# Thursday, January 20, 2011
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Extended Pacific Jet and Resulting Mega-Ridge
GFS Forecast for Sunday Afternoon

Over the next two weeks, the MJO signal currently propagating across the western Pacific is forecast to destructively interfere with the La Nina base state, suppressing convection in the Indian Ocean and Indonesia and enhancing convection near the dateline. This is forecast to result in a transition from upper tropospheric anomalous cyclones to anticyclones near the dateline, and an extension of the East Asian/Pacific jet. These circulation changes may eventually lead to a retrogression of our persistent West Coast ridge, or perhaps a breakthrough of the westerlies underneath the highly amplified ridge.

The key word here is eventually. Over the next week or so, the extending Pacific jet is forecast to reamplify the ridge over the West Coast. But at some point, perhaps near the beginning of February, destructive interference in the Western Pacific will dwindle and convection in the Indian Ocean will strengthen. This should result in retraction of the Pacific jet, and possibly, a West Coast trough. The 240 hr forecast of the 12z ECMWF hinted at this possibility, as did the 18z GFS. We'll see!

After starting out cold and wet, the weather this January in Southern California, and much of the state, has been warm and dry. Monday, Pierce College in Woodland Hills hit a high of 88°F, and Downtown Los Angeles (USC) 84°F. So far this January, only 0.58 of rain has been recorded at Downtown Los Angeles (USC), which is a little less than one-third of normal for the month. However, because of our prodigious December rainfall the water year total at Los Angeles is currently 6.5 inches above the normal for the date of 5.78 inches.

Earlier this month I photographed these mid-level mammatus clouds over the western San Fernando Valley. They were produced by the moisture and dynamics associated with a closed upper level low that was about 390 miles WSW of Los Angeles. To see how the clouds evolved and more about the scenario at the time, see this post on PhotographyontheRun.com.

More information concerning Southern California weather can be found using our WEATHER LINKS page.