textproduct: Columbia

WHAT HAS CHANGED

Aviation Discussion updated for 18z TAFs.

KEY MESSAGES

- 1. Above normal temperatures, dangerously hot at times, likely through Sunday.

- 2. Isolated thunderstorms today and Friday; rain chances increase over the weekend into early next week.

DISCUSSION

Key Message 1: Above normal temperatures, dangerously hot at times, likely through Sunday.

90th+ percentile upper ridging and moist southwest flow over the Southeastern states will persist through the upcoming weekend. Surface dewpoints are expected to be in the 60s to possibly low 70s during the afternoon hours. With temperatures expected to climb into the mid to upper 90s, we will see Heat Index values break into the triple digits Friday and over the weekend. LREF probabilities of reaching Heat Index values of 108F which would trigger a Heat Advisory are very low, generally less than 10 percent. That said, early season heat can lead to a greater risk of heat illness than similar conditions later in the summer. Additionally, the experimental Heat Risk category of Major (3 out of 4) will be in place for much of the forecast area Friday through Sunday, with even some Extreme (4 out of 4) areas starting to show up over the weekend particularly in our concrete jungles of Columbia and Augusta. This increases the potential for an Advisory to eventually be hoisted based on forecaster discretion.

Key Message 2: Isolated thunderstorms today and Friday; rain chances increase over the weekend into early next week.

Surface high pressure will be east of the forecast area over the next several days, and the aforementioned upper ridge will generally work to limit our convective coverage. This is despite ample moisture (PWAT values 110-130% of normal) and expected strong daytime heating. Even so, a few showers or thunderstorms may pop up this afternoon, though CAM solutions currently keep most convective coverage off to our north and northwest.

Interestingly, CSU severe probabilities, specifically for severe wind, are highlighting some potential for some stronger storms Friday into the weekend. This is likely due to the conditions previously described, and we'll need to have some additional support from any shortwaves that line up with our most unstable time period. Model soundings do indicate better instability of over 1500 J/kg SBCAPE, leading to increasing confidence in better convective coverage. By early next week, ECENS IVT values increase to over the 90th percentile and remain there for several days. With this in mind, expect a more active pattern with above normal moisture (and subsequently lower temperatures given higher rain chances) to kick in by Monday and last for several days.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

VFR conditions are expected to continue through the TAF period.

High pressure is shifting offshore this afternoon as light southwesterly to south-southwesterly winds develop. A SCT cumulus deck around 4500-6000 ft has developed and a couple spotty showers have been noted in parts of the CSRA, but confidence in any shower or weak storm impacting the terminals remains too low to add into the TAF. Heading into this evening and overnight, a 20-25 kt LLJ is expected to keep surface winds light and variable while FEW cirrus pass over the region. As has been the case the last couple of days, after 15-17z Friday, another cumulus deck around 4000 to 6000 ft should develop as winds become a bit more westerly around 5-8 kts. There is a slightly greater chance for increased coverage in afternoon showers/storms, but confidence is on the low side for this.

EXTENDED AVIATION OUTLOOK...Isolated to widely scattered diurnal showers and storms possible into this weekend. Greater rain chances are expected early next week.

CAE WATCHES/WARNINGS/ADVISORIES

SC...None. GA...None.