Full-Scale Pattern Change Possible Sooner Than Expected

A couple Monday's ago I revealed my timeline to when I think our abysmal weather pattern will break into a more favorable one for sustained cold and snow chances. I said the first 2 weeks of January will be mainly transitional with a possible "relaxation" around mid-month and a full-scale change by week 4. If today's guidance is any indication of what could be coming in the medium to long range, then this timeline will be moved up by about 1 week. 

Here are the Sea Surface Temp Anomalies of the Pacific and western Atlantic. Not much has changed since I released my Winter Outlook. El Nino peaked and is gradually weakening. The positive anomalies in the east-central ENSO regions are not as anomalous as they were 2-3 weeks ago. The above normal SSTA's off the west coast indicate the +PDO signal is still strong. The waters around the Aleutians are actually cooling. This is not surprising since this area of the Pacific has been under below normal heights for the last couple of weeks. The cool NW and warm NE Pacific SSTA's supports trough-ridge configuration to remain intact for the foreseeable future. However, since the Aleutian trough is modeled to be oriented from NW to SE, parts of it drifts into the eastern Pacific which pushes the ridge over the western U.S. (+PNA). Most importantly, the Aleutian trough helps build heights in the EPO domain extending positive heights into the western Arctic. The -EPO/-AO couplet could reach strong levels by the middle of the month. 

The main reason why we could see the EPO and AO get to moderate-strong negative levels is due to where the Tropical Forcing sets up over the Equatorial Pacific. Not only where it sets up, but the magnitude it exhibits will also influence our upper level pattern. The CFS forecast of the MJO from Kyle MacRitchie shows a very amplified wave forecasted to propagate through phases 7-8-1-2. The EURO forecast of the MJO is not far off. It also shows a moderately amplified MJO wave going through phases 7-8-1-2, but it loses some intensity once it reaches phases 1-2. Meanwhile, 850mb zonal wind anomalies are showing extreme levels of westerly winds just east of the International Dateline. Not coincidental, OLR anomalies are also expected to be negative over the same area. 

Key Points

1. The strong easterlies (blue color) on the left correspond to suppressed convection / less precipitation (brown color) on the right around 120E. 

2. The strong westerlies (red color) on the left correspond to enhanced convection / greater rainfall (blue color) on the right between 180 and 150W. 

3. The location of the -OLR anomalies and 850mb WWB's suggests the North Pacific trough should be located between 180 and 150W, or just S-SE of the Aleutians which is where the negative SSTA's are located. Rising air associated with enhanced convection, or thunderstorms, helps keep the trough in place over the aforementioned area while a ridge develops over the EPO/PNA domains. 

The CFS keeps the -OLR anomalies between 180 and 150W into early February. In light of these developments, I expect the NPAC trough to remain over or just south of the Aleutians with continuous ridging over eastern Alaska / western U.S. / western Canada. Meanwhile, on the Atlantic side, there is a good chance the NAO goes negative by the middle of the month. Let's take a look how it might come together. 

The storm system many of us were tracking around January 10th is likely to bring rain to the area. The 12z EURO OP model phases the northern and southern stream upper level energy around the Ohio Valley. A potent Low Pressure System tracks toward Cleveland keeping the east coast warm sectored. The ridge spike in the west and the amplifying SE Ridge ahead of the strong STJ energy helps phase these two Jets early. What's important is what models do with this storm once it tracks into eastern Canada. 

Above is the 12z EURO 500mb vorts valid Wednesday morning (01/12). Bottom left (GEPS) and bottom right (EPS) are shown in the same time frame as the above image. In the top image, you can see a strong piece of upper energy is rotating around the Polar Vortex into the east-central U.S. Another piece of southern energy evolving from the Sub-Tropical Jet Stream is located just S&E of the baroclinic zone. If the northern and southern Jet Streams phase, it could spark a coastal storm to develop on Wednesday. Due to the location of the Polar Vortex thanks to the high-latitude blocking, there will be sufficient cold air entrenched over the east coast to promote precipitation to fall in the form of snow. The bottom two images do a nice job showing how a -NAO (higher heights over Davis Strait / Greenland) can slow down the flow and push the PV to a lower latitude. What's especially impressive is how the EPO ridge closed off over the western Arctic. The -AO and -NAO ridges are very close to linking, or bridging, in these maps on both Ensemble plots. This is almost textbook of what a "blocking" pattern looks like in the upper levels of our atmosphere. The cold air is cut-off from escaping east and is left stationed over the eastern U.S. Also notice the anomalous trough over the Aleutians. I mentioned earlier how the location and magnitude of the tropical forcing favors an Aleutian trough which in turn pumps heights over western NA. 

I am not convinced a storm effects our area on Wednesday 01/12 yet. I do think one will form, but it's possible by the time it does the baroclinic zone will be located too far off the coast. Reason being, I think the blocking pattern will still be in the process of maturing which could keep the flow just progressive enough to prevent a storm from coming up the coast. If we can get more digging from northern stream energy, that will help pull the trough axis a bit further west and promote a storm along or just off the coast. We'll see where trends take us as we head into the weekend. 

I think the time frame that interests me more is between January 16th and 23rd. By then, the -NAO should be well established along with the -AO/-EPO couplet. The EPS, shown above, show a very impressive upper level pattern. Verbatim this type of pattern gets me very excited. If I'm looking for a Godzilla, this would be the time frame I pay special attention to. It will be interesting to see if models maintain the anomalous -AO/-NAO signal in the medium to long range. If they do, I think there will be exciting times ahead for tracking our first widespread snow event(s) of the season. There is still a long way to go. We'll see how this looks next week! 

Enjoy the rest of your week. 

Best,

Francesco Paparatto 

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