This series of maps depict various aspects of the atmospheric circulation both near the surface and at upper levels.  Select desired field from menu at left or the drop-down menu above.

These maps are based on the NCEP Reanalysis data.  NCEP is an acronym for the US National Centers for Environmental Prediction. 
 

Aids to interpreting plots:

Definitions

Climatology	The long-term average of a given variable, often the 30-year period 1971-2000.
Anomaly	The difference between the observed value of a variable and its climatological value.
Pentad	A 5-day average of a variable, starting from 1-5 Jan, 6-10 Jan, ..., 27-31 Dec.  On plots using pentad data, the date for the "middle" of the pentad is displayed: 3 Jan, 8 Jan, ... , 29 Dec.
hPa	The abbreviation for "hectopascal", a unit of atmospheric pressure.  For comaprison, the atmospheric pressure near the earth's surface is roughly 1000 hPa (its less at higher elevations).  The 250 hPa level in the atmosphere is roughly 10 km above the earth's surface.  One hPa equals one "millibar" or "mb" the pressure units also displayed on some plots.