UNUSUALLY COLD WEATHER IN CATALONIA: MAY 1991

By ALLEN PERRY~ and DENNIS WHEELER’

‘Geography Department, University of Swansea *Geography Department, Sunderland Polytechnic

INCE the days of nineteenth-century travellers such as Richard Ford and George S Borrow, the freezing, snow-clad winters of the Spanish meseta have been the subject of comment and interest. In comparison, the narrow coastal plains of Mediterranean Spain enjoy a wann and altogether more temperate regime, but not one that is spared the occasional attention of frosty conditions. Midwinter cold spells, though rarely prolonged, can induce some surprisingly low minima. This is particularly the case in the most northerly, the Catalan, region of Mediterranean Spain (Fig. 1). In the north of the region, some ten

L 50 km I

Fig. I Relief map of the Catalonia region of north-east Spain showing locations cited in the text

kilometres inland, Gerona’s temperature is recorded to have sunk to as low as -10.5”C and Barcelona, located on the coast and further south, claims an absolute minimum of -6.7”C. Both these record minima are February readings based, as are most others in this paper, on the observational period 1930 to the present. May, on the other hand, is a month more popularly associated with the onset of the Mediterranean summer. Nevertheless, that onset is often delayed by outbreaks of cold northerly air and the tempering influence of a Med- iterranean Sea that has yet to attain its summer warmth. The consequences of these climatic

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effects are seen in the generally unremarkable average temperatures for May in the region. Barcelona's daily mean temperature for May is 17.7"C and Gerona's is 16.7"C. Such means do not reappear until as late in the year as October. But even these warnings were no preparation for the peculiarities of early May 1991 when Catalan coastal districts, especially around Barcelona, experienced some conditions that would, for the time of year, have excited comment in more northerly latitudes but were without parallel in those exoticclimes. Following hard upon thefrostsof late April that did somuchdamage to the Frenchvineyards, such events are a constant reminder of the inherent variability of the European climate.

Whilst much of early May was cool in north-eastem Spain, the coldest weather occurred in short spells around the 4th and again on the 9th. On the coast no air frosts were recorded, though this is scarcely surprising, but the Barcelona minimum on the 9th was a record 4.4"C. The minimum of 6.2"C on the 5th was also unusually low. Daytime maxima were scarcely much better; on the 5th, 8th and 9th the maxima hovered around the 11°C mark. The remarkable features of these latter maxima were their timings; the maximum of 10.9"C on the 5th was recorded at 1410 h local time, but on the 8th the maximum of 11.5"C was recorded as early as 0020 h, while the 1300h reading for that day was 8.6"C. On the 9th the maximum of 11.2"C occurred at 1550h following a reading of 8.2"C at 1300h. Only two other major European low-level stations were colder: Stockholm with 7°C and Reykjavik with 6°C. Further inland, on the higher ground of this mountainous region, temperatures were much lower. Gerona Airport recorded a minimum of 0.6"C on the 6th and Olot recorded - 1 .0"C on the 4th. Barcelona's industrial suburb of Sabadell recorded 3.0"C on the 6th. Closer to the high Pyrenees, Seo d'Urgel recorded a minimum of -3.2"C on the 4th and Tremp recorded - 1 .o"C on the 6th. Even at the normally balmy Reus in the far south of the region the temperature sank to 6.3"C on the night of the 6th. Reus' lowest maximum was 13.5"C on the 8th. As with the Barcelona readings on the same day, the latter was observed at midnight and was followed by a much lower 1300h reading of 97°C. The early hours of the 8th were marked by overcast skies and rain in both Barcelona and Tarragona. Light rain and extensive cloud then persisted for most of the day, accompanied by the amval of an exceptionally cold airmass which one national newspaper, not inappropriately, described as 'Siberian'.

The Barcelona figures in particular can be set against the long-term means. The mini- mum of 4.4"C on the 9th was the lowest recorded for May in Barcelona's 80-year record. It should be noted that the latter figure was also recorded at the international airport which lies in more open ground to the south of the city. The previously lowest May temperature was 43°C and only twice in the past 30 years has the absolute minimum fallen below 7°C. The mean absolute minimum for May in Barcelonais9.PC. The minimum of 0.6"C recorded at Gerona was a record for the station, beating the previous absolute minimum of 1 .o"C set in 1985. The grass minimum on the same night was -0.5"C. The mean absolute minimum for May at Gerona is significantly lower than that for Barcelona at 33°C and reflects the consequences of increasing distance from the sea. The Reus absolute minimum of 6.3"C, though notable, ranked only fifth in the 1960-90 record and is nearly 2degC warmer than the record 4.4"C set in 1977.

In addition to the low temperatures, the region was plagued by some very heavy rain on the 8th and 9th with snow on the highest ground of the Pyrenees and Catalan ranges. Of the daily rainfall totals, the following are worth citing though they fail to compare with the catastrophic events usually associated with the autumn season. On the 8th Badalona recorded 93mm and Barcelona registered 74.4mm. The mean for the whole month in Barcelona is 54mm and the highest 24-hour fall in the period 1 9 3 1 4 was 76mm. On the 9th Susqueda received83Smm and L'Estartit 81 mm. The strong winds which accompanied the rains uprooted trees and palms in Barcelona and, together with local, though not severe flooding, caused a great deal of disruption in the city. The month's rainfall total eventually reached 121.2mm.

Snow accumulated to a depth of over 1 m on the high ground on the Montseny and the Cerdanya region of the eastern Pyrenees. Even more exceptionally, the mountains around Prades in the far south of Catalonia also suffered some notable snowfalls. Most areas above

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Fig. 2 (a) Surface chart (mbar) for1200GMTon 9 May 1991 (adaptedfrom the European Meteoro- logical Bulletin). (b) Thickness of 100&500rnbar layer (dotted lines) and 500mbar contours (solid lines) for 1200GMT on 9 May 1991 (all units in decametres).

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Fig. 3 NOAA-ll infra-red ima e taken (11 1 4 2 % ~ ~ on 9 May 1991. The lee cyclone over the weslern Mediterranean is clearly siown. To the windward side of the Alps the northerly airstream is far less cloudy. (Courtesy of Unioersity of Dundee.)

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500m appeared more akin to Austrian pistes than near-summer Mediterranean hillsides. Road closures were as commonplace as they were unprecedented. One stage of the Vuelta de Espana (the Spanish counterpart of the Tour de France) was cancelled when the fearsome Puerto de la Bonaigua, the pass which links the Spanish Val d’Aran (in the upper Garonne basin) with the rest of Spain across the high Pyrenees, was quite impassable. The director of the new skiing resort of nearby Vall-Ter 2000 was a victim of his own meteorological ‘success’ when an avalanche trapped him in his car for 24 hours. He was rescued by firemen, but at least one person died in the numerous avalanches and rock falls that rumbled across most of northern Spain between Catalonia in the east and Cantabria in the west. Snow fell heavily also in the regions of Leon and Castile to the north of Madrid, while the year-long drought of the Basque provinces was brought to a typical conclusion by some heavy rainfalls and severe flooding.

THE SYNOPTIC SITUATION

Figures 2(a) and 2(b) indicate the surface and 500mbar circulations at 1200Gm on 9 May. Figure 3 is a N O A A - ~ ~ infra-red image for approximately the same time. In the upper atmosphere the flow over western Europe became increasingly meridional from the start of the month as a major upper cold trough developed during the first four days. For several days acold pool settled over the southern France-north-east Spain area. The lOO0-500mbar thickness values fell to 534 decametres, approximately equal to the minimum values in the area for May in the 1951-66 period noted by Moffitt and Ratcliffe (1!372). By the 9th the cold trough had expanded to cover much of Europe, with the axis from Poland to Spain. At the surface the first ten days of May showed a generally unchanging pattern. High pressure to the west and north-west of the British Isles and low pressure to the east funnelled a strong northerly airflow over most of western Europe. By the 9th, while the main anticyclone had retreated westwards to mid-Atlantic, a strong ridge over the British Isles linked to another high over Norway. Over southern Europe the main low pressure centre was situated near the Balearics, with north-east Spain under the influence of a strong cold north to north- east flow. This llevant wind, as it is locally known, is popularly associated with heavy rain accompanied by cool and brisk conditions. The depression itself represented a good example of lee cyclogenesis and remained slow-moving, leading to the heavy rainfalls noted above.

CONCLUSIONS

Several recent papers have considered the heavy rain and storms that frequently con- clude the warm summer in Spain (e.g. Tout and Wheeler 1990). In 1991 the first half of May brought almost equally inclement conditions that causeddamage and dislocation throughout Catalonia. Investigations suggest that the low temperatures that prevailed and the quantity of precipitation that was recorded had few parallels in the area at this time of year during at least the preceding 60 years. Although the weather pattern responsible was not particularly unusual, in 1991 it remained almost unchanged for many days and helped to ensure that Barcelona and much of the Costa Brava had a spell of remarkably unseasonable weather.

REFERENCES

Moffitt,B. J . andRatcliffe, R. A. S. (1972)Northernhemispheremonthlymean500mbarand 1000- 500mbar thickness charts and some derived statistics (1951-66). Geophys. Mem. No.117, Meteorological Office, HMSO, London

Tout,D. and Wheeler, D. A. (1990)Theearlyautumnstormsof 1989ineasternSpain.J. Meteorol., 15, pp. 238-248

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