Tag: Quantitative precipitation forecast

Rain Shade Is Major

Locales have individual climatic quirks like baseball parks have ground rules. The Coachella Valley, where the vast majority of our viewers live, is a protected valley. We are flanked by mountains. We get “rain shade.” Real term. I didn’t make it up.

cansac.dri.edu flashloop.php model wrf product 2015022200 3hrPRECIP_ domain _D3

My job is forecasting the weather at KMIR. Our market, Palm Springs, covers a small geographic area. It’s not even a whole county!

People think it’s boring to forecast in the desert. Nah. Sometimes it’s repetitive. I can deal with that. There’s always something interesting going on.

Locales have individual climatic quirks like baseball parks have ground rules. The Coachella Valley, where the vast majority of our viewers live, is a protected valley. We are flanked by mountains. We get “rain shade.” Real term. I didn’t make it up.

The San Bernardino Mountains are north, San Jacinto and Santa Ana Mountains west and the Little San Bernardino Mountains are off to the east. We’re wedged in tight.

A small storm hitting SoCal this weekend will drop nearly all its rain before it gets to Palm Springs! The largest rainfall will be on the eastern slopes of the Santa Ana’s. The east face of the San Jacinto range should drain most of what’s left. The tallest mountaintops will get snow.

The notoriously awful QPF (Quantitative Precipitation Forecast) from the GFS model say .06″ Sunday and another .04″ Monday at Palm Springs Airport (PSP). John Wayne Airport (SNA), west of Palm Springs and on the coastal side of the mountains, is forecast for .33″, over three times as much.

There’s are reasons Palm Springs gets less than six inches of rain in an average year. Rain shade is major.

Rain Coming And Folks Are Excited

gfs-bufkit

“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.