WoFS Forecast Viewer

NSSL Warn-on-Forecast System

WoFS Product Descriptions

This site is the visualization tool for the National Severe Storms Laboratory (NSSL) Experimental Warn on Forecast (WoF) System (WoFS). Events can be chosen by clicking the “Forecasts Dates” menu in the top left section of the web page. If a domain images appears, the WoFS has either not started running yet or there is not a forecast for that chosen hour.

Forecast initialization times may be found to the top right of all product images. Different forecasts can be accessed by clicking the times seen under the “Forecast” menu on the left side of the page. The period you are currently viewing will be red. Forecasts out to 3 hours are only available for initialization times at the top of each hour. Forecasts initialized at each half hour only run for 90 minutes. All products within a 90 minute/3-hr forecast are unaffected by data assimilation. To display products with more current radar data assimilated into the forecast, the viewer must choose a later initialization time from the “Forecasts” menu. Choosing a forecast initialized a half hour later means radar data has been assimilated two additional times. For more information on how the WoFS is run, click the “WoFS Details” link on the main page.

The WoFS products are organized by five categories including: Environment, QPF/Rad/Sat, Severe, Rotation, and Verification. Products can be chosen by placing your mouse over product categories and clicking the red product options. For fields not considered “summary” products, at the top of each product is the “Forecast Minute”. Users can mouse over each minute from 00-90 (or 180 for 3 hour products) in five minute intervals to see how the product evolves through the forecast period. The forecast minute is reflected in the valid time located to the top right of the products below the initialization time. Titles are found on the top left of each figure. The first title most often represents the primary variable being displayed through the color bar in the bottom left. This is the variable chosen from the drop down menu. The secondary title is the description of any overlain products- most often the probability matched mean composite reflectivity.

Common Product Descriptions

Probability Matched Mean Composite Reflectivity
Probability matched mean composite reflectivity is overlain on the majority of WoFS products. Reflectivity values above 35 and 50 dBZ are contoured according to the colored lines at the bottom of the product. The probability matched mean is a statistical technique that restores amplitudes representative of an individual member to the ensemble mean. This reduces the smoothing of the mean field; particularly at later forecast times as individual member solutions diverge.
Max Values
Max values are provided for percentile and probability matched mean products. Values are located at the bottom right of the associated products. The location of the maximum value within the domain is noted by a black plus sign (+).
Ensemble probability products display the probability from 0 to 1 of a variable exceeding a specified threshold at each grid point in the domain. A probability of 1 indicate that all ensemble member forecasts exceed the threshold.
Percentile products range from the 0th to 100th percentile value in increments of 10% For example, values for the 50th percentile (median) displays the value where 50% of ensemble members are equal to or below the value at each grid point.
Ensemble Mean
The average of the 18 members in the WoFS.
LSRs and Warnings
LSRs (Local Storm Reports) and Warnings appear on many verification products. Green polygons indicate valid flash flood warnings, blue polygons indicate valid severe thunderstorm warnings, and red polygons indicate valid tornado warnings for a given time. Green circles are severe hail reports, red triangles are tornado reports, and blue boxes are severe wind reports.

General Product Examples