Fast moving jet stream winds keep an unsettled weather pattern

There are two types of flow patterns within the jet stream: zonal and meridional.  Zonal flow means the jet stream - our highway for storm systems - moves from west to east and are running parallel with the lines of latitude. Jet stream winds are fast moving, pushing low pressure systems through within a day.  This is the type of pattern we have this weekend and next week. 

A parade of low pressure systems will move over the Pacific Northwest and into the Midwest next week.  Each one bringing with it a little more cloud cover and a small chance for showers.  Since these are not originating from the north, they have very little cold air associated with them.  This will keep temperatures next week in the middle 40's.  And while the chance isn't great, there will be a possibility for a few low impact showers Sunday afternoon, Tuesday night and Wednesday.  Nothing measurable is expected.

When the jet stream shifts into meridional flow, this means bigger changes are coming.  This is the pattern that has those big dips called troughs and big rises called ridges.  The jet stream winds are not as fast and storm systems tend to last for a couple days.  This type of pattern also leads to significant warm ups and cool downs.  By late next week the jet stream will shift into more of a meridional flow.  This is where our highs in the 50's will be coming from.  But it's also going to allow the atmosphere to be filled with a little more moisture from the Gulf of Mexico - meaning the likelihood of rain, and possibly thunderstorms by next Saturday or Sunday, the 12th and 13th.

Looking out longer range, it doesn't look like this pattern will be changing.  Several more 'larger' storm systems are forecast to move through, especially in and around the 16th and 19th-20th of December.  Stay tuned!