WRAL WeatherCenter Blog

Mike moss stated that we were only -7 or so inches of rain this morning,yet the weather page sites over 10 inches..Who is right?

Posted February 26, 2008

MIKE MOSS SAYS:        David,      Both! I didn't mean to cause any confusion, but while the "drought monitor" box on the web page references rainfall since 1 January 2007, and a deficit that has (through 25 Feb 08) reached 10.39 inches at RDU, I've been choosing to take the approach of using a rolling 1-year period for my Saturday and Sunday morning weathercasts - I try to be clear that I am referring to a one year window, or "the past 365 days," etc to differentiate that number (which stands at 8.15" below the normal amount of 43.05" through Feb 25 08) from the other.

Because both approaches have pros and cons, it's worthwhile to be exposed to both numbers from time to time and see how they are trending, along with some shorter term anomalies like the past 30 or 90 days, as different aspects of our environment respond at different rates to rainfall. For example, while much of our area remains in a serious hydrologic drought due to low streamflows, depressed groundwater levels and partially depleted reservoirs, occasional rains over the past 2-3 months, combined with winter's cool temperatures and low evaporation rates, have kept the upper reaches of the soil reasonably moist, so that we would not be considered in an agricultural drought at this point.

Fortunately, you're not stuck with a single measure of precipitation anomoly on our web site. Go to our "almanac" page and click on "rainfall charts," and you'll see graphs showing the observed versus normal rain for RDU covering the past one, three and 12 months, along with a graph of "year-to-date" and one that begins at 1 Jan 2007.

It is worth noting that RDU happened to fins itself under a couple of relatively heavy, but localized rainfall systems during the past year or so, and many surrounding areas, especially covering the upper reaches of the Neuse watershed (that feeds Falls Lake and the Durham City reservoirs) have rainfall deficits over the same time frame that are more on the order of 14-20 inches. This helps explain why drought officials have us in an exceptional category even though the RDU deficit itself doesn't strike most people as extremely large.


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