1. INTRODUCTION. Hellström, SMHI. This includes all record highs and dates for Sweden. 2 Data provided by Jari Tuovinen, Helsinki, Finland.

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1 European Heat Event of July 2010 By Richard H. Grumm National Weather Service State College, PA Contributions by Jari Tuovinen Finnish Meteorological Institute 1. INTRODUCTION A significant heat event affected Europe during the second week of July It will be shown that this event occurred with a progressive strong subtropical ridge (Fig. 1) which pushed high heights deep into northern Europe. The ridge originated over the eastern Atlantic and developed and moved eastward into central and northern Europe. The heat affected a large portion of Europe and set record high temperatures in Germany, Sweden, and Finland. The city of Lund along the south coast of Sweden peaked at 34.3C on 11 July breaking the previous record set back in The records began back in 1753 thus the records span 257 years 1. Based on information from SMHI records were set at other stations with 150 or more years of records including 33.7 at Visby breaking the record of 33.0 set in 1865; 33.3 at Örebro tied the record set in 1941; and 33.4 at Jönköping tied its high also set in High temperatures for two sites in Finland are shown Table 2 the data span 8-14 July. The range at these two sites were 28.7 (85F) to 34.2 (94F). The reading of 34.2 was the third warmest reading measured in Finland in the past 75 years 2. The record high in Finland was observed in Turku at 35.9 in July During the July warm episode, overnight lows were in 1 Details on records were provided by Sverker Hellström, SMHI. This includes all record highs and dates for Sweden. 2 Data provided by Jari Tuovinen, Helsinki, Finland. the mid-20s (mid 60s-70F). The warmest day was 11 July when the small town of Målilla, Sweden (coordinates N ', E ') recorded 35 Celsius. This same location holds the all-time record high for the country of 38.0C set back in July In addition to the warm daytime temperatures at these high latitudes, overnight lows were unseasonably warm. Both Sweden and Finland experienced warm overnight lows with temperatures remaining above 20C at most locations. Headline news stories characterized the event as a heat wave with tropical warm nights. Sweden and Finland both experienced problems with overheated trains and locally strong thunderstorms with downbursts producing damage to cars and buildings 3. In Germany, people were rescued from over heated trains. The heat strained air conditioners on three high-tech ICE trains. Temperatures inside the cars exceeded 50C which lead to heat related injuries and rescues 4. Germany endured a prolonged heat wave in July with some stations reporting daily highs near 40C (104F). Typical of many heat waves, this event produced strong thunderstorms on 14 July. There were reports of strong winds and downburst damage in western and northern Finland. The high moisture content of the airmass produced MLCAPE values of JKg -1. The deep moisture likely contributed to the high CAPE producing a relatively high latitude severe weather event. 3 Provide again by SMHI 4 Yahoo news story 12 July 2010.

2 In Sweden a news report from 13 July suggested 5 cm hail fell in central portions of the country with local areas of flash flooding. This note will document the heat event and associated pattern during the period of 7-13 July It will be shown that in addition to the strong high latitude extent of the subtropical ridge, there was a surge of high moisture into the air. The above normal precipitable water likely contributed to the extremely warm overnight lows temperatures. 2. METHODS The pattern was reconstructed used the NCEP GFS and were possible the JMA 1.25x1.25 data (Onogi et al. 2007). All data were plotted in GrADS (Doty and Kinter 1995). The focus here is on the pattern over Europe and northern Europe associated with the record and prolonged warm episode. The anomalies were computed from the NCEP/NCAR re-analysis data (Kalnay et al 1996) as describe by Hart and Grumm 2001 and Grumm and Hart Unless otherwise stated, the base data for the means and standard deviations were computed by comparing the GFS to the NCEP/NCAR 30-year climatological values. For brevity times are referred to in the format of 14/1200 for 14 July UTC and 08/0000 UTC for 08 July 2010 at 0000 UTC. 3. RESULTS i. overview Figure 1 shows the large scale view of the pattern from eastern North America into central Europe. Initially, a strong subtropical ridge was present over the eastern Atlantic which moved eastward into Europe (Figs. 1a-d) while a concurrent ridge Date MAX degree C MAX degree F 8-Jul Jul Jul Jul Jul Jul Jul Jul Jul Mean Table 1. High temperatures for Finland. Salo, Kärkkä had the highest value on 11 July. Highest values on 15 & 16 July were set at Kovola. All other temperatures are for either Lammi Evo or Puumala. was present over eastern North America. The ridge over eastern North America peaked on 6-7 July 2010 (Figs. 1b-c). Heights over central Europe peaked over 5880m (Fig. 1f) and showed +2SD height anomalies. Figure 2 shows a European centric 500 hpa height and anomaly field. These data depict the 5880m closed high over Germany on July (Fig. 2f-g) which drifted northward over Russia on 12 July (Fig. 2h) and the weakened extremely high latitude close 5820m upper-level ridge over Finland and Russia by 13/1200 UTC (Fig. 2i). The anomalies with the height center were in the +2 to +3SD range. Figures 3-5 show the 850 hpa temperatures, the precipitable water anomalies, and 700 hpa temperatures The 850 hpa temperatures peaked near 20C over Germany at 11/1200

3 UTC (Fig. 3g) which had +3 to +4SD temperature anomalies. The 850 hpa temperatures were about 2C cooler at 12/1200 UTC (Fig. 3h). Over Finland the 850 hpa temperatures rose to 16-18C with +3SD temperature anomalies at times over northern Russia. The precipitable water values were high over most of the heat affected region (Fig. 4). The high moisture content of the air likely increased the capacity of the air to hold heat and produced the tropically warm overnight lows over 20C. A telling heat wave pattern often has deep warm air. Thus, the 700 hpa temperatures are shown in Figure 5. From Poland and into Northern Russia the 700 hpa temperatures above ~5C represent +2SD anomalies (Fig. 5a). These high temperatures would peak over 9C with +3 to +4SD 700 hpa temperature anomalies at 13/1200 UTC. Values over 8C were present at 12/1200 and 13/1200 UTC (Figs. 5h-i). ii. northern European view Figure 6 shows the 500 hpa heights and anomalies over northern Europe from 06/1200 UTC through 14/1200 UTC. The heights peaked between 11/1200 and 12/1200 UTC with a 5880 m contour building into the region. The 5820 m contour and +2SD height anomalies reached southern Finland at this time. The closed 5880 m contour was over Estonia, northeastern Russia and southern Finland at 12/1200 UTC (Fig. 6g). An extensive 5820 m closed high was parked over northern Russia at the end of the period (Fig. 6h-i). Figure 7 shows the 850 hpa temperature over northern Europe. The 18C contour with over 3SD temperature anomalies reached Sweden at 11/1200 UTC (Fig. 7f). The 16C contour extended over northeastern Russia and Finland from 12/1200 through 14/1200 UTC (Figs. 7g-i). The 850 temperatures were generally 2-3SDs above normal with some locally higher values. Figures 9-12 show 4 panel displays of several key fields associated with heat waves and warm episodes. The period from 11/1200 to 14/1200 UTC is covered. These data show the strong subtropical ridge at 500 hpa (Figs. 9a-12a) with large height anomalies; deep warm air with over 2SD 700 hpa and 850 hpa temperatures (Figs. 9b- 12b & Figs. 9c-12c). In addition to the deep warm air and the strong ridge, these data show the high PW air and PW anomalies over the region. PW anomalies peaked at +5SDs above normal at 11/1200 UTC over southern Sweden (Fig. 9d).. 4. CONCLUSIONS A long duration heat wave affected central and northern Europe in July In northern Europe the heat appeared to peak in the 7-15 July 2010 timeframe. The event was associated with unseasonably high midtropospheric temperatures and a large subtropical ridge. Many temperature records for the day were set in northern Europe. Sweden broke a high temperature record which had stood for 257 years. The pattern of this heat event appeared to share the characteristics common to many midlatitude heat events. The most persistent and predictable feature with heat waves is the strong upper-level subtropical ridge. Brugge (1991 & 1995) noted the impact of the subtropical ridge on European and North American heat waves. Galarneau et al. (2008) examined the impact

4 of anticyclones in the subtropics and midlatitudes. They looked specifically at large closed anticyclones and produced climatology of these features. These large ridges are often associated with areas of above normal temperatures and can displace convection into higher latitudes as moisture surges about these features. Heat waves and droughts over North America have been studied by many (Chang and Wallace 1987; Changnon et al. 1996; Kunkel et al. 1996; Livezey et. al 1996; Lyon and Dole 1995; Thwatyes 1995; and Namias 1982). All of these studies relate the event to the large and persistent ridge. Some studies associated the impact of high humidity and persistent heat to impact and fatalities due to the heat (Schar and Jendritzky 2004; Palecki et. al 2001 and Changnon 1996). Goklany (2008) showed that cold and warm episodes account for the largest number of weather related fatalities. Thus, forecasting heat waves and taking precautions are critical to reduce the deaths associated with these costly events. The 2003 European heat wave was estimated to have led to several thousand deaths, mainly of aged people (Schar and Jendritzky 2004). The data shown here suggest that the pattern of this heave event shared the common characteristics of previous mid-latitude heat waves (Lipton et al 2005). This included the deep warm air with temperature anomalies to 700 hpa, a large subtropical ridge and a surge of high PW air over the ridge. The surge of deep moist air can act to keep overnight temperatures high and increase heat stress. As noted in Figure 9, the PW anomalies peaked at +5SDs above normal at 11/1200 UTC over southern Sweden (Fig. 9d). The surge of high PW are about the subtropical ridge is a common feature of mid-latitude heat events. It appears that this feature accompanies high latitude heat episodes too. This likely produced the tropical overnight conditions with lows persistently above 20C. It is known whether there were heat related fatalities. Figure 12 suggests a surge of dry air from the west and a shortwave over the ridge. This may have contributed to the high latitude severe weather experienced in northern Finland on 14 July Yet another characteristic associated with heat waves. Knowing the patterns associated with heat waves is important. Forecasting these patterns is equally important. But perhaps the most important issue is conveying this information to individuals show and reduces the loss of life during these events 5. Acknowledgements New reports from Finland, Germany, and Sweden from various agencies and Yahoo news. Albany map room for information and access to information on the event. Swedish data and generalized weather provided by Sverker Hellström SMHI. Information on Finland provided by Jari Tuovinen, Helsinki, of the Finnish Meteorological Institue. 6. References Brugge, R., 1991: The record-breaking heat wave of 1-4 August 1990 over England and Wales. Weather, 46, Brugge, R., 1995: Heat waves and record temperatures in North America. Weather, 50, Chang F.C., and J.M. Wallace, 1987: Meteorological conditions during heat

5 waves and droughts in the United States Great Plains. Mon. Wea. Rev., 115, Changnon, S. A., K. E. Kunkel, and B. C. Reinke e, 1996: Impacts and Responses to the 1995 Heat Wave: A Call to Action. Bull. Amer. Meteor. Soc., 77, Galarneau, T. J., Jr., L. F. Bosart, and A. R. Aiyyer, 2008: Closed anticyclones of the subtropics and middle latitudes: A 54-yr climatology ( ) and three case studies. Synoptic-Dynamic Meteorology and Weather Analysis and Forecasting: A Tribute to Fred Sanders, Meteor. Monogr., No. 55, Amer. Meteor. Soc., [Available at the AMS Online Store.]. Goklany, I. 2008: Deaths and Death Rates from Extreme Weather Events: Journal of American Physicians and Surgeons 14 (4): (2009). Kunkel, K. E., S. A. Changnon, B. C. Reinke, and R. W. Arritt, 1996: The July 1995 Heat Wave in the Midwest: A Climatic Perspective and Critical Weather Factors. Bull. Amer. Meteor. Soc., 77, Lyon, B., and R. Dole, 1995: A Diagnostic Comparison of the 1980 and 1988 U.S. Summer Heat Wave-Droughts. J. Climate, 8, Namias, J., 1982: Anatomy of Great Plains Protracted Heat waves. Mon. Wea. Rev., 110, Palecki, M. A., S. A. Changnon, and K. E. Kunkel, 2001: The Nature and Impacts of the July 1999 Heat Wave in the Midwestern United States: Learning from the Lessons of Bull. Amer. Meteor. Soc., 82, Robinson, P.J : On the Definition of a Heat Wave. Jour. of Applied Meteor.40, Schar, C., and G. Jendritzky, 2004: Hot news from the summer of Nature, 432, Wagner, J.A., 1981: Weather and circulation of August Mon. Wea.Rev., 108, Thwaytes, R., 1995: Northern Hemisphere heat waves. Weather, 50, Lipton, K., R. Grumm, R. Holmes, P. Knight, and J.R. Ross, 2005: Forecasting Heat waves using climatic anomalies. Pre-prints 21 st Conference on Wea. and Fore. and the 17 th Conference on Numerical Weather Prediction, AMS, Washington, DC. Livezey, R. E., and R. Tinker, 1996: Some Meteorological, Climatological, and Microclimatological Considerations of the Severe U.S. Heat Wave of Mid- July Bull. Amer. Meteor. Soc., 77,

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7 Figure 1. GFS 00-hour forecasts of 500 hpa height (m) and height anomalies over Europe from forecasts initialized at 1200 UTC a) 5 July, b) 6 July, c) 7 July, d) 8 July, e) 9 July, f) 10 July, g) 11 July, h) 12 July and i) 13 July Return to Intro.

8 Figure 2. GFS 00-hour forecasts of 500 hpa height (m) and height anomalies over Europe from forecasts initialized at 1200 UTC a) 5 July, b) 6 July, c) 7 July, d) 8 July, e) 9 July, f) 10 July, g) 11 July, h) 12 July and i) 13 July 2010

9 Figure 3. As in Figure 1 except for 850 hpa temperatures (C ) and temperature anomalies.

10 Figure 4. As in Figure 1 except for precipitable water (mm) and precipitable water anomalies.

11 Figure 5. As in Figure 1 except for 850 hpa temperatures (C ) and temperature anomalies

12 Figure 6. As in Figure 1 except for 500 hpa heights and height anomalies over northern Europe from 1200 UTC 6 to 14 July Return to regional section.

13 Figure 7. As in Figure 6 except for 850 hpa temperatures. Return to regional section.

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