Cold Coming, La Nina possible this spring?

Record warming in the stratosphere should deliver a healthy cold shot around the 20th of january:

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MJO signal favours a southeast ridge and further NW inland storm track with a trough along the california coast.

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After the initial shot of arctic air we may see the pattern move to a very stormy one for ontario and quebec with a more la nina like look for the last few days of january and first half of february. The LRC supports several storms in this time period. The Pacific SST's resemble a weak east based la nina look which favours cold in the great lakes and northern plains. It looks like their will be some warming in western regions as subsurface warmth upwells.

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GLAAM is moving into a weak phase 4/5 which favours a la nina type of pattern. Frictional torque values are negative between 30 and 60 north. With the MJO stalling in phases 6 and 7 the SOI will pop positive with pressure falls near darwin and a HP anomaly further east. Trade winds are present in the equatorial pacific will LP anomalies propagating eastwards across the northern pacific which will strengthen the la nina that may come on this spring. Right now a la nada biased cool looks present.

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8-10 day means look la nina like:

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Winter Comeback On The Way

Their is some very interesting weather to talk about this morning! First let's take a look at the latest ECMWF forecast for the MJO. Notice the eastward propagation through phases 4,5 and 6 which line up nicely with our January thaw that I believe is coming to an end by the 18-23 of january. This lines up well with the MJO wave which is entering phase 7 which  favors eastern cold by the 18th. The UKMET ensembles have a similar outcome and are basically in line with the european albeit more amplified.

Paul Roundy's OLR site goes out a little bit further into the long range. From now until the 18th we can see the MJO transitioning from phase 6 to 7 but it gets really interesting from the 19th to 26th when the MJO propagates into phases 8 and 1. During this time period the stratospheric warming event begins to push arctic air into the mid latitudes. This is one reason why I believe the cold will eventually progress eastwards after the 20th of january.

Phases 8 and 1 of the MJO look like this in January:

Phase 8

Phase 1

 Quite a battle will be going on from the 16th to 25th as the arctic air is pressing against the southeast ridge. A baroclinic zone will set up across the appalachians, interior northeast, eastern great lakes and the coastal plain. With a SE ridge and east based blocking in place most storms will take more of an inland track but some east coast storms are very possible.

500mb height field shows the blocking connecting over the pole and a stormy pattern for the interior

 Now let me explain some of the other players on the field. A very important observation is the current  SOI drop caused by the eastward propagation of a kelvin wave in the pacific. This is yet another sign that will help to transport very cold air into north america which is in line with the MJO and SSW events. Daily contribution to the SOI is well negative. This drop in the SOI will force a compensation across north america which will help flip the pattern to colder.

Another interesting player on the field is the extreme amount of blocking that is forecast to take place. It looks like the ECMWF and GFS are showing what should happen given the physical drivers on the field which i have displayed for you guys. The 06z GFS OP is pumping two strong ridges, one across alaska and another across eastern greenland. These ridges connect over the top which really allows the cold air to penetrate the east. An event like this is called a cross polar flow pattern which means that the jet stream extends so far north that it can pull siberian air(extremely cold air) well south into the north american weather pattern. The GFS shows this type of setup with a deep trough over the central and eastern u.s. Keep in mind this is a run of the operational past 240 hours out so caution is warranted. The ensembles have a less amplified solution which is common this far out.  The CPF event continues for several days as the PV collapses southwards after the 20th.

The european OP is moving towards the GEFS:

The NAO responds:

As you can see current observations from the tropics, stratosphere, indices and now the modelling are all pointing towards a huge change in the overall North American weather pattern. Don't put away the shovels just yet the second half of winter is going to be a wild ride!

Sudden Stratospheric Warming Event Intensifying

A major stratospheric warming event is taking place across northeast asia and expanding northeastwards towards the north pole. The most notable warming is taking place between 1mb and 30mb in the upper stratosphere.
Notice the sudden stratospheric warming at 10mb:

This warming is beginning to work its way down to the 50 and 70mb levels. The effects of the SSW event are causing an expansion in the stratosphere which suppresses and cools the troposphere. This event also weakens the polar jet stream which allows the cold air bottled up across the arctic to move southwards into mid latitudes. Currently a positive arctic oscillation(strong polar jet stream) is in place but that should change soon as the stratosphere continues to warm and weaken the vortex. Their are three reasons why I believe that the stratospheric warming event will continue to intensify throughout the next week which will cause the sensible weather across north america to become very cold for the end of january and into february.

Part 1: East Asian Mountain Torque Spike

East Asian Mountain Torque Values are increasing and have spiked positive which will help to strengthen planetary wave breaking events across east asia. In simpler english, the current warming that is taking place across east asia will continue to feed warmth towards the north pole. Weakening of the polar vortex has already taken place from our current warming and the negative phase of the QBO. Further warming in the next seven days will be too much for the PV to withstand. You can see the rapid warming in the upper stratosphere on the loop below.

Current warming will cause a complete split in the polar vortex which is shown on the european stratosphere forecast for day 3. Notice one piece of the vortex is centred across north america with a weaker piece in central europe. This weakening of the vortex will cause a huge amount of arctic air to get transported underneath into central and eastern north america. A 2-3 week lag time occurs between the SSW event and cold air transport to the surface which means that we can expect the cold to reach eastern north america by the 20th-25th of january. Very cold air will last until the beginning of february with this setup.

Part 2: West Pacific Kelvin Wave 

Latest observations point towards another kelvin wave formation across the western pacific. Kelvin waves are pockets of warmth that move eastwards along the thermocline(subsurface boundary between cold and warm water) in the equatorial pacific. Kelvin waves contain westerly wind bursts aloft which cause two major implications on our weather pattern. 1) Transport warm water from the western pacific into nino regions 3 and 4(central pacific), further enhancing the el nino and subtropical jet disturbances. 2)  It Causes major drops in the SOI by transporting major warmth into the upper atmosphere. The atmosphere always need to balance itself out so it therefore cools north america as a result of the SOI drop. Relating this back to out stratospheric warming event the kelvin wave helps to transport additional warmth into the upper atmosphere which disrupts the polar vortex even further. Take note of the kelvin wave located near 140 east longitude and 100 meters below the surface.

 All of these atmospheric factors point towards a major stratospheric warming event continuing to intensify which will weaken the polar vortex and transport arctic air into north america from mid january to the beginning of february. The cold will invade the west and northern plains first with the frigid air moving in between the 12th and 20th. The cold should progress east by the 20th as is natural when a large amount of arctic air is pushing eastwards and spreading out into an upstream ridge.  The core of the cold will be focused at the ohio valley, midwest, great lakes and northern new england as opposed to the mid-atlantic states.

GFS temperature anomaly forecast from the 15th to 20th of january:

 This cold weather pattern will continue into the beginning of february and perhaps beyond if more stratospheric warming events continue to occur. The GFS and ECMWF forecast models believe that another warming will happen in about 7-10 days.

Winter Is Coming Mid Month

In the Equatorial Pacific we can see the upwelling of colder then normal SST anomalies from 140w to 90w.

This has contributed to the cooling of nino regions 3, 2 and 1. Further west the recent kelvin wave and WWB has caused subsurface warming in the western nino regions. Intensification of the WWB near 120w has worked to upwell warmth along the thermocline.

We will see another spike in SST anomalies in nino 3 and 4 as the warming reaches the surface further east and MJO propagates into the western pacific around the 15th. This should help to enhance -OLR anomalies causing further warming in nino 4. The west/central based warmth along with the SOI drops should allow for significant cooling across eastern and central north america in late january and february. A tropical cyclone NE of New Zealand is contributing to pressure drops near tahiti but as it moves out a strong HP anomaly should move into the area. MJO propagation across the Eastern IO/maritime continent will allow for further SOI rises in the short range as low pressure anomalies continue across southeast asia. This signals a relaxation in the subsurface warming/SOI drops for the short term but as the EAMT gets going we should see these LP anomalies attempt to move eastwards in line with the MJO wave around mid month.

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The ECMENS are coming more in line with the GEFS pointing to an east based -NAO, -EPO and neutral to -PNA developing past the 15th which forces the core of the cold into the rockies/northern plains with storminess across the st lawrence valley, interior northeast and ohio valley. A strong SE ridge keeps the east coast above normal in this time period. Past 300 hours the GEFS is pointing towards a shift west in the blocking which allows the cold to propagate east and sets up the east coast for more storminess. Take the GEFS FWIW at this range but this is possible as the effects of the SSW slowly beat down the SE ridge from the 20th onwards. The brunt of the cold and snowfall should stay north of 1-95 with this setup overall. We are seeing conflicting signals between the unfavourable MJO, SOI drops, SSW and central based ENSO warming but i expect the cold to win out in much of the east by the 20th as the MJO losses amplitude and other cold signals win out. 

Major Stratospheric Warming Event

MJO in phases 4,5 and 6 will cause a very warm pattern until the 15th of january with a ridge in the eastern part of north america and a +NAO/AO combination. The wave will be fairly strong but will propagate eastward quickly, limiting the warm pattern to a fairly short period of time.

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After the 15th the wave will weaken and move towards the COD and could move into phases 7 and 8 later in late january or february but that is still uncertain right now. Phase 7 looks like this in january, notice the east based -nao, +PNA and -EPO pattern with a trough in the bering sea.

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A less amplified MJO wave means after the 15th we need to look for other factors that will influence our weather pattern across north america. An active pattern will likely return mid and late month as an active SE ridge is present with a trough digging into the west/eastern rockies. A large thermal gradient will set up a BZ across the eastern GL, ohio valley and interior northeast. Look for several snowfall opportunities past the 15th as more cold air gets established into the pattern with pieces of arctic air moving down from western canada. Also a very active west pacific LP wave train has set up with poleward movement of frictional torque. This lines up with a weak phase two of the GWO(more of a la nina pattern) and means that we can expect a stormier pattern mid to late month.

Further down the road the effects of the current SSW will take hold on the east as the trough in the west eventually progresses eastwards. An initial warming has already weakened the vortex with warming near the pole but another warming event will take hold across northern canada with rossby waves and a +EAMT reinforcing the warming. This should be enough to cause a complete collapse of the PV. A wave 2 pattern will set up, splitting the vortex with one piece moving onto our side of the globe and another towards eurasia. With a two week lag, expect very cold temperatures to move into the east past the 20th of january. With a strong trough in the west large pressure rises should occur across NW canada which will press against the ridge before the cold wins out by the 20-25th. The GFS is probably too fast with bringing the cold air eastwards which is in line with its MJO forecasts. The ECMENS and euro weeklies are beginning to catch on to the colder pattern and a -NAO/AO pattern caused by the SSW event.

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Looking Ahead Into February and March

For my February analog set i looked for years with a similar temperature trend to this year as well as a similar 500mb setup. I put less focus into the ENSO trend with these years because of the weak signal this year but most of my years are central/west based el nino's. First lets start off by taking a look at what this december looked like to try and match it up with previous years. Take note of the above normal temperature departures that take over much of the lower 48 states as well as eastern canada. Very cold air is locked up across NW canada including northern B.C. A tongue of cold extends into the prairie provinces with much warmer temperatures dominating further SE.



500mb height field shows a strong trough in the west with a ridge upstream across eastern canada and blocking towards greenland. Notice the strong ridge across the bering sea which causing energy to dump into the west promoting an eastern ridge most of the time. Another key feature is the trough centered west of hawaii which promotes a ridge in the bering sea and a trough in the west. For eastern cold we like to see the trough east of hawaii to pump a western ridge and an eastern trough.



Now lets look at some past years with a similar match to december 2012 so that we can try and get a better handle on what might occur down the road. Taking a look at surface temperatures we can see the warmth dominating over much of the u.s extending up towards eastern canada and greenland. All of the cold air is locked up further NW which is very similar to this years december pattern.



On the 500mb height field we notice a ridge in the bering sea as well as a trough west of hawaii which is very similar to this year and is a key player for the north american weather pattern. A trough is centered along the west coast and gulf of alaska with ridging further east across the central and eastern u.s. Blocking is found across hudson bay and greenland although weaker then this year.



Lets take a look at what february and march looked like in these years. 
I like what the february analogs look like and believe that a broad based trough across the nation makes sense. The -PNA regime will probably continue but cold will be able to penetrate the east with more blocking over the top. With the SSW event taking place, it should drive the cold air south for the end of january and much of february. An active storm track will set up for the first half of the month in the eastern great lakes, quebec and the northeast.
500mb setup shows the trough retrograding off the east coast and another broad trough across the continents midsection:


Surface Temperatures are pretty inline with my thinking but i think the coldest anomalies will be focused further NW across the prairies, northern plains as well as NW canada with the tongue of cold extending into the northeast. A SE ridge may get going later in the month:


Heading into march we can see the warmth is confined to the southern u.s with the cold air locked up much further north with a positive NAO. March is still pretty far out and is a low confidence forecast at the moment but I do believe that the southern u.s will average warmer then normal with temps being held back across the great lakes, northern plains and west coast. How much colder then normal is still uncertain right now but i feel the most confident along the west coast within the negative PDO regime. A late start to spring is likely along the west coast with an early start to spring in the SE, midwest and mississippi valleys.
2m Temps:

500mb heights:
 

Observations Point Towards Pattern Change Despite Temporary Warmth

Convection is beginning to redevelop around the date line this morning which is a good sign and means that the MJO is beginning to transition into more favourable phases 7 through 1. Right now most of the convection is across the indian ocean or in phases 2 through 5 of the MJO. Redevelopment of convection around 180 west will force a strong trough in the bering sea and a large thermal gradient between cold arctic air and warm tropical air. This thermal gradient will cause more storminess in the bering sea and will amplify the MJO wave as it propagates around the COD. A more active STJ will then become established with a PV dropping south from Stratospheric warming influences. This spells trouble for storminess across the eastern great lakes and interior northeast with very cold air across the prairies, west and northern plains.
Notice the convection redeveloping around 180 west with negative OLR anomalies present




The 8 to 10 day forecast from the GFS and ECM show the SE ridge and SW troughiness common in phases 2 through 5 of the MJO.

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Long Range January Outlook

The MJO is headed into unfavourable phases 3,4 and 5 for the second week of january. This correlates well with the january thaw across the east advertised by the ECM and GFS model guidance. With the neutral enso state we should be watching the MJO, SOI values and stratosphere for guidance as other signals have less of an effect on the overall north american weather pattern.

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Temperature anomales from the GEFS:

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According to the GEFS, signs are pointing towards a more favourable MJO pattern for the last week of january and into the beginning of february. How fast the MJO wave propagates around the globe varies between the ECMWF and GFS. The euro is much slower with the MJO wave and continues to bank on an unfavourable pattern into the beginning of february. The GFS builds frigid air across central and western canada in week two and three of january. This allows the cold air to move east for week four with the SSW event coming up.

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The european weeklies are showing a much different solution with much warmer then normal temps in the east for weeks 2 through 4 in january and the cold air locking up in the west and prairies. This is enough to make you second guess yourself, especially because this is the best performing model. I am still not convinced that the cold won't deliver in the second half of january. Now let's all remember that the MJO has a large effect on the subtropical jet stream but does not drive the polar jet stream. This means that a southeast ridge will be favoured in the second half of january as well as a trough in the southwest. With the upcoming SSW event the PV will drop south into central and eastern canada which will shift the polar jet south and cause a -ao pattern. The stratosphere will be the major driver of our weather pattern across canada. Although the southeast and east coast may be near to above normal that does not mean that we are out of the woods in eastern canada. What I see setting up in the second and third week of january is a frigid pattern in the west and prairies and an active SE ridge causing the storm track to form along the BZ across the st lawrence river valley and eastern lakes. By the forth week of january and first week of february the PV should drop Southeastwards leading to a colder then normal pattern across the east. The PV is already on our side of the globe which means that the cold air is much more available then last year and is not likely to propagate into other parts of the globe. With the MJO heading into more favourable phases around the last ten days of january a much colder and snowier pattern looks increasingly likely, despite the european's frightening outlook.

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