Heat's on this week...
Posted May 23, 2011
...At least outdoors, meaning most of us will have the A/C on inside to keep comfortable. In addition to the increase in temperatures we've seen through the weekend, we've gradually seen our dew points trend from low 50s to upper 50s to low 60s, and should see dew points in the mid 60s to near 70 at times over the next couple of days, paired up with afternoon temperatures that should climb in to the low to mid 90s for much of the area through at least Thursday or so.
As a reminder, we usually don't notice humidity too much in terms of discomfort, even with very warm temperatures, when the dew points are in the 40s and 50s. We start to notice a little humidity when dew points climb into the 60s, and by the upper 60s to around 70 it is noticeably muggy. Another point to take is that when dew points are in the upper 50s or below, there is no "heat index" effect that causes it to feel warmer than the actual temperature, but those effects increase as dew points rise through the 60s and up.
To go along with the added low-level moisture, we're expecting a stretch of temperatures not far off of records for the date (the first image shows a model estimate with a band of highs in the 90s through much of the southeast for Tuesday afternoon). Those record values, for RDU, are 95 (Mon), 95 (Tue), 93 (Wed), 94 (Thu) and 92 (Fri). Right now, the only day that our forecast reaches the record is on Wednesday. Of course, there is some uncertainty attached to any specific temperature prediction, and we're close enough that a high that exceeds our forecast by only a couple of degrees may tie or set a new record. Combined with humidity, our next several afternoons will feature heat index values that run in the mid to upper 90s.
One other effect of the added heat and low-level moisture is to potentially energize thunderstorms a bit, although how intense they become is also dependent on passing weather systems and on temperatures and moisture at higher altitudes. For now, we're expecting storms to be rather scattered in nature today and perhaps more isolated on Tuesday and Wednesday. However, where they do form, especially this afternoon and evening, they could be strong enough to produce some damaging downburst winds or large hail in a few spots, with a very slight chance of tornado formation, mainly across northern parts of the state. Due to this potential, the Storm Prediction Center has about the northern third to half of the state under a slight risk for severe storms at that time (yellow shaded area in the second image).