<p>With increasing temperatures in Norway, the possibility of heat waves are assumed to increase. The Norwegian Meteorological Institute (MET Norway) is testing ways to monitor heat waves  and possibly implement an operational warning system for heat waves in the future. For this work, it was necessary to assess the development of observed heat waves in Norway.</p><p>Heat waves were computed from daily minimum and maximum temperatures for the period 1961-2020, for three example stations and maps. For the stations, time series were assessed. For the maps, an observation-based dataset on a 1×1 km grid was used. The two different normal periods 1961-1990 and 1991-2020 were also compared.</p><p>The method to qualify a heat wave determines the number of heat waves in a given summer. There are different methods used internationally. MET Norway wants to find a method that works for Norway, and maybe in cooperation with surrounding countries. The last couple of years we have had the same criterias as used in Denmark; the mean value of maximum temperature of three consecutive days ≥ 28 degrees. In this study we have looked at different methods to qualify a heat wave in Norway, since the Danish method indicated heat waves too frequently, also during the spring. The method for heat waves is based on the maximum and minimum temperature combined. We have looked at different temperature limits and different number of days. For other weather warnings, a 2 years return period is used for a yellow warning. When testing different methods, we found that the mean value of maximum temperature for 5 days ≥ 28 degrees combined with the mean value of minimum temperature for 5 days ≥ 16 degrees were likely to occur seldom enough and also give some heat stress to people and nature.</p><p>Climate services has worked together with the forecasting group at MET Norway to propose a method to use for both forecasting and climatology. This summer (2022) the heat wave monitoring system will be tested operationally, and an evaluation is due in the autumn.</p>

To design a building adapted to local climate requires a number of different climate indicators, one of them is design temperatures (DUT) for summer and winter.  The classic definition of summer design temperature was the maximum temperature exceeded 50 hours a typical year, and for winter the coldest three day average temperature. Looking into different descriptions of the DUT, there are distinct discrepancies. One example is for DUT-winter, where some instances describe the three coldest consecutive days and others the DUT-winter as a return period (e.g. 30 year) based on observations, similar for DUT-summer where some define it as 50 consecutive hours, others as individual hours summed together. The above uncertainty of definition is combined with the uncertainty of representation. The classic construction of DUT is based on observations from a representative station, interpolated to e.g. the municipality of interest. This method opens for the uncertainty of representation of the observational site and correctness for the interpolation.  Standards Norway contacted MET Norway to update the values of the DUT summer and winter in Norway to be calculated for the latest normal period, 1991 - 2020. In this work a new method to calculate DUT summer and winter was proposed and accepted: Instead of using single observational sites as a base, national climate grids calculated on a daily basis at MET Norway covering the entire country with a 1x1 km resolution is used as a basis Instead of a single temperature representing e.g. a single day is a statistical based approach applied. The method that was selected was a Bayesian-GEV approach where the output was calculated for 1 to 5 days average for highest and lowest mean temperature, with return values for 2-200 years.  This new approach resolves partly the challenge of representativity and interpolation by using robust and well documented spatial interpolation. The statistical approach also provides more well documented and robust statistics than the older approach. This approach creates a challenge since the new datasets represent something different than the older approach, and thus challenges the standard built on these datasets.  The distribution of the datasets will be renewed. Previously one had to buy the datasets from e.g. Standards Norway or other commercial vendors, the new dataset will be distributed openly from MET Norway, and implemented in e.g. the API frost.met.no  Besides the DUT, an extended information package containing daily temperature range and absolute humidity is calculated based on representative stations.

Snow loads are an important consideration in the design of buildings. Particularly in parts of Norway where heavy snowfall is common, it is important to know the weight from snow on houses to avoid structural damage or collapse. National standards and building regulations have been focusing on snow loads since 1949, and these regulations have been revised several times.    The Norwegian Meteorological Institute (MET Norway) produces daily interpolated data sets of precipitation and temperature with a 1*1 km resolution as part of our regular service. Data from 1957 - dd are included. These data sets are then used by the Norwegian Water Resources and Energy Directorate (NVE) to generate "Snow Water Equivalent" (SWE) interpolated data sets, grids, using a hydrological model.    In this study, the SWE grids are  used to produce snow loads with a 50 year return period for Norway, for two different periods 1961-1990 and 1991-2020. Three different methods for calculating the 50-year return period of snow loads are compared. In addition, the old normal period, 1961-1990, is compared with the current normal period, 1991-2020. It is typically shown that the snow load decreases in the lower-lying areas and along the coast of Norway. In higher altitude areas and in parts of Northern Norway, where there still are cold winters, the snow loads have increased.    Snow loads are also extracted for each municipality center in Norway, to compare to the current national snow loads standard. This method is suggested, and about to be adopted, for future use in the design of buildings in Norway.