Stratospheric Ramblings

The current state of the atmosphere is such that we saw a pretty robust MJO wave over the west pacific. This, combined with building pressure over asia, has helped produce a burst of west pacific typhoons over the last two weeks. This has triggered a positive feedback loop as these typhoons have distributed latent heat and negative potential vorticity anomalies downstream. This has helped pump the west pacific ridge and contributed to a strong bering sea trough( -EPO/WPO pattern). So why does this have any significance in relation to the strat? Stagnant bering sea troughiness and a very potent EAMT event(trigerred by tropical forcing over the W Pac) has really helped trigger a wave 1 response over NE siberia. Mean H5 pattern in the last 7 days shows the -WPO/-EPO setup.

Currently, the stratosphere is in a strengthening state which it should be at this time of year. As the heat source(EAMT + W PAC typhoons) for this warming fades, the vortex should rebuild stronger then it was before. -AAM anoms propagating equatorward will also help rebuild the vortex, with a potentially long period of a +AO coming up. In any case, it is a good sign to see such a strong fight against the vortex in a west QBO year. I suspect this won't be your typical +QBO year as we are in a westerly shear phase which promotes more pertubations to the vortex. In addition, we have a more poleward the normal 0 u line, with a greater then normal build up of ozone over the north pacific. These factors should make a major warming easier this winter.

The analog years I have been using for the stratosphere are 85-86, 01-02, 80-81, 90-91 and 08-09 which all have a neutral ENSO state(with the exception of 08-09), a +QBO shear phase and low solar activity. All these wintera had some form of a SSW event with the exception of perhaps 85-86 which didn't make as much of an impact at the surface. I'll give 2001 and 2009 as examples, with a 2-3 wk lag for the peak H5 response.

2009:    H5 Reflection:

Notice how the cold signal is muted across NA while their is a very strong -VE anomaly across western europe.

2001 had the opposite pattern with warmth in W europe and cold anoms across NA:

500mb setup 2-3 weeks later

If we look at all +QBO shear years, without isolating for solar or ENSO we get the following H5 setup. The important feature to note is the strong East PAC ridging and bering sea trough which would help promote a mid/late winter wave 1 response as well. The euro monthlies have also been hinting at strong GOA ridging, which combined with aforementioned factors make a good case for a SSW this winter.

So the point being made here is that you can see significant SSW's in downwelling +QBO years, especially when other factors are favourable for development. Although significant SSW's can occur, placement of the coldest anomalies at 500mb will only favour some locations across the N Hem, whether its europe, asia or NA.

Positive Arctic Oscillation Increasingly Likely To Start Off Winter

We are seeing a pretty strong -AAM anomaly propagating equatorward currently which helps support a +AO/+NAO pattern. The GEFS consensus keeps the index positive all the way into mid november.

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This type of pattern means a stronger vortex and a northerly displaced jet. Luckily a strong piece of the polar vortex is expected to park over eastern canada through early november. This may be caused, in part, by the neutral enso/+QBO regime which favours a cooler late oct into early nov period for the east. We have seen a wave 1 response across the bering sea area which has also helped bring the chill, along with an active east asian jet.

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What this also means is a recovery of the vortex is likely to occur by mid november, with a potentially positive AO regime setting up through early winter. The SAI/OPI has been the opposite of last year with a sharp negative trend in snow cover since early october. Ridging is expected to continue south of 60N across siberia so I would expect this trend to continue with snow cover ending off at near normal levels.

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If we look at the 10 most positive AO winters we find the following SLP setup near the north pole. Notice the -MSLP anomalies near siberia.

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This year we have seen below normal MSLP across northern siberia as well.

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The likely scenario IMO is the AO index remaining on the positive side through much of november and december with a SE ridge in the means and the core of cold/ winter storms aimed towards the midwest. This does not mean we cannot see a wintry pattern along the east coast, especially for new england, and the northern tier. Dec 07 is a good example of this. The +AO game is risky though as we will need to depend on a -EPO and favourable pacific setup to deliver the goods. The pattern does look ripe for a SSW event by jan/feb with a more poleward 0 line in the mean wind department as well as a large ozone build up from previous ENSO warming. This will likely play a role in hampering the AO state by Jan-March. 

Tracking Strong Coastal Storm

The GFS and ECMWF are in pretty good agreement right now with the overall setup of this storm. The euro has a weak coastal low developing of the NJ coast before major intensification occurs once it reaches the gulf of maine/Atlantic canada.

 Right now the euro ensemble spread has a weaker surface low, with a more neutrally titled trough/ weak frontal wave developing. The devil will likely be in the details, which the OP euro would likely pick up on first.

Euro ENS has little spread in the guidance:

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To get a stronger storm for the interior northeast, we need to see the trough go negative a little bit earlier. The current NAO forecast argues for a spike towards neutral in this time frame which would help pump heights off the SE coast, and perhaps encourages a further west/stronger storm. It doesn't look like the I-95 corridor has a good shot at snow, although higher elevations in the interior could potentially see something. Given the more amplified nature to the pattern, I am keeping an eye on this although the euro ENS solution is probably best for now unless the euro OP trends the other way over the next few runs.

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Updated Winter Maps/Indices Forecast on Preliminary Winter forecast

Just want to give a heads up to everyone that I have updated my december, january and february temperature and snowfall forecasts. I have also updated the indice forecasts. Check it out if you have a chance and don't forget to leave any  questions or comments you may have.

November Warmer.... core of cold shifts west

A +AAM transport has occurred over the pacific basin during the past 10-15 days... which has aided in the development of a very warm pattern east of the rockies.
We saw this pattern at 200mb since october 1st:

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The poleward AAM transport was well established during this timeframe. I added a red arrow to illustrate this event better. This pattern favours eastern IO convection which has been helping enhance the west pacific tropical "flare up".

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Now this is where it gets interesting... the GEFS has a very strong MJO wave moving into phases 8/1. This pattern usually coincides with negative EAMT and frictional torque anoms. We are seeing the opposite pattern currently.

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Given typical progression of the GWO, what should happen next is an increase in easterlies between 30N-30S, eastern u.s troughiness favoured for the rest of october and an MJO wave moving towards phases 7,8 and 1 for the first half of november. This shifts the core of the coldest air over the northern rockies and interior west, with some intrusions into the great lakes/midwest at times. An increase in convection is likely over the central pacific/dateline area given the pattern. Euro weeklies/JMA agree with this overall pattern evolution. If a CCKW can coincide with the GWO, this would help increase confidence on developing convection over the central pacific. Keeping a close eye on the wave developing between 60-120E. Lets see if the euro shifts to this type of MJO setup... right now the ensemble members are all over the place with the ENS mean parked over the null phase.

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Weak Stratospheric Warming Event On the Way

We are currently seeing a nice build up of ozone across the mid and upper stratosphere... with our current base state breeding a more poleward then normal 0 line in the zonal mean wind department. This means that the upper stratospheric vortex is more vulnerable then normal to any waves that attempt to disrupt it.

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A strong east asian mountain torque event is occurring right now, acting as a trigger. This is the strongest EAMT event we have seen since early september. EP heat flux anomalies have already been strengthening from 1 to 50hpa.

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EAMT:

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A classic wave 1 response has been occurring already with warming focusing around the bering sea/north pacific area as well as northern europe. By hour 96 we see a major uptick in heat flux with warmth propagating down towards 100hpa. What this means it that we can expect a weakened vortex in late october, extending perhaps into the first week of november. This supports the cold pattern showing up on the modelling in the long range.

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What is concerning is the response that should occur afterwords in mid to late november, causing the vortex to strengthen even more then before. The LR models such as the euro and JMA have a warmer then normal month for the east which seems plausible given the pattern. To see the stratosphere already responding to wave breaking events is definitely positive for those wanting a SSW event later this winter. Downwelling +QBO/la nada analog years support more of a late january into feb event... should be interesting to track.

Major Pattern Change in 10-15 day period

ECWMF 500mb forecast for hour 240 shows the 180 degree turn around for much of the northern plains and upper great lakes. This should translate eastwards in the 10-15 day forecast period.

Long range guidance is beginning to look really interesting. Euro ensembles in the 11-15 day period have a strong trough over the east with a -EPO/-NAO couplet. This should help expand snow cover across north america with the potential for the coldest air mass of the season for much of the Gl's/NE. A recurving typhoon around october 16th correlates well with the troughiness the euro has been showing from the 21th-25th. The GFS, euro and JTWC are in good agreement with a recurvature track.

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Would be nice to access GWO graphics, but the Gvt shutdown is blocking the data. In terms of stratospheric anomalies, warming is focusing towards the bering sea and great lakes region by day 9, with a wave 1 pattern dominant on the euro/GFS. This should help deliver the chill into the east. The PV still remains centred towards northern russia with the heaviest snowpack across siberia as well. Hopefully we can see this setup pattern turn around by november.
GFS 70mb 216 hour forecast

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Late Winter Stratospheric Warming Likely

Warm SST's between 180W and 120E has been helping strengthen the MJO wave in phases 5-7 over the last 3 weeks. This, combined with a strengthening GOA cool pool and confused atlantic tripole has helped develop a very warm pattern in the eastern part of the CONUS.

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Upward motion has generally been strongest in octants 5-1 of the MJO over the summer months. With a similar tropical pacific SST configuration continuing this means that this overall MJO setup should stay fairly consistent unless pattern drivers shift. Long range modelling such as the cfsv2 and ecmwf have been showing a warm pool developing in the central tropical pacific by late fall/early winter. If this setup forms then the MJO will tend to focus more towards the cold winter phases 7-1 as opposed to 5-7 which we are seeing right now. The question continues... can we see this shift occur.

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Another important shift we need to see is a cooling of SST's south of newfoundland and nova scotia. This has been very unfavourable for a -NAO pattern and has been causing heights to rebound very quickly along the eastern seaboard. Good news is that solar activity is expected to drop off and indications are pointing towards a pattern change by late october with a more favourable pattern for blocking. Siberian snow cover continues to remain well above normal but it is important to note that we want to see an increase in snow cover south of 60N according to an updated paper from Cohen et al.

Confidence continues to stay high with regards to a warm DEC in the east with a wet and cool pattern in the west. Analogs and modelling continue to stay in decent agreement. In sharp contrast, JAN-March looks increasingly interesting across the eastern CONUS. Looking back at +QBO, Low Solar and neutral ENSO years (85-86,90-91, 80-81 and 01-02) I found that in all cases their have been at least one late winter stratospheric warming event. With the expected warming ENSO state things could get very interesting in late winter and early spring if warmth can work its way down to 500mb. With an overall state of low solar continuing, this winter should be no different then the analog years with late winter EAMT events helping disrupt the upper stratospheric vortex.