78 NC counties and 1 VA county are under alert, including Wake, Cumberland, Durham, Johnston, and Orange counties. Details
Published: 2007-11-10 11:41:44
Updated: 2007-11-10 11:41:44
Posted November 10, 2007
MIKE MOSS SAYS: JC, You've essentially described a positive feedback process, and while it is difficult to neatly define or quantify, there is a tendency for a persistent prior lack of rain to make it more difficult to generate rainfall under some conditions. This is especially the case with convective rainfall during the warmer parts of the year, when a lack of evaporation and transpiration from soil and plant surfaces can effectively reduce the instability required to sustain a convective updraft that may have, with more humid low-level conditions, developed into a rain shower or thunderstorm. This kind of effect is less a factor with regard to cool season precipitation, and with respect to rare large-scale summer systems (like tropical cyclones or their remnants), because the larger scale stom systems may transport significant moisture in from other locations, and because these organized systems are not so dependent on convective instability to produce significant precipitation. For example, the system that affected us a few weeks ago, due in part to a stalled upper level low west of us and a slow moving stream of moisture feeding our way off the western Atlantic and Caribbean, produced around 3-6 inches of rain over central NC in 3-4 days, despite how dry it had been over most of the area for several months leading up to that event.