textproduct: Columbia

WHAT HAS CHANGED

Heat Advisory extended through Sunday evening. Scattered storms with some strong possible today and tomorrow. Aviation discussion updated for 18z update.

KEY MESSAGES

- 1. The high heat and humidity continues with temperatures likely peaking on Monday.

- 2. Isolated to scattered afternoon and evening convection expected this weekend.

DISCUSSION

1. The high heat and humidity continues with temperatures likely peaking on Monday.

The high heat and humidity is expected to continue into the early part of the work week despite weakening upper ridging. High temperatures on this afternoon should generally rise into the mid-90s which and combine with high humidity to produce max heat index values between 105 and 110 in most locations. A few locations could see a Heat Index over 110 today. Temperatures could be slightly cooler Sunday, thus heat index values could be slightly lower than today as well. However, values are still expected to flirt with our criteria of 108 tomorrow. That along with the fact that this has been a prolonged stretch of abnormally hot conditions, decided to extend the Heat Advisory through 8 pm Sunday. On Monday, model guidance shows anomalously high 850mb temperatures perhaps exceeding 10 degrees above normal yielding surface temperatures in the upper 90s and lower 100s. The humidity is unlikely to relent meaning another day of dangerous heat index values to start the new work week. A trough during the mid to late portion of next week may finally break the threat of extreme heat with daytime temperatures closer to seasonal values. The bottom line is whether you are outdoors for work or play, continue to take appropriate precautions and limit time in direct sunlight during peak heating hours.

2. Isolated to scattered afternoon and evening convection expected this weekend.

The flattening ridge should result in isolated to scattered convection during the afternoon and evening hours this weekend. As has been the case during the last few days, any robust convection has the potential to produce damaging wind gusts. The lack of winds aloft means that localized flooding is also possible, primarily if rain falls over normally flood prone areas. Guidance has kept the chance for precipitation low on Monday and this appears to be due to the highly anomalous 850mb temperatures mentioned in the previous section. This should result in sufficient capping over the forecast area for Monday, with any rain arriving towards evening as a shortwave moves in from the northwest potentially eroding the cap. More typical August rain chances are then anticipated, perhaps increasing during the mid to late portion of next week when a trough may set up over the eastern CONUS.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

VFR conditions likely outside of scattered convection this afternoon and evening.

Typical summer cumulus has developed across the area with light and variable winds, generally from the southwest to southeast. Scattered convection is once again developing, with coverage expected to increase between 18z-00z. Thunderstorm activity will be somewhat more widespread than in previous days; however, a PROB30 group for -TSRA was maintained at all sites. A TEMPO or predominant group may be needed as confidence increases. Activity should diminish after sunset, with the potential for fog/stratus once again dependent on rainfall amounts and coverage. Similar conditions are expected Sunday, with light and variable winds generally from the west-soutwest. Typical afternoon convection will again be possible.

EXTENDED AVIATION OUTLOOK...Diurnal chances for thunderstorms continue each day through the weekend.

CAE WATCHES/WARNINGS/ADVISORIES

SC...Heat Advisory until 8 PM EDT Sunday for Scz036-018-020>022- 025>031-035-037-038-041-115-116-135>137. GA...Heat Advisory until 8 PM EDT Sunday for GAZ040-063>065-077.