Ken Clark

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UPDATED! Big, Cold Southwest Storm Next Week

February 15, 2013; 1:40 PM ET

Just a quick update to my original post from Friday. Though both the GFS and European have come in with lower precipitation amounts, I do not buy that. Dynamics are still just as strong with only a slight nudge to the east of the track of the main upper-level disturbance. Therefore I am not going to fall victim to the whim of the models' output for precipitation and stick to my guns for now. More times than not, these storms bring more precipitation, not less, than models indicate especially in southern California and Arizona.

ORIGINAL POST BELOW:

Sunny skies and unseasonably warm weather covered all of California and Arizona today. Tomorrow will be another warm, tranquil day for this time of year. However, looming on the horizon is a big change coming in the form of much colder weather, rain and snow early next week.

This next storm will strike starting Monday night in northern California and spread into southern California Tuesday then east into Arizona late Tuesday night and Wednesday. The storm is likely to bring precipitation to the entire area, with the heaviest precipitation across the southern third of California and Arizona. The trajectory of the storm will bring the most Pacific moisture and greatest support aloft across these areas. The models, uncharacteristically, are fairly uniform on the track and therefore my confidence is higher than normal for a storm this far away. What I don't believe in some of the models is the amount of precipitation. While the European was higher on the amount on precipitation yesterday for this storm it now seems the GFS has along with the Canadian seem to have a better handle on these details. Given the dynamics involved higher amounts are better than lower to me. So here are some of the details.

In California:

-Rainfall northern to central California averages 1/3 to 2/3 of an inch.

-Snow levels plummet Tuesday reaching 2,500 feet in the north to 3,000 feet in the southern Sierra and coastal range by Tuesday afternoon and drop another 500 feet Tuesday night into Wednesday for central California.

-Resort levels pick up 8 to 16 inches of snow but several inches of snow could accumulate down to 3,000 feet.

-A little light rain and drizzle can occur anytime west of the mountains of southern California, but the heaviest rain will fall in the afternoon into part of Tuesday night before becoming showery later Tuesday night with a few showers lingering into Wednesday. Rainfall amounts of 0.50 to 1.00 inch seem likely with locally higher amounts in the lower foothills of the coastal slopes.

-Snow levels start out at 4,000 feet in the Los Angeles County mountains and east and 4,500 to 5,000 feet San Diego but fall to 3,000 feet late in the day and down to 2,500 feet everywhere Tuesday night and Wednesday. Resorts could pick up 1 to 2 feet of snow with 4 to 8 inches down to pass level (Grapevine/Cajon/Highway 14) and maybe a couple of inches down to 3,000 feet. If this happens major travel problems are likely through all the passes.

-Expect temperatures to be 25 to 30 degrees colder than they are today and will be tomorrow for Tuesday and Wednesday.

In Arizona:

-Precipitation will develop from west to east later Tuesday night and Wednesday with the heaviest precipitation Wednesday.

-Deserts will pick up 0.25-0.50 of an inch of rain with locally higher amounts possible, and there may be thunder and lightning.

-Snow levels also become very low dropping to 4,000 feet Wednesday. This can bring substantial accumulation to Rim Country with 3 to 8 inches possible down to 5,000 feet. Mountains above 6,500 and 7,000 feet could pick up 12 to 18 inches with chances of up to two feet.

-There will likely be travel problems across the state as well, especially the major road, I40, across the northern part of the state.

Keep track on the latest with this storm on AccuWeather.com and I will be here Monday to bring you any changes.

The views expressed are those of the author and not necessarily those of AccuWeather, Inc. or AccuWeather.com

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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.