It's a revolver door....

State of the Climate | Synoptic Discussion | November 2012

Synoptic Discussion

Monthly upper-level circulation pattern and anomalies.

The weather pattern this time of year normally consists of the seasonal battle between subtropical high pressure (High, or upper-level ridge) to the south and the polar jet stream and associated storm track to the north. As the sun angle decreases during Northern Hemisphere autumn and early winter, polar air masses get colder and expand the polar jet toward the south. During November 2012, several weather systems moved through the jet stream's westerly circulation over the United States, bringing above-normal precipitation to the northwestern parts of the country. Butupper-level high pressure, centered over the Southwest to central Rockies, fought back, setting up a pattern which mostly kept moisture away from the central and eastern regions and much of the Southwest. Cold frontssweeping across the Plains and into the South and East brought below-normal monthly temperatures to much of the country east of the Mississippi River, while the upper-level ridge kept temperatures warmer than normal across much of the West for most of the month. This weather pattern inhibited the formation of tornadoes, reduced the coverage of snow, and expanded the area and intensity of drought.

http://www.ncdc.noaa.gov/sotc/synoptic/2012/11

~A.