When does El Nino data begin to predict this year's precip. levels in CONUS

[the_photon]

Hey all,

A general question about using El Nino ENSO and SST (20 C isotherm, etc.) to predict precipitation levels in the continental US.

I could be highly misinformed, but it seems like somewhere I read that it's not until about April or so that any of the El Nino Zone data starts to actually correlate with summertime precipitation (May-June-July-Aug) levels in the western and central parts of the continental US.

I've also noticed that most precipitation forecasts at the US Drought monitor extend well in to next year, but never seem to say anything other than "Equal Chances" when looking more than about three or four months into the future.

It this true at all? Is there some kind of time "window" where say, the depth of the 20 C isotherm in El Nino zone 4 starts to correlate with June precipitation in Oregon?

I'm sure this is a rather large topic with a rather large answer. If you need to give me a link to a site explaining this then that would be okay too.

Thanks,

the_photon

 

[John Olexa]

Maybe these links will help ?? Because, I'll be darn if I know! http://www.elnino.noaa.gov/ http://www.esrl.noaa.gov/psd/enso/

 

[Jeff Duda]

I've also noticed that most precipitation forecasts at the US Drought monitor extend well in to next year, but never seem to say anything other than "Equal Chances" when looking more than about three or four months into the future.

I can't really speak to your other questions, but the reason you see a lot of "EC", especially on longer-range forecasts, is because predictability is very low at such long ranges. A forecaster would have a very difficult time justifying forecasting one particular phase of ENSO or temperature or precipitation 3, 4, 5,...12 months out. Because there are three regimes they are predicting (above average/Nino, below average/Nina, and approximately average/neutral), then they are forced to predict each regime to be equally likely (i.e., having a probability of 33.3% each). Thus, "equal chances".