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.

Reduced 13% 734 x 560 (64.36K)

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.

 Reduced: 90% of original size [ 565 x 695 ] - Click to view full image

EAMT:

Reduced 18% 773 x 1000 (87.39K)

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.

Reduced 13% 732 x 560 (41.74K)

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.

Reduced 38% 1024 x 768 (591.92K)

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

 Reduced: 89% of original size [ 575 x 575 ] - Click to view full image

 

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.

Reduced 38% 1024 x 768 (320.35K)

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.

 Reduced: 93% of original size [ 546 x 546 ] - Click to view full image

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. 

GLAAM Can Be Very Important Factor In Winter Pattern Shaping

Few things we want to look for as we get closer to the winter season...

If we take a look at last years mid and late winter turn around we notice some very interesting trends from the GWO, FT and global MT's. 

Last winter's 250mb height pattern from Dec 1 to Jan 15th had a fairly strong belt of positive heights between 60 and 90N with some lower heights over the mid latitudes and a -AO/NAO/PNA pattern. Strongest blocking was focused over siberia/N Europe with GWO/PDO forcing helping drive a -PNA. This was not a very wintry pattern for the east.

 Reduced: 90% of original size [ 565 x 436 ] - Click to view full image

A strong positive momentum transport in NOV/ early DEC meant very warm conditions for most in the east and central CONUS. If we examine the FT chart we notice a transition to negative anomalies between 40 and 60 north in time for the second half of winter with positive momentum transport between 60 and 70 N. This was a major driver that helped the winter turn around to colder along with 2 SSW event's. 

Reduced 18% 773 x 1000 (132.26K)

During the second half of winter and early spring their was a large increase in lower heights over the 30 to 60N area with stronger blocking over western greenland.

 Reduced: 90% of original size [ 565 x 436 ] - Click to view full image

If we take a look at our current Surface torque anomalies we are picking up similar to where we left off last winter with negative anoms near 50N and positive anomalies further North. Overall global Surface torque is positive as well. Lets see how this evolves as we move towards winter. 

Reduced 18% 773 x 1000 (147.97K)

Current H5 pattern has been pumping higher then normal heights over the tropics with a fairly broad hadley cell. With our expected solar drop off in the next few weeks we should see this pattern slowly reverse. 

 Reduced: 90% of original size [ 565 x 436 ] - Click to view full image

 

Playing With Some Analog Years

Been playing with some potential analogs for the upcoming winter. I looked for Neutral ENSO years (between -0.5 and 0.5 ONI in DJF period), with a downwelling +QBO and AP Index below 12. I double weighted +AMO/ -PDO years in the set. A few important notes was the very consistent -NAO pattern showing up, as well as a weak -EPO much of the time. The SE ridge began to strengthen in february but is fairly weak in DEC/JAN.
December 500mb Pattern:

 Reduced: 90% of original size [ 565 x 436 ] - Click to view full image

January:

 Reduced: 90% of original size [ 565 x 436 ] - Click to view full image

Feb:

 Reduced: 90% of original size [ 565 x 436 ] - Click to view full image

Dec temps:

 Reduced: 90% of original size [ 565 x 436 ] - Click to view full image

January:

 Reduced: 90% of original size [ 565 x 436 ] - Click to view full image

Feb:

 Reduced: 90% of original size [ 565 x 436 ] - Click to view full image

In terms of OLR their was very strong tropical forcing over africa with an MJO phase 7-8-1 look which is helping to drive the more el nino'ish h5 configuration. STJ looks very inactive though due to the mean SST setup in cool neutral/ weak la nina territory

ENSO Conditions Swaying Towards Cool Biased Neutral

Although ENSO conditions have been warming recently, signs pointing towards an SST setup edging more towards cool neutral conditions as we head into october. Easterlies continue to dominate much of the tropical pacific basin with a decrease in cloudiness as well, indicative of strengthening cool SST's.


Cloudiness:


SOI values continue to oscillate with bursts of negative and positive numbers, although biased well positive in the 30 and 90 day means. At the subsurface, we are seeing a fairly strong cool anomaly below a patch of warmth responsible for the recent ENSO warming and -MSLP burst over the tropical pacific.

MSLP from sept 15-25:

 Reduced: 90% of original size [ 565 x 436 ] - Click to view full image

SST change since july 25th:

 Reduced: 90% of original size [ 565 x 436 ] - Click to view full image

Subsurface anomalies support gradual cooling... but we will see what happens.

Cool neutral years per the DJF ONI index with a westerly shear phase of the QBO look like this in winter.

 Reduced: 90% of original size [ 565 x 436 ] - Click to view full image

H5 look when isolated for -PDO years only.

 Reduced: 90% of original size [ 565 x 436 ] - Click to view full image