textproduct: Columbia

WHAT HAS CHANGED

Minimal changes to Key Messages. Aviation discussion updated for 12z TAF issuance.

KEY MESSAGES

- 1. Diurnal thunderstorms expected through this weekend.

- 2. Well above normal temperatures with dangerous heat index values possible this week.

DISCUSSION

KEY MESSAGE 1: Diurnal thunderstorms expected through this weekend.

Little change is expected in the overall pattern today as the trough gradually weakens and shifts east, with heights rising ahead of the ridge building into our area. Before the ridge becomes firmly established, another round of isolated showers and thunderstorms will be possible. Abundant moisture will remain in place, supporting diurnally driven convection during the afternoon. Activity should be fairly minimal; however, heavy rainfall will remain the primary threat from any pop-up storms that develop, with the overall severe threat remaining low.

KEY MESSAGE 2: Well above normal temperatures with dangerous heat index values possible this week.

Ridging will continue to build as the subtropical ridge becomes established over the southeast this week. Confidence is increasing in a return to hot and humid conditions, keeping a strong taste of summer in place into September. EC ensemble 500-mb height anomalies are forecast to exceed the 97th percentile Monday, rising above the 99th percentile through midweek. The strong upper-level ridge will promote significant subsidence across the region, which should generally suppress convection. The result will be a prolonged period of well-aove- normal temperatures, supported by ensemble temps at the 700/850/1000-mb levels reaching or exceeding the 99th percentile. Temperatures will climb into the mid to upper 90s by midweek and remain there each day into next weekend. The combination of anomalous heat and increasing low-level moisture will result in heat indices reaching 100-105 degrees, with some locations potentially higher.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

Restrictions again through the morning hours, then possible again towards Monday morning.

Satellite and surface observations showing quite a bit of low stratus has developed this morning across both the central Midlands and much of the CSRA. Ceiling restrictions remain ifr/lifr at issuance, and should hold through 15z before finally improving into mvfr. Vfr conditions then expected this afternoon by 17z as mixing becomes better. Can not rule out an isolated shower through the day anywhere, but better coverage expected over the far eastern Midlands. Have only placed Prob30 in OGB for this afternoon at this time. Guidance once again indicating the potential for restrictions to develop late tonight at all locations.

EXTENDED AVIATION OUTLOOK...Drier conditions expected early next week, but brief early morning restrictions still possible.

CAE WATCHES/WARNINGS/ADVISORIES

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