Official Winter 2014-15 Outlook

Hello everyone and welcome to Severe Weather Centre's 2014-15 preliminary winter outlook. Throughout the course of this discussion, I will look at the current state of several important climate indices, including Sea surface temperature (SST) anomaly patterns, oceanic oscillations and atmospheric patterns across the globe. I will attempt to predict where they will end up in the months ahead and how these oscillations will impact our winter across North America. I will also go through my analog years in detail. At the end of the outlook temperature, precipitation and snowfall departures will be posted for the winter season as a whole.

ENSO and Global SST's

ENSO Strength?
As you can see, the tropical pacific basin is currently dominated by above normal temperature anomalies, with strongest deviations from normal across the Eastern Pacific(nino regions 1+2). 

The latest nino SST anomalies valid 06z August 31st are as follows. Note the East Based characteristics:

Nino 1+2: +0.679

Nino 3: +0.302

Nino 3.4: +0.15

Nino 4: +0.264

Current ENSO forecast from the IRI has el nino headed into weak-moderate territory. This is in line with our forecast.

After an ONI decline in the summer months, we are currently in a downwelling Oceanic Kelvin Wave (OKW) phase yet again. Downwelling and upwelling phases of the oceanic kelvin wave typically last between 5-8 months, beginning in the far western pacific near 140E and ending near the coast of South America. This means that we will have at least some warming/downwelling component across the tropac through december/january with cooling of the subsurface likely to resume as we get into mid-late winter. This could have implications on the march forecast once these anomalies begin to impact the surface. 

What's interesting to note on a global scale is the rapid cooling of the SST's in and around Northern Australia, Papau New Guinea and Southern Indonesia. This has helped increase pressures near darwin and lower pressures further east, bringing the 30 day SOI mean below -10. This SOI dip works in tandem with the OKW phase shift. In the zonal wind department, we continue to struggle to develop anomalous westerly winds west of the dateline. This has been the case ever since the early spring when the "super" kelvin wave propagated the pacific. 

 If we look at our current SLP pattern across the globe and contrast it with a typical setup before a strong el nino we can get a better idea on how strong this el nino will likely become. Some obvious differences are present between the two maps. The first thing is the above normal SLP anomalies along the equator this year. The pattern before strong nino's had above normal anomalies near Indonesia with below normal anomalies the further east you go(refer to map two). Also notice the very negative AAO/SAM before the strong nino years(driven by positive frictional torque anomalies near 50s). This year's AAO had been more transient, leaning slightly positive in the means. All these factors lead me to believe that we are headed for a moderate el nino, not a strong one, which will begin to weaken late winter into the spring.

SLP anomalies from 7/29-8/29 2014

SLP Pattern proceeding strong El Nino years

Antarctic Oscillation data and forecast

Nino Positioning?

I was researching east based el nino years yesterday and found out some interesting statistics on the topic.  

1)Looking back to 1950, I could only find one East Based El Nino year(1951-52) within the forecast IRI range (defined as a year with a mean DJF TNI value above zero and an ONI peak between +0.3 and +1.3c). This was quite a shock and proves that the majority of EB nino's occur when the ONI is above +1.3 in DJF (e.g 97-98,82-83 and 72-73). 

2)  The vast majority of years with a strong GOA(Gulf Of Alaska) warm pool, akin to this year, end up having negative TNI values throughout the DJF winter period. This is not just a coincidence, as these two SST signatures actually feedback off each other. A strong GOA warm pool correlates to a negative EPO and positive NOI in the fall season which correlate to warmer SST's in western ENSO regions.

Heres the SST-NOI correlation. Note the stronger cooling in nino regions 1+2. As the GOA ridge strengthens this fall/early winter eastern ENSO region anomalies are expected to cool off,leaving a WB signature in its wake. Many climate models are suggesting this type of evolution with the CFSv2, JAMSTEC, UKMET, JMA and ECMWF included.

Typical Modiki composite from the JAMSTEC site is posted below. Note the GOA and Western Mexico warmth which is very similar to this years setup.

For the reasons posted above, I am favouring a west based el nino setup this winter, but a basin wide Nino would not surprise me either.

Solar

Looking over some of the daily sunspot and solar flux data it is pretty evident that we have began to slowly decline from the second solar max of cycle 24. This dual max is common in quiet cycles and tends to be lagged by the Geomagnetic activity(AP Index) max. With that we can expect mean monthly SSN numbers to be between ~80-50 as we enter this fall/winter.

Current AP progression is at a record low(since 1932). Since the solar polar field flipped polarity back in the early spring, a significant increase in AP is not expected as we head towards winter.

Here is a composite of the low AP/Easterly QBO years. Keep in mind that most of these years were coupled with very low monthly SSN's as well, which is why the blocking was so strong. 

If we isolate the years that were not Smin years, we get a bit of a different look(note the smaller sample size).

 Both maps are not great analog composites to use as I don't think we see a typical -QBO/Smin Northern Annular Mode progression this winter( this implies a strong -NAO in the means with an early SSW). Despite this, blocking is likely to show up this winter given the very warm water near greenland and alternate factors I will investigate in the next section.

NAO/AO

In almost every winter forecast the AO and NAO can make or break a winter for eastern canada and the united states, although mean +AO/NAO winters can still end up cold and snowy for many areas(last winter is a great example of this). To help predict the state of the AO and NAO there are a few drivers that are very important to track closely over the fall, not including the factors already mentioned(extent of solar dropoff and greenland SST warmpool). 

1) The KOE (Kuroshio-Oyashio extension) is a group of two current's found over the NW pacific. The Kuroshio current carries warm tropical water from the north equatorial current and allows it to flow along the east coast of japan and out to sea. The Oyashio current does the opposite as it brings cold subarctic water from the alaskan stream south of the bering sea, along the NE coast of Japan and out to sea.  The Kuroshio and Oyashio currents meet and form the North Pacific Current or kuroshio extension that runs from west to east across the North Pacific at mid latitudes near 35N. 

So why is this important for our winter? Peer reviewed papers have found that el nino correlates very well to a +PDO pattern and a cool KOE, allowing warmer then normal SST's to build over the top across the bering sea and sea of okhotsk. This cool-warm signature in the fall correlates to a -NAO/AO pattern in the upcoming winter as it correlates to east asian cyclogenesis, a southern displaced pacific jet and more blocking over the pole. Note the KOE-Nino correlation below.

 If we look at the top 10 positive AO winters and subtract the top ten negative AO winters we notice the KOE SST configuration in the early fall which correlates to a +AO/NAO. This is something we need to look for this fall as it has nice lead time on the state of the AO.

2) We just came out of a long lasting la nina period. ONI spikes coming after at least a double nina look like this with no ENSO sorting. Note the -AO and -NAO.

3) Positioning of the nino is huge. If my theory on the likely hood of a modiki is correct, then enhanced blocking is likely over greenland and eastern canada. It is well known that a west-based Nino yields a zonally overturning cell rising from 180 and sinking over SA, which weakens the SA HC. A weaker HC -> weaker ST warming -> weaker eddy heat flux in the mid latitudes -> reversal in the Ferrell cell circulation and meridional mass field / PV gradient which equals to blocking. A lack of blocking in EB nino's allow's the ridge to amplify across the eastern part of the CONUS, whereas in WB nino's the trough amplifies with blocking over the top.

4) SLP pattern across N Siberia in October. This goes hand in hand with SAI feedbacks, which looks at snow cover growth in october over southern siberia. Below are Positive AO El nino december heights at 250mb with Oct SLP anoms on the left. Notice the negative SLP anomaly across N Siberia and the response across North America. Also note the warm KOE feedback with a northern displaced pacific jet and strong ridge east of japan/+WPO.

Map on the right courtesy of Anthony Masiello

-AO years are completely opposite in December. 8 of those 10 +AO December years remained persistent with a +AO in January as well. In february, the correlation mattered less as troughiness still dominated over the northeast/great lakes in the majority of el nino years. 

Map on the right courtesy of Anthony Masiello

QBO and SSW

Current zonal wind anomalies show the descending -QBO shear with negative anomalies at 10mb and 30mb. 50mb anomalies are still slightly positive, albeit dropping off quickly.

30mb QBO correlation to 500mb heights

Out of the 6 years with a January sunspot number between 40- 90 and an easterly QBO, all six years had at least one significant SSW event that winter. 2 of the six years(72-73 and 98-99) had more then one SSW event.

72-73: November and February
98-99: December and February
12-13: January
03-04: January
60-61: March Final Warming
70-71: January

Out of the 7 years since 1950 following more then two winters of la nina conditions, all of the years had at least one SSW event(ozone likes to build up across the poles during extending la nina periods which contributes to SSW). Its very interesting that our upcoming winter falls under both categories and both groups appear very prone to SSW events in wintertime. Because of this, confidence on at least one SSW event this winter is high to very high.

51-52: Nov and Feb
57-58: Feb
72-73: Nov and Feb
76-77: Jan
86-87: Jan
02-03: Jan
09-10: Feb

Analogs

For my analogs this winter I focused on years with -QBO shear headed towards -QBO minimum post winter. I also looked for weak to moderate el nino's with a +PDO, GOA warm pool and neutral/+AMO couplet(not all years were +AMO). My solar requirements included declining monthly SSN in the fall and monthly SSN's between 90-40 in the means. This winter, I looked for fewer years that were really good matches instead of the typical 6-10 years that are mediocre matches. Because 1951-52 was a -PDO year, I double weighted all the other three years.

December

January

February

March

As you can see the analogs are supporting the other indices which show that this winter could be mighty impressive across a large portion of North America. We have the GOA warm pool, warmth across the davis straights, a potentially West based or basin wide el nino with declining solar. On top of this we are coming off a period of long lasting negative ONI anomalies which have allowed cold air to build up across the pole. The +AO summer has only contributed to this(evident by the bounce back in arctic sea ice and below normal arctic temperatures over the summer). 

Now for the part that most of you have probably been waiting for...

Key Points

• A much warmer then normal winter is expected across the pacific northwest and Alaska, especially late in the winter season
• The core of below normal temperature anomalies are expected to develop across new england in december before shifting west towards the great lakes and plains states by mid and late winter. Well below normal temperatures are expected across the great lakes and northeast with slightly below normal temperatures for the plains states.
• Storm track will favour the mid atlantic and northeast in december and january before a SE ridge begins to shift the mean storm track further west favouring more frequent inland runner/miller B setups later in the winter.
• With an el nino in place the STJ is expected to remain active, encouraging a split jet setup and frequent phasing opportunities. This trough handoff is illustrated well in the february and march analog composites.
• A mean NW flow is expected for the intermountain west/prairies meaning upslope events will be pretty common, especially when the STJ is active.

Indices forecasts(Mean over the DJFM period)

NAO: Negative

AO: Negative

PNA: Slightly Positive

EPO: Negative

WPO: Very Negative

December-March 2014-15 Temperature Outlook is posted below. Above normal temps shown in orange, below normal in blue and well below normal in purple.

Winter Precipitation forecast(DJFM) is posted below. Above normal in green, with below normal anomalies in yellow.

Snowfall forecast. Well above normal snowfall in the purple with above normal anomalies in blue and below normal in red:

Thank you for taking the time to read severe weather centre's 2014-15 winter outlook. If you have any questions, comments or criticism feel free to ask away in the comments section below or you can tweet me with your questions to @blizzardof96. Have a wonderful day!