It’s early days yet in terms of a forecast for 2009-10 flow on the Colorado River. Because it depends on the amount of snow that falls on the Colorado Basin’s mountains, there is great uncertainty this early in the year. But the map below can give us some hint about the probabilities:
What you can see is the expanding area of abnormally dry conditions across southwest Colorado. A few good snowstorms can wipe out a precipitation deficit quickly in conditions like that. But antecedent soil moisture conditions do matter, because dry ground soaks up moisture that would otherwise run off into the river. The Nov. 1 soil moisture map from the Colorado River Basin Forecast Center (it’s a big jpeg, you can see it here) showed soil moisture deficits throughout the basin. The most recent median forecast for flow into Lake Powell is 83 percent of the long term average.
One thing about soils in S. Cal.. if they have been in a dry state for extended periods they become hydrophobic. So, the first rains after a long drought, just run off and barely penetrate. Fire helps make soils less hydrophobic… but only if they are not too hot.