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In October, Doc Weather published a Moon-watching article in the basics section of this site. The gist of the article was that the Moon, when transiting the United States tends to push settled high-pressure areas to the east as it is transiting the continent. At the end of the article Doc Weather gave some dates when the Moon would be transiting the continent. Those dates were December 12 to 18, 2004 and January 8 to 14, 2005. Let's look at the charts for those dates and see what happened.
On the 12th of December 2004, a settled, finger-like high-pressure area was situated over the West Coast as the Moon approached from the west in the longitude of Hawaii. On the 13th the Moon had passed Hawaii and was now approaching the West Coast. On that day, the high shifted to the east over the Great Basin. On the next day, the 14th, the Moon had caught up with the air mass as both the Moon and the high approached the High Plains. On the 15th the Moon passed the air mass and it faded rapidly so that on the 16th a weak ridge moved past the Mississippi Valley. As that happened a new area of high-pressure emerged off of the West Coast close to the original position of the high on the 12th at the start of the lunar transit period.
In January 2005 the effect of the transiting Moon was even stronger. A very developed area of high-pressure emerged in the east Pacific on Christmas day. It surged north and established itself as a major ridge over the Aleutian Islands for the next two weeks. This was a very long-lived and tenacious high. On the 7th of January 2005 the ridge consolidated into what is known as an omega block. The omega block is pictured in figure 2 as the long pendulous mass of air going up from Hawaii into the Aleutian area. The circulation around the eastern side of this block brought very cold air down the coast that triggered massive flooding in Los Angeles. On the 9th of January the Moon made it's first approach to the West Coast since the December passage described in the first paragraph. The block over the Aleutians had maintained itself for most of that time when the moon was transiting the Atlantic, Eurasia and then the western Pacific. Now the Moon was returning across the Pacific towards the coast. What would happen to this monumental block as the Moon approached it from the west?
The chart shows that on the 9th as the Moon approached the Hawaiian Islands the block began to fade over the Aleutians. On the 10th, as the Moon passed to the block the dislodged high-pressure mass had moved to the southeast. On the11th as the Moon passed on to the continent this large mass of high-pressure air had lost its strong center and was collapsing towards the coast. On the 12th, as the Moon was transiting the Gulf Coast the once strong block was now just a drifting ridge. Finally, on the 13th, as the Moon was entering the Atlantic, the ridge was an open mass of general high-pressure crossing the coast in the wake of the Moon, that was now moving past Florida. This high was in place for weeks and was only moved on by the passage of the transiting Moon.
It would appear then that the transiting Moon sequences are something to keep a weather eye on. The next one starts on February 6th as the Moon once again approaches Hawaii for its February transit. Lets watch and see if the stable and dominant highs now in place over the West Coast, High Plains, and Northeast and will be moved eastward and neutralized by the motions of the transiting Moon.