Where to begin.... Going to cover the current state of the MJO, why I feel our chances are better in Jan vs this month, and why the MJO is cycling in a La Nina type pattern, referencing the Walker Cell and Pacific MJO disruption.
First off, the MJO is currently pushing through the eastern IO and towards the MC, which is beautifully shown in the visual below. Note the twin low pressure systems (LP/HP is mirrored south of the equator), which indicates the upward/convective phase of the MJO is directly to the east. A simplified version of the MJO is also posted below to help out visually
The MJO once again is in a favorable location for PNW cold, but just because the door is open doesn't mean the cold will come in unfortunately. Granted, as I'm typing this, it's in the 20's, feels like the teen's, and a strong north wind is howling. Just because the models took away the blast we were hoping for, doesn't mean the MJO hasn't been a huge benefit so far this season in determining our windows of opportunity.
As we progress throughout winter, the MJO plays a more significant role in our weather as it truly "wakes up" in a sense. Not only does it's overall amplitude increase, it's overall duration increases as well. Given this, I believe the next go around with the MJO should result in better potential for the PNW.
As many have noticed, a reference has been brought up to the Nov cold snap. The progression actually has many similarities....
Looking at the top image, you'll notice that the areas of blue shading represent convection, while the areas of yellow shading represent suppression. The solid red lines are associated with the MJO wave, which you can easily spot out during the mid-late November time frame. I had to do some photoshop work, but I combined the 2014 OLR anomalies with the new 2015 forecast anomalies to demonstrate that the wave will be very similar to the previous one. The MJO as of late has been initiating just west of 90E, which is around the central Indian Ocean (phase 2/3), and have been weakening just west of the dateline (phase 6/7). The fact that the MJO hasn't been roaming around in the central Pacific and western Indian Ocean is the reason for the continued cold snaps we've seen lately. Phases 4-6 are considered La Nina phases, while 8-2 are considered El Nino phases, with phases 3/7 being transitional phases. When the MJO is centered over the MC, in an ideal situation, we see a -PNA/-EPO/+NAO pattern, which consists of a blocking ridge over the Pacific, trough over the west, and a ridge over the east. As the convection associated with the MJO propagates into the west Pacific, we see an extension of the jet occur, forcing the -PNA ridge over the west coast. This in turn creates a +EPO due to the formation of an Aleutian low, which creates the stormy and atmospheric river setups we've already experienced. These 2 polar opposite setups have been occurring much quicker this season due to the MJO only focusing its attention in phases 2/3-6/7. However, there are also other variables at play of course, which can alter the overall configuration. The +PDO also entices an extended jet due to the cool SST's over the western and central Pacific promoting low pressure development.
With that said, the reasoning as to why the MJO has been cycling in a La Nina type circulation is due to a unique Walker Cell setup. The Walker Cell, or Walker Circulation, is a model of the air flow throughout the tropics. Typically during an El Nino, the relaxed trade winds allow warm water to travel eastward, which causes moist air to rise in the lower levels over the pacific creating upper level divergence. To the west and east of the upper level divergence, the air cools and dries, thus sinking back down to the lower levels. The low level westerlies beneath the sinking air over the Pacific continue to push water toward the upward phase of the WC (Walker Cell), creating a full circulation. La Nina conditions mean the warm pocket of water is located around Maritime Continent, with the upward phase of the WC also being located in the same area. I probably did a horrible job at explaining it in words, but a visual will help out. The whole reason the MJO is in a more La Nina circulation this season is due to the WC also resembling a La Nina circulation. The upper level divergence of the MJO is what is responsible for the thunderstorm activity it produces, and when the MJO propagates into upper level convergence, it weakens the MJO's structure, resulting in a break down.
I'll post some final thoughts tomorrow.... time to get some sleep!
While we may not have scored quite as nicely as we would have liked this go around, I believe we have one more solid shot that will be as good as any, if not better. If tropical forcing continues on the path we've seen so far, this current wave should push over the Pacific and weaken/die around phase 6/7 during mid month. As the wave progresses east, we should see the PNA ridge shift over us (+PNA), the jet stream strengthen and extend, and the mean trough will shift over the east, resulting in a El Nino type pattern. Once a new wave fires up over the IO sometime around the second half of Jan (looks like the 15th-20th at this point), I'm expecting to see a gradual shift to La Nina conditions once again. Quick disclaimer... this could all change given a SSWE igniting a drastic change in the overall tropical forcing regime
Compliments of @webberweather...