textproduct: Columbia

WHAT HAS CHANGED

Updated Key Message #2. Aviation discussion updated for 00z TAFs.

KEY MESSAGES

- 1. Heat Index between 105 and 110 possible Thu and Fri

- 2. A couple storms possible this evening, rain chances pick back up late this weekend and early next week.

DISCUSSION

- 1. Heat Index between 105 and 110 possible Thu and Fri

Ridging aloft shifts further east late Thursday and Friday helping to suppress convection and pushing daytime highs into the mid to upper 90s, possibly around 100 degrees. Downslope winds are expected over the region with adiabatic heating helping to push temps above normal both days.

Thursday: the ridge axis will still be to our west which could allow shortwave energy to dig down into the forecast area and promote convection with just a weak capping inversion in place. Downslope flow and deep mixing will allow dewpoints to drop into the low 70s or around 70 degrees in the afternoon. The NBM, which had Td values 5 to 8 degrees too warm the previous day was disregarded. We should see Heat Index values reach 105 for most areas Thursday, but a few locations could near 108 (Heat Advisory criteria). Between the chance of afternoon convection and marginal HI values, we believe confidence is too low to issue a Heat Advisory at this point.

Friday: With ridging almost directly overhead we should see greater suppression of convective development. Temperatures will once again approach 100 degrees. Even after accounting for the warm bias in the NBM, dewpoints should be high enough to near or possibly exceed Heat Advisory criteria.

- 2. A couple storms possible this evening, rain chances pick back up late this weekend and early next week.

A couple storms are pushing out of the Upstate toward the northern Midlands this evening and have exhibited decent cores on them, thus a couple stronger pulse storms sneaking into the CWA could be possible over the coming hour or two. Another loosely organized MCS is seen back into central KY, nearing northern TN in the coming two hours. Model guidance remains insistent that this will largely decay before moving down the eastern slopes of the Appalachians with little to no activity reaching the northern FA. Given the verification from the previous night, there is concern that the cold pool driven system will hold together a bit longer than CAMs show, so there is the low chance some of this activity nears the northern FA due to the large scale outflow potentially reaching the FA. If this solution occurs, a couple stronger wind gusts cannot be ruled out but the risk for any severe weather is quite low. Overall, confidence in this system reaching is limited as instability wanes and the more favorable environment is located west of the Appalachians.

Global ensembles favor ridging flattening out late this weekend and early next week with troughing possibly developing over the eastern US near the end of the forecast period. Atmospheric moisture will be above normal during this time frame with mean PWAT values near or above 2 inches. Above normal moisture and zonal flow favors at least a chance of showers and thunderstorms each day.

AVIATION /00Z THURSDAY THROUGH MONDAY/

VFR conditions generally expected through the TAF period, with low confidence in possible scattered overnight convection.

Radar showing some isolated storms in the Upstate but not sure they will hold together long enough to impact terminals. Airmass generally unchanged with warm and humid conditions expected to persist. Light and variable to near calm winds overnight then picking up from the west around 6 to 10 knots after 15z. Isolated diurnal convection possible but confidence too low to include at this time.

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

CAE WATCHES/WARNINGS/ADVISORIES

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