NOAA KLM User's Guide

Section 9.6.1

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9.6.1 Weekly Snow and Ice Mapping

During the 1966 to 1999 weekly snow and ice mapping era, the primary data source was Advanced Very High Resolution Radiometer (AVHRR) hardcopy visible imagery acquired from NOAA Polar Operational Environmental Satellite (POES, United States). Secondary data sources included on-line visible imagery from Geostationary Operational Environmental Satellite (GOES, U.S.), Geostationary Meteorological Satellite (GMS, Japan), and European Meteorological Satellite (METEOSAT, European Organization for the Exploitation of Meteorological Satellites), hardcopy National Ice Center (NIC, U.S.) sea ice edge maps, the United States Air Force (USAF) three-dimensional (3-D) Nephanalysis snow product, and surface observations. These products became available at various times in subsequent years. The two crucial problems with the weekly product when used for short-term forecasting were its temporal and spatial resolution. The infrequency of the weekly product created significant errors in the near surface temperature forecasts when the map was used for initialization of the National Weather Service's (NWS) Numerical Weather Prediction (NWP) models, and the grid used in the models had a higher resolution than the weekly snow and ice map.

Snow and ice cover identification was made by the manual inspection of hardcopy polar orbiting satellite imagery and graphics products, on-line video loops of multiple geostationary satellite images, and the previous week's analysis. The former process was largely manual and time consuming, and took up to ten hours to produce a map during the snow season. Map quality was dependent upon the availability of clear sky visible satellite imagery and the meteorologist's experience. The analysis from the previous week was carried forward when cloud cover obstructed the view of the snow/ice boundary during the entire week. The final hardcopy 190 kilometer resolution snow and ice chart was prepared by the analyst by manually transferring the observed boundary lines to the map after all snow and ice boundaries were identified. The polar stereographic base map displayed coastlines, seas and large lakes, international and U.S.state political boundaries, and a latitude-longitude grid. Snow cover was indicated by the irregular solid black lines contiguous with the stippling. Ice cover was delineated by the base map's coastlines and contiguous open circles. The map's key listed the satellites from which imagery was used in preparing the final map. Each week the analyst drew a new map by hand, then digitized the extent of snow and ice cover through the use of an 89x89 line grid overlaid on a polar stereographic map of the Northern Hemisphere which created an electronic version for archival storage at the National Climate Data Center (NCDC). Quality control was either self-imposed by the meteorologist performing the analysis or by the focal point meteorologist. Upon completion, the hardcopy snow and ice chart was faxed to users in the NWS National Centers for Environmental Prediction (NCEP) which included the Environmental Modeling Center and the Climate Prediction Center, the U.S. Department of Agriculture, universities, foreign governments, and other customers.


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