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.

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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. 

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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.

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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. 

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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. 

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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:

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January:

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Feb:

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Dec temps:

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January:

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Feb:

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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:

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SST change since july 25th:

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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.

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H5 look when isolated for -PDO years only.

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Long Range Lookout: Technical Discussion

Couple interesting factors showing up...

Relative AAM tendency is on the rise, meaning the Gulf of Alaska trough is coming back into play with a +EPO/WPO couplet dominating the next two weeks. Euro weeklies indicating the potential for this feature to stick around well into october. 

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Need to keep a very close eye on this. If the GOA vortex continues to be a factor as we head into late october/november it could very well come into play by winter.

Current SLP pattern since september 1st has a lack of greenland blocking and strong AK trough

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Current SLP pattern looks fairly similar to september 2011 which preceded a winter with a very strong AK vortex.

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I am in no way saying that this winter will be anything like 2011-12, just pointing out some similarities. In fall of 2011 we saw a large pickup in solar activity. This helped cool the stratosphere and raise 500mb height anoms in the tropics. Poleward propagating +AAM, Indian Ocean tropical forcing, a raging hadley cell and a cooling stratosphere did not bode well for blocking and helped force troughiness around AK. The good news is that Solar activity is expected to drop off over the next few weeks which should make the pattern more supportive of a -NAO/AO. 

Solar forecast can be found here: http://www.swpc.noaa.gov/ftpdir/weekly/27DO.txt

The AAM forecast is also expected to head the other way with negative anomalies favoured near 30N:

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Another positive is that the MJO wave has been remaining predominantly in the el nino phases over the summer with very weak propagation into phases 2-5. Whether this continues remains to be seen as the Indian Ocean has warmed over the last month in tandem with ENSO. 

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Fall and Winter analysis with the help of 1990-91

After writing a post yesterday regarding the winter of 1990-91, I have been shocked at the similarities with this year. When I look at analog packages, finding one great match can be much more valuable then a smoothed set of years with conflicting signals. In this post I will analyze the 1990-91 winter and explain how it may tie into our fall and winter forecasts.


Starting with the temperature pattern in September 1991 notice the amazing similarities to this year with the core of heat over the northern plains and cooling across in the northeast as well as southern texas, florida and arizona.

This year:

September 1990

Below is the 500mb pattern so far this september. A few important features include the western canada ridge with a band of lower heights extending from alaska towards western greenland. Also take note of the ridging on the asian side of the pole as well as a ridge east of Newfoundland. The lower height centre south of Norway is very similar in both years as well.

 September 1990

Looking further into the fall and winter here are what the next few months looks like in 1990-91 compared to the european monthly forecasts. These two factors alone are a huge player in the fall forecast.

October 1990 surface temps

European forecast

November 1990

European Forecast

December 1990

Precipitation

European Forecast

 November and December should stay warm in the east this year with a fairly strong southeast ridge but I do see more arctic air entrainment in the west then the euro is showing. Storm track will remain inland towards the great lakes/ohio valley as well as the B.C coast. Heading into January the cold continues to bleed further and further east in 1991 which is where I see this winter going. By february, I have some disagreements with the analog years portrayal of the upcoming pattern. It floods the entire CONUS with mild pacific air and widespread warmth. A strong alaskan vortex is present with a lack of greenland blocking. 

Given this years lower solar regime, warmer SST's in the northern atlantic and warming ENSO state I expect a pick up in blocking by february with a cold month on the way for the eastern u.s. Thanks for reading and have an amazing rest of your week!