Wet pattern eases as spring sets in
Posted March 30, 2016
It was hard to escape the fact that we went through the latter part of 2015 with a lot of cloudy days and a lot of rain relative to normal. The wet pattern was especially notable in the September to December time frame (including 12 days in a row with measurable rain at Raleigh-Durham International Airport in late September to early October), but, at least in readings from the RDU airport, we've ramped down to something much closer to "normal" precipitation rates recently.
There are a couple of ways to visualize this.
First, when we look at a graph of how much rain has occurred at RDU over the past 30, 90 and 365 days, and how those compare to the normal (30-year average from 1981-2010) for those periods, we can see that the values for the past 30 and 90 days turn out to be very close to normal, with percentages are very close to 100. We remain significantly, though not extremely perhaps, above normal over the past year, with 134 percent of the normal precipitation for that time frame.
A cumulative chart of of observed (yellow) versus normal (blue) precipitation for the past year, shows the periods where rain amounts built up more rapidly than others. You can find similar charts for the 30 and 90-day periods in the "Almanac" section of WRAL.com (just click on "RDU Rainfall Charts").
Of course, precipitation often varies from one part of the area to another, sometimes sharply, and while it may even out somewhat over time, it doesn't necessarily do so completely.
Maps of North Carolina that show the rainfall departure from normal over the past 30 and 90 days make clear which areas got more or less rainfall than the measured amount at the airport.
As an example, on the 90-day anomaly map, we see that the "very close to normal," light gray shaded area that includes RDU also covers much of the I-95 corridor region, but southwest of Raleigh the yellow contours highlight areas with precipitation about 2-4 inches below normal over that time frame, while eastern parts of the state were notably wetter, with a good bit of light blue indicating 4-6 inches above normal.
You can dig deeper into the specifics of location and time on the National Weather Service site.
As I write this, we're in the third of three bright and dry days in a row, but it appears we're headed for at least some periods of rain and perhaps a few thunderstorms as we close out the week and (possibly) start the weekend, thanks to a slow moving frontal system and upper-level trough that will drift across the region.