FI Charts ( T120+ onwards) Winter 2020 **READ MOD NOTE IN FIRST POST**

AuntySnow wrote: »

In fairness now,those are 120's on Friday
Those more or less happened
Beyond 120 most certainly didn't which was my point

Artane2002 wrote: »

the GFS is an outlier and the ECM doesn't look far off what the GFS was showing this morning. I'd expect the pub run to revert back to what was being shown this morning.

King of Spades wrote: »

It’s interesting that you are writing off January yet both MT and met eireann are forecasting cold and wintry weather to arrive by the middle of next week.

Billcarson wrote: »

But that was if it was a quick troposphere response, which it clearly isn't. The response time can be quick or somewhat slower,like weeks down the line. So I wouldn't give up yet.

Atm there is a minor warming taking place in the strat.
Still an evolving situation imo.

The possible effects of warming in the stratosphere on our weather
Date 01/14/2021

A polar vortex that was severely weakened in January 2021 can also affect the weather in Germany in the coming weeks. But how does this event affect us and can statements be made at all?

Last Sunday (01/10/21) Dr. Bonewitz described the current strongly weakened state of the polar vortex in the stratosphere and the development that led to this event (see link).

The polar vortex is an extensive high altitude low caused by the negative winter radiation balance prevailing in the high latitudes. With prevailing westerly winds (the polar night jet), it influences the weather not only in the high but also in the middle latitudes and indirectly (via the stratospheric or global circulation) also in the tropics. The vortex can temporarily weaken due to various external influences, followed by warming, which can peak at 30 to 50 degrees Celsius within a few days, a so-called "sudden stratospheric warming (SSW)". In extreme cases it is even possible that the climatologically dominant westerly winds change into easterly winds, which is the definition of a "striking SSW" (or major warming).

The weakening of the polar vortex can then work its way from the stratosphere to the troposphere in the following weeks and have a lasting effect on the weather events that are sensitive to us. But to anticipate it right away - clear statements cannot be made here, because the predictions in this subject area are mostly very uncertain and should be treated with caution. One reason for the uncertainties is that between 1979 and 2019 there were just 26 weeks of pregnancy. In addition to the small amount of data, it was also found that these events were associated with a high degree of variability with regard to the effects on the troposphere, our weather layer.But what can be said now? With the help of statistical evaluations of the general weather conditions occurring in the European-Atlantic area after SSWs, one can estimate possible developments or tendencies, i.e. ideally assign repeating typical weather patterns. Whether, where and with what intensity these will arrive can only be estimated at a comparatively short notice even today with all this technology (see the linked medium-term article from January 2nd).

After we had the first wind reversal at the beginning of January, the next should take place in the second half of January, which is definitely a striking event for the stratosphere. The question now arises as to how this development can affect our weather, including the results of the scientific paper by Domeisen et al. Linked below. is used: This work comes to the conclusion that after a SSW, from a statistical point of view, a clearly negative NAO (see DWD Lexicon) often prevails. It is also stated that depending on the prevailing general weather situation at the time of SSW, certain scenarios for the weather events subsequently arise in Northern and Central Europe, among others.

In short, in the negative phase of the NAO, instead of a strong low pressure area over Iceland, a high pressure area is expected there, which is also indicated by the current forecasts of the European Weather Center (ECMWF in Reading) for the further course in January. As a result, it is not possible to establish a "low pressure highway" from the west that constantly brings mild Atlantic air to us, but rather the low pressure areas have to move far south and thus potentially tap into very warm air masses. Meanwhile, the air mass over Siberia and Scandinavia is increasingly cooling (among other things the result of the weakening polar vortex, which keeps the cold air in the "healthy" state near the North Pole and is now weakened and cannot prevent the outflow of polar air mass).Further information can be found in the paper.

In fact, in the coming weeks the cold air body that has so far prevailed over South and East Asia will increasingly shift to Siberia and also cover Scandinavia - see the graphic attached to the topic of the day, where the anomaly values ​​(deviations) of the 2 m temperature from one 20-year model climatology for January 18-25, 2021. The prediction is made more difficult by the fact that the temperature contrasts between the land masses and the North Atlantic intensify due to the approach of the Arctic body of cold air, including to Canada. This stimulates the formation of strong low pressure areas. Their influence on Europe in the form of very mild air masses and the Arctic cold air expanding into Northern Europe are a breeding ground for events that may potentially deviate from the climate,be it in the form of particularly mild / stormy phases or strong north / east winds with icy cold. The past has shown that strong cold air ingresses occur more frequently in Northern and Central Europe after an SSW, but there is no guarantee for this. The option for a section with arctic air masses is given solely by the proximity of the body of cold air, as well as the formation of distinctive air mass boundaries with all the harassment that winter weather has to offer. This can also be seen in the wild jumping of the weather models in the extended medium term (end of January) between very warm and icy cold, but very often with increased storm potential for Western and partly also Central Europe. As the effects of a SSW, they should work their way down,affect the weather in the troposphere with an average delay of around 10 to 15 days, but a technically exciting second half of January and an interesting February can be imminent.

How extreme such an event can be became apparent at the turn of the year in the Asia-North Pacific sector. Since the polar vortex weakened early, especially over Asia, there repeatedly icy polar air flowed south and drove the air pressure in Mongolia, among other places, to over 1090 hPa at the end of December, which would represent a new world record after verification. After the icy air mass reached the north-western North Pacific with maximum temperatures of well below minus 40 degrees Celsius in some cases, numerous violent storm lows developed, with a core pressure of estimated 921 hPa and 924.8 hPa (both records) measured on Shemya (Alaska) at the turn of the year has blown the previous air pressure record for extra-tropical low pressure areas in the North Pacific.In addition, massive amounts of snow fell over parts of Japan (in the mountains and partly down to the coastal regions) (e.g. Takada with 103 cm in 24 hours and 187 cm in 72 hours, both values ​​an all-time record even for the snow-tested region).

It doesn’t have to be that extreme and it certainly won’t be that extreme, but compared to the past calm weather months alone, the increasing dynamics will probably be felt. And isn't this uncertainty also exciting - where is this journey going?

Dipl.-Met. Helge Tuschy

German Weather Service forecast and advice center Offenbach, January 14th, 2021

Copyright (c) German Weather Service