textproduct: Columbia

WHAT HAS CHANGED

Heat Advisory remains through Sunday evening. Aviation discussion updated for 00z 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. Temperatures could be slightly cooler Sunday, thus heat index values could be slightly lower than previous few days. 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 /00Z SUNDAY THROUGH THURSDAY/

VFR conditions likely through midnight, then potential for visibility restrictions late tonight and into Sunday morning.

Scattered showers and storms this evening have remained mostly just outside of taf locations. This should continue through sunset, then any activity should be diminishing. Expecting mainly dry conditions then overnight, then possibly an isolated shower or storm Sunday afternoon. At this time confidence in thunderstorms Sunday is lower than past few days, and will leave out mention of any Prob30 groups for now. Bigger issue late tonight that could bring restrictions is potential for some patch to areal fog formation towards sunrise. Guidance is consistent with bringing mvfr visibilities after 06z at all sites, with potential for ifr between 10z-13z. Due to multiple models showing that, along with the lamp probabilities, will begin 5sm at 06z, with tempo period from 10z-13z down to 2sm. Conditions should be improving after 13z, with vfr expected for the remainder of the day outside of any of those isolated afternoon showers/storms. Winds through the period mainly calm, to light and variable.

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 SCZ016-018-020>022- 025>031-035-037-038-041-115-116-135>137. GA...Heat Advisory until 8 PM EDT Sunday for GAZ040-063>065-077.