Hi, When I watch the weather on WRAL, I hear how far we are behind on rain amounts for the year. I always wonder what the standard deviation is for yearly rainfall and where we stand in relation to +/- 3 standard deviations from the average. Is this a non-normal year or does this year fall in the -3 standard deviations from the average?
Posted September 18, 2007
MIKE MOSS SAYS: Kermit, Using data from the current "climate normals" period of 1971-2000 at RDU, the average yearly precipitation is 43.1 inches, and the standard deviation about that mean is +/- 6.4 inches. By comparison, today's (17 Sep 07) snapshot deficit since Jan 1 is 6 inches. After Friday's rain, RDU is also about 2 inches above normal for the past 365 days, due largely to heavy rains late last year and early this year. Also, RDU has been a little wetter on a fairly local basis than many surrounding areas over the past several months (August excepted), so going strictly by the RDU numbers, one might not expect as much of a regional drought impact as we really find exists based on a broader look at streamflows, reservoir levels, soil moisture and groundwater impacts.