Friday, September 21, 2007

Late Arrival

It is actually raining now! I am posting the current radar as proof. Earlier, we saw lightning. I opened the windows so we can enjoy the sound of rain falling on the leaves of the tree outside our bedroom window. Ooh, I just heard thunder.

It is so tough to be a weather geek in LA.

Many people were making fun of Angelenos and meteorologists today. I can explain everything. There is a perfectly reasonable explanation why so many traffic accidents occur when it rains here. It is because it rains so seldom.

Road grime is greasy. It builds up on the roads unless rain washes it away. LA is a desert. When the first rain arrives after a long dry spell, and we have a lot of long dry spells, the roads become incredibly slick. Accidents can happen even to good drivers (not that I am saying we are uniformly good drivers here). People from wetter parts of the country don't properly appreciate the difficulty of living in a desert with so much traffic and, hence, road grime and so little rain.

About the other matter. People have been making fun of meteorologists all week because it seemed like the predicted rain would never come. First, it was supposed to arrive Wednesday. Nope, Wednesday was sunny. Then it was supposed to arrive on Thursday, anther bright sunshiny day. Why can't we get the day right?

It has to do with the difficulty of predicting the behavior of a cutoff low, an area of low pressure hemmed in by surrounding higher pressure areas and removed from the jet stream. For technical reasons that I don't completely understand but my coworkers do (it involves technical terms like isobaric and hydrostatic), cutoff lows don't have any place to go. So, they tend to stagnate over areas. When they do move, their motion is highly unpredictable, depending on slight pressure differences. (They can retrograde!) It is much harder to make landfall predictions for a cutoff low than for a big old hurricane with lots of momentum.


  1. We're not a desert. We're Mediterranean!

  2. You are so right. We are almost a desert. But we get more than 10" of rain annually on average so we are not a true desert.