Time period | Mean | Min. | Max. | S.D. | Mean of Summer | S.D. of Summer |
1983-1987 | 22.127 | 14.326 (Feb.) | 28.948 (Jul.) | 4.711 | 27.395 | 0.716 |
1987-1992 | 22.182 | 15.156 (Jan.) | 28.281 (Jul.) | 4.430 | 27.460 | 0.605 |
1993-1997 | 21.997 | 14.285 (Feb.) | 28.064 (Jul.) | 4.473 | 27.127 | 0.647 |
1998-2002 | 22.490 | 15.311 (Feb.) | 28.261 (Aug.) | 4.204 | 27.340 | 0.556 |
2002-2007 | 22.383 | 14.786 (Jan.) | 28.929 (Jul.) | 4.452 | 27.397 | 0.840 |
2008-2012 | 22.304 | 13.531 (Jan.) | 28.220 (Jul.) | 4.588 | 27.434 | 0.731 |