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Western US weather expert

Spinning Pinwheel of More Cold, Rain and Snow

5/26/2010, 2:55:25 AM

First, apologies for not posting Monday. Due to some computer problems throughout the day, I just could not get to the posting. I will make up for it here with a rather detailed report of the week's weather.

The concerns from last week that yet another unseasonably cold, wet storm heading far south this week is coming true. Even though there were some differences last week in the models, when push came to shove the initial idea the models had were right.

The leading edge of this storm as of mid-morning was from the Washington and Oregon coast on south to northern California. The morning radar/satellite picture of shows the center of the spinning storm west of British Columbia and the rain moving ashore.

Around this low are going to be several disturbances that will help drag this storm south-southeast and bring enhanced episodes of rain and mountain snow inland. The first of these disturbances will be moving ashore late this afternoon and evening across northern California. This is the 12Z GFS 500mb valid at 4 p.m. Pacific time. The X marks the spot of the disturbance.

Note also the other disturbance on the western side of the low. This is a second disturbance I will talk about in a bit.

Rain now just moving ashore in northern California will spread south throughout the day reaching the Bay Area this afternoon and then moving south into at least parts of the San Joaquin Valley to the South Central coast this evening and tonight. Rain will also be enhanced for a time through western Oregon and then north into western Washington. The tail end of this part of the storm moves through Southern California Wednesday. It is possible that some areas around the LA Basin could get a shower.

The second disturbance will keep showers going Wednesday in at least the northern third of California north through Washington and Oregon

However, yet a third disturbance helps the low bottom out late Thursday into Friday. This will pull the low south to just off the northern California coast late Thursday then across northern and central California Thursday night into Friday. Here is the 12Z GFS for late afternoon Thursday.

This is likely to bring even more showers to at least the northern half of California, as far south at least as Pt. Conception and all of the San Joaquin Valley. There even could be a few thunderstorms develop. The most concentrated area of rain will be in California during this period though there will be scattered showers farther north.

And finally, yes, there will be snow for the Cascades and also in the Sierra. Probably hardest hit will be the southern half of the Cascades and the northern and central Sierra. Mostly all snow will fall above 6,000 feet in the Cascades and 7,000 feet in the Sierra but will be lower than that by later Wednesday through Friday. Parts of the Sierra will pick up a foot or more of snow before this is all said and done.

During this whole time, temperatures will be averaging below to much below normal especially with regard to daytime temperatures.

At the end of this tunnel, however, is some good news. Once the storm departs after Friday, a big warm-up occurs from California on east and south over the weekend. In fact, some sections of California by Sunday will be 5 to 10 degrees above normal. That will contrast with temperatures as much as 15 to 20 degrees below normal tomorrow through Friday.

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

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Western US weather expert