An unusually high amplitude jet stream is resulting in the extreme transport of temperatures and an interesting alignment of precipitation across the nation. Note how the jet stream dips well to the southwest before pushing abruptly northeast. The red-shaded area indicates a maximum of wind speed. These cores of strong upper jet winds indicate a very active and intense jet stream.
Cold air has dipped well southward with Los Angeles recoding its coldest temperature (34 degrees) in 22 years Sunday. On the other hand, the eastern U.S. has experienced unusually mild weather 70-degree-temperatures spreading over much of the Mid Atlantic and Southeast U.S. In fact, the delination of cold- to warm-air is clearly seen with a mix of snow, freezing rain, and rain associated with the system.
Here is summary of precipitation from this recent active jet stream episode. The pockets of red indicate isolated streaks of 5-inches of rainfall. From a water resources recharge standpoint, note the widespread area of yellow. This area received 2- to 5-inches of rainfall.
Surplus soil moisture anomalies since January 1 are indicated in green. This area, extending from Louisiana northeast acor0ss most of Mississippi, a large part of Tennessee and Kentucky, and portions of Alabama are vulnerable for enhanced runoff and the potential for flooding. This increased vulnerability will likely persist through the rest of the month.
In fact, a number of rivers are in, or forecast to rise into, flood due to the recent rainfall. This image shows the river locations expected to flood. The red and purple spots are expected to experience the more significant flooding.
In the BWO Weekly Water Outlook, I discussed the role of the MJO teleconnection with possible enhanced precipitation. The MJO transitioned and intensified into the 5th Phase last week and now is transitioning into the 6th and 7th phases. It is interesting to see where precipitation is enhanced in these phases. You can see that precipitation can be enhanced over the South Central U.S. into the Ohio Valley during a Phase 5-6-7 active MJO. Considering the tap of Pacific moisture this weekend, this is very likely a contributing factor towards the recent significant rainfall.