"Pressure anomalies" refers to deviations or variations from the normal or expected pressure in a given system or location. It indicates when pressure levels are higher or lower than what is typically observed in that area. Full definition
A positive summertime sea level pressure anomaly over the central Arctic Basin is featured. (arcus.org)
Conversely, low sea level pressure anomalies over the Beaufort Sea and Canada Basin keep the Arctic Ocean pack ice up against the western entrance. (nsidc.org)
«One study (Bates and Meehl 1986) reports a reduction in blocking (defined as areas of high pressure anomaly which persist for more than seven days) in the southern hemisphere, and changes in the positions but not the intensity of blocking in the Northern Hemisphere though no information was provided on the statistical significance of the results. (realclimate.org)