• Renato R. Colucci

Weather evolution Week n. 46, November 15-21, 2021

Temperatures generally mild and above mid November's average, especially at high altitudes, no significant precipitation. Moderate easterly winds on the eastern areas of FVG and on the Slovenian and Croatian coasts

We analyze the possible synoptic evolution of week 46 from 15 to 21 November 2021, making use of the two main meteorological and climatic models freely available online: the European ECMWF model, the American GFS model and the CFS climate model.

All agrees in forecating the establishment of a mighty Atlantic high pressure system stretching from the Azores to the British Isles. This configuration will be able to divert the Atlantic zonal flux to Scotland and Scandinavia. Weak disrupted fronts will only affect Northern Europe and then will be moving towards Eastern Europe.

On the other hand, cyclonic circulation in the Mediterranean basin persists, particularly active at high altitudes in North Africa, as can be seen from the image below which shows the expected pressure anomalies at the geopotential height of 500 hPa.

The following image instead shows the expected ground pressure anomalies averaged over the entire week 46, with the anticyclonic axis arranged from west to east blocking the zonal flow over central Europe.

As can be seen in the animation below from the GFS model, this synoptic configuration will probably be responsible for a meteorological weather characterized by an almost total absence of rprecipitation throughout the Alpeadria region, with the exception of a weak wet return between Tuesday and Wednesday which could bring weak rainfall only in northeastern Italy, Istria and Slovenia.

The map of cumulative total precipitation anomalies predicted in Europe by the CFS climate model also shows a negative anomaly of more than 30% over the entire Alpeadria. The Mediterranean basin will instead see a positive precipitation anomaly, particularly marked on the Balearic Islands, Sardinia and Calabria.

In this situation, temperatures are forecasted to remain rather mild at all altitudes, except for the night and early morning temperature inversions which will tend to form in the second part of the week and towards the next weekend.

This situation will probably increase the daily temperature range with a moderate cold in the morning and very mild temperatures during the day. Both the European ECMWF and the American GFS models are quite in agreement on this hypothesis.

In the following animation we show the evolution of the temperature anomalies at the geopotential altitude of 850 hPa (about 1400 m altitude) of the European ECMWF model.

In the following animation we propose the evolution of the temperature anomalies at the geopotential altitude of 850 hPa (about 1400 m altitude) of the American GFS model

In the following animation, provided by the American GFS model, we see the temperature anomaly expected on the ground in the same time interval

Such configuration will not be favorauble to heavy snowfall throughout the Alpine area, and in particular in the Alpeadria region. The only possible snowfalls, although at relatively high altitudes, are relegated to the central-western Alps. The eastern Alps should remain substantially dry.

In particular, on the Italian side of the western Maritime Alps, the heaviest snowfalls are expected in the first part of the week, and especially on Monday. Locally, snow accumulations close to one meter in thickness will be possible. In the cmap below the GFS model shows the total precipitation expected in form of snow from now to Sunday 21 November.

What has just been described represents a synoptic trend based on modeling products freely available on the net, and does not constitute a weather forecast.

For day-by-day weather forecasts for the Alpeadria region, we suggest to look at the weather bulletins provided by the official meteorological services Osmer-Arpa, Zamg, Arso

The maps reported and discussed in this article are taken from the tropicaltidbits.com portal. For model updatings we suggest referring directly to the web portal.

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