Tuesday, November 25, 2008
This week will be uneventful. Today, a week front will move in during the day--with some light rain in the interior somewhere between roughly 10 AM and 5 PM (see front on satellite picture). Wednesday will be dry with sun. And then a weak system will move through late Thursday, But the big story is what will happen on Friday through at least Sunday...a huge ridge or area of high pressure.
The main chart used by meteorologists to see such ridging progress is the 500 mb chart...which shows conditions around 18,000 ft. At the level approximately half of the air is above and below. The lines are height lines, the height of the pressure surface above sea level..with high heights corresponding to high pressure. So if you see the lines buckle to the north....that is what we call a ridge and is associated with fair weather. Wind parallel the height lines with higher heights to the right.
The three images show the height lines for Friday, Sat, and Sunday around 5 PM. Note how the heights over the eastern Pacific and west coast are very high. The area of strong winds...the jet stream..is where the lines are very close together and the jet stream will be avoiding us...heading north.
The end result will be complete drying out. The exact weather depends on the exact location of the ridge. In one orientation we get offshore flow and clear skies...and in another we tend to fog in and get poor air quality. We will know more about that in a few days.
Posted by Cliff Mass at 6:27 AM