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The recent flooding and heavy snow pattern on the West coast was the product of an unusual high-pressure pattern known as an omega block. In the omega block a high that has formed at a low latitude suddenly surges north as two low-pressure areas drop south and bracket the lower reaches of the high. This forms a shape in the jet stream resembling the greek letter omega (this looks like a horseshoe). Figure one is an example of the sequences leading up to the formation of an omega block. In image A an area of general high-pressure is flowing under an area of general low-pressure. In image B the high-pressure starts to grow stronger and surge up from the south. In this pattern this air mass. surges to a higher latitude as the low- pressure areas to the north get drawn to a lower latitude around the retreating high. In the third image the high-pressure area has formed a separate cell at a high latitude and the lows have dropped down into the area that the high has just vacated, forming the omega. In this type of pattern the jet stream stays intact all around the top of the horseshoe and the lows stay in place for as long as the high latitude high stays locked in its place. In general a five day duration is most common for this type of block. The area in the high-pressure zone has clear weather. The area around the western low has stormy weather and the area around the eastern low not only has stormy weather but the storms are very cold due to the cooling of the air as it passes across the top of the omega.
In the summer this type of block can set up drought conditions in the area of the high-pressure. In the winter the low pressure areas can sit and spin for days delivering front after front to stricken parts of the country. This was the pattern (figure 2) in the first week of January 2005 when an omega block in the eastern Pacific kept strong storms locked into the PNW and the circulation around the eastern lows brought record rains and snows to the West Coast.
The image in figure three shows the pattern that set up the conditions for the emergence of the omega. In late December, a strong low latitude low was situated on the two 45° jet curves from the western pair of eclipse points. On the 21st of December, Saturn (in Gemini) began aspecting these two western eclipse points to high-pressure as it moved in arc This is shown by the two blue jet curves over the eastern Pacific. After the move, high-pressure took the place of low pressure in the eastern Pacific. At the same time, the lunar node, in the vicinity of the eastern pair of eclipse points, was aspecting the 72° jet curve from the solar reflex point at 26° Pisces to low pressure. This is shown by the red jet curve that runs up the West Coast. The Pacific block pushed the jet stream to the north in the eastern Pacific and cold descended into the N Plains states by entering into the PNW at the place where the low-pressure curve crossed Vancouver Island. After crossing the Plains this track delivered record snows to the Ohio Valley.
In figure 4 the high-pressure has moved to the west in the Gulf of Alaska. This was in response to a Jupiter motion in arc on the 28th of December. On the basis of this motion Doc Weather had predicted good rains with the jet to the south on the West Coast between the 2nd and the 4th. The chart shows that the Jupiter motion in arc influences the western 45° jet curve, from the solar point, to high-pressure (blue) but the more easterly placed 45° jet curve from the lunar reflex point at 10° Libra was now influenced to low pressure (red). As a result the previous high against the coast, broke down and migrated west to sit on the 45° jet curve that was still under a high-pressure influence. This is a typical motion for these well situated blocking highs. They migrate to the closest high-pressure jet curve when the jet curve they are sitting on shifts value due to a motion in arc event. With the westward migration of the block the jet stream dropped down along the low-pressure influence of the 45° jet curve from the lunar reflex point at 10° Libra (red). In the meantime the lunar node, over the eastern Atllantic, had also shifted on the 28th. This shift brought high- pressure values to the 72° jet curve from the solar reflex point at 26° Pisces (blue). This created a blocking situation along the mountains of the western Cordillera over the Pacific Northwest. As a result of these motions the east Pacific jet looped up into a high latitude area over the Aleutians along the high pressure 45° jet curve and then the loop to the south along the low- pressure jet curve centered the east Pacific polar jet against the Cordilleran block in the Pacific Northwest locking it in place. The resulting jet stream resembled image 4 going into the New Year. The locked low began sending fronts down the coast into California.
It should also be noted that in the longitude of Hawaii Mercury and Venus were carrying on their tandem motions at low declination angles. The potential for strong events from these tandem motions has been described in Doc Weather in a number of places and here is another example of how low latitude tandem transits direct the jet stream on the West Coast to drop to the south in unusual patterns. See the article in Hotspots titled Venus has a new boyfriend for details.
In figure 5 we see the situation that arose on the third of January when Pluto (in Scorpio), moving in arc, stimulating low-pressure values along the whole eastern Pacific (red curves). The lunar node was still influencing strong high-pressure along the 72° jet curve in the Pacific Northwest (blue curve) so the low-pressure areas along the coast were not able to break through the blocking pattern to the east. This was so even though the blocks never showed up on the 500mb chart during this time. A more general high-pressure area along the coast kept the lows to the west of Vancouver Island locked in place. Due to the shift to low-pressure along the western 45° jet curve from the solar point at 26° Virgo, the high that was situated there lost its moorings on that curve. The high wandered about in the high latitudes over Alaska and tried to spread eastward to the general high-pressure area that was being influenced by the 72° jet curve from the lunar node. This motion only increased the locking pattern on that jet curve and the trapped low circulated off the coast spawning a whole phalanx of fronts that marched south along the Cordilleran block along the coast bringing torrential rains to southern California.(blue arrow)
The last image shows the shift that took place on the 7th of January. Jupiter moved in arc on the same day that the node also moved in arc. These moves radically altered the pattern over the eastern Pacific. The chart shows the western 45° jet curve in the eastern Pacific still under a low-pressure influence (red curve). However the eastern jet curve from the solar point at 26 Virgo shifted to high-pressure values (blue curve). This centered the high latitude high over that curve and created the onset of a strong omega block. This pattern was supported by the nodal shift that placed low pressure (red curve) on the 72° jet curve from the lunar point at 10° Aries. This had been the blocking influence in the PNW for almost two weeks. With these motions the high situated between the two low-pressure jet curves locked into an omega blocking pattern. The low that was locked against the coast slowly began to drift to the south followed by strong cold from the eastern side of the omega. With this motion, a final burst of torrential rains poured into Southern California bringing mudslides to the coastal areas and record snows in the Sierras.
Just as the storm started drifting to the south the moon approached the coast from the central Pacific. This lunar motion helped move the still potent storm to the east away from the coast finally giving some relief from the relentless rains. Doc Weather had also predicted rain storms for the coast in the second week of January 05 based on three aspects, the lunar transit, the tandem motion of Mercury and Venus near Hawaii, and the shift to low-pressure on the 72° jet curve from the node. What was unexpected was the extent that these influences would interact with each other to produce the remarkable storms of January 2005.