Monday, April 17, 2023

What's Driving The Big Temperature Changes?

We just came off of the warmest seven day period since the middle of last September. 

64, 74, 80, 82, 82, 80, 79

Winning lotto numbers...not bad considering is occurred between April 10 and the 17th.  Look at these temperature ranking during the period. 

We came off of a highly variable March. No long stretches of warmth. A nine day stretch with below normal temps in the middle of the month. 

Why the pattern become consistently warmer?

The answer lies in the MJO (Madden Julian Oscillation). We need to look at the tropical Pacific. 

The MJO (read about it here) moves in varying magnitudes from west to east along the equator.  Here is a nice animation.  Green is more cloud cover. Brown colors are less cloud cover.  Notice how the northern Pacific jet stream fluctuates as the MJO moves through different phases (1 to 8).

Here is cross section of what is occurring.

How does something that is on the other side of the earth impact our weather?

Notice the temperatures in early March when the MJO was in a super-strong phase 8-1, slightly warmer than normal than it moved into a cooler phase (2 & 3) which connects with the cooler than normal mid March.  MJO then spun back around to phase 7-8-1 (lower magnitude) which connected to the 70s and 80s we had last week. The MJO impacts are different depending on the season.  You'll notice the MJO in similar phases (April 17 to 30 forecast but weaker) to early the March phase (stronger).  This looks to connect with a cooler next 7-10 days across the eastern 2/3 of the US.

There are always many drivers at work impacting the weather pattern. The MJO was just one of many influencing our weather with summer like temperatures last week.