Griteater's Winter Outlook (19-20)

[griteater]

Griteater’s Winter Outlook (19-20)

 

Report Card – Last Winter’s Outlook

No way to hide it, my outlook from a year ago was not good.  After last year’s debacle, I told myself I wasn’t going to do an outlook this year, but alas, here I am.  I can’t help it.

My best call from last year’s outlook was my NAO prediction where my forecast maps indicated a +NAO in Dec, a –NAO in Jan, a neutral NAO in Feb, and a +NAO in Mar.  The NAO numbers last winter were: Dec (+0.09) / Jan (-0.42), Feb (+0.35), Mar (+2.35) – from Dr. James Hurrell’s PC-Based NAO calculation.

My worst call from last year’s outlook was…practically everything else!  These maps deserve D’s / F’s:

 

 

 

 

Forecast Discussion (19-20 Winter Outlook)

 

VP/OLR Pattern

One of the key characteristics of ENSO involves the behavior of the atmosphere atop Indonesia.  Subsidence, High Pressure, and Reduced Convection in Indonesia are defining features of El Nino.  Uplift, Low Pressure, and Enhanced Convection in Indonesia are characteristics of La Nina.

The Aug-Oct averaged VP shows a pattern consistent both with El Nino, and with the ongoing, highly elevated +IOD (Indian Ocean Dipole)…with subsidence over Indonesia, a strong area of uplift over Africa and the Western Indian Ocean, and a weaker area of uplift in the Central and Eastern Pacific.

 

Accordingly, the Aug-Oct averaged OLR shows the main center of action again over the Africa to Indonesia sector with enhanced convection in Africa into the Western Indian Ocean, and reduced convection in the eastern Indian Ocean and Indonesia.  Enhanced convection in the tropical Central Pacific is typically present during El Nino, but is notably absent in the image.

 

Key Points…the +IOD is currently much stronger than normal, and I believe it will linger longer than normal thru most of the winter.  The associated centers of VP and OLR anomalies shown above represent what I feel will be the background tropical forcing pattern for the winter.  I do believe we will see some level of uptick in Dateline convection in the mean pattern, but still at weaker levels than typically seen in weak El Ninos.  This favors a background tropical forcing pattern this winter of MJO phases 8-1-2.  You can view the favored upper level pattern (200mb) for each MJO phase based on the month and day of the year using the Seasonal Cycle of the MJO tool from Dr. Paul Roundy - http://www.atmos.albany.edu/facstaff/roundy/waves/rmmcyc/index200reg.html

 

 

AAM Chart

Here’s a chart showing a 2 month running mean of Global AAM values for all El Nino years since 1958.  The current value (thick black line) is the lowest of all years on the chart, and the steep decline from spring to fall is in stark contrast with last year’s progression (thick blue line).

 

Here are what I view to be the top 2 matches to the current AAM progression during weak El Nino years:

 

Here is the composite 500mb pattern from those 2 winters.

 

Key Points…the composite for the two best matches for AAM progression / Weak El Nino shows a weak Aleutian Low anomaly, Western North America ridging, an Eastern Canada / Northeast U.S. trough, and a +NAO.

 

 

QBO & El Nino

I expect the zero line transition from +QBO to –QBO to reach 30mb sometime around the beginning of the New Year (for the monthly averaged QBO) - https://www.geo.fu-berlin.de/met/ag/strat/produkte/qbo/qbo_wind_pdf.pdf

The image below is a comparison of prior weak El Ninos that occurred during a similar match to the current QBO progression (similar state of descending –QBO) versus prior weak El Ninos occurring with a directly opposite, descending +QBO progression (as seen last winter):

 

Here’s the same image for just the modern years (post 1980):

 

Key Points…the descending –QBO / Weak +ENSO composite (which we have this winter) shows an Aleutian Low anomaly, Western North America ridging, an Eastern Canada / Northeast U.S. trough, and an east-based –NAO.  In contrast, the +QBO counterpart shows weak troughing along and off the Pacific NW coast, ridging across much of the U.S….but also a –NAO.

 

 

500mb Pattern – Last 12 Months

The image below is a comparison of the 12 month 500mb averaged pattern prior to the upcoming winter vs. the same image leading into last winter.

 

Key Points…the image hints at perhaps a shift in the +NAO pattern that has persisted over the past several years.  Both images show a positive anomaly center over Alaska.

 

 

North Pacific SSTs

I looked at August-October averaged SSTs over the bulk of the North Pacific for generally weak +ENSO years.  Here’s a table that summarizes the data using the eastern U.S. as a reference point for the winter result.

 

Key Points…the North Pacific SST pattern leading into weak +ENSO winters doesn’t appear to have much predictive power towards the winter outcome (except for maybe the last entry in the table, which is an interesting one).  The NPac SST pattern would evolve thru winter based on the winter 500mb pattern .  For example, a pattern with an anchored Aleutian Low and Western North America ridging would lead to a +PDO SST structure.

 

 

Indo-Pacific SST Pattern

The image below is a 500mb composite of winters with a “best match” to the current SST spatial structure across the Indo-Pacific for generally weak +ENSO years.  The key characteristics of the SST pattern are a +IOD combined with a Modoki +ENSO pattern.  Older SST analogs can be obtained here: https://www.esrl.noaa.gov/psd/cgi-bin/gcos_wgsp/printpage.pl

 

Key Points…this image contains some old analogs, but the blocking signal with an eastern U.S. trough is noted.

 

 

Polar Cap Heights

The image below from Judah Cohen (twitter @judah47) shows the Polar Cap heights during October and continuing into November with a recent GFS Ensemble forecast.  The “Polar Cap” refers to the high latitudes, say 65N to 90N.  The image generally shows below normal heights in the stratosphere (10mb to 100mb), and above normal heights in the troposphere (below 100mb).

 

 

Key Points…a non-blocky  winter (i.e. +AO/+NAO) is strongly favored when the stratosphere and troposphere are in sync, and both contain below normal heights in November.  In contrast, a blocky winter is strongly favored when the stratosphere and troposphere are in sync, and both contain above normal heights in November.  There is a disconnect between the two this November, which is a more common occurrence than the two being in sync.

 

 

Low Solar

Solar Parameters – if we use a simple 1 to 5 scale of 1-Very Low, 2-Low, 3-Moderate, 4-High, and 5-Very High to describe the current solar forcing, here’s how I would rate a few of the key parameters:

 

Solar Flux / Sunspots: 1-Very Low

Solar Geomagnetic Activity / Solar Wind: 2-Low.  There is a fairly large coronal hole on the sun that becomes earth facing every 27 days or so…and during this time, enhanced solar wind is sent toward earth.  Look for it to become earth facing again around Nov 20^th.  The current geomagnetic activity is low, but to date, it hasn’t been as low as the previous solar minimum (2008-2010).  However, the geomag with that one was anonymously low compared to other cycles.

Bottom Line: I would expect that we will end up characterizing the upcoming winter as a winter when solar flux/sunspots and geomag/solar wind were both low <AND> in the low point of the current solar cycle.

 

Here is a 500mb composite of winters when solar flux/sunspots and geomag/solar wind were both low and at the low point of their respective solar cycle.  Added weight was given to 1998, 1996, 1965, and 1954 for also being very good QBO matches with respect to the +QBO to –QBO transition.

 

 

Key Points…the composite signals high latitude blocking, particularly with the NAO.

 

 

High Latitudes Dashboard

Below is a chart summarizing some select signals for predicting the winter AO/NAO (some of which have been mentioned above):

Blocky = -AO/-NAO

Non-Blocky = +AO/+NAO

 

Key Points…the SST pattern, solar parameters, and November precursors all point toward a blocky winter in the high latitudes.

 

 

 

Forecast – Key Ideas

 

Here are the key ideas associated with my forecast:

 

Cold winter east of the Rockies.  Not wall to wall cold, but colder than normal vs. the mean over the period from December to March.  That’s what the analysis tells me.  If I’m wrong, so be it.

I believe the pattern over the Western North America coast is going to have plenty of variability, but with above normal height anomalies in the mean.  With the low frequency tropical forcing focused in the Indian Ocean to Indonesia sector, and with potentially less than normal Dateline convection compared to typical +ENSO winters, I would not expect to see a strong, anchored Aleutian Low as is sometimes the case with El Nino.

The stratospheric polar vortex is currently near record strength for early November.  However, a classic vortex weakening pattern is forecast to develop as we go into the second half of November.  Based on this, and the aforementioned factors in the outlook above, I’m calling for the first Dec-Mar averaged –NAO since the 2012-2013 winter.  I like the idea of one of the 4 winter months having a strongly negative NAO, with the Dec-Mar averaged NAO being moderately negative, in the 0.80 to 1.20 range (Dr. James Hurrell PC-Based NAO calculation).

I would place the odds of Kocin/Uccellini storm(s) this winter to be near average to above average compared to the relatively higher climatology since 2000, particularly for Northern New Jersey to coastal Maine.

I would place the odds as higher than normal for a blockbuster winter pattern to develop for a few weeks at some point this winter over the eastern 1/2 of the country (-EPO/+PNA combined with –NAO).

I like the idea of a highly amplified western ridge / eastern trough pattern occurring over a few week period sometime in January or February (or at the end of Jan into Feb).

I project the southern stream / subtropical jet stream activity this winter to be near normal compared to all winters, but slightly below normal compared to weak El Nino years.

I purposely stayed away from including monthly maps in this year’s outlook.  Getting the seasonal pattern correct is hard enough.  We can make some educated guesses about the monthly forecasts, but I find that it’s hard for the forecast success to match the level of effort involved in making the monthly forecasts this far in advance.

 

 

 

Forecast Maps

 

 

[EasternLI]

Thank you for sharing. My thought process has been similar. Especially the +IOD and the NAO. I don't put anything together like this mostly because of time restraints, but if I did it would be very similar. So good luck and I hope it verifies. 

[raindancewx]

Good luck. My map wasn't that different from yours - although I never include March. I just think the cold is shifted counterclockwise a bit from what you have, out of the South and a little deeper into the West with the PDO near Neutral. The PDO tends to not go positive Nov-Apr if Nino 1.2 is near 20.0C in October, or colder. Also went somewhat warmer in the Lakes because they were warmed up a lot in July-Sept - you can kind of see in November that the cold has had some trouble crossing west-east across the Lakes in full force as a result.

My sense for this winter is that for various reasons, even though a lot of cold air is around, it will have trouble locking into a set of locations for any extended period. So the waves of severe cold in the West (Oct), and now East (Nov) are both part of the pattern, as are the corresponding warm responses (Denver had record cold at times in October...and then it was near 80F there yesterday,  the South had incredible heat in early October and incredible cold now, etc). The coldest spot will be in between the movement of the cold waves I think. If you were to go by Oct/Nov, I'd say Missouri and Kansas is that spot, edge of the cold West in October, well into the cold in November so far. I think the mechanism for the cold moving around is probably some combination of the PDO fluctuating a lot or the blocking/tropical forcing changing a lot throughout the winter. 

Nino 4 is still very warm which favors a warm North in December, but it is forecast to cool off as the heat drains/expands East toward Peru later in the winter. December 2013 but 2F warmer in most spots (to account for Nino 4) seems about right for the East to me.

[stadiumwave]

Great forecast & method!