(Image source: NOAA)
An upper level low that originated this weekend west of the Appalachians has now transitioned all the way to the New Mexico, Arizona border. If it continues this motion, it will exit the continent somewhere near Baja or Southern California this weekend, having pushed over 3,000 miles against an extraordinarily week Jet Stream.
Yesterday, a second low developed in the wake of the first over the southeast, slowly drifting east to west behind the first.
Today, this double barrel retrograde system brought rains and localized flooding to a wide region including Florida, Georgia, the Carolinas, Texas, New Mexico and Arizona. Miami, which consistently suffers from flooding these days due to an antiquated water management system unable to cope with encroaching seas and more intense rains brought on by climate change, was blanketed by high waters. City offices handed out sandbags to residents who saw roadways, golf courses and yards disappear beneath the flooding rains.
In Atlanta, warnings were issued as a local river approached flood stage and waters continued to rapidly rise as Houston experienced flooded roads and dangerous driving conditions. Less heavy downpours were reported throughout the Carolinas and into New Mexico and Arizona. The western rains may be welcome, as they help to alleviate drought conditions that have lasted for more than a year. In the east, rainfall has saturated many areas causing added concern for what is expected to be a busy hurricane season.
This rainy, backwards moving weather has been facilitated by an extraordinary weakness in the Jet Stream over the US. The pattern and weak upper level wind flow have resulted in retrograde weather affecting much of the US, now for five days running. You can view these dual weather systems moving backward over the US via the following NOAA animation:
The first retrograde low can be seen moving into Arizona, the second is centered over Georgia, and another system looping over Maine and into the backward upper level wind pattern will potentially recurve into the East Coast over the next 36 hours.
Dr. Jennifer Francis of Rutgers University has been presenting compelling research that shows that Arctic sea ice loss significantly affects the upper-level atmospheric circulation, slowing its winds and increasing its tendency to make contorted high-amplitude loops. Such high-amplitude loops in the upper level wind pattern (and associated jet stream) increase the probability of persistent (that is, longer-duration) weather patterns in the Northern Hemisphere, potentially leading to extreme weather due to longer-duration cold spells, snow events, heat waves, flooding events, and drought conditions.
Given the strange backward moving weather events of the past week, weather system motion retrograde to typical upper level flows may also be a likely result.