Since last Wednesday I’ve been talking about the chance of the Palm Springs area getting a few sprinkles this Thursday. In most places caring about an iffy forecast for a tiny event so far in advance would be a non-starter. Not so in the desert where long time residents look forward to our few cloudy days!
So, here we are Monday. This is the sixth day since rain was first mentioned. I’m barely closer to knowing than I was then!
First, an admission. Without supercomputers no one could attempt a seven or eight day forecast. The atmosphere’s just too complex. But computer’s have shortcomings. I use the GFS model this far out.
The entire globe is covered by the GFS at a base horizontal resolution of 18 miles (28 kilometers) between grid points, which is used by the operational forecasters who predict weather out to 16 days in the future. Horizontal resolution drops to 44 miles (70 kilometers) between grid point for forecasts between one week and two weeks.
One point every 18 miles! At that resolution mountains disappear. Everything becomes a coarse approximation.
Later today Thursday will be seen in the much higher resolution CANSAC (California and Nevada Smoke and Air Committee) WRF model. CANSAC’s WRF only sees out 72 hours, but with 2km (1.2 mile) resolution.
For the geekiest reading, here’s the hardware CANSAC uses to run the WRF.
The CANSAC WRF real-time forecast system is operated on an SGI® ICE 8200 high-performance computer. Specifications are:
256 cores (Intel Xeon X5570)
384 GB RAM memory
20 TB disk space.
In the interim lots of human expertise is needed. The mountains west of the Coachella Valley are critically important. The models might not resolve them well, but I have to. They are a major reason we see less than six inches of rain in an average year (just over two inches since this year’s ‘wet’ season began in October).
I said Wednesday the coast was much more likely to see rain than Palm Springs. That still holds true.
If we get anything it will be tiny. In the desert that’s enough to perk ears.