textproduct: Columbia

WHAT HAS CHANGED

Little change in the overall forecast, with daily afternoon storm chances and increasing heat/humidity next week. Aviation discussion updated for 12z TAFs.

KEY MESSAGES

- 1. Diurnal showers and thunderstorms, some strong, each day.

- 2. Increasing heat and humidity is expected next week.

DISCUSSION

- 1. Diurnal showers and thunderstorms, some strong, each day.

A wavy, nearly stationary frontal boundary extending from the central and southern Plains into the Northeast will continue to serve as the focus for scattered showers and thunderstorms across portions of the eastern CONUS. Expect another round of mainly diurnal showers and storms to develop Friday afternoon. The latest HRRR and HREF suggest somewhat lower convective coverage compared to Thursday, though confidence remains low given the poor model performance over the past several days. The overall environment will remain very similar to yesterday, with sufficient instability and moisture in place to support a few stronger storms. Forecast soundings continue to indicate a favorable profile for wet microbursts. PWAT values around 2 inches, combined with slow storm motions and already saturated soils will once again support the potential for heavy rainfall and localized flash flooding. This should continue into the weekend, with scattered to isolated showers and thunderstorms expected each afternoon/evening. However, coverage should trend slightly lower each day.

- 2. Increasing heat and humidity is expected next week.

As an upper-level trough shifts into the Northeast over the weekend, surface high pressure will gradually build southward into the FA. 90th percentile heights will foster highs climbing back into the mid- 90s through much of next week. There remains some uncertainty regarding convective chances next week, as guidance continues to differ on the placement of a front near our area. Some solutions keep the boundary close enough to support daily afternoon and evening showers/thunderstorms, while others keep it farther north with more isolated convection. The eventual position will also influence daytime temperatures, as cloud cover from diurnal convection could temper afternoon highs during peak heating. Nonetheless, a combination of temperatures in the low to mid-90s and dewpoints in the low to mid-70s will likely push heat indices toward or over the 100-degree mark for several days next week.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Widespread ifr/lifr cigs and vsby restrictions possible through the early morning hours. A return to vfr is expected by mid to late morning.

Plenty of low-level moisture remains across the region from all the rainfall that occurred yesterday. All this moisture has combined with light to calm winds to produce areas of br and fg across the area early this morning. Visibilities dropping at times to around 1/2SM through sunrise. Conditions should slowly improve through the morning after sunrise, but vfr is not anticipated to develop until between 14-16z. As for any rainfall through the period, guidance shows at least isolated activity this afternoon as the sea-breeze moves inland. However considering guidance based coverage has been slightly low the past few days, expect to see at least scattered activity along the boundary as it moves through the area. Have continued with Prob30 grouping for any active development at all locations from early afternoon through at least close to sunset. Winds will remain light, generally from the south.

Later tonight, the potential exists once again for the redevelopment of ifr/lifr conditions at all locations.

EXTENDED AVIATION OUTLOOK...Diurnal thunderstorm restrictions possible through the period, with additional early morning restrictions also possible each day.

CAE WATCHES/WARNINGS/ADVISORIES

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