March 12-16 Potentially Significant Storm System

I'm eyeing a potentially significant storm system around the March 12-16 timeframe.

Shown above are ECMWF model projected 500mb height anomalies over the North Pacific, valid on March 6th. We want to take a look at Japan in this image, which is on the left-hand side of this graphic. If we look at Japan, we see deep purples over the island nation, indicating the presence of anomalously low heights. This tells us there is a storm system afoot; the purples indicate the storm is of the stronger variety when compared to other systems. How can weather in Japan relate to weather here in the US? If we use the 6-10 day correlation, explained by Joe Renken, which states that a storm system in Japan can affect the United States 6-10 days later, we find that this storm system would be expected to create a storm in the United States during a March 12-16 time period. 

There is something I'm watching in this time period and on model forecasts. If you were to animate the maps over the North Pacific, you would find that it almost seems like two separate systems impacting Japan over the March 6th time period, but the proximity to one another makes it seem like one big storm. It might take a little while to determine if this really is one strong system or two moderate systems, but until then, it's better to err on the side of caution and discuss how a single, strong storm system could impact us.

We can actually figure out the projected track for this storm as well, by using a tool titled 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. Since this season's cycle has been holding at around 57 days, we can go back from the March 12-17 period and arrive around the  January 16-20 time period. The image above shows observed 500mb height anomalies from the January 16-20 timeframe, where North America is located on the upper right portion of the image. If we look at what the atmosphere was like in that mid-January period, we find a defined northwest flow scenario, with strong ridging over the West Coast leading to deep negative height anomalies across the East Coast. The jet stream below for the same January 16-20 period reflects this northwest flow.

If you're a weather buff, you probably know where I'm going with this. If not, pay close attention. The northwest flow scenario involves the jet stream shooting north into Alaska due to that massive ridge of high pressure, before plummeting south into the Southeast and then north again across the East Coast. In the January 16-20 period, we also saw support from the subtropical jet stream, which helped to enhance wind speeds and phase the two jet streams. If a storm were to come along during this northwest flow scenario, it would most likely become enveloped in the jet stream, and become a coastal storm. To sum up, if the LRC cycles again to be even somewhat close to what we saw in mid-January, I would anticipate a Nor'easter or some sort of coastal storm for this March 12-16 period. Lots of time for this to play out, but historically, the East Asian correlation and LRC have been doing very well, and I see no reason to discount them now.

It's also worth noting that with this system we could see a rather pronounced severe weather threat. As we enter spring, storm systems can become more 'dynamic', for lack of a better term, and pull up more moisture to enhance the severe weather threat. The jet stream, which naturally strengthens as we enter spring and summer, could only add fuel to this potential severe weather fire. I'll have more on this aspect a little later down the road.

To sum up:

• A storm system will impact Japan in the March 6th period, leading to a storm threat in the US over March 12-16.
• Cold weather is also anticipated during this timeframe.
• Based on two reputable indices, we could be looking at a Nor'easter for this time period.
• If there are two storms instead of one, like we discussed at the top of this post, there could be two coastal storms (but that will need more investigation).
• There could be a severe weather risk with this event.

Andrew

Weekend Snowstorm Targets Midwest, Ohio Valley

I'm expecting a snowstorm to impact the Midwest, Ohio Valley and East Coast this weekend.

As the graphic above shows, I anticipate the heaviest snow to extend from northern Missouri through Illinois, Indiana, Ohio and into Pennsylvania and New Jersey. West Virginia and Virginia will also be impacted by heavy snow. I anticipate we see amounts somewhere in the 6-8" range over the Midwestern states I just mentioned, while areas along the East Coast have a higher upside, possibly near 12". With this storm comes the threat for freezing rain, and I expect this threat to reside from Arkansas into Kentucky, eastward through the Virginias. Pinpointing the location of freezing rain is difficult, and with model guidance still having numerous issues handling this event, do not be surprised if my forecast chances later today. I based this map off of the 12z GFS, seeing as the system has finally made it ashore and a general forecast with this layout appears to be the consensus at this time.

A look at enhanced water vapor imagery shows the storm system making its way onshore, throwing out massive amounts of moisture ahead of it, as the warmer colors show. The circulation of the storm remains just offshore of California, a bit east of that swath of dry air depicted in dark blues. As the system makes its way onshore, we should see model guidance improve and (hopefully) settle on a solution, as the weather balloons sent up by each National Weather Service office at 6 AM and 6 PM (central time) each day will be able to ingest data from the storm, which then feeds into the models to make a more accurate forecast.

There is some talk about model guidance underdoing precipitation in this storm, and also being too far south. The jet stream is predicted to be aligned in such a way that the storm would normally push further north than it is currently projected to go, and we would typically see the heaviest snow shifted to the north as well. However, with models standing their ground on the storm staying south, and both the northern and southern jet streams now "sampled" by those weather balloons, having been onshore for some time, tells me that the storm will most likely stay on its southern track. The under-doing precipitation claim is a bit more difficult to decipher. On one hand, model guidance is notorious for over-doing precipitation when you compare observed precipitation to forecasted precipitation, but in this scenario, we will have a strong jet stream and Gulf of Mexico moisture feeding into the environment, which would usually help enhance precipitation totals. I want to wait for a bit before making a call on that issue, because it'll most likely take a close analysis of radar trends to determine how model guidance has been handling that aspect of the storm.

Andrew

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