Vorticity0123

Seasonal forecasts are usually presented as three-month averages (like the one below). Why are seasonal forecasts not regularly provided on a monthly scale? Is this mostly related to predictability? I understand that forecast skill in seasonal models mostly comes from persistent boundary conditions like SST anomalies (e.g. El Niño/La Niña). However, I would expect some boundary conditions to provide more predictability and more amplified anomalies in the first two months month rather than in the third or fourth month. For instance, the relatively shallow Baltic Sea could provide a high likelihood of warm conditions in the neighboring countries in the first two months when it is anomalously warm at the initialization time. However, its predictive value can be quickly lost when it cools down quickly after a cold episode. This in contrast to La Niña, which tends to be more persistent over time. To recap, I would expect monthly forecast anomalies to have some added value, because some climate predictors only provide skill at a monthly rather than at a seasonal scale.

It's quite remarkable that up to now this year has seen a strong tendency towards ridging over Central-Southern Europe. If you look at the 500 hPa gph anoms for this year from January 1 up to November 6, the anomalous ridging over Central Europe is quite clear. Last month was no exception to the observed trend as shown below: (500 hPa gph anoms period Oct 1 - Nov 6). What I am wondering is whether these anomalies could persist throughout the winter as well. Of course it is far too simple to assume that the observed anomalies this year imply that the winter of 2022-2023 will continue in the same way. Still, I wonder what factors like the persistence of La Niña or other tropical / extratropical forcings have led to the tendency for European ridging to occur, and whether similar forcings could result in a higher likelihood of European ridging for the upcoming winter. Looking at the seasonal model runs from November, you can see that most do not suggest more European ridging than average for the upcoming winter. These models should capture the tropical or extratropical forcings like La Niña well. Hence, I suspect that the hypothesis that European ridging this winter is more likely because we have observed much more ridging over Europe is more likely false than true. GPH analysis plots have been made using this link: https://psl.noaa.gov/data/composites/day/ Link seasonal models: Charts | Copernicus CLIMATE.COPERNICUS.EU