Statistically beyond a 100 year flood. Of course, nature doesn't follow stats. Vacation canceled so I could cover the flooding, hope you heard our special coverage on-air with Mark Arum and me and the rest of the news and traffic team Monday afternoon and evening 4-8pm. I'll reschedule the vacation.

I wanted to cover the causes which have been neglected with all the breaking coverage.

It starts with the northern hemispheric flow which developed early last week a double Omega block configuration of the jet stream combined with a Rex block. As the blocking terms imply it blocks weather systems from moving so they remain locked in place. The jet stream resembles the Greek letter omega. We had a double-- off each coast-- very unusual, with a cut-off low underneath the upper high to its north, that's a Rex block.  This is the equivalent in the upper air flow of having multiple obstructions in multiple pipes clogged in your home plumbing so nothings moving, that's number one.

Number two is GA being on the East flank of a stuck tropical low pressure system (not a tropical storm but close) that came up out of the gulf of Mexico into LA moved North and stalled under the blocking pattern. This gave us a dual moisture source off the Atlantic from the Omega block high over New England and gulf of Mexico pure tropical air coming from the south and southwest, this deep tropical air mass had an unusually high rainfall efficiency in the saturated atmosphere-- so when it rains the drops are larger and more concentrated than typical, think orange concentrate, you get more rain per cloud than in a more average moist air mass: precipitatable water levels in the atmosphere were greater than 2 inches-- more like the deep tropics.

Third factor, occasional short-wave disturbances (upper-level energy lifting mechanisms, swirls or ripples of low pressure waves in the jet stream) aloft which aided surface convergence (through upper-level diffluence and divergence) which added lift to the atmosphere squeezing out the soggy sponge clouds even more.  The series of short-waves coming in periodic waves, and with the SW to NE flow stuck thanks to that blocking, it remained in place for days instead of being a transient pattern as would be the norm.

Fourth, related to all of the above. With the persistent Southwest flow of super-saturated gulf air containing upper-level disturbances when a single storm cell, group of cells or line of rain formed from the upper-air divergence and low-level convergence it remained in place wherever it set up, so one time the west side might be pounded while the rest of the area was drier then the next time it would be opposite etc. Further aggravating factor is said air flow aloft was light, so instead of heavy storms coming and going at the typical 25-55 mph speed of severe storms, they were putt-putting along at just 5-15 mph allowing them to keep the downpours going on and on for longer than normal with any given heavy cell. It's interesting to note if you looked at the daily weather map for the days in question there was no surface front or other feature over the area, had you just looked at fronts and surface pressure you would not have expected much rain!

And with the flow parallel to the the rainclouds instead of perpendicular, the cells moved over the same areas instead of moving THROUGH them, because there was no "push" thanks the the air flow being parallel along the path of moisture convergence.  This is the so-called "training effect"... cloud bursts along a train track in the sky following the same path, like box cars loaded with rain water crossing over the same spot over and over because the atmosphere is blocked from moving the track, 9-15 inches of rain commonplace with some 18-20 inch totals.

All these unusual factors at once coming together repeated from time to time for 7 days and reaching a peak in a 24-36 hour period = the perfect storm. Seeing the sun again, priceless.