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Weather Throws Us a Knuckleball

Mar 4, 2010; 2:05 PM ET

With spring training getting underway, it's appropriate to use a little baseball metaphor today, as I did in the headline. We all know that closed lows can be a weatherman's woe. Computer models tend not to handle these well, and the next storm is no exception to the rule. I will try to get some glove on this storm, hoping not to boot it and make an unforced error.

Once again, I will show a satellite picture of the Pacific to get things started.

A mass of clouds off the Northwest coast on south with the back edge along 135W is the beginnings of this next storm. What is going to happen is that a lot of energy digging south on the western side of this trough will force a closed low to form by Friday morning just inside of 130W off the northern California coast. This low will then slowly dig almost due south a fair distance off the coast. Here are two maps from the GFS showing the position of the low Friday morning at 12Z and Saturday morning at 12Z.

Friday Morning:

Saturday Morning:

Earlier in the day, the NAM was farther east with the low, bringing more precipitation to the east, and was quicker with the rain developing Friday and Friday night. But the 18Z run of the NAM has come in and now pretty much agrees with the GFS. The 18Z GFS is pretty similar to the 12Z run of the same model.

What this means in general is that rain will be slower to develop from north to south than we had and will not move as much inland. Rain will develop along the northern California coast Friday morning and will keep developing to the south during the day and night. This rain could be light and even spotty. Rain will make little progress to the east, and may not make it at all into the Central Valley through much of Friday night. Rain does not arrive until after 12Z Saturday along the Southern California coast with only light rain amounts in central California. Again, two more maps from the GFS at 18Z Friday and 18Z Saturday showing precipitation that has fallen in the previous six hours.

GFS Friday Afternoon:

GFS Saturday Afternoon:

Note that my arrival time of precipitation is still a little faster than the GFS.

The most significant precipitation this storm brings will be in the southern third of the state, developing from west to east Saturday through Sunday morning. The cold low will produce showers and, in spots, a thunderstorm. Any shower can have a hard downpour, and any thunderstorm could have small hail and an isolated funnel cloud or waterspout. Snow levels are likely to drop to 4,000 to 4,500 feet with 6 to 12 inches above 5,000 feet in Southern California. Total rain amounts in central California will be light, especially in the Central Valley.

Precipitation will not move into Arizona until late Saturday night and Sunday from west to east.

The big difference from what this storm looked like from yesterday to today is that it will be slower, and its effect will be much less inland in central and northern California and across the Sierra than it looked yesterday.

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About This Blog

Ken Clark
Ken Clark's Western U.S. weather blog tackles daily weather events with commentary from one of the most experienced and trusted Western U.S. weather experts.