|Data: NCEP reanalysis daily 250 hPa geopotential
height on a 2.5 x 2.5 deg. lat/lon grid.
Base Period: 1961-1990
Data Source: NCEP
The plot indicates the pentad (5-day) average of the
250 hPa geopotential height as unlabelled grey contours (contour interval
30 gpm). Shading indicates the corresponding geopotential height
anomaly with blue indicating negative, and yellow shades positive, anomalies.
Shading begins at +/- 25 gpm. NCEP is an acronym for the National
Centers for Environmental Prediction, US.