Long Range Outlook: January 1, 2014

ECMWF (left), GFS (center) and CMC Long Range 500mb anomaly forecast

Long Range Discussion
January 1 2014

Multi-model guidance above for the 8-10 day period shown is in average agreement, with highest disagreement area over northern Canada into Greenland, leading to additional disagreement over the Northeast United States. Model confusion revolves around whether to allow development of strong low pressure over Greenland, which would then help chances for ridging out towards the Northeast and East Coast. ECMWF and GFS are in the "best" agreement of the three model suite, with the ECMWF centering the anomalous low pressure west of Greenland and the GFS strengthening said low pressure system and placing it south and east of Greenland. The difference in location will affect the large-scale weather pattern, with a more compact solution with that upper-latitude low pressure system as exhibited by the ECMWF leading to stronger ridging along the East Coast. On the other hand, if the system is to be placed east of Greenland, the low pressure would be elongated from the Bering Sea out to the waters east of that land mass, and that would temper ridging prospects in the East US.

Model guidance is in good agreement on ridging keeping a chokehold on the Arctic Circle, which will prohibit reformation of the polar vortex across that area, and thus will keep the risk for cold weather across lower latitudes rather high. All modeling systems are also in agreement on ridging appearing over the southern Gulf of Alaska and into the north central Pacific, and we also find a consensus among the guidance with deep low pressure over the Bering Sea into Alaska. Now, for the long range that we are watching over for this time period (8-10 days out), this means we will be seeing a pattern that will most likely keep out extreme cold weather like we will see to kick off the upcoming workweek. In the long-long range, this somewhat-anti-cold pattern will flip over.

This map from Michael Ventrice shows 200 hPa velocity potential anomalies over a time-longitude graph. Blues and dashed ovals indicate the presence of enhanced convection (and thus a Madden-Julian Oscillation / MJO wave), while solid ovals and warmer colors signify a suppressed MJO wave. Taking a look at past, present and future conditions, we see how the MJO wave has been progressing across the Indian Ocean and towards the central Pacific for some time, oscillating through the various phases of the MJO. Some dynamical models were giving off a false "dead MJO" signal, where the guidance indicated the MJO was too weak to track. In reality, this was another body of enhanced convection firing over South America. This dual-placement of tropical convection is referred to as a "Wave 2" pattern, due to the two waves of active convection. In reality, the MJO signal was always oscillating around the phase space, as the progression of the MJO wave in the graph above shows. Now, as we look ahead, the GFS projects the MJO wave to continue pushing east, to be centered at the ~170E longitude mark around January 10th. This is a classic forecast of the MJO pushing through Phase 6 (centered around 160E), and Phase 7 (centered around 180). Model guidance should see an intensification of either the zonal flow across the US or ridging on the East Coast, as ridging in the US is common in a January Phase 6 event. A January Phase 7 event results in significant ridging in the West that will then transition us into the mid/late January cold blast that I began discussing earlier today.

Teleconnection forecasts from the ESRL agency appear to be handling the upcoming pattern decently well, with a few spots that may be refined in future forecasts. The Pacific North American (PNA) index is projected to be deeply negative in the short term, meaning deep troughing across the West US. I expect we see this deep negative forecast moderate to more neutral territory, as the MJO does not really support such a huge -PNA event. I find it more likely that this strong troughing will be more displaced to the east, as ensemble guidance supports. From then on, we see another negative PNA spell before spiking positive. I have good confidence in that +PNA spike in the long range, with some decent confidence in relatively neutral PNA values in the medium/long range. For the North Atlantic Oscillation (NAO), the index is projected to remain positive throughout the forecast period. I figure we will see a slight negative trend in the long range +NAO values, as an MJO Phase 7 supports more negative NAO values. However, other than that, I feel confident in the prolonged +NAO forecast. The West Pacific Oscillation should stay positive for much of the forecast period before a reduction to neutral or negative territory comes about in the long range in response to the transitioning MJO. I disagree with this WPO forecast. The East Pacific Oscillation (EPO) looks to me like it will be more negative than positive. The medium and long range EPO is projected to be positive, but ensemble guidance disagrees and places the EPO at a more neutral or slightly negative stance. I expect we will see some correction in that direction for future teleconnection forecasts.

To summarize, I anticipate some warmer weather arriving in the wake of brutal cold for the second week of January, before we see a trend towards colder conditions in time for the end of that second week and into the third week of January.

Andrew

Polar Vortex to Unleash Historic Cold Across Plains, Midwest

There are increasing signals that we will see the polar vortex unleash potentially historic levels of cold air upon the nation, mainly targeting the Plains and Midwest.

Kyle MacRitchie

The Madden-Julian Oscillation (MJO) is projected to move into Phase 6 as we progress into January. For those who don't know, the Madden Julian Oscillation involves the placement of enhanced tropical convection over the Equatorial Pacific, extending from the Indian Ocean to roughly the middle of the Pacific Ocean nearly due east of northwest South America. The MJO entering Phase 6 means that the enhanced tropical convection will be northeast of Australia. After that Phase 6 movement, it looks like we will head on in to Phase 7 of the MJO, and that's the one we need to keep an eye on. This forecast, made by four separate CFS ensemble members, shows us entering Phase 7 around January 15th.

MJO Phase 7 500mb Height Anomaly Composite

If we take a look over RaleighWx's Phase 7 500mb anomaly chart, we see that Phase 7 of the MJO in January sees major ridging forming over the Western US and well into Canada, even over the Bering Sea. This is a classic example of a positive Pacific North American (PNA) index, which alters the jet stream so that the jet stream spikes north in the West due to that ridging, and then plummets southward in the Central and East US. This leads to a pattern highly conducive for cold weather in those areas. Adding to that conducive pattern is the highly negative North Atlantic Oscillation (NAO), as is exemplified by the heavy ridging over Greenland. All of this ridging across the upper latitudes then allows a negative Arctic Oscillation (AO) to form, which only adds to the intensity of the cold air in the US. All in all, the Phase 7 really creates the best environment that we can look forward to in the medium/long range for some cold weather.

This is all good and fun, but the really interesting stuff comes up when you take a look at the Climate Prediction Center's analog-produced upper air outlook for the medium range.

Does this chart look familiar? It should, because the anomaly placements are almost identical to the Phase 7 composite above when viewing the North American continent. We see extreme ridging over the Gulf of Alaska, which then allows for the formation of not only a deeply negative EPO (a key player in this impending brutal cold spell), but also a classic McFarland Signature look.

This image from the National Weather Service in 2010 shows what the McFarland Signature looks like. You have the massive ridge set up across the Gulf of Alaska and into the West Coast, and this leads to deep negative height anomalies developing just to the east, usually in the Central and East US. These deep negative height anomalies allow frigid air to be transported from the upper latitudes down into the United States, and I anticipate a very similar situation to evolve here again in the medium range time frame.

Taking a look back at that analog image above the McFarland picture, we see not only the well-established McFarland Signature/-EPO, but those deep negative anomalies being projected as very pronounced across the Central United States. Based on how pronounced those anomalies are, as well as analyzation of the jet stream and temperature patterns during this timeframe, it does appear that the polar vortex would be entering the United States. This wouldn't be any low pressure system; if this were to happen, we're talking record cold. Remember that the polar vortex is the low pressure system that sustains the cold air in the Arctic, so bringing a portion of that vortex down south into the US could be disastrous for farmers growing crops not only across portions of the Central and Eastern US, but also down in the South.

Model guidance is in good agreement about the polar vortex first affecting the United States around January 6-8. Beyond then, we may have to wait a little while until the MJO gets into Phase 7 before we see a resurgence of cold.

ECMWF Temperature valid Tuesday morning.

GFS Temperature valid Tuesday morning.

Andrew

January 1-3 Significant Winter Storm - Part I (Midwest, Great Lakes)

This post will address the first part of the January 1-3 winter storm, where anomalously strong clipper system will lay down significant snows in portions of the Midwest and Great Lakes. You can find the link to Part II, which addresses the effects on the Northeast, at the bottom of this post.

Global model guidance is in agreement with an Alberta Clipper system dropping down from Canada and traversing the Plains to enter the Midwest. Model discrepancies begin to evolve early on, namely when the NAM model takes the snow swath unusually far north into Central Wisconsin. More recent runs of that model have corrected southward back towards Southern Wisconsin and Northern Illinois, but that model will still have to be monitored. GFS/GGEM/ECMWF models hold the consensus with this super-charged clipper, as all three bring about significant snows stretching from Iowa to Chicago back into portions of Indiana and near Ohio.

Global model guidance has been putting down liquid amounts around 0.6" to even 1.0" in northern Illinois into Michigan, and it is those areas highlighted above by the ECMWF that we are monitoring in this post. This event is actually a combination of as many as three different clipper events, with the third one bringing the most snow around New Year's Day. Because they're clippers, right off the bat we are going to most likely see higher snow-to-liquid ratios than usual. A typical snowfall has a 10:1 ratio, which means 10 inches of snow could be melted down into 1 inch of water. In this case, however, we're thinking that places like Chicago could see snow ratios of 15:1 or even 18:1, which means 1 inch of water could theoretically be fluffed up into 18 inches of snow. The ECMWF model above gives downtown Chicago 1" of precipitation, thanks to some additional lake enhancement, and if we were to use a 15:1 ratio throughout the whole event, maybe ending on higher ratios in response to possible lake enhancement, I could envision up to 15-17" of snow. Realistically, that is unlikely to happen. I find the ECMWF to be too bullish (overdone with precipitation) for my liking. The GFS/GGEM seem slightly more in line, with amounts closer to 8-15" being produced. This event would be a significant one if it were to verify as it stands right now. And while I don't trust the 15"+ forecast being implied by the ECMWF, it is theoretically within the realm of possibility.

My thinking for this part of the event is that the areas of southern Wisconsin, northern Illinois, northern Indiana, southern Michigan and northern Ohio will receive heavy snowfall from this system. Based on current model projections, I would issue a call for 10-15" for those areas (with potentially higher isolated amounts), but based on a slight concern models may draw back on QPF projections (quantitative precipitation forecasts, also known as precipitation forecasts), I'll go with a conservative 8-12" for the aforementioned regions, with the very possible chance for higher amounts.

For Part II of the January 1-3 Significant Winter Storm, please click here.

Andrew

January 1-3 Significant Winter Storm - Part II (Northeast)

This post will address the potentially significant snowstorm that is aiming for the Northeast. If you would like to see Part I, where I address the potentially significant snowfall in the Midwest and Great Lakes from this storm, please click here.

Tropical Tidbits
Valid January 2nd, morning.

The mean sea level pressure from the GFS model shows how this potentially significant snowstorm may evolve. We see the super-charged semi-clipper that was elaborated on in Part I over Indiana, but then we see another low pressure system skirting to the east of high pressure based in Georgia. It is these two bodies of low pressure that we are monitoring closely for what they will do. Current projections include phasing (combining) of the two systems, but the question is: When will they phase? In this case, timing is key.

Model guidance remains at least slightly uncertain with when these two systems will phase into one, stronger low pressure system. It is believed that the earlier the systems phase, the more snow they can spread on to more residents of the Northeast. Similarly, the later the systems phase, the less snow they provide to fewer residents.

Tropical Tidbits
Valid January 2nd, afternoon.

Roughly 12 hours after the first image in this post, the GFS model has the two systems interacting. Originally, these two systems were at 1010 millibars just three hours before this image you see above. Now, with the low pressure system offshore the Northeast stronger than the one just south of Pennsylvania, it is apparent that the clipper system will be transferring its energy east to the system offshore New Jersey. Just a handful of hours later, the system has phased into a sub-1000mb system. However, it is further offshore than many in the Northeast would like, leading to less snow.

The GFS isn't the only solution in the mix, however.

The ECMWF is slower with this system, having it phase completely on the morning of January 3rd. Because timing is key with when these two systems will phase, it is apparent that this timing difference between the ECMWF and GFS is a significant factor in each guidance system's solution. The ECMWF has this system phase earlier and become stronger than the GFS, with an added bonus of keeping the system closer to land than the GFS. The precipitation and MSLP image above from the ECMWF, again valid on the morning of January 3rd, shows a 978 millibar storm system due east of New Jersey, spreading intense snowfall across Pennsylvania, New York, Vermont, New Hampshire and into Maine. Even coastal regions to the south of NY, VT and NH get in on some snowy weather. The snowfall image from the ECMWF below paints the full picture:

Also worth noting is that the ECMWF Ensemble Prediction System (EPS) is on board with the earlier phasing.

So what do I think will happen?
I'm thinking we do see something along the lines of the ECMWF verify. I do not believe we see the huge ~24" totals (models have a tendency this winter to back off of big precipitation forecasts just prior to an event), though significant snowfall is certainly within the realm of possibility, even likelihood. I feel we see a swath of heavy snow ("heavy snow" meaning 8"+) stretching from New York/Pennsylvania out to Maine in very similar fashion to what the ECMWF portrays above. I would also monitor future model runs to keep an eye on that southern cutoff of snow totals for coastal regions, as I feel those areas will have to go into the event with a 'now-casting' mindset.

Andrew

ECMWF Ensemble Control Floods Midwest with Historic Cold

The long range ECMWF Ensemble Control model has put out a forecast that sends record-breaking cold deep into the Midwest and Ohio Valley, sending temperatures into a free-fall below -20 degrees.

The ECMWF Ensemble Control is a member of the ECMWF Ensemble Prediction System (EPS), which is comprised of 52 separate ECMWF model runs, each of which has been changed a little one way or another to create a big ensemble that is currently considered the most prestigious in the world. One of those 52 members is the ensemble Control, which is called a control member because it has not been  deliberately changed like the other ensemble members.

The pattern that will be setting up in 10 days (close to the forecasted image above, which is valid for next Wednesday) does look rather supportive of a cold weather pattern in the United States. I have yet to dig deeper into just how favorable the pattern will be, and I plan to do so sometime on New Years Eve or New Years Day. Until then, just keep in mind that this cold pattern is here to stay. Maybe not as intense as what is shown above, but it will be cold.

Andrew