Severe and Winter Weather
Around the world, severe thunderstorms can occur year-round but are focused primarily in the local warm season, accompanied by heavy rains and dangerous lightning, and sometimes by large hail, damaging winds, and tornadoes. In the United States, severe thunderstorms are defined as those that produce hail reaching a size of at least one inch (2.54 cm) in diameter, produce a wind gust of at least 58 miles per hour (26 m s-1), or a tornado. They are often accompanied by widespread lightning capable of injury to people on the ground, damage to electrical infrastructure and power outages, and initiation of wildfires. Wildfire threats are particularly high in the dry and mountainous west, where lightning-triggered wildfires can spread rapidly. Distinct severe weather seasons are focused in the southeastern states in the fall and early spring, followed by a seasonal migration of severe weather into the central United States through mid and late summer.
Impacts of severe weather can be observed through a variety of NASA remote sensing systems with products relevant to hazard monitoring, assessment, and recovery. The Global Precipitation Measurement (GPM) mission and a broader international constellation of passive microwave sensors can be used to map thunderstorm cores and areas of heavy, perhaps flooding precipitation through the Integrated Multi-Satellite Retrievals for GPM (IMERG) dataset. When heavy rains persist over time and flooding is of concern, precipitation estimates from IMERG can be combined with streamflow and inundation models to assist end users with predicting the likelihood and extent of river flooding. To validate these models and assist with flood mapping, measurements of visible and near-infrared land surface reflectance from NASA’s MODIS aboard the NASA Aqua and Terra missions, the NASA/NOAA VIIRS instrument aboard the Suomi National Polar-orbiting Partnership (S-NPP) mission, and the multispectral imagers aboard the Landsat-7 and Landsat-8 missions can be used to map flood water extent. Active remote sensing, such as synthetic aperture radar measurements from the European Space Agency’s Sentinel-1A and Sentinel-1B platforms, or data from other international partners can be used to provide mapping of flood water through cloudy scenes that frequently occur with heavy rainfall events. In addition, damage to the land surface can be observed from these sensors, helping to map damage from long-track and intense tornadoes or extensive hail scarring of vegetation, assisting with geospatial analysis and quantification of crop or insurance losses. In some cases, changes in the land surface as a result of severe weather can be long-term with recovery mapped over subsequent years by NASA and partnering agencies.
Winter storms are accompanied by widespread heavy snow, strong winds that can contribute to blizzard conditions, and often a transition zone from snow to rain that may include heavy accumulations of ice contributing to an increased likelihood of long-term power outages.
Precipitation remote sensing from the Global Precipitation Measurement (GPM) mission can help to map these heavy snowfall rates along with other passive microwave instruments that contribute to the Integrated Multi-Satellite Retrievals for GPM (IMERG) product, helping to fill gaps internationally where ground based networks may be lacking. Following significant winter storms that contribute to widespread ice accumulation and power outages, unique observations from the Suomi National Polar Orbiting Partnership (S-NPP) Visible Infrared Imaging Radiometer Suite (VIIRS) Day-Night Band can contribute to the remote sensing of changes in light emission from the surface, helpful for monitoring power outages and longer-term recovery. In addition, land surface remote sensing from the Moderate Resolution Imaging Spectroradiometer (MODIS) aboard Terra and Aqua, VIIRS from Suomi-NPP, Landsat-7 and Landsat-8, and other platforms can leverage their multispectral imaging capabilities to map the geographic extent of snow, helpful for mapping the extent and duration of snow cover on the ground.
In some scenarios, mapping snow cover and change is critical, as rapid snow melt in the spring season can contribute to additional streamflow, runoff, and flooding, particularly when combined with heavy springtime rainfalls. These imagers can also be used to map ice cover and ice jams that contribute to upstream river flooding and impacts on river transport. In these cases, other remote sensing techniques can be applied to map flood water and extent, including application of synthetic aperture radar to provide a higher resolution depiction of flood water and extent, particularly in vegetated or urban areas and regions that remain affected by cloud cover.