Last week, California was baking in record heat with the hottest weather of the season for many places. What a difference a few days make.
A cold, closed 500 mb low just west of northern California late afternoon Monday will swing south and east Monday night and Tuesday, passing right through central California Tuesday. Though there is not a lot of moisture associated with this weather-maker, ahead of, and under, this low are likely to be scattered showers and thunderstorms in the lowlands. These are likely to reach as far south as parts of the Central Coast and San Joaquin Valley.
It will be cold enough in the Sierra high country for snow, and accumulating snow at that. Here is a look at what the GFS has for temperatures at 500 mb and 700 mb around midday Tuesday. Temperatures are as low as minus 22 C to minus 24 C at 500 mb and minus 4 to minus 6 C at 700 mb.
These temperatures are cold enough to bring snow levels down to 7,000 to 7,500 feet. Expect to have periods of snow showers, even with thunder and lightning in spots, later Monday night and Tuesday, ending Tuesday evening. Snow accumulations above 7,500 feet are likely to average 1-3 inches, but there could be locally higher amounts. This does not sound too bad if it was midwinter. However, this is the time of year that hikers and campers head to the high country. This big change in the weather could lead to some very unpleasant weather conditions if caught out in it, especially if one is not equipped for it. There is also likely to be snow fall over the road passes of the Sierra, like Donner Summit, but no major travel delays are expected as a lot of the snow will melt especially during the daylight hours, but any brief snow or slush accumulation can lead to slippery conditions.
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The remainder of the week a large building ridge of high pressure takes over
There will be more showers and thunderstorms are likely that can produce very heavy downpours in Arizona.
This rain caused problems with flash flooding producing some damage and there were a few swift water rescues.
Computer models are insistent that a rather strong piece of energy will move through California Tuesday, bringing more widespread rainfall.
This will make for a very hazardous period for firefighters into early Friday night.