2012-2013 Winter Forecast Review: Why the Forecast Failed

I had been heralding this winter as one that would vindicate the winter (or lack thereof) of 2011-2012. I explained how multiple atmospheric factors were supportive of a much better pattern for cold and snow across the nation. But that never materialized. Today, on February 10, 2013, much of the nation is again well below normal on winter snowfall. It's time to see where I went wrong.

The first thing we must review is the El Nino-Southern Oscillation, or ENSO index. This index tracks the anomaly of sea surface temperatures in the Equatorial Pacific. Above normal temperatures are known as El Nino's, and below normal sea temperatures are referred to as La Nina's. This winter, the eastern Equatorial Pacific did not have a specific water anomaly. It was neither above or below normal. This is called a Neutral ENSO situation. In Neutral winters, the atmospheric pattern is much harder to figure out. The ENSO stage really drives the overall pattern of each winter, so a neutral ENSO winter means the forecasts become much harder to predict, as we observed this winter. Due to a lack of a defined ENSO stage, more mesoscale patterns are left to drive the winter, and we observed this with the unfavorable Pacific pattern ruining winter.

500 millibar height anomalies over the last 60 days are pictured above, where reds are high pressure and blues are low pressure. Purple defines no anomaly. This winter's lack of snow can be blamed on the pattern in the Pacific Ocean. We saw low pressure dominating the Bering Sea too often to be comfortable, and this low pressure anomaly then led to low pressure on the West Coast of the US. In response to low pressure in the West Coast, high pressure then had to form in the East US to balance out the 500mb height anomalies. Strong high pressure was then encouraged to form in the north central Pacific. This was sort of a good and bad thing. At times, this high pressure was able to provoke a more favorable Pacific pattern. At other times, it provided the base for the anti-snow Rex Block formation on the West Coast.

Taking a look up towards Greenland, we find a very favorable last 60 days. High pressure tended to stick around that region, which is called a negative North Atlantic Oscillation (NAO). In the negative NAO, high pressure forms in Greenland and storms tend to follow the Nor'easter track. Cold weather is encouraged in the Northeast as well. If you're now wondering why that didn't all occur with such a favorable negative NAO, just look at the Pacific and there's your answer.

This Pacific pattern can also be blamed on the negative Pacific Decadal Oscillation, or PDO. In a negative PDO, colder than normal water temperatures are present in the Northeast Pacific. This encourages low pressure formation in that area, which can then shift onshore into the West US. This onshore shift creates that low pressure in the West, high pressure in the East situation that we discussed earlier. I did make a note of it on my final winter forecast (click here), but did not emphasize it enough. It is clear that, had I put more emphasis on the negative PDO, my forecast would have been milder and thus more accurate of this winter.

Analog years for Precipitation

Last 90 Days percent of normal precipitation

These were my two analog packages for the winter of 2012-2013. I used winters that had a weak/moderate El Nino after 2 La Nina's. This was before it was clear that there was not going to be an El Nino and that there would be a Neutral ENSO state instead. My precipitation analog image (top) turned out to be a solid failure. My analogs predicted below normal precipitation in the Ohio Valley and Midwest. That did work out in most areas, but a spot of above normal precipitation in North IL and parts of Indiana didn't make it as accurate as I wanted it to be.

My temperature analog forecast, pictured above, was a massive bust. Warmer than normal temperatures prevailed across basically the entire nation for January, with the Ohio Valley and Midwest getting the worst of it. The Northern Plains didn't even work out for December- that region was slightly below normal. Although the January data isn't in yet, I have a feeling above normal temperatures will be across the board once again, further hurting my analog years' forecast.

One big component I was counting on to really bring in the cold for the nation was Siberia. As many of you may or may not know, snow cover anomalies in Siberia during the month of October can help predict the following winter's temperatures over North America. You see, these snow cover anomalies then have implications on the Arctic Oscillation. If half of the month of October had below normal snow cover, one would expect the first half of the following winter to have a positive Arctic Oscillation (a.k.a. warm temperatures). In October 2012, we had very below normal snow cover for the first half of the month. This actually did correlate nicely with that part of my winter forecast, which called for a warm December into January. However, the back half of October had very above normal snow cover, and made me think that the last half of January and all of February would be colder than normal for the US. Well, we did get some better shots of cold air, but the pattern was (and still is) too progressive to entrench any solid cold air. I think this part of the Siberian-based forecast will fail for February.

If I were to rate my winter forecast thus far, with all variables used in my forecast considered and my forecast for the rest of February included, I would have to grade this as a D on the basic school grading system. I feel that the success with December from Siberia pushed it up from an F, but other than that nearly everything else went haywire and did not end as I had expected.

I am not quitting my long range forecasting, this is just one of those years. We look to have a new ENSO state going into summer, so that could very well help in the winter of 2013-2014.

Comments and feedback are appreciated below, whether they be positive or negative. I will allow comments both opinions, but will not accept comments with over-the-top positive or negative feedback.

Andrew

Surface Analysis -- Sunday, February 10

Prognosis... Blizzard event continues in the Northern Plains. Low pressure system down to 992 millibars is centered in Nebraska. Heavy snow is ongoing in South Dakota into Minnesota. Heavy rain showers are also occurring in southern Minnesota into Iowa and Illinois. Mixing precipitation is occurring more-so into northern Iowa and Minnesota. Further south into the South Plains and by the Gulf Coast, severe weather is ongoing. A squall line of heavy thunderstorms is present in eastern Texas and northern Louisiana. East Arkansas into western TN/KY are other states experiencing some form of thunderstorms. A small, weak area of lower pressure centered south of Houston appears to be connected to this main storm system. High pressure in the Mid-Atlantic will be pushed east as the squall line progresses east and the main storm system shifts north and east. 

February 19-22 Potential Winter Storm

Several model runs have been toying with the idea of a potentially major winter storm during the timeframe of February 19-22. Let's dive right in.

We'll start with a recent run of the American GFS model. Here, we see a very strong storm system centered in southern Illinois. The solid blue freezing line is far enough south for the Lower Great Lakes and parts of the Midwest to get snow. If we compare the precipitation forecasts to the legend, we find that cities like Chicago and Quad Cities may get 1.25'' to 1.50'' of water, which would equate to 12-15'' of snow for those areas. This particular forecast is valid the early, early morning hours of February 22nd. For you children wondering if this would cause a snow day, I can tell you right now yes it would. However, we are a long way out, and this solution will likely not happen.

We now move onto a more recent run of the GFS model, now valid for the evening hours of February 22nd. We see there is still a strong storm system in the area, but the system is further north and east than the earlier forecast. Precipitation is much more toned town, but heavy accumulating snow would still be falling in southwest Wisconsin, north Illinois and east Iowa. Those regions would see above 5 inches of snow in many areas, possibly more than 7 inches in the lighter blue. Again, we are a long time away and this will also likely not come to fruition. However, if I had to choose between the above forecast and the image at the very top, this one is more likely to actually happen.

These two images are forecasts from the GFS Ensembles averaged out for mean sea level pressure, 850 millibar temperatures and precipitation. Each image is from a different forecast, not just one model forecast for different times. The images are indeed pretty different, but do print out the same solution: There is potential for a storm in the area around this timeframe. The top image is much drier than the bottom, and the low pressure center is centered in Gary, Indiana. The bottom image holds much more precipitation, and the low pressure center is down on the southern Illinois/southern Iowa border. The presence of ensemble support adds confidence in a situation i'm not that optimistic in to begin with.

This image is of individual GFS Ensemble members from the very top image. If you look closely, you can see that top image in the upper right hand corner of this multi-panel forecast. The other ensemble members do show a winter storm, but to varying degrees of strength. Low pressure placement is also a component that is not resolved. Both issues are expected to occur, as we are still over 300 hours away from this potential event. I will need to see many, many more model and ensemble forecasts that support this idea before I can gain further confidence in this matter.

Andrew

Pattern Overview From February 9 to February 23

This is a discussion of the atmospheric pattern from February 9th through February 23rd.

Our analysis begins with the tropical convection index called the Madden-Julian Oscillation, or MJO. We currently see the MJO in Phase 1, with the strongest tropical convection occurring in west Africa or into the Indian Ocean.

When the Madden Julian Oscillation is in Phase 1 during the second half of winter into March, cooler temperatures tend to prevail across many areas east of the Front Range, especially prevalent in the Great Lakes and into the Northeast. Temperature anomalies can average a few degrees below normal, and this phase is best known for providing the aforementioned regions with the best opportunities for cold outbreaks. We are not seeing that cold trend get too strong at this time, however, because the MJO is very close to the center circle. When the MJO tracks into that center circle, it means convection is too weak for any adverse weather to be inflicted on the nation. In coming days, we will see the MJO rebound back into a modest-strength Phase 1, but then swing around into Phase 2, as the ECMWF model illustrates above. If we look again at the charts on the left, we find temperatures bounce back to relatively normal (but still cool) levels for those east of the Mississippi. A striking difference is the sudden appearance of well below normal temperature anomalies in the Rockies. It is plausible that we could see these below normal temperature anomalies appear as we progress into the next several days. Precipitation wise, while Phase 1 does favor coastal storms as exhibited by above normal anomalies in the Southeast, this wet sector shifts more inland into the southern Ohio Valley during Phase 2. This tells me that we could see storms stay more inland and affect the Ohio Valley more-so than the Northeast. That's not to say coastal storms will be rid of the equation, but they will begin to find a discouragement for such a coastal track. Before long, we are entering a modest Phase 3. This is the last favorable phase before the cold anomalies leave. Phase 3 holds the cold across much of the nation, and precipitation continues to move more inland, now more towards the southern Plains and even into the southern Midwest.

Medium range forecasts for 500 millibar heights by the European model (left) and American model (right) show general agreement in the setting-up of low pressure anomalies across the East US, and high pressure anomalies across the West US. This is a textbook example of a good scenario where to get cold and storms to flow into the East. Depression of heights in the East leads to a suppressed jet stream, which allows cold to flourish in the region. The suppressed jet stream strengthens the subtropical jet stream and provides additional opportunities for coastal storms. Long range forecasts do show this example of storms dropping south from the Pacific Northwest as the two jet streams merge and the storm then heads up the coast. A lack of high pressure over Greenland is a major catch that could put a flaw in this system. Without the high pressure over Greenland, I am hesitant to believe that this scenario will lead to big Nor'easters. While they are indeed possible, the lack of Greenland high pressure could lead to these storms just going out to sea rather than hanging around on the East Coast. This situation will have to be carefully watched before any decisions are made about who gets the storms and who is left out.

A long range concern of mine is the development of an Omega Block in the Bering Sea. An Omega Block is where high pressure sets up in any given area. In response to elevated pressure anomalies, below normal pressure anomalies (low pressure) must set up on both the left and right sides of the original high pressure system, forming the Greek letter Omega. The last time we saw an Omega Block in the Bering Sea, an unfavorable pattern evolved in much of the nation. If this Omega Block is to develop, low pressure on one side of that high pressure could stretch down into the northeast Pacific Ocean and West Coast. Long range model guidance has been hinting at such a scenario, and if it were to evolve, high pressure would make a solid (and likely successful) attempt at establishing itself over much of the nation. The MJO cycling towards Phases 4-5 doesn't help either, as Phase 4 introduces warm temperature anomalies across much of the nation.  If this Omega Block were to happen, and the low pressure did develop in the NE Pacific and West Coast, it would probably occur beyond the 20th of February. During this timeframe, the Madden Julian Oscillation would most likely be in Phase 4, which aligns nicely with the Omega Block's attempt at hoisting high pressure and warm temperatures over the nation.

Weekly Prognosis:

February 9 - February 16: Threat for coastal storms remains through the week. Valentine's Day likely to bring Nor'easter. Accumulations flirting with one foot in spots. Warm temperatures and high pressure prevails in West US until end of week.

February 16 - February 23: Persistent low pressure moves out of East US. Pacific pattern begins to turn unfavorable, Madden Julian Oscillation begins cycling through Phases 3 and 4. Cold temperatures early in week are erased by gradual warm up into end of week. Coastal storm threat remains, may be suppressed from unfavorable Pacific pattern.

Andrew

President's Day Potential Nor'easter

The new American GFS model is predicting a massive Nor'easter to develop off the coast of New England around President's Day.

The energy for this storm is projected to drop south from the Pacific Northwest and strengthen as it enters the southern Plains. From there, it swings east and develops a negative tilt as it pushes northeast into the East Coast. The development of a negative tilt means the highest vorticity values at the 500 millibar level are positioned to the southeast. This is observed in the upper left hand panel of the above forecast image, which is valid for the night just before President's Day.  Typically, negatively-tilted storm systems are watched in the spring, when cold air can run aloft and provoke stronger thunderstorms than positively-tilted storm systems. As you might guess, positively-tilted storm systems have their highest vorticity values tilted towards the Southwest. The presence of a negatively-tilted winter storm would likely increase precipitation totals as cold air runs aloft and convective snow bands are enhanced. Thundersnow would naturally be more widespread in the presence of cold air aloft.

Snow totals from this system in a 24 hour period would approach the one foot mark, especially in western Pennsylvania. West Virginia and eastern Kentucky could surpass 6 inches, as well as western parts of the state of Virginia (not the state WV). New York, eastern Tennessee and portions of Maine could see shovelable snow, while other states get more of a quick, light accumulation. This forecast is certainly going to change, but this potential must be closely monitored. High latitude blocking will be increasing, leading to higher chances for these Nor'easters.

Andrew