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griteater

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  1. ^ Thanks all for the feedback...appreciate it
  2. I posted my forecast thoughts on the upcoming winter here: https://www.33andrain.com/topic/1785-griteaters-winter-outlook-19-20/
  3. 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 20th. 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
  4. I'm still spooked from last year when the SSW didn't downwell and February acted like La Nina instead of El Nino...I'm trying to recover before the 10 count
  5. Right or wrong, I've come to prefer viewing the MJO solely via the VP structure/movement. Here is the VP phase space diagram to go along with the week 1-2 maps you posted (it's a lot cleaner than the typical MJO RMM phase space diagrams) - all from MVentrice: http://mikeventrice.weebly.com/mjo.html
  6. Iso - the November Global AAM Anomaly is actually the 2nd highest since 1958, and the Oct-Nov is 4th highest, placing it among the super ninos and other select years. - https://twitter.com/griteater/status/1067482391407673351
  7. Matt - take a look at this one - https://journals.ametsoc.org/doi/pdf/10.1175/JAS-D-11-0209.1 "Overall, an easterly QBO wind anomaly in the lower stratosphere leads to a weakened stratospheric polar vortex, in agreement with previous studies, although not because of changes in the subtropical critical line." "downward propagation of the QBO in the equatorial stratosphere, upper stratospheric equatorial zonal wind, and changes in the tropospheric circulation appear to be less important than lower stratospheric easterlies for the polar stratospheric response."
  8. Enjoyed the write-up Iso. You continue to push the science forward, kudos. Love the NAO predictor. I spent more time in this arena with my outlook this year as well, looking for more clues. If we do in fact see a 10mb SPV that is stronger than normal along with a solid -NAO, that would be quite the call. Good luck and thanks for taking the time to post it.
  9. Thanks for the compliments Iso (and thanks to all others as well!), appreciate it. I realized this morning that I forgot to post the snowfall map in the outlook, lol. So here it is. I find precip maps to be extremely difficult to predict. Sure, you can get an idea from the projected pattern, but then you have to account for convective (down south) vs. cold sector precip etc...so, it gets quite complicated IMO. I'm staying away from that for now. On the climo base, I just state that I'm predicting against the 81-10 base and go with it that way (i.e. stating that up front). Thanks again.
  10. I posted a winter outlook here - https://www.33andrain.com/topic/1488-griteaters-winter-outlook-18-19/
  11. Griteater’s Winter Outlook (18-19) Forecast Maps Quote “It is our view that doing the science and going through the steps is as important as coming up with the right answer. A lot of people don't understand this, as the emphasis in our culture is on getting the right answer. For example, if I forecast the winter pattern based upon the number of socks in my dresser drawer and the forecast turns out to be correct, it doesn't mean my technique was scientifically based and/or it can be used in the future.” Dave Tolleris (wxrisk.com) – November 2016 Forecast Parameters ENSO Related Parameters SSTs – it looks like we are going to have a borderline Weak – Moderate Nino. Given our low ONI starting point this fall, I think it will be difficult to reach Moderate Nino using a definition of requiring at least 3 consecutive Nino 3.4 ONI tri-monthlies of 1.0 or higher. Equatorial SOI for Aug-Oct was -0.2. Here is how that compares with all years since 1949 - https://twitter.com/griteater/status/1059539528803848192 Global AAM for Sep-Oct was right around 0. Here is how that compares with other El Ninos since 1950 - https://twitter.com/griteater/status/1059536786706305024 Upper Level VP Anomalies averaged over Jul-Oct show subsidence over the Indian Ocean and Western Atlantic, with uplift over much of the Pacific and over the Eastern Atlantic / Africa. OLR anomalies averaged over Jul-Oct show below normal convection extending from Africa thru the Indian Ocean. Otherwise, no significant anomalies are noted. Equatorial Upper Ocean Heat Content east of the dateline is above to well above normal. Equatorial Sea Level Anomalies are above normal across the full Pacific basin MEI – the Oct and Nov releases of the MEI have it on the borderline of neutral / weak Nino. El Nino Base (SSTs) – with the October data now in, here is an updated graph showing the progression of this year’s Nino SST base (thick black line) compared to other Ninos since 1950. Looking at the 24 prior Ninos on the chart, 22 of the 24 either remained in the relative portion of its “swim lane” or moved west from Fall to Winter. The only 2 years that made a noteworthy move east were 82-83 (mod east > strongly east) and 86-87 (mod west > weak west). We are solidly in the west-based camp this year, and I would expect that to continue thru the winter. The previous graph is based on the E Pattern vs. C Pattern of El Nino SSTs from this paper from Takahashi et al. Here is an image of the E vs. C Patterns. In my view, this image captures the best method for visualizing the SST patterns of El Ninos at the opposite ends of the spectrum. Global SSTs – outside of the equatorial Pacific, noted SST anomalies are: 1) cool anomalies in the eastern Indian Ocean and Maritime Continent, 2) mostly warm North Pacific anomalies, 3) cool/warm dipole in the North Atlantic, and 4) warm Arctic. PDO – the PDO isn’t in a strongly positive or strongly negative phase at the moment. QBO – I have been maintaining updates to the Berlin QBO chart since updates were dropped on the site for some reason back in March. With the latest update now in for October, we see that a flip from -QBO to +QBO has now occurred at 30mb. The +QBO is descending down through the stratosphere at a steady rate. I now expect the +QBO to reach 40mb by December, and reach 50mb by Jan-Feb. 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 to 3-Moderate due to periodic increased geomagnetic activity from the release of enhanced solar wind from rotating coronal holes. In the big picture, solar forcing is relatively low, but it’s not super low like the winter of 2009-2010, and we likely won’t reach this solar cycle’s absolute minimum, with the possible combination of very low solar flux / sunspots and very low geomagnetic activity, until sometime over the next 2 years. Forecast Discussion Pacific / North American Pattern El Nino Patterns As a part of putting this outlook together, I first binned each of the +ENSO winters (El Nino and Positive Neutral) since the 1870’s based on the Pacific / North American pattern for Dec-Mar. I used Sep-Nov to Jan-Mar ONI from Eric Webb’s Ensemble ONI for ENSO determination. Not all +ENSO winters matched a specific pattern, but here is the breakdown of the 7 common +ENSO patterns that I noted: If we remove the high end strong and super Ninos on the high end, and remove the years that are barely +ENSO on the low end (via SSTs), we get the following results: Here’s a view of each pattern in order of most common to least common in the previous chart, using composites of the cases from 1895 to 2014 (these are the dates I can retrieve for composites of both 500mb and detailed U.S. surface temperatures): Note: in the last image, 1987 didn’t actually have an East Aleutian Low, but its pattern of zonal flow, ridge in southern Canada, and U.S. temperature distribution of warm north / cool south fits the mold here. I left out the super ninos in these composites which would have all been in this group. The next step is to try and determine the base pattern for the upcoming winter from those previous images. Statistics On statistics alone, we see that the first 2 patterns have occurred more than any of the others during El Ninos (Aleutian Low / Western North America Ridge & North Pacific Ridge / Eastern U.S. Trough). El Nino Strength and SST Base Outside of East Based Super Ninos, the data suggests that the Nino SST base doesn’t necessarily give us strong clues regarding the specifics to expect with the winter pattern. The Nino base does however provide a general framework for the expected U.S. temperature pattern. Ninos that were East Based, Trending East into East Based, or Basinwide – in 75% of cases (6 of 8), the result was warm anomalies over most of the U.S. or warm in the East. Exceptions: 1976-1977, 1969-1970. Ninos that were West Based, Trending More West Based, or Trending into West Based – in 75% of the cases (12 of 16), the result was cool anomalies over most of the U.S., cool in the East, or cool in the SE / South. Exceptions: 2004-2005, 1994-1995, 1991-1992, 1953-1954. Velocity Potential (VP) Anomaly Pattern I reviewed the summer to fall progression of the VP anomaly pattern for each Nino since 1979 (there are limitations with the VP data prior to ~1979). I viewed the maps in 3-month increments (Jun-Aug, Jul-Sep, Aug-Oct). Along with SSTs, the advantage of using VP data is that it tends to give clues ahead of time about what we may be able to expect with the upcoming winter pattern. There were 2 types of patterns that I saw while reviewing the VP data, which I will refer to as 2-cell and 4-cell. Here is a summary: Here are Jul-Oct VP anomaly / subsequent winter pattern composites for each VP Anomaly Pattern Type (I removed the Super Nino years in the 2-Cell composite): This year’s VP Anomaly pattern is in the 4-Cell camp, and with enhanced subsidence in the Indian Ocean. Repeating El Nino Patterns Anthony Masiello (twitter: @antmasiello) recently made the astute observation that “a lot of weaker Nino winters are like chameleons; they take on the characteristics of the interannual (but usually intradecadal) climate period.” - https://twitter.com/antmasiello/status/1046792232248991744 With that in mind, I went down perhaps a slightly different path and noted that regardless of strength, El Nino patterns do tend to be similar within their time period. Here is a list of El Ninos that occurred in a time period close to each other and exhibited similar winter patterns. This concept suggests that the upcoming winter may very well share some pattern characteristics with the recent Weak El Nino of 2014-2015. The High Latitudes North Atlantic Oscillation (NAO) We are currently in the midst of a remarkable stretch of +NAO readings. The NAO has been at least +1.00 or higher in 7 straight months, and in 9 of the last 10 months. In addition, the NAO has been negative in only 3 of the last 20 winter months (Dec-Mar). This is a strong +NAO background environment. Greenland Blocking Index (GBI) I’m a sucker for a good teleconnection index. One index that I’m surprised I personally haven’t seen any mention of in the weather/climate community is the Greenland Blocking Index, or GBI (though it may be in the Research Portal, ha). The GBI is quite similar to the NAO, but what I like about the GBI is that its key anomaly center calculation at 500mb is located squarely in the most influential blocking region of the NAO domain, Greenland and the Davis Strait. Another way to view the GBI is to say that it is an index of the west-based NAO. In contrast to the specific domain focus of the GBI, there are various calculations for the NAO. Some of the calculations are based on a difference in normalized SLP between Portugal and Iceland, or the Azores and Iceland (Station-Based), while others are based on SLP or 500mb anomalies across a wider longitudinal region of the North Atlantic (Principal Component-Based). Here is a link to the paper describing the GBI from Edward Hanna et al. - https://rmets.onlinelibrary.wiley.com/doi/epdf/10.1002/joc.4673 And here is a link to the GBI timeseries with monthly data - https://www.esrl.noaa.gov/psd/gcos_wgsp/Timeseries/GBI_UL/ With the GBI, the sign is reversed from the NAO, so in simplified terms, +GBI means Greenland Blocking or above normal heights over the GBI domain, while -GBI means a lack of Greenland Blocking or below normal heights over the GBI domain. Here are composites for some of the strongest Greenland Blocking winters on record alongside some of the weakest Greenland Blocking winters on record (since 1950). Below are those same composite years for the September, October, and November prior, with my comments on what I see as the key differences. For September, note the difference in and around Greenland. The -GBI has a clear signal for negative height anomalies. For October, note the difference in far North Central Russia and into the Arctic along 90E. There are positive anomalies in this region on the +GBI composite, and negative anomalies on the -GBI composite. For November, note the difference across the Arctic. There are large scale positive anomalies on the +GBI composite and large scale negative anomalies on the -GBI composite. In essence, in the +GBI progression, above normal heights build over the Arctic in September, become stretched out across far northern Eurasia in October, then congeal over the polar cap in November. In the -GBI progression, below normal heights build over Greenland in September, become stretched out across northern Russia in October, then congeal over the polar cap in November. As for this fall, the September map (below) is clearly in the -GBI camp. There isn’t a clear signal on the October map (not shown). For November, ensemble forecasts as we progress through the month hint at a 500mb pattern that is more closely tied with the -GBI camp, with the stratospheric and tropospheric polar vortices becoming moreso centered over the polar cap. In totality, I’d say the fall pattern at 500mb is more suggestive of a -GBI winter (i.e. lower amounts of Greenland blocking compared to normal). North Atlantic SST Dipole Pattern On the Sep-Oct averaged SST map, there is a dipole pattern in the North Atlantic with cold anomalies stretched out over the far North Atlantic just SE of Greenland and warm anomalies extending from off the Northeast U.S. coast over to the Azores. The last 13 times this type of dipole pattern was present in the fall, 10 of the subsequent winters went on to have a -GBI winter (i.e. low amounts of Greenland blocking). In addition, 10 out of the 13 Decembers of those same years experienced a -GBI. The 13 winters matching this North Atlantic SST dipole pattern are: 17-18, 15-16, 13-14, 11-12, 94-95, 92-93, 90-91, 89-90, 88-89, 84-85, 83-84, 82-83, and 75-76. Interestingly enough, the correlation fails miserably when looking at years prior to 1975. From 1900 to 1974, I found on reanalysis charts 15 cases of said North Atlantic SST dipole pattern. In those 15 cases, only 5 led to a -GBI winter. I’m going to lean on the more recent climatology here and say that this year’s North Atlantic SST pattern favors a -GBI in both December and averaged over the full winter. QBO, Solar, & The Stratospheric Polar Vortex (SPV) Based on the current QBO progression of early winter -QBO in the 40-50mb layer with a mid-late winter switch to +QBO, the best QBO matches for the upcoming winter in the key 30mb to 50mb layer are: 1954-1955 1977-1978 1984-1985 1994-1995 1998-1999 2001-2002 4 of those 6 winters saw a sudden stratospheric warming (SSW) in early winter (exceptions: 77-78 & the Pinatubo contaminated winter of 94-95). Here are a few more details about each of those occurrences: 1954-1955 – Canadian Warming in Dec / SSW in Jan (per the Berlin site data) 1984-1985 – SSW in early Jan (per Amy Butler’s SSW table) 1998-1999 – SSW in mid-Dec 2001-2002 – SSW in Late Dec / Early Jan There is debate about the mechanism for how the QBO modulates the Stratospheric Polar Vortex (SPV), but this paper from Garfinkel et al. states that a -QBO in the lower stratosphere at 50mb leads to a weakened SPV, regardless of downward propagation of the QBO. Finally, in 3 of the 6 years listed above (54-55, 84-85, and 01-02), the 500mb pattern in Dec consisted of below normal heights in Alaska and Greenland, with above normal heights over northwest and/or north-central Eurasia. This pattern configuration is similar to those hinted at on current extended ensemble model runs. Ridging in northwest and/or north central Eurasia is a precursor pattern for disturbing the SPV. Given all of the above, in my view, the chances of an SSW or significant SPV weakening in early winter (Dec – early Jan) are higher than the climatological mean (note: if an SSW were to occur this winter, it would likely lead to a cold period in the Eastern U.S. given that the background ENSO state favors an Eastern U.S. trough). Other Forecast Thoughts Trends Over Recent Winters Over the past 4 winters (15-16 Super Nino Excluded), we have seen a rather consistent pattern of Alaska & Western North America Ridging / Hudson Bay Low Vortex / +NAO / and higher than normal heights across the southern tier. I would expect this winter to fit in with the overall theme here, but with adjustments. Euro Seasonal My biggest takeaway from the Nov release of the Euro Seasonal is that it lessened the amount of Greenland blocking compared to the Oct release, particularly in Dec and Jan. It also moved the core of the Eastern U.S. negative anomaly center from the Southern Mississippi Valley to off the Northeast coast. Northern Stream / Southern Stream I have a largely west to east zonal flow regime forecasted for Dec. For the Jan-Mar time period, I would roughly project the following with respect to Northern Stream / Southern Stream flow: 1) Northern Stream dominant flow 50% of the time 2) Split Flow pattern 25% of the time (Jan would be the target month) 3) Other non-related pattern 25% of the time (pattern variability) Cold Air Outbreaks I would project the number of cold air outbreaks east of the Rockies to be slightly higher than the winter normal, especially in Jan & Feb. Report Card From Last Year’s Outlook My best call from last year’s outlook was when I stated that I “favor the development of a “North” North Pacific Ridge that is variable, but biased to the northwest in the mean winter pattern.” My worst call from last year’s outlook was my projection of a Western U.S. Trough / Eastern U.S. Ridge for December. Finally, here are the grades for my Snowfall and Dec-Mar Temperature maps:
  12. We are definitely going thru a period of intraseasonal MJO related forcing at the moment (1st chart). And on the topic of AAM, the 2nd chart here shows that the ‘climo’ Nino AAM progression calls for a dip in AAM in the fall, followed by a rise in the winter.
  13. Here is a table of July-October averaged AAM prior to the oncoming winter. Using an estimate of +0.40 AAM for this October based on the AAM chart above, the Jul-Oct monthly average this year comes to -0.30. This places it 15th out of the 22 El Ninos since 1959. If we remove the 3 Super El Ninos in which AAM would understandably be anonymously high, this year's value would place it 12th out of the 19 El Ninos. Thus, the current 120 day AAM is well within the range of expected values for a developing El Nino. As a recent comparison, the monthly AAM during the 2014-2015 El Nino was negative 11 out of the 12 months in 2014 and negative in both Jan and Feb of 2015.
  14. Typhoon Yutu is the culprit for those westerly winds there. This fits with the climatology of developing El Ninos where hurricane and typhoon activity tends to be enhanced due to -VP anomalies in the Pacific...and those storms can enhance westerly wind anomalies along the equator.
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