68 NC counties and 1 VA county are under alert, including Wake, Cumberland, Durham, Johnston, and Orange counties. Details
Published: 2013-09-18 08:12:00
Updated: 2013-09-18 09:22:26
Posted September 18, 2013
By Mike Moss
We're fortunate to live in one of a few places in the country with a nearby meteorological instrument called a profiler. Date just made available online has given people in the area access to data from two profilers, thanks to NOAA, the N.C. Department of Environment and Natural Resources and the U.S. EPA.
The instruments in question are radar wind profilers, which can measure a nearly continuous record of wind direction and speed through the lower to mid-level of the atmosphere (up to between about 15,000 and 20,000 feet) and are combined with piggyback system called a radar acoustic sounder system (RASS) that uses a very interesting measurement technique to estimate temperatures from the surface up to about 2-4,000 feet.
This combination can be very helpful in monitoring things like transport and dispersion of pollutants, the evolution of passing frontal systems, development of enhanced wind speed in low-level jets and as a check on potential precipitation type in the winter.
While these systems are fairly sparse in numbers across the country, there are now five of them active and current in North Carolina, including one in Research Triangle Park and another in Clayton. I've included a link above that any of you interested in accessing the data can use.
You can select a given site by clicking the star or dot (note the green ones indicate current or very recent data is available), and can make some choices about how the plot will look and what time period is covered.
As you probably noticed, after a warm and at times humid Monday this week, we had a cold front move through later in the day that ended up bringing us a cooler and less humid day on Tuesday. The profiler image above captures this process as seen above the RTP profiler and sounder. The left hand side of the plot starts at about noon on Monday and ends on the right hand side around midnight twelve hours later.
The afternoon winds are from the northwest below about 5,000 feet, but as you'll see when the initially shallow layer of cooler and less humid air began moving in in force, those low level winds shifted to the north and then northeast, and as the depth of the cooler airmass increases through the evening, so does the depth over which the winds turn to the northeast.
The shaded area near the bottom of the image indicates temperature, and we see that drop from upper 80s Monday afternoon to upper 60s by midnight, on the way to falling into the 50s by Tuesday morning.
In the days to come, those winds will be fairly light and then start shifting toward the southeast and south as we head into Friday and Saturday, warming us back up some and turning us a little more humid as we head into the weekend.