Preliminary Winter 2013-14 Outlook

Regional Breakdown

East

The winter will start off slow this year with warmer then normal temperatures dominating december, despite a -NAO pattern. Lower then normal snowfall is likely across the mid atlantic and coastal plain while the interior northeast, northern new england and eastern great lakes have the potential to see normal snowfall. The storm track will stay predominantly inland with one branch of the jet stream dominating. Great lakes cutters will occur most frequently as well as colorado lows. Apps runners and coastal lows will be less common but can occur once or twice in december. By January and february cold air masses will shift eastwards into the region as the storm track continues to shift SE. The southeast will continue to remain warmer then normal but winter will pack a punch to the north. I am expecting above normal snowfall in the eastern ohio valley, great lakes and interior northeast. Slightly colder then normal temps are likely across new england and the northeast with clippers sliding southeast. The NAO will stay variable in january with a strong GOA high/-EPO dominating. In february, snowy conditions are likely across the ohio valley, great lakes and the northeast. If one month will deliver a couple coastal's for the I-95 snow geese it will happen in february. The storm track will continue to shift SE as a more el nino type of pattern sets up with a +PNA setup. The Southeast stays warm and dry in february as a weak southeast ridge holds up.

Western U.S and Rockies

Winter will really pack a punch this year across the region if cool water can hold up in the tropical pacific. A -PNA, +EPO and +QBO could be able to deliver consistent troughiness in the northern part of the region but transience will likely dominate with large swings in temperatures. Below normal snowfall is likely in december and january for the intermountain west, northern rockies and pacific northwest. Cooler then normal temps are likely for the same area while warmth and dryness are likely to develop at times across arizona, southern california and new mexico. I see a battle zone from colorado to the SW as this is where large temperature swings may take place. The bering sea ridge will shift SE for february with a +PNA pattern resuming and the west warming up. Near to slightly above normal temps are likely for february across most of the area.

Central U.S and Great Lakes

Large temperature swings are expected across the area with the warmest conditions in december and colder then normal temps in january and february. The storm track will remain over the area for much of the winter with above normal precipitation expected.  Alberta clippers will be a common storm track especially over the eastern part of the area. Panhandle hook tracks will be common this winter, as well as colorado lows which will bring large dumps of snow from time to time.  The SE ridge will be a huge factor this winter as it will work to steer systems inland. Exact strength of this ridge will depend on the strength of the cool water in the tropical pacific. In my opinion the SE ridge will begin to shift SE throughout the winter as la nina begins to fade towards feb-march. If we see a stronger la nina to begin the winter, I expect that much of the great lakes area will see above normal snowfall. If we see more of a neutral ENSO signal then near normal snowfall is most likely.

Reasoning Behind the Forecast

ENSO

For this upcoming winter I am expecting a neutral ENSO state, biased cold with nino 3.4 remaining between 0.0 and -0.5C from normal. I will explain my reasoning in this section.

First off, current global Sea surface temperatures(SST's) look like this with nino 1+2 at -1.1C, nino 3 at -0.7c, nino 3.4 at -0.3c and nino 4 at -0.1c.

Currently we have easterlies dominating the west pacific at 850mb from the date line towards the Philippines. This will help prevent any subsurface warm water near 180w from moving towards the eastern pacific. SOI values have been variable throughout July and August although positive values have dominated overall. Upper level westerlies are present at 200mb, indicative of la nina conditions.

The mean sea level pressure pattern is typical of a la nina with high pressure dominating most of the pacific. Lower than normal pressures are present across southern asia, indonesia and australia.

Looking further into the future we can see that very strong easterlies are expected to develop near and just east of the date line with westerlies over the maritime continent. This wind pattern signals an increase in equatorial rossby waves over the tropical pacific which will help strengthen the chances of a la nina. Blue colours indicate easterly winds at 850mb while yellow and red indicate mean westerlies.

Currently we have a mix of warm and cool temperature anomalies below the surface in the tropical pacific.
                           

Much of the warm anomalies have been struggling to make an impact at the surface as an overall -PDO regime is dominant. This oscillation helps feed cold water down into the eastern pacific, thus increasing the odds of a la nina. As you can see in the cold PDO phase, la nina's occur much more frequently.

Minimal warming is expected at the surface in my opinion despite what the ECMWF and CFS models are showing. Temporary warming is possible but any sort of long term warming is very unlikely to occur. This is clear in the ENSO probability forecast from IRI.

 If we look at the ecmwf's SST forecast from august last year it was forecasting a moderate el nino for NDJ which was completely opposite of what actually happened. I suspect that the model is off again this year and wouldn't be surprised if it trended cooler in the next few months.

The ENSO forecast plume has most of the dynamical models forecasting el ninos while the statistical models have la ninas or neutral winters developing. This year the nino 1+2 temperature anomaly in July was -1.4c.  In years where the nino 1+2 are below -1c in July, we find that 83% of the time there is a la nina in the following winter, 17% neutral with 0% el nino. By using history as a tool we can infer that the statistical models have the edge on the upcoming season.

Analogs

For my analog set this year I looked for neutral ENSO years biased cool or weak la nina years. All of my analogs ranged between 0.0 and -0.7 on the ONI index in NDJ and DJF. The years in the analog package all had -PDO's as well. This process narrowed it down to a set of 6 years including 1961-62, 2001-02, 1996-97, 1956-57, 1967-68 and 2012-13. In this chart are my years,  numbered in order of preference with ENSO, PDO, AMO, QBO, NAO and PNA values included. The ENSO value listed is the lowest point in the NDJ and DJF tri-months. My best two years are 2001-02 and 1961-62. Both years had ENSO track very closely with this year and where I think we are headed. The AMO and PDO matched well with this year as well. 1961-62 also had a very strong warm pool in the gulf of alaska, similar to this year.

If we look at the december 500mb composite we notice a few very important features including a strong -NAO, bering sea ridge and western canada trough. 

December temperature composite in the U.S looks very warm over the eastern part of the country with cold over the northern rockies and SW. I am expecting above normal temperatures in the east although not to this extent. All of my analog years have a warm december in the east and southeast with the exception of 1961 which was near normal.

 Notice the wetness over the interior southeast and northwest with dryness along the SE coast and towards the plains states. An inland storm track is favoured for december.

For January The arctic air shifts eastwards towards the great lakes, northern plains and eastern canada. A -NAO is absent in january but the EPO is negative. A moderate southeast ridge is still present.

U.S Temperature Departures has warmth in the southeast and cold centred over the northern rockies.

The January precipitation Analogs look very dry along the west coast and in the east.

In february the trough continues to shift SE as well as the western ridge. Note the +PNA setup and what looks like a fairly neutral NAO. Very intense cold is present across central and western europe.

February temps has the cool pool over the northern plains and great lakes.

Precipitation

QBO and Stratospheric Warming

What is the QBO? The Quasi-Biennial Oscillation (QBO) is a slow oscillation in the strength and direction of the zonal wind in the lower and middle stratosphere over the equator. It has a period of roughly 28-29 months (hence the 'quasi-biennial' title) and has been observed for more than 50 years now in climatological records. The alternating wind regimes develop at the top of the lower stratosphere and propagate downwards at about 1 km (0.6 mi) per month until they are dissipated at the tropical tropopause. 

We will be in a positive QBO phase this winter which makes it more difficult for heat to be transported from the tropics to the polls in the stratosphere. The westerly phase of the QBO can still produce SSW events, especially when solar activity is low. A good example of this is in january 2002, one of my analog years for this winter. Notice the sudden warming at 70mb near the north pole.

When solar activity is low more SSW events tend to occur as shown on this chart. With the solar max behind us, we are beginning to take a downwards spiral in an already quiet period for the sun. The current sun spot cycle is one of the smallest in over 100 years. For these reasons, I wouldn't be surprised if we do see a SSW this winter.

Besides influencing SSW events, the QBO phase can also work to alter the placement of the north pacific ridge. In la nina or neutral winters that have a +QBO we find that 12/15 cases have a northerly placed pacific high. This agrees with my analog package that has a similar height field with a strong trough in the west.

Here are the years mentioned with only 1956-57, 1996-97 and 1962-63 in -QBO phases.

Arctic Sea Ice and Jet Stream Relationship

Arctic temperatures has been much colder then normal this summer.

 So you might be asking yourself, how will this effect the upcoming winter. Last year we had a well below normal snowpack at this time of year as a result of a very warm arctic with record low sea ice extent. Last years north american snowpack still managed to spike well above normal in time for winter. This year we have near normal snow cover as a result of the cold temperatures. With this years head start I am expecting some pretty impressive snowpack growth, further strengthening alaskan cold air masses. The pacific branch of the jet stream will dominate overall, but the arctic jet stream may get involved as well, especially if any prospects of a SSW come to fruition. In late winter the STJ may come to life as well. For this two occur a few things would have to happen. 

1.  We need to see enhanced troughiness across eastern asia this winter, causing the westerlies to strengthen in the SW pacific.

2. SOI values dropping off as a result of this or any other tropical forcing(kelvin waves, MJO)

3. Late winter warming of ENSO regions 3.4

Most forecast models support the development of warmer SST's in the tropical pacific by late winter. If this occurs a little earlier then expected and SOI values begin to drop in february and march we may see an end game similar to last winter. Its a wild card, but is worth watching.

NAO and Blocking

Currently in the atlantic basin we notice warmer then normal SST anomalies south of greenland and off the east coast of canada. This warm AMO tripole correlates well with a -NAO pattern which is a definite wild card this winter. How strong and how often this -NAO pattern occurs will dictate the strength of cold air masses and snowstorms this winter.

Most of my analog years have negative a -NAO for two out of the three winter months and I think this year will be no different. Here are the temperature effects of the NAO on various ENSO states.

The CFSv2, a long range american climate model has been showing this type of pattern setup for a few runs now. Here is its current run, notice higher heights around greenland with a trough over the eastern part of the u.s. this pattern evolution is most likely in feb of this winter in my opinion as I believe that a +PNA is likely in feb as the bering sea ridge shifts east. In december and january the mean trough positioning should be further west.

Winter 2013-14 Indice forecast (updated as of Oct 20th)

NAO: Weak to moderate -NAO

PNA: +PNA

ONI: -0.2 to -0.7c 

PDO: Weak to Moderate Negative PDO

AMO: Positive AMO

QBO: Positive at 30 and 50mb

EPO: -EPO

AO: Weak Positive AO

Now to my favourite part of the outlook, the month to month breakdown.

December

• Very cold conditions expected across alaska, and the prairie provinces of canada.

• Warmer then normal temperatures are expected for the east, ohio valley, tennessee valley and gulf coast states with an inland storm track likely. 

• Wetter then normal conditions are likely across the interior southeast, interior northeast and eastern ohio valley.

• Mixing events are likely along the coastal plain and in the ohio valley while northern new england and the  great lakes region experience above normal snowfall.

• Above normal snowfall is expected across the plains states.

December Temperature Forecast

December Snowfall

January

• A strong GOA ridge will continue to dominate with lower then normal heights over eastern and central canada. A shift SE in the PV is expected in january.

•  A weak to moderate southeast ridge will set up shop during the month, with warmth continuing across the southeastern u.s.

• Much below normal temperatures are expected across the northern rockies, plains states, northeast, canadian prairies and the great lakes

• An east based pattern -NAO pattern will be favoured.

• Near normal temperatures are expected in the ohio valley, eastern midwest and northern mid atlantic which is where the storm track is expected to set up.

January Temperatures

January Snowfall

February

• The GOA ridge will continue to shift SE in february with a neutral to positive PNA pattern likely to develop.

• Above normal snowfall is expected across the I-95 corridor. DC, philly and new york may have the best chance to see a major snowstorm this month.

• Above normal temps are expected to continue across the west coast this month.

• Colder then normal temperatures are likely across the great lakes region as well as central canada, ontario, quebec and much of the eastern CONUS.

February Temperatures

February Snowfall

I really hope you guys enjoyed my winter outlook. A lot of research and hard work was put into this! Feel free to post your thoughts, comments and any questions you may about this winter and I will answer them as soon as possible. You can also ask me questions via twitter to @blizzardof96.