Omega blocking ensures a dry week

High pressure is providing sunshine in excess in the Alps right now. With the exception of the Eastern Alps tomorrow night, it will remain dry and sunny next week. After the weekend, temperatures also rise. Is there any hope for the return of winter?

In this weather report:

• Some snow in Austria Saturday night
• Omega blockade
• A look at the ensembles and the NAO index
• Sudden Stratospheric Warming (SSW) on the way, what does it mean for us?
• Stormy in Sicily

Some snow in Austria

Some snow may temporarily fall in eastern Austria in the evening tomorrow, but don’t expect much. In most ski areas it will remain dry, only in the eastern ski areas such as Hochkar there might be around 5 centimetres of snow. The snowline will be around 500 - 800 metres.

Omega blocking

An omega blocking (named after the omega shape) prevails in the following days. It once again gives several sunny and calm days next week. Instead of cold easterly winds, the Alps will be in significantly milder air. The freezing level will rise up to around 3,000 metres and in the valleys temperatures can reach above 10 degrees. So on lower southern slopes, we may also encounter the first firn. Such a system is often very difficult to get out of place, so we may just have to deal with this weather type for a longer period of time. We are now at the beginning of the second decade of February: winter is far from over! Just enjoy the beautiful weather in the Alps now (do check that the avalanche danger is still regionally critical due to an alpine skiing problem), but those powder days will come!

Some small chances

In between, some disturbances on the edge of the high pressure system may well provide some precipitation. The weather models show some chances for the end of next week with some cooling and possibly some snowfall on the north side. At the moment, these are not serious snowfall chances with large amounts and I do not expect more to be calculated in the coming days, but at least temporarily it could get a bit cooler again.

Since little else will change at this timeframe, I am trying to look a bit further ahead already. Of course, I have to add that this is a long-term forecast, so anything can change and eventually throw a spanner in the works.

Ensembles & NAO

A look at the ensembles shows that things remain marginal in terms of new snowfall. Until the end of next week, the ensembles of the two weather models are pretty much dry, but temperatures do drop a bit again. We also take a look at what the North Atlantic Oscillation (NAO) will do. The NAO is an index for the air pressure difference between two regions, the Azores and Iceland, and describes the strength of the western circulation and the path of the jet stream across the Atlantic. A positive NAO means low pressure over Iceland and high pressure over the Azores with a strong westerly flow. Strong positive NAO phases with a powerful Azores high and a deep low pressure core around Iceland are usually not the perfect winter picture in the Alps. The jet stream then tends to be too northerly. A negative NAO with more high pressure over Iceland and a low-pressure system around the Azores actually opens up some more chances for more snowfall in the Alps, although this is not necessarily the case either. We see that the NAO is currently positive and (with a small dip) remains positive until deep into February. Really bigger differences we only see in the extended range forecasts from March onwards, where we see some signals of a blockade over Greenland, which could have interesting implications for Alpine weather. Again: ‘signals’, ‘could’, ‘possibly’, it’s all still reading the tea leaves.

Sudden Stratospheric Warming

Speaking of the long term, there may be some interesting developments from the stratosphere later this season. Indeed, here in the atmospheric upper chamber, we are currently experiencing a Sudden Stratospheric Warming (SSW). The stratospheric polar vortex (and thus not the jet stream in the troposphere (read more here)) is usually very strong in winter and traps the freezing cold upper temperatures around the polar region. In contrast, a weaker polar vortex can actually create a weaker jet stream that can meander more.

Right now, we are experiencing a disruption of this stratospheric polar vortex. How this happens is quite complex and I won’t cover it here now, but if there is interest I can write a separate blog at some point about the SSW, its origins and its possible impact on our weather.

The disturbance causes the westerlies of the polar vortex to weaken. In this case, the core of the low-pressure area in the stratosphere is shifted. In some cases, the warming may even split the low-pressure core. A split of the low-pressure area more often has a faster impact on weather in the troposphere than a shift. As the latter now seems likely to happen, it could just take 3 to 6 weeks before it has any real influences on weather at our place. It is important not to jump to conclusions with such weather developments. Screaming headlines like “beast from the east expected” and “extremely cold and snowy spring expected” should not be taken seriously, but an SSW does open up chances for weather. Even then, everything has to fall into place, because it could happen that a solid cold snap misses the Alps and we are still in dry and mild conditions here. That an SSW can have a hefty impact on winter weather showed 2018, with a whole host of PAs as a result, so hope is always a good thing.

Storm in Sicily

And finally, back to the violent storm in Sicily. As expected, a lot of snow fell (and is still falling) in this region above 1000 metres. Around the Etna, snow amounts are staggering with locally more than one and a half metres of snow. At the same time, the lower-lying areas are suffering enormous nuisance from the storm, including flooding, high waves and very strong wind gusts.

Read also:

• What is an ensemble forecast?
• What are low- and high pressure areas?
• What is a northstau/nordstau?
• What is a southstau/südstau?
• What is föhn?
• What is a retour d’Est?
• What is the jet stream?