, it will not describe all the weather occurring for that time period, it will only display one brief description.

5. Finally, at the bottom of each icon's cell, the high or low temperature is shown: highs for day periods and lows for nights. For example, tonight's low is 37 degrees, with Thursday's (tomorrow's) high being 61 degrees Fahrenheit.

After the Forecast at a Glance section, the 7-Day Forecast splits into two columns. Appearing first in the left-hand column is the Detailed 7-Day Forecast, a pure, textual description of the weather over the next 7 days:

7-Day Forecast textual graphic. Shows the text portion of the forecast with its 7 days of textual description of the forecast weather.

If any hazardous weather watches, warnings, advisories, statements, etc., currently exist for your Grid point's county, links to each will appear at the top of this section. In this example, a Wind Advisory is in effect for this point, and clicking on it will take you to the text of the statement.

Next, all the 7-day periods are covered one by one, near-term first and day 7 last. The weather is described in more detail for the short-term. Broader generalities are used as the forecasts progress into the future. The boxed example above for the second period, a day period for a Thursday, shows good detail. The expected overall weather is mostly cloudy with a 20% chance of showers beginning after 10 am. The expected high temperature, wind speed and direction are shown. The wind speed is forecast to increase during the day along with the strongest wind gusts.

After the Detailed 7-Day Forecast section, at the bottom of the left-hand column, is a section for the combined grids for all the WFO's across the country: the National Digital Forecast Database:

National Digital Forecast Database (NDFD) graphic. Shows two NDFD maps, which link to NDFD.

In this section there are two pictures, both are links to the National Digital Forecast Database, where the images can be seen in more detail. The first picture depicts the minimum temperature grid for the current time period for the southwestern United States and links to the grid viewing interface. The second picture shows the weather grid for the current time period and links to the grid viewing interface. In this example, rain is forecast in northern California, with fog along the southern California coast.

Now, Back up to the top of the right-hand column! This is the Detailed Point Forecast map:

Map with grid box for Susanville selected.

This map shows you the selected grid square for the forecast, and gives you a chance to refine your aim, if your first "point & click" missed your desired location. The cross hairs show you the exact location you clicked on within that red box. The map is a Google Map, used under license from Google. A link to a page describing the license and the limitations with the map are under the Disclaimer link at the top.

This map works similar to any map produced by Google as you can zoom in or out and move the map to a different location. The main difference is that when you click on the map, you will view a forecast page for the point you clicked. You can see the task is a little easier with this map. You are at a smaller scale (more zoomed-in) than the one on our home page. You can also zoom in more if you desire by using the navigation options in the upper left hand corner of the map. In addition, the default map is the one that shows topography as the background. As with other Google Maps, you can also change the background to a satellite picture or a street map by clicking on the buttons in the upper right corner of the map.

At the bottom are two icons that are links. The first on the left, KML, is a link to a forecast file that will open in Google Earth. The right icon is a link to the forecast file in XML format.

The next section below the map is called Current Conditions.

Your 7-Day Forecast finds the automated observation site closest to the point you clicked and shows you the senor's most recent observations.

Current conditions graphic. Shows an example from Reno-Tahoe Airport.

For this example, two examples are included. In the left hand example, the 7-Day Forecast picked Grasshopper for the Susanville Grid point This is a Remote Automated Weather Station (RAWS) used for fire weather. It is identified, as shown in the red oval. The time of the most recent observation is also shown just below the location. In the right example, for a Grid point in the Reno/Sparks area, the observation at the Reno-Tahoe International Airport is shown. There are slight differences that will be mentioned below. It is important to note that automated sensors do break occasionally. While one is inoperative and not reporting, this display may show the phrase Not a Current Observation.

Selected weather elements follow. Temperature, humidity, wind speed, gust speed, wind direction, barometric pressure, dew point, wind chill or heat index are shown. Current weather and visibility may be shown (in this example for Reno only), depending on the instruments for that site.

Finishing off this section are two links for additional observations. One link, "More Local Wx:", shows you other nearby stations, while the other, "3 Day History:", shows observations for the last three days at this sensor.

Continuing down the right-hand column, we next come to Radar and Satellite Images:

Radar and Satellite graphic. Shows two links. One to a Reno radar website and the other to the national satellite imagery website.

The two small pictures are not static icons but actual snapshots of recent radar and satellite coverage. They are also links to full sized Radar and Satellite displays.

At the bottom of the right-hand column is the Additional Forecasts & Information section. It contains links to other forecasts or formats:

Additional Forecasts & Information graphic. Shows links to other information, each described below.

Zone Area Forecast for (zone name)
Shows the forecast for a larger pre-defined area dependent on political boundaries such as county borders, climatology, or both. This forecast 'zone' is described by the zone name. In this case, the zone name is Lassen-Eastern Plumas-Eastern Sierra Counties.
 
Forecast Discussion
This takes you to the Reno Area Forecast Discussion, the why and science behind the forecast.
 
Printable Forecast
Isolates the forecast elements and reformats them, ready for printing on 8.5 x 11 inch paper.
 
Text-Only Forecast
Further isolates the textual forecast elements (Detailed 7-Day Forecast) for printing on 8.5 x 11 inch paper.
 
Hourly Weather Graph
Allows you to quickly switch to the Hourly Weather Graph Forecast format for the Grid point already displayed.
 
Tabular Forecast
Switches to the Tabular Forecast format for the current Grid point
 
Quick Forecast
An icon-based forecast format for the current Grid point
 
International System of Units
Redisplays the full 7-Day Forecast with temperatures shown in Centigrade rather than Fahrenheit. Wind speed will also be converted from miles per hour to kilometers per hour. Once displayed in Centigrade, the Printable Forecast and Text-Only Forecast links will honor the conversion and report in Centigrade too. Note that the temperatures and winds are the only conversions performed. Depths are still in inches and distances are still in miles.
 
About Point Forecasts
A help page with a subset of the information on this page. This page briefly describes how point forecasts are created and what they represent, but focus more on the other types of forecasts available, the hourly graph and tabular forecast described above.
 
Hourly Weather
Displays a document with a summary of observations from the area over the past hour.
 
Mountain Top and other Remote Weather
Takes you to our remote weather page with observations from mountain tops and other remote locations around our area.
 
Road Conditions
Links to both Cal Trans and the Nevada Department of Transportation.
 
Aviation Products
Link to our aviation forecast page.
 
How to use this page
Links to this document.
 
Forecast Weather Table Interface
Takes you to another page that enables you to select the format your forecast is in.

The Grid point forecast is just a small part of the National Weather Service's efforts towards a National Digital Forecast Database (NDFD). Go to the NDFD Home Page for complete information.

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