A classic "Nor'easter" is a strong weather system that originates in the U.S. Southeast or over the Gulf of Mexico, which then travels northeastward (hence the name) along the East Coast of the United States. These storm systems are characterized by heavy rain and snow and whipping winds, and often cause flooding, coastal erosion and blizzard conditions. Nor'easters can happen in any season, but they mostly occur in late autumn and winter.
In late April 2012, however, a powerful spring nor'easter dumped heavy, much-needed rains in the Mid-Atlantic and northeastern states, and also delivered surprising early spring snow in the eastern mountain regions (Figures 1 and 2). This late spring storm was particularly unexpected due to the very mild winter conditions that had preceded it, the subject of two recent news articles, "NLDAS data views winter's weirdly warm weather", and "NLDAS data view the fourth warmest winter on record in the U.S."
Satellite and model reanalysis data at GES DISC have been used to visualize the genesis, development, and movement of this storm. Figure 3 is an animation of the global merged IR product, showing the birth of the storm in the Gulf of Mexico. The storm moved northeastward, passing over northern Florida and subsequently over the Atlantic Ocean.
Figure 1. Rainfall accumulation between April 21-23, 2012, generated from the Tropical Rainfall Measuring Mission (TRMM) Multi-satellite Precipitation Analysis near-real-time data product (TMPA-RT).
Figure 2. Snowfall for the 24-hour period April 23-24, 2012, in mm/hr, overlain with surface pressure and surface winds. The figure is based on data from the GEOS-5 model of the Goddard Modeling and Assimilation Office (GMAO).
Figure 3. Animation of infrared (IR) brightness temperatures generated from the Geostationary Operational Environmental Satellite (GOES) merged IR product. The IR brightness temperatures primarily indicate cloud cover.
As it moved over the warm waters of the Gulf Stream, the storm intensified, as seen in a second animation of sea level atmospheric pressure (Figure 4). This intensification of a low-pressure system is similar to what occurs when tropical storm systems encounter warm ocean waters. Then, as shown in Figure 5, strong southerly winds conveyed moisture to the Northeast, resulting in heavy rain and snow in the region.
Figure 4. Animation of sea level pressure (in millibars) obtained from GEOS-5.
Figure 5. Merged IR brightness temperatures overlain with sea surface pressure (boxed numbers) and surface winds (white arrows) from GEOS-5.
The April nor'easter also dropped snow, up to 13 inches in some places, on the mountains of West Virginia, western Maryland, Virginia, and Pennsylvania. The NASA MODIS Snow & Sea Ice Global Mapping Project provides daily snow cover analyses for regions around the world, based on data from the Moderate Resolution Imaging Spectroradiometer (MODIS) on the Terra and Aqua satellites. The image for April 24 of the eastern United States shows the main snow track (also visible under broken clouds in Pennsylvania), as well as narrower tracks in two regions closer to the coast, the Dolly Sods Wilderness and the Blue Ridge Mountains in Shenandoah National Park (Figure 6).
Figure 6. MODIS snow analysis for April 24, 2012, showing snow cover in West Virginia, western Maryland, southwestern Pennsylvania, the Dolly Sods Wilderness, and Shenandoah National Park.
Meteorologist Bob Ryan of ABC 7 News in Washington, DC, found this Webcam picture of the snow falling in Shenandoah National Park during the April nor'easter on April 23.
Figure 3 was generated from the NASA GES DISC Hurricane Data Analysis Tool (HDAT).
Figure 4 was generated from the GEOS-5 model data, http://opendap.nccs.nasa.gov:9090/dods/GEOS-5/fp/0.25_deg/assim.
Precipitation images were generated with Giovanni (http://giovanni.gsfc.nasa.gov).
MODIS snow and ice analyses are available from the MODIS Snow & Sea Ice Global Mapping Project.
The image of snow on Skyline Drive was provided by meteorologist Bob Ryan, ABC 7 News, Washington, DC, from a Webcam located at the National Park Service Visitor Center.
Text and data images authored by Dr. Zhong Liu, NASA GES DISC/George Mason University. Additional text and editing by James Acker, NASA GES DISC/Wyle IS LLC.
The GES DISC is a NASA earth science data center, part of the NASA Earth Science Data and Information System (ESDIS) Project.
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