More active pattern settles a bit
Posted March 27, 2012
Coming out of a winter that saw below normal precipitation and the development of moderate drought conditions across much of central NC, we've actually ended up with a number of rounds of shower and, in some cases, strong or severe thunderstorms over the past week or two. All of this did produce more substantial rain for parts of the area, along with a few reports of strong winds and hail reaching severe criteria (meaning 1" or greater in diameter).
The most recent round of activity was generated by a large, slow-moving upper level low that crossed the state over the course of the weekend. Since then we've gotten back into a much drier regime, and in fact today we'll have temperatures that fall below normal for the first time since March 10th, along with very low humidity. We do warm back up tomorrow, but in general most projections for the next week or indicate relatively dry conditions, although with a couple of brief and potentially scattered exceptions this weekend.
How did we fare with some of the recent activity in terms of our rainfall? As often happens with convective systems that include showers and storms more so than widespread steady rains, there was a bit of a feast and famine character to the resulting rainfall totals. One way to assess them is with contour maps showing how much rain was estimated by a combination of radar data and rain gauges used to constrain the radar-based values to a realistic range. The NWS makes such images available at their precipitation analysis page, which I've included a link for.
I've also gathered four images from the server, showing how much rain fell across central NC during the week ending Monday morning, and what percentage of normal that amount of rain represented. I also included a similar pair of maps for the past 30 days. Looking those over, we see that a lot of our area got some decent rainfall in the past week , but there is certainly some variability. While a lot of the area got 1-3 inches of rain during the week, there were some spots that missed out in a relative sense, with only .25-.5 inch for parts of Hoke, Lee, western Harnett and Moore counties, with a similar minimum in eastern Johnston county. On the other hand, there were a couple of notable areas that got really soaked, with 4-6 inches across southwestern Wayne and northern Sampson counties, with a similar band just to the southeast across parts of Bladen and Duplin counties. A sizable area from Durham county northward also got rain in the 2-4 inch range.
The 30-day maps largely highlight these same area for substantial rainfall amounts, but it's perhaps more instructive to look at the percent of normal map for that longer time span. There, we see that a large part of the area has only received between about 30 and 70 percent of normal rainfall, but that there are also some wetter pockets and bands associated with the rains of the past wee or two, including the area around Durham where 125-200% of normal rainfall for the period has occurred, and again those two streaks southwest of Goldsboro and Kenansville, where totals for the period were about 150-250% of normal.
It will be interesting to see if drought designations change much this week when the new maps are released on Thursday. Some of the rain was quite substantial, but my guess is that the large areas that are below-normal over a longer time span, along with low groundwater levels and streams that rapidly fall to low flow levels once rains subside, will result in a continued moderate drought assessment, even though short-term moisture at topsoil level is pretty abundant and should continue to support a rather "green" look to our early spring.