Wunderground launches BestForecast; Giovanna kills ten in Madagascar

Weather Underground's meteorologists have spent over five years developing and testing a powerful forecasting system called BestForecast, which has been used to provide all of our forecasts for non-U.S. locations for the past several years. After some final improvements made in the past year, the forecasts from BestForecast have become competitive with forecasts from the National Weather Service (NWS) over much of the U.S. As of today, BestForecast forecasts are the default on the site. What's cool about BestForecast is that we can make its forecasts specific for any site that collects weather data. We gather several years of weather data from a site and optimize the forecast to suit the unique microclimate of a particular station. Thus, "backyard meteorologists" that own and maintain one of the more than 22,000 personal weather stations that record and send live weather conditions to Weather Underground will now have a forecast specifically generated for their own backyard. BestForecast also gives the expected precipitation amounts (in inches), and provides ten days of forecast information, instead of the seven days provided by the National Weather Service.

Users can evaluate the reliability of these forecasts themselves and get a second opinion by switching back to the National Weather Service forecasts that were previously published. In some areas, the National Weather Service will out-perform BestForecast, so play around with using both, and see what works the best for your location. Web site visitors can switch between best forecast and NWS forecasts using the switch "BestForecast" ON|OFF at the top of the forecast page. To create transparency in our forecasts, wunderground.com will publish the recent accuracy of its temperature forecasts over the past 20 days for every location, alongside the accuracy of the NWS. The accuracy is given in terms of the Root Mean Square Error (RMSE), in degrees Centigrade. A lower RMSE is better. The "MaxT" number is the verification of the daily high temperature forecasts, while the "Average" number is for the hour-by-hour forecasts.

A video demonstration of BestForecast is available on the wunderground.com About Our Data page.


Figure 1. Visible image from NASA's Terra satellite of Tropical Cyclone Giovanna over Madagascar, taken at 10:45 UTC Wednesday February 15, 2012. At the time, Giovanna was a tropical storm with 45 mph winds. Note the extensive plume of runoff and sediment stirred up by the storm flowing southwards along the east coast of Madagascar. Image credit: NASA.

Tropical Cyclone Giovanna kills ten in Madagascar
At least ten people were killed by Tropical Cyclone Giovanna in Madagascar, which hit the island nation as a powerful Category 3 storm with 125 - 130 mph winds at 22 UTC Monday night. An estimated 600,000 people lived in areas that received hurricane-force winds, but the eyewall of the storm missed the capital of Antananarivo, which received peak winds of 38 mph, gusting to 55 mph. Many remote areas that were affected by the storm have not been heard from yet, so the full extent of Giovanna's damage is not yet known. Giovanna is currently in the Mozambique Channel between Madagascar and Mozambique as a tropical storm with 50 mph winds, and is slowly intensifying. Latest computer model forecasts from the GFS and ECMWF models conflict, with the ECMWF model predicting the storm will swing around and pass very close to the southern tip of Madagascar next week, and the GFS model predicting landfall in Mozambique this weekend. Meanwhile, Madagascar must also keep an eye on Tropical Cyclone Thirteen, which is gathering strength over the waters to the east of the island, and is on a course that will bring it close to Madagascar next week.

Jeff Masters