December 2025 Short/Medium Range Forecast Thread

[John1122]

Been reading on the MJO today as I wait for the Tennessee game to start. The MJO phase only affects North American temperatures apparently in relation to the proposed in the paper, MVP (multivariate PNA). For instance, in the article I am reading, phase 5 is only warm if the MVP is also negative. 

This is from that paper. 

"The MVP is the first combined EOF of 20–100-day OLR, 850-hPa streamfunction, and 200-hPa streamfunction over the North Pacific and North America. The North American temperature patterns that follow each phase of the MJO change with the sign of the MVP. For example, real-time multivariate MJO (RMM) phase 5 usually leads to warm anomalies over eastern North America. This relationship was only found when the MVP was negative, and it was not associated with El Niño or La Niña. RMM phase 8, on the other hand, usually leads to cold anomalies. Those anomalies only occur if the MVP is positive, which happens somewhat more frequently during La Niña years. Composite analyses based on combinations of the MJO and the MVP show that variability in the Pacific jet and its associated wave breaking play a key role in determining whether and how the MJO affects North American temperatures."

The article can be found here. 

https://journals.ametsoc.org/configurable/content/journals$002fmwre$002f141$002f11$002fmwr-d-13-00118.1.xml?t:ac=journals%24002fmwre%24002f141%24002f11%24002fmwr-d-13-00118.1.xml

[John1122]

I remember a few years ago we passed through phase 8 and it didn't get cold. I believe it was an el Niño, so the mentioned/proposed MVP likely wasn't favorable. 

I do believe ph 7 is generally normally BN here in winter. The article I linked above noted that phase 7 seemed to be unaffected by the state of the proposed MVP.

[Carvers Gap]

That is insanely good information, John.   

[John1122]

I do like that we may get to phase 8, and low amp (which is usually the coldest version of 8) and that La Nina is much more likely to produce a +MVP, which means a deep Eastern trough.