Cool for a little longer in Richmond, but warming this weekend | Weather

Even though temperatures nudged into the 80s on Tuesday, the next couple of afternoons will remain a shade cooler than normal. But for Friday and the weekend, the humidity will surge upward, and afternoons will return to the middle to upper 80s.

Through Friday, the chance for showers is small, although not quite zero. Much of the energy for a larger storm is being held far to the north of Virginia, in the form of a driving rain and wind for coastal New England on Wednesday.

Neither Saturday nor Sunday look wet in Richmond, although a quick shower or thundershower cannot be ruled out yet. The weather pattern becomes more favorable for numerous showers and thunderstorms on Monday and Tuesday of next week, as the higher humidity returns to central Virginia.

A report from the nonprofit First Street Foundation has made a lot of headlines over the past couple days or so. Its online tool is one effort to help visualize the impacts of the warming climate on health and property over the length of a typical mortgage — 30 years.

Like any study of this magnitude, there are assumptions and imperfections. However, the broader results are consistent with the current scientific understanding of a warming climate.

Digging into the figures, the report indicates that in an average summer, Richmond currently has about seven days when the heat index is above 105 degrees. But 30 years from now, assuming a modest greenhouse gas emissions scenario, that number will increase to 17 days.

Within these broader averages are the occasional extremes, including the prospect of reaching thresholds that have not been observed before. But just how hot and humid has it been in the past?

A heat index above 115 is exceedingly rare in Richmond, happening only four times. The highest one came the afternoon of July 17, 1980, when a southwest breeze took the temperature to 100 degrees. The humidity was at a truly tropical level (dew point temperature was 77), which yielded a heat index of 116.7 degrees.

The First Street analysis suggests that 30 years from now, the heat index will reach 125 about once every year or two. Take the same humidity level from that July day in 1980, and pair it with an air temperature of 106 degrees: The result is a heat index of 125.

Richmond’s all-time record high is 107 (1918). But it also reached 105 degrees in back-to-back days in 2010.

Getting those levels of heat and humidity at the same time is not easy but, in the coming years, the chance of reaching it will continue to rise. Other parts of the country have crushed all-time heat records in the past couple of years. A heat index of 125 degrees will not be common in 30 years in Richmond, but it may not be as far-fetched as it sounds.