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The late season major snowstorm that is just exiting its birthing place in the northern Rockies was seen a year ago by Doc Weather and predicted in the recent March forecast The pattern that set it up started on the 15th of March as a surge on the 72° jet curve (blue) from the new lunar eclipse point moved north into the Central Gulf of Alaska. This is depicted in figure 1. This surge, which was triggered by a movement of the lunar node, promoted the growth of a digging trough against the West Coast at that time. The trough grew southward in response to the strong surge of the ridge movng northward.
The ridge slowly drifted east from the Central Gulf of Alaska for the next few days as the trough remained almost stationary over the PNW. The trough pressed against the Sierras and Cascaded and the drifting ridge pressed against the trough deepening it and bringing moderate rains to the West Coast.
At the same time a high pressure area began forming over the western Gulf of Mexico on the 45° jet curve from the new eclipse point( blue curve over the continent). On the 15th this low latitude high was moderate in strength. But, as the trough over the West Coast deepened and dug south along the coast, it began to interact with northwestern flow around the high. This is shown in figure 2.
The high over the Gulf of Mexico grew more compressed and gained in strength as it began to block the eastward passage of the trough from the southwest. This response effectively wedged the trough in between the slowly migrating ridge over the Pacific and the ridge locked into the lee slopes of the Rockies over the High Plains on the 17th and 18th of March. Something eventually had to give way in this standoff. What gave way was that the irresistible west to east motion of the ridge over the Pacific nudged the trough eastward into a more intimate contact with the moisture flow around the western flank of the high over the Gulf of Mexico. The moisture from the south met the cold from the north and the result was a major March snowstorm for the northern mountain states.