Preliminary ENSO Outlook for Winter 2014-2015

As we close out the winter of 2013-2014, I suppose it's time we start looking at forecasts for the El Nino-Southern Oscillation (ENSO) phenomenon for this summer to see what ENSO state we may see in the winter of 2014-2015.

Before we begin, let's establish what the El Nino-Southern Oscillation is.

The El Nino-Southern Oscillation (ENSO) phenomenon involves sea surface temperature anomalies over a portion of the Equatorial Pacific, namely focusing on the waters west of Colombia and Ecuador. In the image above, the Climate Prediction Center shows distinct El Nino environments (left two panels) and La Nina environments (right panels). During an El Nino, water temperatures to the west of Ecuador usually warm up significantly. These warm temperatures then produce anomalously high levels of tropical convection (as warm waters make air rise, creating thunderstorms), and the whole process leads to an El Nino pattern. During a La Nina, we see the opposite, where colder than normal water temperatures are observed, leading to anomalously low levels of tropical convection. As you can see by the image below, the El Nino patterns and La Nina patterns during the winter months have different impacts on the US.

Now that we know what the ENSO phenomenon is, let's move on to the model forecasts.

We'll begin with the NCEP's CFS model. The CFS projects monthly and seasonal values for the ENSO phenomenon, and also gives out precipitation, SST, temperature, etc. forecasts for the world. The CFS model indicates we will see steady rising of sea surface temperatures in the Equatorial Pacific throughout the spring, summer and beginning of fall, before we reach SST temperature anomalies above 1 degree Kelvin, which is equal to over 1.8 degrees Fahrenheit. This would qualify as a strong El Nino, something we haven't seen for a while (we have been in an unprecedented lack of El Nino events since 2010; the four-year stretch since 2010 has included neutral ENSO and La Nina events). This strong El Nino would then likely continue on into the winter of 2014-2015. However, because the CFS model is notorious for forecasting an El Nino that never comes true, I'm not buying this forecast. While I do believe we see an El Nino event by this summer 2014, I don't believe it will be a strong El Nino.

Next, we will continue with the ECMWF model's forecast. The ECMWF model projects the ENSO phenomenon out to roughly 6 months forecast time, and uses its prestigious 52-member ensemble prediction system in its forecast. The ECMWF model also projects that we will see an El Nino by the summer, though its rise to an El Nino is more exponential than linear- we saw the steady rising trend in sea surface temperature anomalies (SSTAs) in a linear fashion by the CFS, and now we see an exponential increase in SSTAs around May and June 2014. By July 2014, ECMWF ensemble guidance has water temperatures at 1 degree Celsius above normal, which equates to 1.8 degrees Fahrenheit above normal. This would also qualify as a strong El Nino, but once again, I'm skeptical of these strong El Nino forecasts. While they're possible, I'm not so sure they're probable.

Next, we'll take a look at the Japanese ENSO model prediction. The Japanese model forecasts the ENSO phenomenon out to just after July 2014, about the same forecast time period as the ECMWF model. The Japanese model goes for a forecast similar to the ECMWF, where we see a jump in SSTAs around May and June, before arriving in the ~0.8 to 0.9 degree Celsius anomaly. That would constitute an El Nino, though it would be weaker than projections by the CFS and ECMWF. I find this forecast much more logical- it's always a gamble when you go with strong El Nino or strong La Nina forecasts. Usually its better to go with a weaker, albeit still substantial forecast.

Next up is the Australian Bureau of Meteorology's POAMA model. The POAMA model projects the ENSO phenomenon out to October, with a forecast time period of roughly 8 months. The POAMA model takes the current cool-neutral ENSO state to neutral by June, and borderline-El Nino by October. This forecast might be a little too weak with the idea of an El Nino- I wouldn't be surprised to see an El Nino declared by late summer (around August or September). However, the POAMA does give us a glimpse at the other side of the forecast envelope, when comparing it to the bullish ECMWF/CFS forecasts.

Next, we'll take a brief glance at this trio of forecasts. These three forecasts are under the LDEO model domain, which gives forecasts out to December 2014, meaning its forecast time period is roughly 1 year when we see that the red observation line stops at December 2013. In these three projections, we see that a weak El Nino or warm-neutral ENSO state is favored by the winter of 2014-2015. I expect we see an El Nino by this time, so these models may be a little too under-aggressive with this situation.

The next item to analyze is the NMME model suite. The NMME is a compilation of various global model guidance systems, all of which project the ENSO phenomenon using an ensemble set out to 8 months. In this graphic, we see the projected ENSO values by operational and ensemble members from the CFS model (red), two separate versions of the CMC model (CMC1 in green and CMC2 in navy blue), the GFDL model (light blue), NASA's model (pink), NCAR's model (yellow), and the NMME suite mean (black dashed line). The NMME suite is in decent agreement on a steady rise to El Nino conditions by the end of summer, something I do believe is likely. The NMME mean has the El Nino in weak to moderate condition by August, something I think is more probable than possible, especially considering history would suggest an El Nino is long overdue this next winter. In summary, I agree with the NMME projection.

The next suite of models to observe comes from the International Research Institute for Climate and Society. These models project the ENSO phenomenon out to the August-September-October period, meaning the forecast timeframe is around 10 months. This graphic gives us a look at a variety of model guidance systems from around the world. Each different model is displayed in a different color, with the average ENSO prediction shown in the solid yellow line. We see that the ensemble prints out a borderline-El Nino by the fall months. Considering we are almost certainly heading towards an El Nino next winter, this forecast is a good median in the envelope of forecast models.

This final model shows the SST anomaly forecast for the December-January-February 2014-2015 period from the SCRIPPS institute. The SCRIPPS institute model projects the ENSO Phenomenon out to this DJF period. We can see that the model shows a strong El Nino by late winter. As I've gone through all of these models, some of which have been showing a strong El Nino, I still hold my belief that these models are likely too strong, and a weak to moderate El Nino is more likely. These details will be cleared up in the months ahead, of course.

Andrew

February 12-14 Potentially Significant Snowstorm

Model guidance is beginning to jump onboard the idea of a potentially significant snowstorm in the February 12-14 period.

We begin with the snowfall forecast from the CMC (Canadian) model. The CMC model goes all-out on this storm potential and throws down amounts over 12" in northern Georgia and a wide swath of North Carolina into Virginia, before laying down amounts near 24" in the Mid-Atlantic and New England regions as the storm bombs out to a minimum sea level pressure value of 961 millibars.

This is the CMC model forecast of 6 hour precipitation values and sea level pressure contours. We can clearly see the storm in all its might, dropping intense snows of nearly 4" per hour on coastal areas affected by the wintry side of this storm. The storm then deepens to 961 millibars 6 hours later as it pulls away from the East Coast. Taking the paralyzing snowstorm aspect out of this storm for a moment, the CMC would be printing out a potentially life-threatening event, due to the strength of this storm. We would be talking about severe wind damage, possibly catastrophic if this storm actually verifies. Luckily, I highly doubt we see a solution just like what the CMC here says. However, I do think we have to watch out for a storm in this time period.

This image above shows 500mb observed height anomalies on the left, and sea level pressure/high pressure-low pressure denotations/cloud cover denotations on the right. Both panels were valid on February 4th. If you've been with The Weather Centre for a while, you know how we use a rule created by Joe Renken that states a storm system in East Asia then results in a storm in the United States 6-10 days later. Looking at the panel above, we see that a strong storm system was observed cutting north across Japan on February 4th, as the deep blues in the left panel over Japan tell us. If we move ahead 6-10 days from that February 4th timeframe, we find ourselves with a potentially significant winter storm in the US in a time period of February 10-14. I have a good feeling this CMC model projection is indicating that this is the correlating storm. Since the Japan storm was strong, I have a feeling this storm in the US will be strong as well.

The CMC isn't the only model showing a big winter storm in this timeframe...

The ECMWF model also puts down significant snowfall from the Mid-Atlantic to the New England regions, though we see snowfall amounts reduced and moved a bit east compared to the CMC. The CMC model has always retained a bias of being too strong with storm systems, and it's more than likely that this bias is affecting its forecast at the top of this post as well. However, we still can take into consideration the idea that the CMC is printing out a general storm hitting the East Coast, and that idea is something the ECMWF agrees on. We see snowfall amounts of over 12" slamming northern Georgia and into the Carolinas, before a strip of 10-15" snow amounts strike coastal areas in the Northeast.

The ECMWF precipitation forecast at the storm's maximum impact shows the heaviest precipitation on the eastern flank of the storm system, with the system overall weaker than the CMC (which can be explained by the CMC's aforementioned bias), and cold sector precipitation (snow) much more scant (once again attributed to the CMC's bias).

The only model guidance system that isn't jumping on the idea of an East Coast snowstorm is the GFS.

The GFS model actually has the storm begin as two low pressure systems that eventually congeal into one system at the time this forecast graphic is valid (February 13). We can see that the majority of precipitation here is rain, which is located offshore, with snow hitting only coastal areas.

Snowfall amounts from the GFS model aren't even worth mentioning, with 2-4" accumulations only found near the coast.

So why is the GFS so different from the ECMWF?

When comparing normalized 500mb height anomalies from the 12z ECMWF and 12z GFS, both at forecast hour 96, it's not so much that the synoptic pattern is different, but more about how far south the storm pushes before it makes its jump up the coast. The GFS model on the left is noticeably weaker and further south with the storm in terms of these normalized 500mb anomalies when compared to the ECMWF, which has a stronger, slightly further north system. Another issue also appears to be how ridging is aligned downstream of the storm in the Atlantic. We see high pressure a bit suppressed in far eastern Canada, towards Nova Scotia in the GFS on the left, with the ridging more pronounced and stronger in the ECMWF forecast on the right. What's interesting is that the pattern upstream is in near-complete agreement among the models. We see a strong system over Alaska, with strong-yet-suppressed ridging across the Southwest US. Normally, this upstream agreement ought to result in agreement on the evolution of the storm, but in this case, it looks like it will be an issue of just how far south the storm goes. If we count the higher accuracy of the ECMWF and CMC models versus the GFS model as of late, as well as model guidance tendencies for the storm to track too far south and the ECMWF being rather consistent on this idea of an East Coast snowstorm, I think it's best to support the ECMWF/CMC solution in terms of track, NOT amounts. Amounts will be determined further in the future.

Andrew

February 10-12 Significant Southeast Snowstorm

Once again, we're looking at the possibility of a significant snowstorm in the Southeast US.

The NAM model above shows projected snowfall amounts over the next 84 hours. In this forecast, we see significant snowfall hitting the states of Arkansas, Tennessee, Mississippi, and Alabama, as well as North and South Carolina. The NAM model puts down amounts of 4-8" in eastern Arkansas, northern Mississippi and southwestern Tennessee, as well as in portions of North Carolina. The NAM model had previously been showing amounts well in excess of 12", though its latest numbers are far more believable.

This image shows the high resolution NAM model forecast snowfall over the next 60 hours. While it retains the name of the NAM model, it is more closely associated with the WRF modeling system, has better resolution in its 'foundation', if you will, and only goes out to 60 hours instead of 84. The high resolution NAM model has a similar forecast as its lower resolution counterpart, laying down bands of 6" amounts in eastern Arkansas and western Tennessee. The high resolution NAM is more open to putting down some big snows in Louisiana and central Mississippi, though due to its snowy bias we'll have to wait and see what other high resolution guidance says. The model also agrees with another spot of heavy snows in western North Carolina, but because the model only goes out to 60 hours, it doesn't capture the full snowfall of the event in eastern North Carolina.

To sum up:

•A significant winter storm is expected to impact portions of the Southeast.

•Arkansas, Tennessee, and North Carolina are at risk for snowfalls in excess of 6".

•Travel may be severely hampered- stay home and plan ahead as best as possible.

Andrew

Arctic Cold to Abruptly End in Mid February, Return in March

It's looking like we will see the recent Arctic cold come to a quick end in mid-February.

The image above shows the GFS Ensemble 500mb height anomaly forecast for February 17th over the western Pacific. We see strong ridging present over Japan and much of eastern Asia, with another swath of positive height anomalies displaced further east to the south of Alaska. Using the idea that a storm system in Japan can signal a storm in the US 6-10 days later, we can find that this strong ridge over Japan should also come back to haunt the US 6-10 days later. That would place warmer and quieter weather over the nation in the February 23-27 period. Considering high pressure should be affecting Japan both before and after this February 17th forecast graphic, it would be reasonable to think that this warmer/quieter weather may extend into early March, as well as closing out the last week or so of February.

This warm trend can be seen by the Earth System Research Laboratory's (ESRL) Analog Temperature 8-14 day outlook, as is shown below:

-

As we move into early March, it looks as though we will be heading into new phases of the Madden Julian Oscillation (MJO). Looking at the March 8th MJO OLR anomaly forecast, in the middle panel of the left side of the images above, we see deep blues spread out across the waters to the southwest and southeast of India. These deep blues represent enhanced tropical convection, and it also means an active phase of the MJO will be evolving.

If we compare that March 8th forecast image to the MJO OLR Composite image from the Australian Bureau of Meteorology, we see that the blues on the forecast image line up the best with MJO Phase 2 and MJO Phase 3, which are seen as the second and third images down from the left-hand side of the panels above. If we look at the low amplitude Phase 2 MJO (which guidance predicts we see when the MJO does enter Phase 2 before transitioning to Phase 3) 500mb height anomaly image below from scotlandwx.co.uk , we find that deep negative height anomalies are favored over the East US, resulting in colder than normal weather. The troughing in the Gulf of Alaska remains present, with suppressed ridging over the north central Pacific Ocean. Long range ensembles favor this type of set-up for the middle-late portions of February, and it's very possible this continues into March. To clarify, while the set-ups may be similar from mid-February onward, I currently only expect warmer weather for the mid-late parts of February due to East Asian ridging. Beyond that period, into early March, indications of East Asian ridging dissipate, allowing cold weather prospects for early March to flourish.

Low amplitude Phase 2 MJO 500mb height anomaly composite

The 500mb height anomaly composite for all amplitudes of a Phase 3 MJO also favors some cooler weather in the East US, though the cold is more restricted to northern parts of the nation.

So, let's sum it all up.

•We are looking at warmer weather over the United States in the closing week of February, possibly extending into the opening days of March.

•The pattern after the early-early March warm-up looks chillier, with a potentially favorable MJO (keyword is potentially due to the typical long range forecast caveats and inaccuracies) and favorable signs from East Asia after ridging moves out.

Andrew

February 13-15 Potential Snowstorm

It looks like we may see a winter storm along the East Coast in the February 13-15 timeframe.

The GFS model indicates we will see a negatively tilted trough work its way down into the Northeast and Mid-Atlantic around Valentine's Day, in the midst of an established northwest flow regime. We see this regime set up as a result of storminess over the Gulf of Alaska, and a suppressed ridge in the West US.

The GFS model wants to take what appears to be a strong clipper system eastward into the Northeast in association with the trough we saw in the image above. The clipper then transfers to the coast on the morning of Valentine's Day, resulting in snowfall for the interior Northeast. Rain looks to be the preferred precipitation type on this model solution for coastal regions. Since this is still in the long range GFS, none of this should be taken verbatim- we're trying to pick out the general pattern that could then yield a winter storm. In this case, the northwest flow with an Alberta Clipper transferring offshore seems like a rather likely scenario if the opportunity arises for a clipper to form around Valentine's Day.

The ECMWF has a similar situation, with the 500mb height anomaly forecast highly indicative of the northwest flow regime we discussed. The suppressed ridge and storminess over the Bering Sea is clearly evident, though the ridge in the Southwest is so suppressed the flow is borderline-zonal in that area. Nonetheless, we can still see the northwest flow alignment across the contiguous United States (CONUS).

The ECMWF model has the storm system impacting the Mid-Atlantic primarily, before heading off out to sea, only scraping coastal portions of the Northeast. This solution would lay down snowfall in the Mid-Atlantic states of North Carolina, South Carolina, West Virginia, and Virginia. This particular ECMWF model forecast lays down over 13" of snow in these areas, but these amounts would be better off cut in half for more accurate (but still slightly overdone) amounts.

So why will this storm hit the Mid-Atlantic and Northeast?

The answer lies in the jet stream and 500mb level. Here in the jet stream, we see the storm system well defined in the Central US on the 12th of February. If we look closely at the winds surrounding the jet stream, we see a jet streak (area of higher winds within the jet stream) positioned to the right of the trough. Typically, when a jet streak is to the right of the trough, the trough will lift north. This same principle applies here, as we then see the trough lift north and east, tilting negative as it does so to indicate the storm has reached maturity.

The 500mb level, shown two images above this jet stream graphic, also supports the storm lifting northward. We see a strong ridge of high pressure located well offshore of the East Coast of the US, which would nearly assure the storm lifting northward. Additionally, the trough beginning to tilt negatively in the East US would help out with the storm wanting to move north.

So what can we establish right now?

-The synoptic pattern looks favorable for a winter weather event in the East Coast, thanks to an evolving northwest flow pattern.

-A potential storm system is being modeled on forecast guidance that may impact the East Coast of the US.

-If a storm system does form in the United States, it looks like it will be favored to bring snow to inland portions of the East Coast, rather than coastal regions.

Andrew