When Will It Get Cold?
At least we're not in the 60s to near 70 like Christmas week, right? It is colder, but still above average. I'm going to geek out here a bit and show you some the things driving our weather pattern and the POTENTIAL for cold air down the road. I caution you, this is long range stuff and it can easily bust.
Below is the GFS Ensemble near surface temperature anomalies valid January 18th. There's a tremendous amount of cold over Canada, especially western Canada. That's good news if you are looking for and wanting cold air. What can bring it south?
Right now, there's a strong trough over southern Alaska in the upper levels. The flow around the ridge to the south (eastern Pacific) and the flow around the trough (counterclockwise) is feeding much of the United States with Pacific air. That trough needs to go away and a ridge (in red) needs to build into Alaska and western Canada to shove the cold air south (map above)
Now onto a teleconnection index I like to look at called the "EPO". That stands for Eastern Pacific Oscillation. See the 0 line? It runs in the middle from left to right. The model also goes out in time from left to right. Notice the Euro Ensembles keeps the EPO in the positive (top) for a long time. That correlates to troughing over the eastern Pacific and up into Alaska. It keeps the cold out of the United States. Once it goes to near 0 or negative, that's a signal for Alaskan and western Canadian ridging. That's good if you want cold air. The flow around the ridge dislodges the cold air and sends it south.
The GFS ensemble shows the same thing. I dip to negative on or after the 17th.
Now, look at that! The GFS ensemble valid the 18th places a ridge right where the trough is located now. There's a downstream trough over southwest Canada into the Pacific Northwest. While this is an improvement, it's not everything I would like to see. That ridge over Alaska needs to be further east and hugging the west coast. This would help dislodge the cold air and send it south, but where EXACTLY? Typically, it comes charging down the plains, but we'll see how much gets into the intermountain west IF the long range models are correct.
Again, I caution, long range forecasting is VERY TRICKY! At least there's something to watch.