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Pattern February Discussion

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Storm5 said:
12z euro is boring as can be days 7-10

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I thought that was our money timeframe!? Atleast that almost gets us to mid-month, then the 15 day suck runs, will put us into March and we can truly put this dumpster fire behind us!
How bout them Tarheels!?
 
12z euro rolling the ridge east by day and by day 10.....
f5a9cca319f0bddaca3d4f4e743dc138.jpg


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This is February, so hopefully we can pull something out of the hat within the next couple of weeks. I wouldn't give up yet, we still have little time to improve.
 
If we're going to fail, let's go all the way. Two straight winter months of well well above would be borderline amazing. I've seen plenty of previous winters that have had one month of well well above but I've never seen a winter that could be like this. Not recently, and 11/12-12/13 were bad winters. Maybe in the mid 00s though but not to this extent.
 
Dr. Cohen
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  • The Arctic Oscillation (AO) is currently positive but is predicted to trend negative during the week and remain close to neutral the next two weeks.
  • The positive AO is reflective of mostly negative pressure/geopotential height anomalies in the central Arctic and on the Eurasian side of the Arctic and mixed pressure/geopotential height anomalies in the mid-latitudes. With predicted lowering heights over Greenland and Iceland, the North Atlantic Oscillation (NAO), which is currently negative, is predicted to be mostly positive the next two weeks.
  • Ongoing strong poleward heat flux in the stratosphere is resulting in a significant stratospheric warming (SSW)/weak polar vortex (PV) event that is likely to have important impacts on the Northern Hemisphere (NH) atmospheric circulation in the troposphere.
  • The immediate response from the PV weakening has been increasing tropospheric ridging/positive geopotential height anomalies over northwestern North America directly under the stratospheric ridge and a deep tropospheric polar low along the north slope of Siberia near the displaced stratospheric PV.
  • Rising heights over Alaska and Northwest Canada are forcing troughing/negative geopotential height anomalies accompanied by a cooling trend downstream over the Eastern United States (US). This pattern looks fairly stable over the next two weeks, however the ridging near Alaska is predicted to retrograde towards Eastern Siberia with time.
  • Meanwhile, counterclockwise circulation around the polar low over the north slope of Siberia is transporting North Atlantic maritime air into western Eurasia, including Europe, resulting in a trend to milder temperatures across the region.
  • However as has been the trend for much of the winter, blocking/positive geopotential height anomalies are predicted to return to the Barents-Kara seas and Scandinavia. This is predicted to once again block mild, maritime air from reaching Asia leading to a cooling trend across the continent. For now at least, Europe, which is to the west of the block, is predicted to remain mild.
  • How the PV continues to respond to the poleward heat flux and how much of the circulation changes associated with the ongoing PV weakening reach the surface, will be important for the weather across the NH for the month of February. The weather models are known to be poor at simulating the influence of SSW on the tropospheric circulation and therefore I expect large model forecast volatility and uncertainty.
Therefore longer term, I anticipate that the SSW/weak PV event does favor colder weather in the Eastern United States (US). My thinking for why the Eastern US will turn more persistently colder in the coming weeks is based on the strong ridging/positive geopotential height anomalies predicted centered near Alaska in the stratosphere. That feature looks to be relatively persistent and in my opinion should favor downstream troughing over the Eastern US. Some model forecasts continue to predict the Eastern US trough to be transitory with the pattern transitioning to a trough in the Western US with ridging in the Eastern US. This has been the dominant pattern this winter resulting in relatively cold temperatures for western North America and mild temperatures for eastern North America. It is certainly plausible that this pattern continues to dominate for the remainder of the winter, especially with the cold sea surface temperatures persisting across the mid-latitudes of the North Pacific. But I expect that even if this pattern does return, it will not be persistent but rather transitory with the pattern returning once more to one that favors cold temperatures in the Eastern US.
 
The EPS keeps trending toward a higher and higher amplitude of the MJO getting to phase 8 in mid-Feb. Now it has amp getting higher than 2.0 2/11-15! I've already done an extensive study of Jan MJO (see blog) and determined that outside the circle phase 8 averaged near normal in the SE (lots of variability as just outside was quite cold...so averaged warmer well outside). I decided it would be worthwhile to check past instances of Feb well outside the COD in phase 8 and see how Atlanta was during those:

1. 1978: 2/7-10, 2/23-28. ATL quite cold with an average 8.7 colder than norm. (Caveat: most of that winter was cold wherever was the MJO). They got two days with traces of snow.

http://www.bom.gov.au/climate/mjo/graphics/archive/MJO_phase/197801.phase.90days.gif


2. 1988: 2/21-29. ATL averaged 1.4 colder than normal. No wintry precip.

http://www.bom.gov.au/climate/mjo/graphics/archive/MJO_phase/198801.phase.90days.gif


3. 1999: 2/16-21. ATL averaged 0.8 warmer than normal. No wintry precip.
Note that the MJO dropped to just outside the circle just after this and got much colder with 0.4" of snow.

http://www.bom.gov.au/climate/mjo/graphics/archive/MJO_phase/199901.phase.90days.gif


4. 2006: 2/4-9. ATL averaged 6.0 colder than normal & got a trace of snow.
Similarly to 1999, it then dropped to just outside the circle and got even colder with two days having a trace of snow.

http://www.bom.gov.au/climate/mjo/graphics/archive/MJO_phase/200601.phase.90days.gif


5. 2010: 2/7-13. ATL was very cold with an average of 11.0 colder than normal along with a major snow (3.6") as well as a trace on another day! (Caveat: this was a very cold winter throughout regardless of where was the MJO thanks largely to historic levels of -AO/-NAO blocking.)

http://www.bom.gov.au/climate/mjo/graphics/archive/MJO_phase/201001.phase.90days.gif


6. 2012: 2/9-10. ATL averaged 2.0 colder than normal with no wintry precip.
It got somewhat closer to the circle 2/11-12 and got much colder.

http://www.bom.gov.au/climate/mjo/graphics/archive/MJO_phase/201201.phase.90days.gif


7. 2013: 2/1-2. ATL averaged 5.4 colder than normal with no wintry precip.

http://www.bom.gov.au/climate/mjo/graphics/archive/MJO_phase/201301.phase.90days.gif


8. 2014. 2/26: ATL was 8.7 colder than normal with no wintry precip.

http://www.bom.gov.au/climate/mjo/graphics/archive/MJO_phase/201401.phase.90days.gif


9. 2016: 2/25-26. ATL averaged 4.9 colder than normal with a trace of snow.

http://www.bom.gov.au/climate/mjo/graphics/archive/MJO_phase/201601.phase.90days.gif
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Summary: an impressive 6 of the 9 instances were solidly colder than normal. 2 of the other 3 instances were slightly colder than normal while 1 was barely warmer than normal. 4 of the 9 had wintry precip.: 3 had traces and one had major snow.

The 45 days averaged an impressive 5 colder than normal.

The EPS is forecasting a lengthy stay (a week or so) in high amp phase 8. 1978, 1988, 1999, 2006, and 2010 (1st 5 on the list) had similar length stays in high amp 8. Three of those five were solidly cold with wintry precip. (though 2 of those 3 were overall very cold winters) while the other two were near normal with no wintry precip.

Conclusion: With the EPS forecasting a high amp phase 8 for 2/11-15+, the above analysis suggests a good chance that much of the SE US will average at least a little colder than normal with a chance for much colder than normal, especially if the expected negative AO prior to then were to linger. Furthermore, IF the MJO were to subsequently drop down to lower amp phase 8 (to just outside of or within the COD), the potential to get even colder would be good, especially if not cold just prior.
 
ForsythSnow said:
You mean next run lol. Let's see
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metwannabe said:
yes it is and honestly if things don't really change not only will we be talking about no snow, we're gonna start talking about the drought again.
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If we don't end up with any snow this winter at least we know the following winters can't get any worse then this...I hope
 
Perhaps someone can answer this. People keep banging the drum over this PV split idea. How long does let take before we feel the effects, if at all? What's the threshold? I sure don't see it reflected on the models for sure lol. Alot of warm weather
 
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