Why is the Rain Moving East to West
Written by: Chief Meteorologist Brian Neudorff
Many of have observed and asked me on the KMVT Facebook page, “Why are the storms and rain moving the wrong way?” when they say the wrong way, they mean from east to west instead of the traditional west to east that most of us are use to. This goes back to the weather pattern I mentioned yesterday, called the “Rex Block.”
A Rex block occurs when we get an upper level low pressure system south of an upper level high pressure system which is cut off from the main flow of the jet stream and sits roughly in the same location over an extended period of time. We also call this an atmospheric blocking pattern.
The jet stream and other higher altitude winds move and steer weather systems across the Pacific Northwest and the country. Air rotates around low pressure counterclockwise and clockwise around high pressure. When you get a “high” over a “low” it forms the letter “S” with the winds coming from the bottom of the letter instead of the top.
Because of the wind flow around these two systems the winds come up from the south and then move to the west from the east north of the “Low” and south of the “high” across Southern Idaho then around the high pressure off the Washington coast. This brings moisture, along with scattered showers and storms with it until it can be moved by a change in the jet stream pattern.
We will see this pattern break down as we go into Thursday as the high pressure wins out for the end of the week pushing tthe upper level low to the east and away from the Intermountain West. This will also bring a major warm up to the region into the weekend with highs in the low to mid 80s.