title: numpy min and max functions return nan
body: <p>I have a two dimentional array full of floats representing the difference between two other 2D arrays.  I need to create a contour and map it, but when I try to map the contour I recieve an error stating that my contour needs at least 2 levels.</p>
  
  <p>ValueError: Filled contours require at least 2 levels.
  Error begins at a = np.min(tsEndAvg) and b = np.max(tsEndAvg)</p>
  
  <pre><code> k = int(raw_input("Enter the iteration amount: "))*12
      x = 0
      # Appending Arrays to cover last 360th slot of lon
      lon2 = np.empty(len(lon)+1)
      for l in range(0, len(lon)):
          lon2[l] = lon[l]
      lon2[len(lon2) - 1] = 360.
      # Creating temp arrays for manipulation later
      tssum = np.empty([len(lat), len(lon)+1])
      tsEndSum = np.empty([len(lat), len(lon) + 1])
      ts2 = np.empty([len(lat), len(lon2)])
      time2 = np.empty(len(time))
      tsEndAvg = np.empty([len(lat), len(lon) + 1])
  
  #START WHILE FOR BEGINNING DATA
      while x &lt; k:
          print str(x)
          # x iterates through a slice of time, k is the iteration amount
          # Attempting to grab global sum of surface temperatures over k iterations
          ts = tempts[x, :, :]
          for i in range(0, len(lat)):
              for j in range(0, len(lon)):
                  ts2[i][j] = ts[i][j]
          for i in range(0, 192):
              ts2[i][len(lon2) - 1] = ts[i][0]
  
          tssum = tssum + ts2# Running sum of the global data
          newDate = beginDate + datetime.timedelta(time[x])
          print newDate
          x = x + 1
      # Dividing each data point in tssum by k for the average amount
  #END WHILE
      tssum = tssum / k
  
  #START WHILE FOR END DATA
      x = len(time) -1
      while x &gt; (len(time) - 1) - k:
          # x iterates through a slice of time, k is the iteration amount
          # Attempting to grab global sum of surface temperatures over k iterations
          print x
          ts = tempts[x, :, :]
          for i in range(0, len(lat)):
              for j in range(0, len(lon)):
                  ts2[i][j] = ts[i][j]
          for i in range(0, 192):
              ts2[i][len(lon2) - 1] = ts[i][0]
          tsEndSum = tsEndSum + ts2
          x = x - 1
  #END WHILE
  
  # AVERAGING ALL GLOBAL DATA
      tsEndSum = tsEndSum / k
      tsEndAvg = tsEndSum - tssum
  #END AVG   
      a = np.min(tsEndAvg)
      b = np.max(tsEndAvg)
  
      plt.figure()
      ax = plt.axes(projection=c.PlateCarree())
      ax.coastlines(resolution='50m', linewidth=.25)
      ax.outline_patch.set_visible(False)
      lon2, lat2 = np.meshgrid(lon2, lat)
      plt.contourf(lon2, lat2, tsEndAvg, levels=np.arange(a,b,1)) #ERROR POINTS TO THIS LINE
      name = "SurfaceTempAnom-"+str(k/12)+".png"
      plt.savefig("/Users/Robert/PycharmProjects/CESM/anoms/"+name, dpi=750, bbox_inches='tight', pad_inches=0)
      print('saved: '+name)
  </code></pre>