tes the root mean square error.</span>

<span class="sd">    :param obs: (np.array) - observation</span>
<span class="sd">    :param fcst: (np.array) - forecast</span>
<span class="sd">    :param idc: (np.array) - indices of grid points</span>
<span class="sd">    :return rmse: (np.array) - root mean square error</span>
<span class="sd">    &quot;&quot;&quot;</span>
    <span class="n">size_arr</span> <span class="o">=</span> <span class="n">obs</span><span class="o">.</span><span class="n">shape</span>
   