Spatial and Temporal Distributions of North American and U.S. Surface Fronts Using NOAA/NCEP WPC Surface Analyses

Over the last two decades, several studies have analyzed the spatial distribution of surface and lower tropospheric frontal boundaries on both global and regional scales primarily using objective techniques for frontal identification. No recent study has presented a detailed analysis of near surface frontal features over the contiguous U.S (CONUS). In this study the climatological and spatial distribution of NOAA/NCEP Weather Prediction Center (WPC) surface fronts in North America and the CONUS is presented for a 10-year period (January 2009–December 2018). Archived High-Resolution Coded Surface Bulletins consisting of the latitude and longitude points of each front are used in the analysis. Frontal segments are plotted for cold, warm, occluded, and stationary fronts. The spatial frequency of each front type is assessed for a 1.0° latitude-longitude grid over North America and a 0.25° grid over the CONUS.

At the larger scale, the maximum spatial frequency of all front types in North America occurs offshore in the western Atlantic from the U.S. coast northeastward to Greenland and in the Pacific in the Gulf of Alaska corresponding to areas of high cyclone frequency. Over the CONUS at a smaller scale, the location and magnitude of maximum frontal frequencies are approximately 45 cold frontal segments per year in the lee of the Appalachian Mountains and offshore of the mid-Atlantic coast, 25 warm frontal segments per year over the northern Great Plains and along the Pacific Northwest, 110 stationary frontal segments per year in the lee of the Rocky Mountains, and 20 occluded frontal segments per year offshore in the Pacific Northwest. The minimum frequency for all types occurs over the Intermountain West.

A seasonal analysis of the spatial distribution of frontal segments over the CONUS demonstrates that for all frontal types there is a Winter (DJF) maximum frequency in the number of frontal segments and a notable poleward shift of the maximum frequency during the summer. Cold frontal segments feature a winter (DJF) maxima over the Atlantic and southeast U.S., with a shift of the maxima during the warm season into the Great Plains. Stationary frontal segments have a distinct maximum in all seasons along the Rockies that is most frequent in the winter season. In the Spring (MAM), stationary frontal segments have a secondary maximum along the Sierra Nevada mountains extending southeastward along the Mogollon Rim. Summer stationary frontal segments have a secondary broad frequency maximum extending eastward from the Rockies across the central and southern Plains, north of the Gulf coast, across the southeast US that extends into the Atlantic. Other than the poleward shift in summer, warm and occluded frontal segments do not have distinctive seasonal changes in their spatial distribution.