NH Fall/SH Spring 2023 Discussion Thread

Reached 84 (29 c) on Tuesday which is tied for the 4th latest it’s been that warm. More impressively, all three later occurances were in 2003 meaning only one other year has been this warm this late.

The hottest day ( and first +44c max in AU today at Mardie Station ) of the spring so far....
The Oct record is 46c in 2002

Forecast the next 7 days.

Does Spain get more rain in strong El Niños? I see the autumns of 2023, 1997, 1972, 1957 etc, on the list.

Not really true:



"Figure 17. Schematic depiction of El Niño and La Niña effects on climate in Europe and the polar stratosphere for different seasons. Note that for the pressure centers as well as for the position of the storm tracks and the strength of the polar vortex, absolute values are shown (the relative deviations can be judged from the size and style of the font and arrows), while precipitation and temperature refer to relative values.

[96] The signal in European climate is most consistent in late winter and resembles (though not exactly!) the negative mode of the North Atlantic Oscillation (NAO) for El Niño and the positive mode for La Niña. In early winter the signal is almost opposite in many respects, and a somewhat different signal is also found in spring. Different mechanisms might be involved and together produce a signal that varies with season (with strongest anomalies in late winter), from event to event, and on a low-frequency scale. In general, the signal is close to symmetric for El Niño and La Niña, with some confirmed asymmetries in Mediterranean precipitation and possibly in the North Atlantic SLP anomalies. The imprint in the stratosphere consists of a weak and warm polar vortex in the Arctic stratosphere during El Niño, propagating from the middle to the lower stratosphere during the course of a winter. The stratospheric signal might affect the tropospheric circulation in late winter.

[97] Figure 17 shows the “canonical signal,” which is the dominating signal, e.g., in a clustering analysis. However, not all El Niños show this signal. While this is to a large extent caused by internal variability of the extratropical circulation, there are also some more systematic effects. Depending on the boundary conditions, the ENSO signal in Europe is not always the same. A particularly important factor is tropical volcanic eruptions.

[98] The ENSO signal in Europe is not strong on average but may still be important under certain conditions. Some El Niño events may have a particularly strong effect. The prolonged 1940–1942 El Niño was accompanied in northeastern Europe by three of the coldest winters of the 20th century. This was not only an extreme event but is also important from a climatological point of view. In fact, removing these three winters from the 20th century record of northeastern Europe temperature [Brönnimann et al., 2004], the interannual variance decreases by as much as 17%. Hence one strong ENSO event can be important for the European climate variability of a whole century.

[99] Another important aspect of the studies on ENSO effects on European climate is potential predictability on a seasonal scale. Any improvement of the forecasts would by highly beneficial as currently the seasonal prediction skill for European winters is near zero [van Oldenborgh, 2005]. The studies reviewed in this paper imply that there is some potential predictability of European climate on a seasonal scale induced by ENSO, even though not all model studies are successful and the interpretation of the model results is debated. It will be crucial to disentangle the (possibly predictable) causes of the strong interevent variability such as differences in the tropical signal, modulating factors, and nonlinear responses.

[100] Finally, understanding ENSO effects on European climate might also be beneficial for our understanding and assessment of future climate change. The frequency and strength of ENSO events has changed in the past and might change in the future. Moreover, its teleconnection might change. This is of particular interest in the light of the results by Müller and Roeckner [2006], who predict a strengthened ENSO-NAO relationship in the future."

agupubs.onlinelibrary.wiley.com/doi/10.1029/2006RG000199

www.ecmwf.int/sites/default/files/elibrary/2012/12119-impact-enso-european-climate.pdf

Amber warning for rain over me - and the heavy rain continues all day, so it will be interesting to see where we land. It might be the wettest day ever recorded.

Yesterday had a high of 2.4C and a low of -3.0C, yielding a mean of -0.3C. Normal for the 19th (2003-2022) is 8.6C/2.4C = 5.5C, so the high was the same as the normal low and the day 5.8C below average.

Melbourne in Spring.....

Pretty big diurnal ranges here lately. Was down to 50F this morning and up to 89F as of 2 PM with a forecast high of 93F (which would set a record high). Was up to 94F yesterday which also set a record. Normal is 79/53F.

More bad news, another rain warning for tomorrow. Wettest October on record.

Heavy rain at times during Tuesday may lead to further flooding

What to expect
Spray and flooding could lead to difficult driving conditions and some road closures
Where flooding occurs, there is a slight chance of delays or cancellations to train and bus services
There is a small chance that homes and businesses could be flooded, causing damage to some buildings
There is a small chance of fast flowing or deep floodwater causing danger to life
There is a small chance that some communities will become cut off by flooded roads