textproduct: Columbia

WHAT HAS CHANGED

Heat Advisory issued today from Noon to 8 PM. Aviation discussion updated for 06z TAFs.

KEY MESSAGES

- 1. Heat Advisory in effect from Noon to 8PM today. Another Advisory may be needed tomorrow. Heat Indices between 105-110F expected each day.

- 2. Isolated to widely scattered convection possible today, before rain chances pick up late this weekend and early next week.

DISCUSSION

- 1. Heat Advisory in effect from Noon to 8PM today. Another Advisory may be needed tomorrow. Heat Indices between 105-110F expected each day.

As ridging shifts further east today and especially Friday, temperatures into the upper 90s become more likely with surface dew points mixing out into the low to mid 70s. Confidence in a few spots reaching Advisory criteria has increased today and after collaborating with neighboring offices, have decided to issue a Heat Advisory from Noon to 8 PM today. The main wrench that could be thrown into this is if convection gets going early and coverage is greater than expected, but the 00z suite of guidance is keeping coverage fairly low and favoring the late afternoon into the early evening, giving a window where locations could reach or rise slightly above 108F for heat indices. With the ridge moving overhead Friday, greater convective suppression is expected and temperatures may near 100F in a few locations, as shown in recent MET, MAV, ECS, and NBM guidance. This is leading to HREF probabilities for meeting Heat Advisory criteria between 50-70%, thus another Advisory could be needed with heat indices again topping out near 108-110F. Increased diurnal shower/storm chances into the weekend and early next week limit confidence in the need for additional heat products, but either way, above normal temperatures are expected to continue into early next week as the ridge likely does not become more flattened out until around the mid week.

- 2. Isolated to widely scattered convection possible today, before rain chances pick up late this weekend and early next week.

Another chance for isolated to widely scattered convection will exist this afternoon as the region remains in a northwest flow pattern, but the ridge is expected to gradually work overhead into Friday. As with yesterday, there is generous spread across CAM's in convective coverage this afternoon, but there is a bit more of a consensus that at least a couple storms could develop, posing a threat for strong to damaging downburst wind gusts as SBCAPE values near 2500-3000 J/kg develop with DCAPE values once again nearing or exceeding 1000 J/kg. The potential for greater coverage and intensity is not out of the question, however. This comes as outflow from convection moving out of the Midwest and into the Mid-Atlantic could settle into the region and/or a convergent zone could establish itself in the CWA as shown in latest HRRR/RAP runs. There is low confidence in this scenario, but even if this solution is realized, the main risk would continue to be damaging wind gusts. As has been the case the last couple evenings/nights, will once again need to keep an eye on any upstream convection moving out of the Midwest and its evolution.

Global ensembles continue to favor ridging slowly flattening into early next week, with more chances for shortwaves and/or weakening MCS's to near the FA in a northwest flow regime. PWAT's should remain near 2" through the late weekend into next week as well, so chances for rain are expected each day into through early next week. There is some indication in global models that troughing could begin to replace the ridge toward the middle of the week, but high uncertainty remains in this.

AVIATION /06Z THURSDAY THROUGH MONDAY/

VFR conditions likely through the TAF period with some scattered convection Thursday afternoon.

Convection has diminished across the region with no shower- storm activity expected until Thursday afternoon. Overnight, only some mid-level cloud cover is expected with calm winds. Some brief periodic vsby restrictions typical at AGS and AIK are possible into Thursday morning, but confidence is too low for any sort of TAF mention. Typical summer cu is expected by late Thursday morning with convection developing late in the afternoon and evening. Confidence is high enough for a prob30 group at all sites but this will require some refinement in future TAFs.

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

CAE WATCHES/WARNINGS/ADVISORIES

SC...Heat Advisory from noon today to 8 PM EDT this evening for SCZ016-018-020>022-025>031-035-037-038-041-115-116- 135>137. GA...Heat Advisory from noon today to 8 PM EDT this evening for GAZ040-063>065-077.