Wednesday, July 23, 2014

Current Water Temperatures Support Southeast Ridge Next Winter

Current sea surface temperature anomalies are supportive of the dreaded Southeast Ridge making an appearance next winter.

The image above shows sea surface temperature anomalies from July 11, 2014 to July 18 2014, projected across North America. In this image, we want to focus on the anomalies around the Southeast United States and up through the East Coast.

We see a general presence of slightly to well above normal sea surface temperature anomalies when examining the waters to the west and east of Florida. In those regions, we can observe widespread anomalies over one degree K above normal. Looking up along the East Coast, we see these warmer than normal anomalies still present, though not as intense as those near Florida and the Bahamas.

While this feature may not be as significant when compared to those features in the Pacific, it does hold substantial weight when analyzing the expected climate of the United States this winter. Depending on a multitude of conditions in the atmosphere, there is the potential for a semi-permanent ridge of high pressure to form in the Southeastern United States during the cold season. The durability and strength of this ridge varies on a case-by-case basis, but its presence can never be overlooked when it appears. The ridge allows the storm track to be deflected northward, sometimes bringing winter storms into the Plains if the ridge is strong, and other times into the Midwest and Ohio Valley if the ridge is weaker. What is clear, however, is that this phenomenon spells bad news for winter weather fans residing along the East Coast. This ridge almost always delivers warm, quiet, snow-less weather to those in the East. Unfortunately, if the latter description sounds like you, the chances of these conditions arising this winter have been raised.

The winter weather fans in the East Coast may not want to hear this news, but those in the Plains and Midwest should thoroughly enjoy this latest news, even if it may just be a flash in the pan. We'll have to see how the El Nino situation evolves this fall, hence the flash in the pan reference.


Tuesday, July 22, 2014

Weak Upwelling, Hostile Environment Could Spell Weak El Nino Ahead

A weak episode of upwelling in the eastern Pacific, combined with a continued hostile environment with respect to El Nino formation, could indicate that a weak El Nino may be in store for the future, rather than previous projections of moderate and strong El Ninos.

Michael Ventrice
Shown above is what the concepts of upwelling and downwelling look like. Imagine, for a moment, the eastern Pacific is completely flat, no perturbations or disruptions in the surface or underwater currents. Imagine that the western portion of the water begins to rise. In the Pacific, Kelvin Waves can propagate from west to east along the Equator, bringing about a rise in sea surface temperatures and in the actual water height. As a result, we see water levels in the east drop ever so slightly, likely not even recognizable. As time progresses, in the Pacific, the Kelvin Wave will eventually push east, and the warm waters will push to the surface. As the third panel shows, this sort of motion is referred to as "upwelling", where the subsurface waters push to the surface. In response, a body of water nearby (in this case, the Central Pacific) will exhibit "downwelling" characteristics, where water temperatures will either warm or cool, the opposite temperature anomaly as the anomaly involved in the upwelling incident.

If that was confusing, don't worry, we can explain it better below.

The image above shows the anomalous depth of the 20ยบ Celsius isotherm below the surface in the eastern Pacific. In layman terms, positive anomalies on the chart above mean warmer than normal waters, while negative anomalies mean colder than normal waters. Check out how we've seen a series of cold and warm episodes across the Pacific in the last year. In October 2013, we saw cooler than normal water temperatures shift east with time (hence the slanting down and east with time (left legend) and direction (bottom legend)). In an interesting correlation of how upwelling episodes seem to determine the strength of the following downwelling episode, we saw warmer than normal waters follow quickly in its footsteps around November 2013. This was a classic example of upwelling and downwelling. We saw upwelling occur with the below normal waters in October, as cooler waters were brought from underwater to the surface, and the resultant downwelling episode occurred in November, when surface-originated waters were forced underwater and eastward. We saw an even stronger occurrence of this in January 2014, when upwelling occurred, and then our historic Kelvin Wave induced the upwelling in February and March 2014.

So, it would only be natural to expect an even stronger upwelling phase now, right? Wrong. Looking at that chart above, now that our Kelvin Wave has passed, we see barely any evidence of sustained upwelling. If we consider that the strength of the upwelling episodes (cool anomalies) could actually predict the strength of the downwelling episodes (warm anomalies), one might think that the upcoming downwelling episode may result in more of a weak El Nino than one of a stronger magnitude. Although the correlation discussed isn't exactly how the upwelling/downwelling episodes work, it's worth seeing if such a correlation might be even remotely successful at predicting the upcoming El Nino.

The El Nino has been difficult to come by. This most recent Kelvin Wave, expected to bring us that strong El Nino, couldn't hold its ground and ended up dissipating. Add to that the atmosphere never exhibited El Nino characteristics, and it's all-around bad luck. Some change is on the way, however.

Kyle MacRitchie
The image above shows the long range forecasted MJO phase from the CFS model, from Kyle MacRitchie. This forecast has the Madden Julian Oscillation moving into Phases 8, 1 and 2 by the early and middle parts of August. In simpler terms, this forecast suggests that we will see enhanced convection over the western portion of Oceania and around the Indian Ocean in August. Why is this important? When we see tropical convection in those areas, the atmosphere can respond by pushing this convection eastward into the open Pacific, possibly as far as into South America. If this convection can reach the Indian Ocean and around Oceania, it can create westerly winds from that area into the east Pacific, setting up a favorable environment for El Nino formation. If the convection can actually move into South America, the potential of El Nino-like conditions forming greatly rises. The gist of all of this is, the tables could be turning in favor of an El Nino, after a long time of suffering quite an uphill battle.

To summarize, the upwelling-downwelling pattern we discussed earlier tells us that only a weak El Nino could be in the cards down the road. However, after examining the projected placement of tropical convection in the Indian Ocean, El Nino formation could actually be favored, even if it's only favoring a weak or possibly moderate El Nino (I would place my bets on the former option, however).


Monday, July 21, 2014

First Full Winter Forecast from Long Range Climate Models Released

The first forecast encompassing the entirety of the 2014-2015 winter season has been released from the major long range climate models. Today, we will discuss the three-month averages of temperature and precipitation anomalies. Future posts will break down these averages into month-by-month increments.

The first graphic we will look at shows temperature anomaly forecasts averaged out over December-January-February. In this image, we do see a variety of solutions, with the majority of them supporting a warmer than average winter. The CFSv2 model, the long range forecast from the American weather services, inundates Canada and the United States with a well-above average winter. Only Mexico is safe from the extreme warmth here. The two Canadian weather service projections, labeled CMC1 and CMC2, show different projections. The CMC1 forecast keeps most of the nation warmer than normal through February, only sparing the Four Corners region in the United States, while the CMC2 projections has much of the Central and East US in below-normal temperatures for the winter. Alaska and western Canada look to experience warm weather. Rounding out the top row, the GFDL_FLOR, a version of another American model, has the Plains/Rockies in for a chilly winter, while keeping the North US warm.

Along the bottom row of forecasts, we begin with the GFDL model, a variant of the GFDL_FLOR model we just analyzed. This forecast keeps most of the nation warmer than normal during December, January and February, though a cool reprieve is given to those in the south-central Plains. The NCAR model, another American climate model system, turns on the oven for the Lower 48 while locking Alaska and northern Canada in the freezer. A variant of this NCAR model, the NCAR_CCSM, has nearly all of North America seeing warm readings on the thermometer this winter. Lastly, the NASA model, yet another American-based forecast, shows a cold Central & East US winter, with a warm West Coast, not unlike what we saw last winter.

As for precipitation, the picture is much less clear. The CFSv2 model has a dry Pacific Northwest and New England, but finally brings wetter conditions to the drought-stricken Southwest and South Plains. Additional wet weather continues into the Gulf Coast region. The CMC1 has a snowy winter for the Great Lakes while continuing the above-normal precipitation trend in the Plains, but the CMC2 model brings this moisture to the Ohio Valley, leaving the Pacific Northwest with the driest outlook. The GFDL_FLOR resembles the CFSv2 forecast, drying out the Pacific Northwest, moistening up the Southwest and South Plains, but this time extending this moisture into the East Coast.

Along the bottom row, the GFDL model has a nightmare forecast of wet conditions in Oregon and Washington state, resulting in yet another dry winter for California and the Southwest. Texas and the southern Plains see their winter forecast with added precipitation, but negative precipitation anomalies hold over the Ohio Valley and Northeast. For the NCAR forecast, the entire West Coast observes a very wet winter, also seen in the Eastern US. Only the Central US is kept out of this above-normal precipitation inundation. The NCAR_CCSM forecast brings above normal precipitation to nearly everyone in the Lower 48, except for the Pacific Northwest. Lastly, the NASA model has a very dry West Coast winter, reciprocated along the Midwest and Ohio Valley. Wetter than normal conditions are observed along the Gulf Coast.

Breaking it down, I want to first throw out the NCAR, NCAR_CCSM and NASA model forecasts, as they are known to exaggerate anything they forecast, and generally retain a very poor track record. I feel the general consensus of climate models is too warm, mainly because the primary factor that brought us a cold winter last year is still in place today. I realize that this factor can't control the entire atmosphere, but if anything's going to have a synoptic impact this winter season, it'll be the warm waters in the Northeast Pacific, bringing cold air down south from Canada into the US.
It is rather likely we will see a wetter than normal Southwest, South Plains and Gulf Coast, but beyond that, precipitation anomalies for other areas of the United States are in question. I'm not confident in the East Coast snowy anomalies, nor the both positive and negative anomalies seen across the Midwest and Great Lakes. We will need more time to figure that portion of the forecast out.


Saturday, July 19, 2014

'Death Ridge' to Make First Appearance This Summer

The infamous ridge of high pressure which frequently forms over the Plains in the summer months, nicknamed the 'Death Ridge', will be taking up position this week for the first time this season.

The above image shows forecasted 500mb height contours, wind barbs, and wind speeds in the shaded colors. The forecast image comes from the ECMWF model, and is valid on Wednesday evening. Here, we see a body of strong high pressure originating in the Four Corners region, at a strength of about 597dm, as the contour shows. We see the ridge extending well into Canada, setting up sustained northwest flow over the Midwest and Great Lakes in the process.

Model guidance agrees that we will see multiple disturbances traversing the northern fringes of this ridge, swinging up into Canada and eventually down into the Great Lakes, towards the Ohio Valley. As the systems swing down into the Great Lakes, I expect we will see opportunities for severe weather. These opportunities could be plentiful, depending on the number of disturbances expected to rotate along the perimeter of this large high pressure system.

The GFS model's forecast of the Lifted Index, shown above, also valid on Wednesday evening, gives a good idea of where we might expect some active weather to form. The Lifted Index gives forecasters the ability to see how unstable the air is. Negative LI values indicate increasingly unstable air, and values below roughly -6 can indicate the potential for some substantially active weather. In this forecast image, we see LI values in portions of Ohio and Indiana exceeding -12, highlighting the presence of extremely unstable air. Considering this is a low-resolution model, it could very well be exaggerating how unstable the air will be. Nevertheless, this is a testament to what we may see next week, when some parts of the Central US may be affected by severe weather.

Lastly, we see the GFS forecast for temperatures just a few thousand feet off the ground on Thursday evening. This image gives one example of the areas expected to be hit the hardest by this hot weather, with portions of the Rocky Mountains into the Plains on the receiving end of the worst weather. If you live in the aforementioned regions, prepare for this hot weather by stocking up on water for you and your pets, as well as limiting outdoor activity and making sure your air conditioning unit is up to par.


Wednesday, July 16, 2014

Long Range Climate Models Show Snowy Eurasia in October

Long range models are giving indications that the coming October may feature above normal precipitation in the Eurasia area, something that could then favor a colder than normal winter for the United States.

The image above shows a global probability of above, below, and neutral precipitation anomalies. We can focus in on many areas of the world and try to decipher what they mean for the coming winter, but today, we’re going to keep our attention on the forecast over Russia and the general north Asia area.

This forecast, a probability forecast using a combination of roughly six or seven different climate models from various global meteorological agencies, shows a swath of above normal precipitation probabilities across a good portion of central Russia. In the forecast, we see the precipitation anomalies extending north of the 60N longitude line, an important line in our situation.

A few years ago, Dr. Judah Cohen created the Snow Advance Index, abbreviated as the SAI. Dr. Cohen claimed that by measuring snow cover anomalies in Eurasia, namely north of the 60N parallel, one could decipher temperature anomalies for the upcoming winter. For example, an October with sustained below-normal snow cover anomalies would favor a warmer than normal winter. Similarly, above-normal snow cover in Eurasia for the month of October would then tell us to anticipate a colder than normal winter. In past winters, I have seen the SAI perform quite well, the only exception being this past winter. Thus, I hold this index in fairly high regard in terms of accuracy.

As of now, guidance does favor a wetter than normal October over Eurasia, with some of that likely putting down snow cover in the process. While this is expected to change in the future, this could be an indication that we may expect a snowy October in Russia, which may lead to a colder winter here in the United States.