March 12-17 Potentially Significant Storm System

I'm seeing the potential for a significant storm system in the March 12-17 period.

Shown above is an ECMWF forecast for the evening of March 5th, depicting 500mb height anomalies over the North Pacific. If we look on the left half of the image, we see a deep trough over Japan, one with strength we haven't seen in some time.If we use the 6-10 day correlation, explained by Joe Renken, to tell us when these two systems may 're-appear' in the US, we find ourselves at a March 12-16 potentially significant storm. If this solution were to verify, we could see the strength of the trough translate over to that March 12-16 storm as well. This could mean a significant storm system, potentially accompanied by significant cold weather. It's too far out to tell if this could be a big snow maker, but judging on how the climate is shaping up for mid-March, I would certainly keep an eye out for some snowy impacts.

The GFS model shifts the timeframe a little further down the road to the afternoon of March 7th, but agrees on the idea of a strong storm system over Japan. Again, it'll take a while before we get into details, but it's clear that there is a chance for a significant storm system over the March 12-17 period. I'll have more details on potential tracks in coming days.

Andrew

March 1-4 Potentially Significant Snowstorm

There is a rising possibility of potentially significant snowfall over the March 1-4 period.

The first wave of this snow event will come along on March 1st, roughly around this Saturday. Latest model projections take this system as a rather disorganized system, with lobes of vorticity scattered about the general storm. The jet stream around this system has a jet streak just to the southwest, meaning the storm would be expected to strengthen and dig a bit further south in the process. However, seeing as this system never really develops itself, and with a lobe of the polar vortex to the north in Canada, the best bet would be to maintain the storm where it is. Barring any significant model changes in the future, this first wave looks close to being correct.

The second wave is a bit trickier. We have an elongated band of vorticity, which is able to trace its roots back to Baja California. We also see a large system in Montana, which will have quite an influence on the system. The jet stream looks to have this system in its grips, as the band of air is depressed in the Southwest and rises northward as a result. This is also reflected here on the 500mb chart, as you can see the northeast progression of contour lines from the Southwest to the Northeast. On one hand, we could argue that the jet stream may eventually push this storm further north than projected. However, on the other hand, the lobe of the polar vortex to the north could end up pushing the storm back to the south. If there is to be a shift, I would be more inclined to side with a northward shift, but everything remains up in the air until we get these two waves sampled.

The general idea here is that we are likely to see a snow event in the March 1-4 period. How can I be so sure? Take a look at the graphic above. If you look closely you'll see a bump over Japan in the upper left hand corner, and if you were to loop through the 500mb anomaly charts for Japan over the past few days, you'll see that there have actually been two systems moving through Japan. If we use the 6-10 day correlation, explained by Joe Renken, to tell us when these two systems may 're-appear' in the US, we end up with a rough March 2-6 timeframe, and that really boosts confidence in this snowstorm idea. In the past, this 6-10 day correlation has verified with a high success rate, and I expect a similar story to unfold over the next several days.

Continuing to look outside the models, the jet stream in the Pacific is absolutely roaring right now. Wind speeds are in excess of 150 knots at maximum intensity, and if this event takes advantage of the jet stream (which does look probable), we could be seeing not only an increase in storm intensity, but an increase in the severe weather threat.

Just for a little eye candy, here's what this morning's 6z GFS showed for the snow events. Don't buy into this, the GFS gave out some strange solutions in this run that I don't really agree with. The thing to take away here is that two storm systems are likely in the first week of March, and we could see some significant snowfall as a result.

Andrew

Thoughts on ENSO, East Coast Snowstorms and Spring

This post will address my thoughts on the ENSO situation, the potential for East Coast snow events in the near-future, some additional spring thoughts, and more information on the upcoming severe weather season. This post will be of the more technical variety, so there will be a summary at the bottom for those who may not know as much weather jargon as some others do.

Above, we see the latest data from each monitoring region of the El Nino Southern Oscillation (ENSO) phenomenon. The blues represent below normal sea surface temperature anomalies (SSTAs), while oranges show above normal SSTA values. The El Nino phenomenon is characterized by above normal sea surface temperatures, and the La Nina is shown by below normal sea surface temperatures. Looking over all of the regions, we see that most of them are in a strong cooling period, actually hitting La Nina criteria of -0.5 degrees C anomaly or below. However, Nino region 4 is experiencing sudden warming to El Nino levels of 0.5 degrees C anomaly or above. Nino region 4 is the furthest west of the four regions, as the graphic below shows.

So what's making this region warm so quickly? Well, the answer lies in the sharp cooling trend we've seen in the regions further east, like Nino regions 3.4 and 3.

There's a Kelvin Wave afoot.

Shown above is a two-panel graphic, depicting SST anomalies on a depth by longitude chart on top, as well as a mean equatorial temperature depth-longitude chart on the bottom. Looking at the SST anomaly chart, it is very clear that there is a strong Kelvin Wave present under the surface. Kelvin waves are defined as 'warm spots' in the ocean that traverse the Equatorial Pacific, beginning near Indonesia and ending around Ecuador and Peru. The Kelvin Wave is actually a massive-but-small wave, meaning that while the water height only rises by a couple inches when the wave moves through, the Kelvin Wave stretches a vast expanse of water, and its effects on the climate are even more significant. During an El Nino, we see warmer than normal waters over the surface of the four Nino regions. Kelvin Waves can help to speed up the El Nino process by bringing an expanse of warm water into the Nino regions, about 100 to 200 meters below the surface. If it's 200 meters underwater, how can Nino region 4 at the surface be warming up? Well, check out the top of the SST anomaly image. I circled an area where a finger of warmth has propagated to the surface, and that is what's causing the sudden warmth. But the Kelvin Wave isn't responsible for just the warming aspect; it's also responsible for the significant cooling we're seeing in Nino regions 3 and 3.4.

This graphic, drawn up by Mike Ventrice, shows the sort of situation we're experiencing with the Kelvin Wave. As the Kelvin Wave pushes east, we see sea level anomalies rise in conjunction with the anomalous warmth. Ahead of the Kelvin Wave, we then see downwelling, which lowers sea levels and cools sea surface temperatures, leading to a 'false Nina', where the SSTAs might tell us there's a La Nina, but it's actually just a byproduct of the Kelvin Wave beginning to push east.

This phenomenon of warming-before-cooling has been observed well with the last few Kelvin Waves, as this chart shows. We saw one wave crossing the Pacific in September 2013, with little to no cooling before it; we saw a second wave present in November to December 2013, which did provoke some noticeable cooling before the wave traversed the Pacific, and the latest wave looks to be the strongest one of the three, with even stronger cooling occurring just before the warming. If you think about it, a case can be made for the strength of downwelling before the Kelvin Wave determining the strength of that Wave, as it seems the stronger downwelling episodes occur before the stronger Kelvin Wave episodes. The other Nino regions are experiencing anomalous cooling due to this downwelling, as the circled portion in the chart above shows.

The Kelvin Wave has shown up noticeably on sea level anomalies...

...As well as upper ocean heat anomalies.

Both of these indicators point to the idea that we're probably about to exit this neutral ENSO/cool-neutral ENSO situation we've been in for the last couple of years, and a transition to an El Nino seems more likely. Model guidance has been simulating this rise to a moderate El Nino by fall very well.

The next question becomes, will this Kelvin Wave actually make it to Ecuador and Peru? In order to find out, we have to turn to the western Pacific.

Shown here is a map of 850mb winds (arrows), outgoing longwave radiation (contours) and outgoing longwave radiation anomalies (colors) from the period of January 22nd, 2014 to January 28th. We're going to focus in on the portion of this map I boxed in. If we look at that section, we see the arrows pointing down and converging on the Equator before then pointing eastward. This phenomenon is the result of two Pacific gyres on opposite ends of the Equator. This means that there were two low pressure systems, one on either side of the Equator, that were spinning air towards the other in such a fashion that then allowed the air to be pushed off to the east. How is this possible? Considering low pressure systems north of the equator rotate counterclockwise, and low pressure systems south of the equator rotate clockwise, the winds from each system can combine and push their combined winds off to the east, which can then help with the movement of the Kelvin Wave.

The graphic above gives a good picture of what these two Pacific gyres end up doing. Considering we saw one of these double-gyres in late January, and another one is about to get going, the Kelvin Wave should continue to push to the east, and ought to be able to affect all Nino regions. This raises the question, could we see an El Nino by next winter? I'm comfortable putting down a 'yes' for that question.

Now, the warming of the westernmost Nino region 4 will likely have impacts on our severe weather season. How? Take a look at the chart above. This graphic shows correlations of 200mb winds based on the Nino 4 phase. In simpler terms, for example, when the Nino 4 has below-normal waters, the oranges and yellows (which signify positive correlation areas) would then experience below-average winds. The areas shown in blue (which signify negative correlation areas) would then see stronger than normal winds. In this case, since we have warmer than normal sea surface temperature anomalies over Nino region 4, we ought to watch for at least a slight strengthening in the subtropical jet stream as we enter March, due to the positive correlation depiction over the southern US. Because the current warming is just a little piece of a Kelvin wave and not yet a legitimate El Nino, I'm not expecting the subtropical jet stream to completely go nuts and strengthen out of control. However, it wouldn't surprise me to see the STJ strengthen in the next couple of weeks as a result of this correlation. And, if we have a stronger subtropical jet stream, the risk of severe weather then goes up. Hence, we need to watch out for the severe weather season to ramp up in coming weeks, not only due to the gradual retreat of this harsh winter, but also due to the slightly-strengthened subtropical jet stream.

Let's switch gears and discuss my thoughts for the end of March and into April (forecast for late February and most of March here), as well as why I feel we need to watch out for a snow event along the East Coast in the middle of March.

This image shows 500mb height anomalies over the Northern Hemisphere during the January 22 - January 28 period of this year. In this reanalysis, we see strong ridging over the west coast of North America, producing a northwest flow situation into the East Coast, where a lobe of the polar vortex sat to the north in Canada. Something we can use here is the Lezak Recurring Cycle. The Lezak Recurring Cycle, or LRC, is a tool developed by meteorologist Gary Lezak that, in essence, can enable forecasters to predict the overall weather pattern months in advance. The gist of the LRC involves a cycling weather pattern that develops in October and November of each year; no pattern is the same from year to year. Around mid November, the LRC begins to repeat, meaning we start to see a similar weather pattern in mid November that we saw in early October. This means that the cycling pattern has begun, and it will continue to cycle on a regular, unchanging 40-60 day interval for the next ~10 months before it dissipates over the following summer. If we utilize the Lezak Recurring Cycle for this timeframe, we can extrapolate the January 22-28 period out 57 days (which is the current length of the LRC this season), we arrive in mid-late March. This means that it's very possible we see this late January pattern come back around in late March, northwest flow included. The reason I'm discussing this northwest flow so much is because it has the potential to not only bring us an East Coast snow threat in mid-March, but also has the potential for a severe weather event.

As I discussed above, the subtropical jet stream could be strengthened as we enter March thanks to the warming of Nino region 4. If that occurs while we are in a northwest flow situation in mid-late March, it's very possible we come across a favorable environment for a spring coastal storm. I'm not saying we'll see one for sure, but the last time we saw a northwest flow come about and I thought there might be an East Coast snow event as a result, it ended up coming to fruition.

These images show some possible scenarios for northwest flow severe weather outbreaks, where we would have a lobe of the polar vortex displaced in eastern Canada, with strong ridging along the west coast of North America. Due to the warm pool in the northeast Pacific, it's entirely possible we see sustained ridging stick around in the western portion of North America like we saw in the late January image earlier in this post, which would then lead to some northwest flow severe weather opportunities and snow potentials. Both types of inclement weather potentials would be assisted by the stronger subtropical jet stream.

If we take a look at the 500mb anomaly chart a week after the January 22-28 chart earlier in this post, we see that the environment over the January 29-February 4 period has changed. The ridging has shifted westward into the Bering Sea, leaving the lobe of the polar vortex to weaken and move out of the way, which then results in ridging along the East Coast. I would expect this sort of environment to come back in the closing days of March and opening days of April in accordance with the LRC. In that time period, we may be looking at severe weather threats displaced further west and north, with warmer weather for the East and cooler weather in the West. By this time, we will have probably seen the end of big winter storms, with the exception of a rogue snow event in the northern Plains before winter finally leaves the United States.

To sum up:

•Warming waters in the Equatorial Pacific could have long term consequences for the weather pattern in spring, summer, and into next winter.
•Due to those warming waters, severe weather chances may be enhanced later in spring.
•We are watching for a potential snow event in the East Coast in mid March.
•Late March into April may feature a warm East and cool West.

Andrew

Long Range Outlook: Late February, March 2014 Forecast

This post will detail the expected weather conditions for the end of February into most of the month of March, 2014.

We'll begin with the weather over the North Pacific and East Asia. Shown above is a previous ECMWF model forecast, showing 500mb height anomalies over the aforementioned regions. If we take a look over at Japan, we see some negative height anomalies present, valid on February 20th. If we use the idea that weather anomalies over East Asia can "re-appear" in the United States 6-10 days later, I would expect a stormy and cool weather pattern for the February 26-March 2nd period. But if we look just to the west, we see strong ridging behind that storminess in Japan.

We eventually see that ridging fill into Japan a couple of days later, as this 500mb height anomaly forecast from the most recent ECMWF forecast shows. With ridging expected to hit Japan on February 24th, a warm-up is probable for the March 2nd-6th period. It's worth watching for another storm threat, as we see a depression in the contour lines right over Japan that indicates the presence of a weak storm system. It is possible we see a storm drag warm air north from the Gulf of Mexico to set-up a severe weather threat, but that's all speculation at this point.

Following that initial warm-up in the first week of January, model guidance (the ECMWF Ensemble set, shown above here) wants to bring in a strong ridge of high pressure right over Japan. It looks like this ridge has the potential to bring some seriously warm air into the United States when we see the correlation kick in. With the graphic here valid for February 26th, look out for a warm, quiet weather pattern around the March 4th-8th time period. It's quite possible we see a sustained warm period from March 2nd to the 8th, if these ridges hold together.

Looking out to the last day of February we see the ECMWF bringing in a suppressed ridge into Japan. This tells us to look for that warm pattern to continue in the United States through the March 10th period. Remember to keep track of that Rossby Wave in Alaska, denoted by the powerful ridge.

The weather pattern will then do a flip in the second week of March, as model guidance sees the entrance of a strong trough into Japan on the 3rd day of next month, as the image here shows. This would likely see a return of cold and stormy weather somewhere in the March 9th-13th time period, as we use that 6-10 day gap between East Asian weather and United States weather.

Moving out into the long-long range, we start to key in on the synoptic pattern, and not so much individual features like we were previously analyzing. We've got a good handle on the anticipated weather pattern for the first two weeks of March, so now we can begin forecasting the remainder of the month. This graphic shows you the predicted 500mb height anomalies over the Northern Hemisphere on March 8th. Note the ridging over the Arctic Circle indicating the presence of a negative Arctic Oscillation (-AO) phase, which heightens threats for cold weather in the lower latitudes (including the US). Also note the ridging starting to come back over the west coast of North America. This is part of the Rossby wave train, which is created when several rounds of strong high pressure are pumped poleward. In this case, the train has maintained itself over the northeast Pacific, at times shifting west into the waters just south of the Bering Sea. The way the pattern is aligned here, you'd be hard-pressed to not find a cold forecast for the Central and Eastern US. The flow across the Northern Hemisphere strongly favors a cold middle of March, with the Rossby Waves continuing to form and push northward along the West Coast, leading to cold weather for the populated areas out East. Since this is a 360 hour forecast, things will obviously change, but you get the idea: after the early March warm-up, additional cold weather is possible.

Why is all of this happening? The primary reason is the swath of above-normal sea surface temperature anomalies over the northeast Pacific, as this graphic shows. One of the best indicators of long-term weather patterns is sea surface temperatures. Apart from some sea surface temperature anomalies (SSTAs) defining various oscillations that also affect our weather, these swaths of above or below normal SSTAs correlate to positive or negative 500mb height anomalies, respectively. Thus, it's of little surprise that we are seeing strong ridging over the Northeast Pacific, where this big warm water mass resides. With the warm water still firmly entrenched in the waters south of Alaska, look for a cool spring to also be in store.

What we could end up seeing, if this warm pool becomes a long-term feature, is a northwest flow pattern for the spring season. The screenshot above, from a Storm Prediction Center publication, shows 500mb height contours in two different northwest flow situations, with the severe weather outbreak area circled. As you can see, severe weather events would be more prone to occurring further north during northwest flow severe weather outbreaks, and it's possible we see something like one of these situations evolve if that northeast Pacific warm pool continues to work its magic. I'll detail this more in my upcoming 2014 severe weather season outlook.

Andrew

Second Polar Vortex Intrusion Possible

We may have to deal with another intrusion of the polar vortex in just a handful of days.

Shown above is the GFS ensemble mean forecast of 500mb height anomalies over North America. We see a situation eerily similar to the one that brought about the severe cold in early January 2014. We see a Rossby Wave pushing north into eastern Alaska and Canada, as the strong positive 500mb height anomalies shows. As a result of this strong high pressure, we see a lobe of the polar vortex dropping to the south from Canada. This lobe of the vortex is illustrated well by the deep greens and low contour numbers superimposed on those deep negative height anomalies.

The GFS Ensemble 850mb level (5,000 feet level) temperature forecast for that same timeframe shows how cold conditions may get if this lobe of the polar vortex decides to scrape the United States just to our north again.

The GFS Ensemble Control 850mb temperature anomaly forecast is even stronger, with anomalies as low as -28.4 degrees Celsius in the core of the lobe of the polar vortex.

There's good reason to be concerned about a second intrusion of a lobe of the polar vortex: The Lezak Recurring Cycle supports it.

500mb chart from January 6th

The Lezak Recurring Cycle, or LRC, is a tool developed by meteorologist Gary Lezak that, in essence, can enable forecasters to predict the overall weather pattern months in advance. The gist of the LRC involves a cycling weather pattern that develops in October and November of each year; no pattern is the same from year to year. Around mid November, the LRC begins to repeat, meaning we start to see a similar weather pattern in mid November that we saw in early October. This means that the cycling pattern has begun, and it will continue to cycle on a regular, somewhat-unchanging 40-60 day interval for the next ~10 months before it dissipates over the following summer. This season, the length of the LRC has been pegged at 57 days. If we take the January 6th date and move ahead ~57 days, we arrive in the timeframe of late February, a couple of days within the very cold weather the GFS Ensembles showed above. Considering the LRC has been an efficient tool of use in not only this winter season, but in prior winter seasons, this is likely a real threat of a lobe of the vortex coming south once again.

To sum up:

•The atmosphere looks primed for a strong cold blast in late February that will likely produce anomalously cold weather.

Andrew