textproduct: Columbia

WHAT HAS CHANGED

Confidence increasing in above normal temperatures late this week and over the weekend. Aviation Discussion updated for 18z TAF.

KEY MESSAGES

- 1. Isolated thunderstorms today and Thursday, rain chances increase through early next week.

- 2. Above normal temperatures likely Friday through Sunday.

DISCUSSION

Key Message 1: Isolated thunderstorms today and Thursday, rain chances increase through early next week.

Surface high pressure will be east of the forecast area over the next few days directing moist, SW flow into the region. Ridging will limit our convective coverage despite ample moisture and strong heating. PWAT values at 110 to 130 percent of normal and surface dewpoints in the mid to upper 60s will lead to partly to mostly cloudy skies. Strong heating should lead to a few showers or thunderstorms with model soundings showing up to around 1000 J/kg of SBCAPE in the afternoon. Poor lapse rates suggest the threat of severe weather will be low.

Friday into this weekend, high pressure weakens and additional moisture is reinforced, with PWAT values over 1.75". Model soundings indicate better instability of over 1500 J/kg SBCAPE, while upper level dynamics strengthen particularly Saturday and Sunday, leading to increasing confidence in better convective coverage. Early thoughts gleaned from ensemble patterns and IVT forecasts are that the active pattern with above normal moisture will persist into next week.

Key Message 2: Above normal temperatures likely Friday through Sunday.

With strong ridging and moist SW flow over the region we will see heat index values break into the triple digits late this week and over the weekend. NBM probabilities of reaching heat advisory criteria of 108 are low, generally less than 20 to 30 percent. That said, early season heat can lead to a greater risk of heat illness than similar HI values later in the summer. This combined with an experimental Heat Risk category of major (3 out of 4) for much of the forecast area both Friday and Saturday raises concern for heat related illnesses.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

VFR conditions are expected to continue through the TAF period outside of any isolated shower/storms this afternoon.

VFR conditions continue as 6-9 kt winds out of the southwest develop. SCT cumulus are seen as well with mid to high level clouds streaming in. These conditions are expected to continue the remainder of the afternoon and into this evening before light and variable winds develop tonight. The overall fog/stratus risk is a bit lower tonight with a 20-25 kt LLJ in place, though periodic ground fog near AGS cannot fully be ruled out. More high clouds are expected to roll through Thursday morning into the afternoon as another cumulus deck likely develops after 15-17z. Light winds are expected to be out of the south to south-southwest through the day. In terms of rain chances, a couple spotty showers will be possible during the afternoon but confidence in impacts at the TAF sites is low at this time.

EXTENDED AVIATION OUTLOOK...Isolated to widely scattered diurnal showers and storms possible each afternoon late this week into the weekend.

CAE WATCHES/WARNINGS/ADVISORIES

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