January 25, 2022 4:45 pm

Weather trends for December 2021 Bridge

Francisco Martin Leon 8 min
Two holidays at the beginning of December: 6, Constitution Day, and 8, Immaculate Day

As always, you are trend predictions They do not present the time at a specific point and at use (maximum and minimum temperatures, precipitation, probability of precipitation, cloud cover, etc., predicted). On the contrary, they are given predictions of trends and anomalies with respect to climatological normal values. These very long-term predictions have high uncertainties, which increase with the prediction time.

The period is divided into two weekly intervalsAs will be seen, and will not be entered into the prediction of this weekend, November 26-28, which is presented with the withdrawal of the dana towards Italy, a new entry from the north of very cold air and abundant snowfall in the third north, and rainfall in the Canary Islands coming from the west. Currently, the predominant atmospheric pattern in Europe is that of a powerful ridge or anticyclone in the North Atlantic that generates a very cold northern component input over western Europe.

These are the trends forecast as of the date of the model’s releases on November 25.

Week November 29 – December 6

On December 6, Constitution Day is celebrated, entering this week.

The North Atlantic ridge and anticyclone will continue to be active with entries from the north that will tend to be a north-northwest component for this week, as stable conditions begin to appear in the southwest of the peninsula.

Average maps and anomalies in color scale at 500 hPa, above with blue / orange colors with negative / positive anomalies, and surface pressure, below with positive / negative anomalies in blue / violet. VarEPS-Monthly

Under these conditions, positive precipitation anomalies appear, in the following map and in green tones, only in areas of the northern third of the peninsula. The rest of the zones the anomalies are negative.

Mean maps and precipitation anomalies, PCP, above with positives / negatives in green / orange, and temperature at 2 m, T2m, below with positives / negatives in red / blue. VarEPS-Monthly


Temperatures would be above normal in large areas of the north and east of the Peninsula, while the islands and some areas of the south would be below normal.

Week 7 – December 13

The 8th of December is the Day of the Immaculate Conception, also in celebration.

It appears that the mean atmospheric flow would tend to be more northwesterly at mean levels, 500 hPa. Possibly, the axis of the North Atlantic anticyclone is oriented from a south-north blockade to a west-east axis and approaching the peninsular zone.

The storms would tend to move towards higher latitudes and would only affect the extremes of the cold fronts in the northern third, while the surface ridge would tend to impose more clearly than the previous week, although the signal is not very strong.

Average maps and anomalies in color scale at 500 hPa, above with blue / orange colors with negative / positive anomalies, and surface pressure, below with positive / negative anomalies in blue / violet. VarEPS-Monthly

Rainfall trends in this second week show negative anomalies in the west of the peninsula and the Canary Islands. For the rest of Spain there is no signal.

There are weak signs of thermal trends: negative for the islands and no signal for the rest of Spain.

Mean maps and precipitation anomalies, PCP, above with positives / negatives in green / orange, and temperature at 2 m, T2m, below with positives / negatives in red / blue. VarEPS-Monthly

In summary, the general trends presented by the mean maps of the probabilistic model indicate that the cold north entrances, which affect the Peninsula and the Balearic Islands these days and the end of November, they will gradually roll into winds of a north-northwest component from the beginning of December and will tend to be of winds of a northwest component, with anticyclonic and more stable conditions, except in the north.

A sharp drop in temperatures is not expected with north winds or south wind inputs that will increase temperatures and carry away the fallen snow. Stable conditions, the more the further south, will be associated with less rainfall with the entry of the anticyclonic ridge, except in the northern third where the fronts could bring rains and snowfalls with intense winds in the first week, which will tend to improve. relative in the second week.

Good bridge for everyone.

Annexed

Probabilities of the meteorological regimes for the next days of the Bridge

As a complement, the latest predictions of the probabilities of the synoptic weather regimes foreseen for Europe are presented.

As can be seen, from November 29 to December 6, the time associated with the violet bars would prevail, Atlantic Ridge (ATR), with a time similar to the one we are suffering now with entries from the north. At the end of the week it would tend to seem a signal of the pattern bound to the NAO + (blue).

From December 7 to 13, an NAO + regime (blue bars) could predominate, which is associated with little rainfall in Spain, except in the extreme north. Other types of time regimes cannot be ruled out.

It should be noted that the colored bars indicate the proportion of members or scenarios of the model as a whole that forecast a specific regime for each forecast day: positive (NAO + blue) and negative (NAO – green) North Atlantic Oscillation, Lock Scandinavian (red), Rise or Anticyclone of the Atlantic (purple). The members or evolution scenarios that are not close enough to any of the 4 meteorological regimes are represented by the gray bars (members without regime attribution). The bars with diagonal lines represent the attribution of the average regime of the set. Solid colored bars with solid black outlines represent verification.

Notes adapted from AEMET

The maps presented are those related to anomalies with respect to the 20-year climatology of the European Center prediction model (VarEPS-Monthly), of the weekly mean values ​​of two meteorological variables: geopotential at 500 hPa, surface pressure, temperature at 2 meters (T 2m) in ºC and total precipitation (PCP) in mm. Using statistical techniques, those areas are blanked out where the series of predicted values ​​of the Monthly VarEPS is not significantly different from the series of the climatology values ​​of the model.

The monthly trends are obtained from the products of the monthly forecasting model of the European Center for Medium-Range Prediction. These predictions are subject to uncertainties that, on the one hand, increase as the forecast period increases and, on the other, are higher when an interpretation of the products is made on a regional scale, over relatively small areas.

This entry was published in News on Nov 26, 2021 by Francisco Martín León



Reference-www.tiempo.com

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