Last April and May we had a large-scale pattern that jumped back and forth between Omega and Rex Blocks from the eastern Pacific to central North America. The atmosphere has returned to that pattern this Fall for the last few days. The above is last evening's 500 mb chart (00z anal 7 October 2012, from the GFS). The pattern exhibits a very distinct Rex block over the eastern Pacific. The block gradually weakens during the next few days, as the cyclone at 40N is kicked eastward. That cyclone at 500 mb will impact the Southwest during the coming week as it moves inland; however, models are keeping it as a fairly dry system.
Repeat from last Spring: Historical note - The Rex Block was named for Commander Daniel F. Rex, Office of Naval Research. Rex studied large-scale blocking patterns under Carl-Gustaf Rossby at the University of Stockholm and received his Ph.D. in 1951.
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