11/25/18 The MJO and why it’s important
It is time I talk a bit about the Madden-Julian Oscillation or the “MJO” as forecasters like to refer to it. The Madden-Julian Oscillation is a tropical disturbance that moves clouds, winds and precipitation and pressure changes eastward around the global tropics about every 30-60 days. Typically, in the Northern Hemisphere the late fall, winter, and early spring have the greatest level of MJO activity.
There are phases in the MJO cycle and models predict where the cycle is headed generally 14 days in advance. Below is the MJO forecast. The numbers 1 through 8 correspond to the 8 phase of the MJO cycle. The red and purple lines are the past, the green line with black dots is the forecast for the future. The black dots on the green line are days You literally have to count the dots on the green line because only the past dates are listed (on the purple and red).
Right now we are transitioning from phase 6 into phase 7 (don’t worry I’ll explain the phases in a minute, I have charts!). I mentioned amplitude earlier, anything close to or in that circle means the MJO will have a very little effect on the weather. I labeled that “Null”. The further you go outside the circle the more the MJO effects our weather. I labeled those “Moderate Amplitude” and “High Amplitude”. By counting the dots on the green line you will see we are forecasted to go into a moderate phase 8 around 11/29 and into a moderate phase 1 December 3rd. The red line is the past, you can see that we have been in phases 3,4,5,6 for the last 18 days.
The Phases change depending on what season we are in, so a phase 7 in one month can be completely different than a phase 7 in another month. As you can see from a temperature perspective phases 8, 1 & 2 are colder and generally stormier phases for us.
As I mentioned earlier the forecast shows a move into phase 8 around 11/29, so let’s look at what the model says for 11pm November 29th through 5 am November 30th.
All of this is related to pressure increases and decreases in the Indian Ocean which trigger the changes in the MJO. The long-term forecasters I follow are expecting us to spend longer periods of time in phases 8,1,2 of the MJO (the more amplified you are in a phase the longer you stay in it), and shorter periods in the other phases.
When I have mentioned that EURO or GFS is having problems, I am referring to the fact that it is out of sync with itself.
11/10/18 Model Verification
There are a couple of ways I verify models before I start using them for a post. When it is stormy out I look at the latest model run and compare where the precipitation is compared to where the model’s simulated radar forecasted it to be. I also verify forecasted temps for a particular time. Since we have no local precipitation to track let’s look at how horribly the models verified overnight.
First current 6 am temps, this shows actual temps from reporting stations in Colorado, as you can see at DRO it is 13 degrees.
Now a look at what the models forecasted, first the GFS. 25 degrees! Horrible forecast.
Euro 22 degrees, it still missed by 9.
Now the HiRes model which in my opinion has one accurate run a day and that is the one due out in an hour. I usually never use the overnight run but here it is. 25 degrees! Huge miss.
What does this mean? It means the models had a bad night. When you read in one of my posts that a model didn’t verify well so I have to wait for another run of the model, this is what I am talking about. Bottom line, I don’t trust those models for data for the very short term (6-12 hours). It does not have a dramatic effect on the longer-term outlook.