Breaking the long streak of showers
Posted July 16, 2013
A large upper-level high pressure area that built across the northeastern U.S. late this weekend into the start of the week helped keep showers and storms very isolated over North Carolina Monday, with just a couple of cells near the southern coast and a couple of others very near the South Carolina border in the southern coastal plain and southern Sandhills areas.
However, for the official viewing area of WRAL, there were no showers or storms for the first time in over three weeks!
The last day we could say that about was June 20, and since then a combination of frequent nearby upper troughs and a recurrent feed of very moist air from the south has given us at least a few cells and clusters of showers or storms, and sometimes a lot of them, every single day. That has helped to keep temperatures below normal for the first part of summer and has also led to rainfall amounts far above normal.
From a historic standpoint, it's difficult to go back and look for records that apply to a sizable region like our entire viewing area and check for the greatest number of consecutive days with rain falling at least somewhere, but it's reasonable to think this was one of the longer stretches we've seen like that.
You can more readily check records for individual stations, of course. Taking a look at history from the Raleigh-Durham International Airport (with 69 years of data, and from a site maintained by NC State College (later University) that has records back to 1892), we found that at RDU the longest stretch of days with measurable rain (at least .01") has been 11 in a row.
This has occurred there four times, most recently from May 19-29, 1982. During this wet stretch recently, there have been two different periods when RDU picked up measurable rain five days in a row. At the NC State site in west Raleigh, there was a 12-day stretch of days with measurable rain that ran from July 5-16 in 1950.
Incidentally, on the map above you'll see a .01" total shown for the Rocky Mt-Wilson airport. On occasion, the rain gauges used in automated weather stations will report a spurious rain total due to an electrical glitch, some condensation, vibration due to nearby construction or unusually gusty winds, etc.
We can't say exactly what led to the .01 in this case, but it occurred around 4 a.m. while the station was reporting a long stretch of clear skies and light winds, with no activity evident on satellite or radar, so it would appear to be one of those erroneous readings.