textproduct: Columbia

WHAT HAS CHANGED

Updated both key messages for current conditions, but the overall pattern remains the same. Aviation discussion updated for 18z TAFs.

KEY MESSAGES

- 1. Scattered afternoon showers and thunderstorms possible on today and tomorrow. A few strong thunderstorms are possible later today.

- 2. Dangerous heat possible today and tomorrow, with a signal for a more impactful and intense heat event during the opening days of July.

DISCUSSION

Key Message 1: Scattered afternoon showers and thunderstorms possible on today and tomorrow. A few strong thunderstorms are possible later today.

A decaying MCV has moved over the southern Appalachians and will continue progressing into the FA through the remainder of the afternoon and evening. Hi-res guidance continues to indicate a complex of thunderstorms moving in from the Upstate, with the greatest impacts expected along the I-26 corridor and across across locations north and east.

SPC has upgraded the northern half of the CWA to a Slight Risk (Level 2 of 5) for severe weather. Clusters of thunderstorms capable of producing damaging wind gusts are expected this afternoon and evening, with the highest threat occurring between 3-8PM. Forecast soundings continue to depict inverted V profiles with DCAPE values ranging from 750-1000 J/kg, supporting the potential for strong downburst winds. Long, skinny CAPE profiles combined with high PWAT values will also favor periods of heavy rainfall. While showers and thunderstorms remain possible for the entire area, coverage is expected to decrease quickly has it heads closer toward the CSRA.

Lingering moisture will support another chance for scattered showers and storms on Monday, although confidence in coverage is lower. The sever threat is also expected to diminishing as the upper-level ridge inches closer to the region.

Key Message 2: Dangerous heat possible today and tomorrow, with a signal for a more impactful and intense heat event during the opening days of July.

Heat indices this afternoon are sitting right around 100-104 degrees as dew points remain in the low to mid 70s. Hot and humid conditions will persist into Monday as the ridge strengthens over the eastern CONUS, promoting a steady warming trend while suppressing most convective activity. A Heat Advisory may be needed for portions of the CSRA on Monday, where peak heat index values could approach 108- 110 degrees in the afternoon but this may be limited if diurnal convection starts to develop.

Slightly drier air is expected to filter into the region during the middle of the week, resulting in somewhat lower heat index values, although temperatures will still remain above normal. By late week and into the holiday weekend, the upper-level ridge will start to really flex and strengthen further, with 850-mb temperatures approaching or exceeding 20C. This pattern will support a continued warming trend, with afternoon highs steadily climbing and several locations potentially reaching or exceeding 100 degrees from Thursday through Sunday. Heat indices could soar close to or above 105 degrees. If trends continue, heat products may be needed several days in a row. Be sure to make heat safety preparations now and have a plan to monitor children, the elderly, pets, and anyone without adequate indoor cooling.

The NHC maintains a 20% chance for cyclone formation over the next 7 days off the SC coast. However, guidance has backed off on this quite a bit with development fairly low.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

VFR conditions likely outside of afternoon convection Sunday.

Cumulus clouds are beginning to do the sky this afternoon and instability increases ahead of an approaching shortwave. Scattered showers and thunderstorms are expected to develop over the next several hours, with some capable of 30-40 knot or greater winds. Handling this with a Prob30 at all sites right now but may need to shift to a TEMPO group as thunderstorms increase in coverage. Winds ahead of this continue to look breezy, with 15-20 knot gusts out of the west or west-southwest this afternoon. Expect thunderstorm activity to wane after sunset. Patchy fog is again possible tonight, especially where rain does fall. As we get into the latter portion of this forecast period, look for winds to shift out of the north and northeast behind a backdoor front.

EXTENDED AVIATION OUTLOOK...Afternoon convection will develop again Monday but is less likely for the remainder of the week as ridging builds overhead. Brief early morning restrictions also possible early next week.

CAE WATCHES/WARNINGS/ADVISORIES

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