A Definite Maybe

rtwrfdomainsSince 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.

Rain Coming And Folks Are Excited


“It will be good for the state.” Those were Helaine’s words a few minutes ago. We were talking about the threat of rain in SoCal. We’ve had hardly any since last year’s rainy season–also a dud.

The image above is a screengrab from the afternoon GFS, using BUFKIT. If you want to know what kind of person I am, I find it fascinating. I like charts, graphs and numbers. They like me back!

I’m not going to be a whiner. Drought sounds and is bad. However, our infrastructure was designed knowing we get droughts. It needs much less than normal rain to work properly. No one is being forced to conserve.

We will finally end the fire season. That will be a relief to many. California has a tendency to burn.

Our first rain comes Wednesday evening. A cold front off a low hitting the California Coast near the Oregon border is the trigger. Not a lot. The GFS says around a quarter inch.

Meteorologists are lucky here. I’ve read and seen all sorts of quantitative precipitation forecasts (QPF). It’s our least accurate prediction. They’ll all be wrong, but unlike snow, no one will check up on them.

The rain (and snow) should be significantly heavier farther north, including the Sierra Mountains. They are our sponge! Snowfall in the mountains is slowly released through early summer. Much of what would run to the ocean now flows toward the Southland.

Water from the Sierras is California’s lifeline. It’s how we house people and grow crops in the desert! Like so many other spots in America, we have overcome nature to tame a place not naturally suited for any of what now happens on it.

The second wave of rain arrives Friday morning. The GFS shows three inch range, much more than this area can easily perc. Flooded intersections and slow traffic will follow. Thunderstorms, less frequent here than back east, are possible with heavy embedded downpours.

NEXRAD is pretty bad here. Too much topography. There are lots of holes using individual radars. This is one place where composites help.

During these storms our temperature will stay in the 60s.

Friday’s deluge will taper to showers then some scattered drizzle under cloudy skies through Sunday. People here are looking forward to this brief change. I will miss my friend, the blue sky.

Weather’s Swiss Army Knife

I know meteorologists who don’t use this and for the life of me can’t figure out why!

I try not to talk about weather too much here. I’d rather not be in competition with my bosses business. However, there is a tool I use on a daily basis–BUFKIT.

BUFKIT is like a Swiss Army Knife for weather! It’s freely distributed by the Weather Service as is the data that feeds it. I know meteorologists who don’t use this and for the life of me can’t figure out why!

BUFKIT is a forecast profile visualization and analysis tool kit. It is targeted as a training and forecast tool for the decision makers of the National Weather Service. It is also available to anyone that would like to explore very high vertical and temporal resolution model output for specific point locations.

Weather maps show a large spatial area for one specific time. BUFKIT shows single points for an extended period of time. It’s possible to turn parameters on-and-off so you can look at the atmosphere top-to-bottom as weather systems move through.

I can’t overstate this program’s importance to me.

There’s a fresh version out and since it’s free I thought I’d mention it. If the weather interests you this is a download you’ll enjoy.

I’m Just Watching The Weather

There’s just something rhythmic and soothing and satisfying about our atmosphere, but the only way to see it is through the charts and maps and columns of numbers. The real atmosphere is much too large for us to see more than a tiny piece.

It was snowing on my way home from work. My driveway was coated a half hour ago. Now we’ve gone to a rain/sleet mix and it’ssnow-covered-bush.jpg just wet. The atmosphere’s fickle that way.

I was just spending some quality time with the RUC or Rapid Update Cycle weather model. This would have been unheard of years ago. This bad boy is re-run every hour. Faster computers are totally responsible for making that possible.

It’s a short range model. You look at it to get a feel for the next half of the day.

The RUC is a hybrid sigma-isentropic analysis and forecast system. It has a horizontal resolution of 13 km and 50 vertical layers.

Yeah. Uh huh. My words exactly.

The guts of these models are very heavily dependent on advanced concepts in math and physics. I use the outputs without totally being conversant in the minutiae and magic that makes them tic.

Anyway, I was looking and absorbing when I asked myself, “Why?” Why do I look?

It’s 3:00 AM. Work’s done. There’s nothing I can change for the viewers. Then it hit me. I really enjoy this stuff.

I wish I could explain it properly, because I know most people are intimidated by math. There’s just something rhythmic and soothing and satisfying about our atmosphere, but the only way to see it is through the charts and maps and columns of numbers. The real atmosphere is much too large for us to see more than a tiny piece.

On paper or a computer screen the undulations of the atmosphere begin to make sense. The first time you connect with that is a Eureka moment–like a light switch has been thrown. In the history of man that’s only possible now.