Monday, October 8, 2012

Final 2012-2013 Winter Forecast

"Three words to describe Winter 2012-2013? Cold and Crazy."

Hello everyone, and welcome to my Final 2012-2013 Winter Forecast. Unlike previous forecasts, I do not intend to make this one extremely technical, as some of you looking at this may not be a weather geek like I am. However, if you are someone who enjoys the technicality aspect, you should be able to pick out some of the more complicated things here and there.

Let's jump right into it with a look at the El Nino-Southern Oscillation, or ENSO status.

The ENSO is a phenomenon involving water temperatures in the Equatorial Pacific. If the waters are warm (above 0.5 degrees above normal), this is an El Nino. on the other hand, water temperatures below 0.5 degrees of average, this is a La Nina. Both have big implications for worldwide weather. As you can see above, we are currently in an El Nino.

However, notice that recently, a drop-off of these warm values has occurred. This was accompanied by a sudden disappearance of warm surface sea temperatures (SST) that would otherwise show the El Nino. I have been watching this El Nino for months and have frequently voiced my skepticism on this blog, and it appears I was correct. Should this downward trend continue, I would not be surprised to see a neutral ENSO this winter. In a nutshell, the neutral ENSO is in between the El Nino and La Nina- it is neither warm nor cold, just neutral.

Model predictions for the El Nino widely vary, with some models going for a stronger El Nino, and others going neutral. I prefer to stick with the neutral models and think that will be the solution for this winter, as the El Nino is just not in a good state to keep going on through the winter. But what exactly defines a neutral winter? In other words, what effects does a neutral ENSO winter have?

In a neutral ENSO scenario, it is common to have both the Polar Jet Stream and Subtropical Jet Stream hard at work, supplying their respective northern and southern parts of the country with storms. The Polar Jet Stream appears to be following somewhat of a positive PNA pattern, with the stream plunging south after going as far north as the Arctic Circle. This jet stream is positioned in the central Plains and Midwest. Any areas above that jet stream are likely to have cooler than normal air in place.
The Subtropical Jet Stream, commonly called the STJ, comes through Baja California and through the southern half of the nation. This stream provides the boundary for warmer than normal air in the southern portions of the nation. A wetter than normal part of the country also exists from the Gulf Coast to the southern Ohio Valley. However, I find that there is more to this puzzle than just that.
Notice how the two jet streams combine in the Ohio Valley. A combining of jet streams can very well lead to strengthening of the system, thus providing more precipitation in regions like the Midwest, Ohio Valley, and Northeast. If two storms happen to reach the intersection of the jet streams at the same time, then it is possible that phasing of the storms will occur. Phasing is when two storms combine into one, commonly stronger storm. Phasing storms are known to produce more dynamic weather conditions than regular storms, and thus may produce abnormal precipitation amounts.

The image above depicts major cities across the nation and their snowfall totals in different phases of the ENSO- El Nino, La Nina, or neutral phase. If we take a close look, we can see that cities in the Northwest averaged more snowfall in a neutral phase than in an El Nino, yet less than the La Nina. Cities in the center of the nation had a similar situation, but a few of these cities had more snowfall in the neutral phase than any other phase. This scenario included Chicago and New York City. In the bottom left, more Northwest cities achieved snowfall that fell between El Nino and La Nina snowfall amounts, while cities on the East Coast managed to hit the jackpot for neutral snowfall anomalies, besting La Nina and El Nino averaged totals.
What does this mean? The North-Central and Northeast regions of the nation are prone to more snowfall than normal in neutral winters, while the Northwest is in a less favorable position than other areas. History is always crucial to consider when making a forecast.

You may have heard about it in the news. You may have heard about it from global warming sources. You may have just heard about it. But yes, arctic sea ice is at a record low. You're probably thinking 'So what? Who cares about ice?' Well, you may want to open your ears, because such a dramatic loss of sea ice has far more implications than you may be aware of.

As we all know, ice is cold, and makes surrounding air cold. In the Arctic, such an unusual lack of ice means that the air is now 'warm' for that climate. In situations like this, when we see such warm Arctic environments, it typically means we will have a high pressure system set up over the region. This ridge of high pressure is provided by the unusually warm climate. What this ridge will do is keep cold air away from the Arctic, as high pressure tends to be a situation where warming is favored. This cold air has nowhere to go but down, south into our neck of the woods.

But this lack of sea ice, and subsequent high pressure formation over the area sets off a chain reaction. One of those factors in the 'chain' is something called the AMO.

Effects of a positive AMO on temperatures at the surface
The AMO is called the Atlantic Multidecadal Oscillation. It has a warm phase (positive) and a cold phase (negative), similar to that of the ENSO. In the positive phase, the AMO incites warmer than normal temperatures across the Northern Atlantic, as seen above. These warmer temperatures are reciprocated down into the West US. As of now (and into this winter), we are in a positive AMO.

The AMO is characterized by water temperatures in the Atlantic, hence the Atlantic Multidecadal Oscillation. As stated, the positive phase carries warm temperatures in the northern Atlantic. As I had inferred with the sea ice, or lack thereof, a ridge can set up when the environment is unusually warm. The same goes for the AMO. Notice where the warmest temperatures are found in a positive AMO in the image above- they are found in the waters just south of Greenland and in northeast Canada. This would mean a ridge may very well set up over these areas. And if you know a little something about an index called the 'NAO', you may know that ridging over such areas provides cold air to move south into the Northeast. The same applies to the positive AMO, and that is what we could very well see this winter.

The North Atlantic Oscillation, commonly referred to as the NAO, is a pattern widely recognized by many in the Northeast. A positive NAO brings warm East Coast temperatures and a generally boring storm pattern, while the negative NAO puts on a show and diverts the storm track north. This storm track takes storms down into the Gulf of Mexico, where they gather immense amounts of moisture. From there, the negative NAO takes the storm and shoots it up the East Coast. As the storm system does so, it rapidly strengthens. This strengthening, combined with moisture from the Atlantic, brings intense winter precipitation, ranging from feet of snow to inches of rain in only a couple of days.

Let's look at the chart above for the negative NAO. In the waters by Greenland, we see an area in red marked 'Warm & Less Sea Ice'. Does this look familiar? We already have a lack of sea ice in the Arctic, and the positive AMO is contributing to this. Considering the positive AMO also provides warm temperatures in the Arctic, both factors combine to produce almost a perfect storm for a long-standing negative NAO. We have actually seen the NAO in a negative state for quite a while, likely thanks in part to these mentioned indices. But there is one more index that must be reviewed, for it will be sure to secure what phase the NAO will be through winter.

The values above are the ANOMALIES of their respective levels.
This is a chart of recent values of the Quasi-Biennial Oscillation, commonly referred to as the QBO. The QBO is used to mark winds at the 30mb and 50mb levels, as shown above. In the positive phase of the QBO, winds are eastward. The opposite goes for a negative QBO, in which winds move westward.

If we look at the chart above, we can see that both levels of the QBO have been trending steadily downward, further and further into negative territory. The fact that the QBO is so well into the negatives only solidifies another factor into why the NAO has been so negative recently. It is known that a negative QBO can enhance potentials and strength of a negative NAO, so it's no surprise that the negative NAO has been so prolonged in the midst of this -QBO/+AMO regime.

So by now, we have deduced that there is a very good chance for a negative NAO this winter, meaning the East Coast is sitting pretty. But what about the rest of the country?

This is the 500mb height correlation with the positive phase of the Arctic Oscillation, also called the AO. The AO has a positive and negative phase, and is closely related to the NAO. It is not common for the NAO and AO to both be in the same phase at the same time. In the positive phase, the polar vortex that holds cold air up in the Arctic is strengthened, and the cold air is locked up north. However, in the negative phase, this vortex weakens, and the cold air is unleashed south into the US.

Let's go back to the lack of sea ice. I told you how the lack of sea ice and the +AMO may very well lead to blocking in the Arctic. Well, this is the blocking we want. In a negative AO, frigid temperatures surge south, thereby enhancing the potential for snowfall as colder air greets the precipitation. If we take into account the lack of sea ice, combined with the positive AMO, I find a very good chance for the Arctic Oscillation to be negative throughout the winter, thereby spreading cold air nationwide.

This chain keeps going, into something called the Pacific-North American Pattern, commonly abbreviated to the PNA. The PNA has two phases- the positive and negative. The image shown above is the positive phase of the PNA on the left, with the negative PNA on the right. It is well known that, for best snow potential, the Midwest/Ohio Valley and likewise regions need a positive PNA. The Rockies and portions of the Plains fare better in a Negative PNA. Each phase is like a double-edged sword for different regions.

If you've been closely following what I have been saying, you will see just how interconnected each index is to one another. I'm about to lay out another connection that may only improve the chances for snow and cold for many portions of the Eastern US.

This is an image of both phases of the Arctic Oscillation, as I described above. Why would I be showing this image now, while i'm in the middle of talking about the PNA? Here's why: Look closely at the negative phase of the Arctic Oscillation. The jet stream forms a high arc over western North America before plummeting south into the Great Lakes. Does this look familiar?
A positive PNA includes a ridge over much of western USA and western Canada, with a very stormy pattern over the Ohio Valley and Midwest. If you match up the negative phase of the AO with the positive phase of the PNA, you can see that both contain a ridge in the West and a stormy pattern in the East. These two are indeed connected!

Going back (I apologize if this is getting confusing) to the AMO, a positive AMO warms the Arctic and helps a negative AO. If the negative AO forms, we could very well also have a positive PNA, meaning that the Midwest and Ohio Valley could get snowy. I did some research and did find that a negative AO can lead to a positive PNA, and vice versa.

Precipitation anomalies of positive PDO. Flip anomalies for NEGATIVE PDO.

Temperature anomalies of positive PDO. Flip anomalies for NEGATIVE PDO.
The Pacific Decadal Oscillation, or PDO, is a long-term index used by measuring water anomalies in the northern Pacific. In a positive PDO, waters in the north Pacific tend to be below normal, while a negative PDO contains waters with above normal temperatures. It does seem pretty topsy-turvy, but that's how the PDO works.

Above, I have two images of precipitation and temperature anomalies with a positive PDO. If you flip the shown anomalies, those are what one can expect from a negative PDO. That flip of the anomalies is what I am expecting will help in this winter. This means that the Midwest and Ohio Valley may be above normal in precipitation, while the East Coast is below normal. The entire East US may be warmer than normal, while the Northwest is below normal. However, one must remember that we live in a world with dozens of indices like the PDO, and the PDO is only one. That said, keep in mind what a negative PDO does to the nation, but also remember it is one puzzle piece out of hundreds, if not thousands.

That said, here is my teleconnections summary for this winter.

NOTE: PNA is not listed. I expect it to be POSITIVE.
NOTE: PDO is not listed. I expect it to be NEGATIVE.

I was able to map out storm tracks for 7 teleconnections, and put them in the phase they are most likely to be in this winter. Keep in mind this image is property of The Weather Centre and may not be used without asking and receiving express permission from me.

I combined these tracks to help out my precipitation forecast. I believe that this has immense potential and strength in helping me with my precipitation and snowfall forecast. If you know storm tracks, you may already know what I'm thinking below based on what this image is showing.

I expect the AO and NAO to be negative, owing to the lack of Arctic sea ice, as well as the expected positive AMO and negative QBO. This quad team will bring itself to a point where the East US will end up cooler than normal, some places bitterly cold. The negative AO will assist in a positive PNA, enhancing snowy conditions in places that were high and dry last winter.

For my final set of analogues for this winter, I decided to use weak-moderate El Nino's following two La Nina events. These analogues are general in comparison to previous analogue sets I have used, so take these and use them at your own risk.

500mb height anomalies for analogue years.

Finally, I uncovered some big information recently, which has greatly improved my forecasting method for this winter. In a nutshell, there is a proven three year lagged correlation between the NAO and North American winters. That means that, if this is to be true (which it appears to be), the NAO could drop down to similar levels as seen in the winter of 2009-2010. As you know, the Northeast was bombarded with snow, while other regions were severely deprived of the white stuff.
HOWEVER- remember that every winter is different, and this is only one piece of an incredibly complex puzzle in the atmosphere. But this find could definitely assist in my forecast, which is shown below.

Without further ado, here is The Weather Centre's Final 2012-2013 Winter Forecast.

I decided to go against my analogues (which I am not as confident in) and go for a cooler than normal Eastern and Central US. Cool weather is expected in the Great Lakes and Northeast, thanks to the negative NAO and negative AO expected, as described from the above teleconnections. I did insert a warmer than normal area for the Northwest, in response to a negative AO potential and possible positive PNA, both of which would warm up the region. Note that the Southeast may experience temperature changes thanks to the PDO and typical swings of the more short term indices.

WARNING: Ohio Valley Precipitation forecast has UNUSUALLY LOW CONFIDENCE.
I am anticipating above normal precipitation generally across the East and Central sections of the nation, with an emphasis on the East Coast, thanks to the effects the North Atlantic Oscillation will have. I did also put in a wetter than normal section in the Ohio Valley. This is not something I want to be held against, because there is quite a bit of uncertainty in here. I put it in only to give people an idea and see that there really is potential here. I base this on a -NAO and +PNA.

For snowfall, I am thinking below normal snowfall will be the word for the Northwest and North Plains. However, on the other side, great skiing season is likely across the mountainous regions across the Southwest. Above normal snowfall is likely in the Northeast, but again, those in the Ohio Valley must be wary of this above normal snowfall forecast.

And here's the overall graphic, storm tracks included. I think that the slight El Nino will show for precipitation and storm track, but the presence of a positive PNA, possibly in response to the negative AO, may shift storms into the Ohio Valley and likewise regions, hence my above normal forecast in images above.

This is indeed my last winter forecast for the 2012-2013 winter. I want to thank everyone who has checked out all of my forecasts, and I hope you will stick around for next winter. I will issue updates to long range winter forecasts in the winter months, and I hope you will see those as well.


All images except: QBO Chart, Teleconnections Storm Tracks, Teleconnection Summary, and the last 4 images on the particular were obtained from other internet sources and are not my creations.

Blocking Setting Up In Wrong Places; Situation Similar to Last Winter

The latest GFS Ensemble spaghetti model forecast has strong high pressure, or 'blocking', setting up on the other side of the world, setting up a situation all too familiar from last winter.

Blocking is a term used for when a high pressure system stalls out in the upper latitudes. If this blocking can set up in the right places, snow and cold can flow south into North America. However, if this blocking happens to set up in the wrong places, like on the other side of the world, we may encounter trouble with obtaining cold and snow.

Before you get worried about a last year repeat, know this: We are in an ENTIRELY DIFFERENT pattern and scenario in this year compared to last.

Last year, fall was warm and not many cold shots came our way. In that sense, we had a forewarning. Already this fall, we have observed snow and cold throughout the nation- something many did not experience at all last winter. Additionally, this year, the pattern is much more progressive, meaning that there is less of a chance of a ridge staying put for weeks on end this year compared to last.

While this is not something we want to see during the fall and winter, it would be much worse if this blocking were to stick around for days upon days. If that were to happen, we could have a harder time getting some good snow and cold come winter.


Major Tornado Potential In Midwest Next Weekend??

There is potential for a tornado event over the Midwest next weekend, as a strong disturbance moves into the area.

500mb forecast of the GFS model has a negatively tilted disturbance centered over the Iowa/Minnesota border on Saturday, October 13. 500mb winds are being shown as strong as 80 knots, indicating that this trough is indeed pretty strong. The strongest winds are tilted to the southeast, indicating that this system will be more negatively tilted. A negatively tilted storm allows for cold air to breach the center of the storm and intensify instability. Some of the worst thunderstorms and severe weather events have occurred with negatively tilted storm systems.

The lower level jet stream is also at a heightened state, with winds surpassing 60 knots across much of the Midwest and western Great Lakes. The presence of such a strong lower level jet stream on Saturday evening is worrisome. It is known that the lower level jet stream (LLJ) is nocturnal, and provides fuel for summertime thunderstorms. If the LLJ strengthens overnight, the threat for strong storms and possibly tornadoes grows.

The jet stream itself in the 300mb level of the atmosphere is giving this system some love. The GFS is indicating that a jet streak will form over the Midwest as the system digs into the region Saturday evening. A jet streak is basically a part of the jet stream with stronger winds than the rest of the stream. This particular jet streak is progged at 90-100 knots- a jump of about 20 knots from yesterday's GFS forecast for the same time frame.

As of now, the atmosphere is looking very robust and supportive of some strong to severe thunderstorms. Let's look now at shearing- a crucial ingredient for tornadoes.

This is something called deep layer shear, and is commonly used to find the potential for supercells and tornadoes. A general rule of thumb is that supercells may be found in areas with deep layer shear (DLS) greater than 40 knots. Looking at the image of DLS above, valid for Saturday evening, we find a wide expanse of winds surpassing 60 knots, indicating that this environment is conducive for supercells.

We have now established that the jet stream, lower level jet stream, and deep layer shearing will be present. Already we have a modest set-up for severe weather and possible tornadoes. Let's now take a look at shearing in the lower part of the atmosphere.

This image, still valid for Saturday evening, depicts shearing as shown above, but at the lower levels. Where the above image shows surface-500mb shearing, this image shows surface-850mb wind shearing. This surface-850mb wind shearing can help us establish if there will be wind shear in the lower part of the atmosphere, which is also needed for tornadoes and helps severe weather.
This lower level shearing maxes out as high as 70 knots in the Midwest, now confirming my thoughts that this event has great potential.

This information has combined to tell me that this event does indeed have potential to be a tornadic event. However, there are some crucial pieces of the puzzle that lessen the threat.

•This is not spring/summer, therefore the atmosphere is not as dynamic as it could be.
•Precipitation out ahead of the actual event may dramatically lessen the threat.
•Models are projecting instability to be fairly low.

All in all, we are still a while out from this event. But, in my opinion, the Midwest needs to watch this very closely, as I see great potential for severe weather and possibly some tornadic action. Just how much potential actually comes to a point remains to be seen.