According to a statement from the Portuguese Institute of the Sea and Atmosphere, until October 25, the weather conditions in mainland Portugal will continue under the joint influence of an intense anticyclone located west of the British Isles, although with a tendency to gradually weaken, and a cut-off in the high levels of the troposphere centered in the northwest of the Madeira archipelago, to which the transport of generally tropical air masses from the interior of the Iberian Peninsula is associated.
In practice, this atmospheric configuration translates, on the one hand, into the maintenance of maximum temperatures with values higher than the average values for the time of year (generally between 20 and 25 ° C), and on the other hand, in the possibility of occurrence of showers and dispersed thunderstorms in the Central and South regions, which may be locally intense.
However, from the afternoon of day 26, due to the transport of a very cold and relatively dry mass of polar air coming from Iceland, a significant change of the weather is expected, with the passage of a situation of temperatures to another, where the cold and wind will be the most significant. Thus, a gradual drop in temperature is anticipated from the afternoon of the 26th, as well as an intensification of the wind especially in the west coast and in the highlands (strong north wind up to 50 km / h and gusting up to 70 km / h).
On Saturday and Sunday, 27 and 28 October, maximum temperatures should not exceed 15 ° C, except for the southern Algarve coast and some Alentejo sites, where they may be slightly higher (2 to 3 ° C), and of the North and Center interior regions, where the maximum temperature values should vary between 5 and 10 ° C. For the minimum temperature values, they should be less than 10 ° C, and in the order of 0 to 5 ° C in the interior regions, where the first frost of the season is foreseen. Low temperatures associated with the strongest wind should cause thermal discomfort.
On the other hand, one of the possible scenarios points to the occurrence of dispersed precipitation in the North and Center regions on the 27th, which to occur, should cause some snow in the uplands.