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Record rains in Southern California; Winter 2005 - 03.01.05

A strong blocking pattern brought record rains to Southern California this winter. Find out about this pattern from Doc Weather.

The recent record rains in southern California were part of a blocking pattern known as an omega block. This block gets its name from the Greek letter omega. An omega looks like a horseshoe open at the bottom. An omega block forms when a high-pressure area that is in a low latitude position surges to the north forming a long vertical ridge. At the same time two low-pressure areas dig to the south on either side of the surging ridge. The lows lock in place to the east and west of the position of the ridge. The jet stream flows south to the first low then north again around the high-pressure area then south again around the second low. The patterns around this circulation tend to stabilize as these features feed off of each other. The average duration of the omega block is from five to seven days.



Figure 1 shows an omega block that formed over the eastern Pacific in January 1998. The features just described result in a pattern where the western low draws cold air down to the south and then feeds it rapidly to the north usually with an abundance of water. This is because the cold air moving southward tends to pick up moisture over warmer areas. The moisture is then shunted north where it cools again. Then the jet stream once again digs south and usually deposits the gathered moisture into the western side of the eastern low. The ridge in between is most often the site of very dry weather, while the two lows are often the sites of abnormal precipitation. After a week or so the block usually dissipates and drifts to the east.

From December 30, 1997 to January 5, (figure 1) 1998 an omega block in the Gulf of Alaska created strong rains for northern California and the PNW. The eclipse positions for that event are seen in the solar and lunar points and their reflex points. The 72° jet curves from the eastern pair were being influenced by both Saturn and Jupiter. On December 30, 1997 Jupiter moved in arc putting a high-pressure influence on both 72° jet curves. On that day a ridge grew from the longitude of Hawaii north towards the Aleutian Islands as a low dug to the south in the longitude of the two 72° jet curves On the next day, December 31st, Saturn moved to high-pressure also on both of the eastern eclipse points. This surged the ridge again and stabilized the low that had dug south. For the next four days the ridge from Hawaii to the Aleutians was the site of strong high-pressure as a low formed over the central Pacific to the west of the ridge and a low formed over the eastern Pacific to the east of the ridge. The western low brought heavy rains to the PNW and the Sierras. On January 4th Jupiter moved in arc and brought a low- pressure aspect to the 72° jet curves. The ridge faltered on the 5th and then on the 6th the ridge pinched off in the north and drifted into the polar regions and what was left of it collapsed farther to the south and drifted to the east as the pattern broke down. During this event the ridge occupied a space that was coincident with the placement of the 72° jet curves from the eastern pair while they were under high-pressure aspects.

It should be noted that during December 1997 Mars was transiting the West Coast at its maximum southern declination This influence is often coincident with the formation of omega blocks as well as being a factor in many El Nino scenarios. There was a strong El Nino unfolding at that time. The southern passage of Mars seems to pull the jet stream to the south on the West Coast. This supports the placement of the two low latitude low-pressure areas around the bottom of the omega.



In figure 2 the eclipse grid pattern for the recent flooding in Southern California is depicted. From the figure it can be seen that the important nexus of the four 72° jet curves is placed over the Great Basin. However, the 45° jet curves over the eastern Pacific are closer to the coast during this year than the 72° jet curves were in 1998. This means that any blocking pattern on the western pair of eclipse points over the mid-Pacific will produce a block into the Gulf of Alaska. An omega pattern there would bring a strong jet due south against the West Coast. That has been one pattern in the unprecedented rains in Southern California this winter. Similar to 1998, in 2005, Jupiter was again a factor in forming the flooding and blocking patterns but in contrast to 1998, this time it was placed over the western Pacific. From that position it influenced the western pair of eclipse points. The two 45° jet curves over the eastern Pacific are part of that influence. Once again, similar to 1998, Mars crossing the West Coast at a maximum southerly declination had an influence on the jet stream. This was evident during most of the winter of 2004-05 as a moderate El Nino pattern evolved in the eastern Pacific, although this El Nino was not nearly as severe as in 1997-98.

In figure 2 the planetary influences from Jupiter and the lunar node on the 7th of January 2005 are depicted. From this position Jupiter established a strong high latitude high-pressure area over Alaska as it aspected the lunar reflex point to high-pressure values. This influence manifested as a block on the 45° jet curve from the lunar reflex point (blue). With this aspect a high parked over the eastern 45° jet curve. At the same time Jupiter aspected the solar reflex point to low-pressure. This aspect manifested on the 45° jet curve to the west as a strong tendency to low-pressure (red 45° jet curve). A low formed on this curve. The interaction of the two 45° jet curves set the stage for an omega block. At the same time the 72° jet curve from the solar reflex point was also aspected to low pressure (red curve running southwest to northeast across Southern California. This placement coupled with the Mars low declination transit pulled the jet far to the south.

From the eastern pair of eclipse points the node had aspected the two 72° jet curves over the western states to low-pressure (red 72° jet curves over the Great Basin). The westernmost of these two formed a curve that ran generally parallel to the West Coast from Baja California to Vancouver BC. A low formed on this curve off of the coast in the longitude of Vancouver, where the curve crossed the mountains out into the ocean. The low there received the jet from the high over Anchorage and the circulation of the low directed very cold fronts down the coast and into southern California. This block with the accompanying locked low-pressure areas formed on the 7th and held on until the 11th. During that time violent storms brought stunning levels of snow and rain to the south state. In Reno this was the biggest system to hit that city in 89 years. Eventually, the high moved off of its position as a result of the moon transiting the West Coast on the 11th. Jupiter, aspecting the 45° jet curve from the lunar reflex point kept the block intact from a position at 23° Virgo while the node at 3° Aries kept low-pressure dominant over the West Coast. Taken together the two planets provided a perfect patterning for an omega block.

Rapid shifting of Saturn, Mars and the lunar node dominated the next two weeks by forming a series of changing aspects that supported moving ridge patterns rather than blocking highs. Following this pattern on the 28th of January, Jupiter moved in arc to a new degree that also supported moving ridges on the two 45° jet curves over Alaska. As a result any highs that emerged in the eastern Pacific from January 12th to the 28th would surge briefly to the north, block for a day or two and then move eastward instead of locking into position.



In a curious set of events, the placement of a block stimulated by Jupiter at a high-pressure aspect to the lunar reflex point once again occurred in the early part of February 2005. However, at that time Saturn, aspecting the solar reflex point to strong high-pressure put high-pressure values on the western 45° jet curve over the eastern Pacific. This created a strong condition for high-pressure across the whole eastern Pacific. The node working on the eastern pair of eclipse still kept low-pressure values on the 72° jet curve to the solar point. The shift to high-pressure over the tropical eastern Pacific was in contrast to the pattern of early January, when the western 45° jet curve was aspected to low-pressure and the 72° jet curve against the coast was also aspected to low-pressure. In the earlier pattern this put the sequence starting in the west at low / high / low. This spacing set up the omega pattern. In the later pattern the high linked between the 45° jet curve from the lunar reflex and the 72° jet curve also from the same point. This gave a twist to the formation of storm energies off of the coast.

On the 8th of February, Jupiter, moving retrograde, once again aspected both the 45° and the 72° jet curves from the lunar reflex point in the eastern Pacific to a blocking pattern. Two days later Saturn created a strong high- pressure signal on both the 45° and the 72° jet curves from the solar reflex point. With these two aspects all of the jet curves over the eastern Pacific were aspected to high-pressure. The result was the formation of a broad shouldered high that pushed up from the desert Southwest into the Pacific Northwest (blue arrow). The large blue high-pressure area in the chart shows the block. It had its origins in the two high-pressure 72° jet curves over the tropical eastern Pacific. A smaller high was to the west. By the 13th the high surging up the coast began to block a low that had been sitting off of the coast of southern California (red area) as a general low-pressure area for about two weeks. The growing block pushed the low into the ocean and then prevented it from moving across the mountains. The pattern that established the blocking for this low was the establishment of high pressure on both 72° jet curves from the western pair of eclipse points. The low off of the coast , that had drifted south into the southwest at the end of January was now trapped over the ocean in a space between a whole set of high-pressure areas.

The trapped low over the ocean picked up moisture and began sending it to the east as front after front poured into Southern California (red arrow). The onslaught raged for nine days between the 14th and the 23rd. On the 24th Neptune and the node both shifted to produce high-pressure on the 72° jet curve from the lunar point at 10° Aries in the eastern pair of eclipse points. This shift put high-pressure against the coast to the north and south and closed the storm door into Southern California. The strong buildup of high-pressure against the coast pushed the jet to the north on the West Coast. This brought the first rains into the PNW in weeks. A final storm in Southern California arose on the 26th as the low stationed off of the coast finally passed to the east around the southern flank of the high that was stationed over the whole West Coast instead of just being trapped by high-pressure in the south.

As a final note, Mars crossed the West Coast on February 21st. The longitude for that crossing is either 130° W longitude or 15° Sagittarius. It has been repeatedly observed that when a fast moving planet is transiting the east Pacific that this transit is often accompanied by a southerly placed east Pacific jet stream bringing wind and rain. It has also been observed many times that the turbulent phenomena subside when the transiting planet crosses 15° Sagittarius. The Mars crossing was a dramatic example of this pattern. On the 21st as Mars crossed the coast the low that had been locked in place off of the coast for seven days slowly began to lumber to the east. By the 26th it was over Texas ending a remarkable set of storms for Southern California.