textproduct: Columbia

WHAT HAS CHANGED

The forecast remains on track for showers and thunderstorms this afternoon and again Friday morning.

KEY MESSAGES

- 1. Thunderstorms expected Friday morning, damaging winds are possible but overall the severe weather threat is low.

DISCUSSION

Key Message 1: Thunderstorms expected Friday morning, damaging winds are possible but overall the severe weather threat is low.

An upper level trough is digging into the central US today and will move across the Southeast on Friday. At the surface, a slow moving cold front is draped across the Deep South, west of the forecast area. The upper trough will help push the front further east tonight eventually moving through the forecast area on Friday. Divergence aloft and convergence ahead of the front will increase convective activity late tonight through early Friday.

We expect a few thunderstorms overnight with weak elevated instability in place but thunderstorm chances will pick up before sunrise Friday as the upper trough approaches, enhancing convection. The threat of severe weather is low due to poor low level lapse rates but early Friday morning the wind field strengthens helping to erode the nocturnal inversion. If convection can become surface based then there is potential for a couple of stronger storms to produce damaging winds or possibly a weak tornado. REFS mean SBCAPE values range from 250 to 750 J/kg Friday morning with 0 to 6 km shear around 30 kts, and 0 to 1 km SRH around 50 m2/s2. While not overly favorable for severe weather, some organized convection could develop. The greater threat will likely be in the Pee Dee and northeast of the forecast area where daytime heating will improve low level lapse rates prior to the frontal passage. Mean QPF from the NBM and REFS still generally show 0.25 to 0.5 inches with localized higher amounts of around 1 inch in the PMM where thunderstorms develop.

Convection will push east of the area by midday or so as the front moves through. Dry, cool air then filters into the area Friday afternoon and remains in place through the weekend. Beyond that dry weather and seasonable temperatures are favored.

AVIATION /18Z THURSDAY THROUGH TUESDAY/

An interesting TAF period is on tap as a slow moving front approaches the forecast area from the west. VFR conditions should give way to MVFR and IFR conditions later tonight, though the extent of ceiling restrictions is uncertain.

MVFR and IFR ceilings were fairly common across the area earlier this morning, especially at AGS/DNL/AIK. These are lifting and thinning out across the area, though widespread cumulus is likely to develop in its place as we warm up. These are expected to remain VFR for the rest of the day, though there may be brief periods where we see MVFR. The airmass is moisture rich currently, with PWs >1.5" across the area. This isn't yielding too much in the way of shower activity, though that may change as the afternoon goes along and the trough/front approaches from the west. Introduce VCSH at 00z because of the expectation that more showers will be around. A more robust shot of moisture/forcing will approach after 06z tonight, with all guidance showing widespread showers developing across eastern Georgia and moving through the sites as Friday morning goes along. Guidance continues to show some instability around this evening, with values >500 j/kg of CAPE across the area. Thunderstorms are expected as a result, though their coverage is uncertain enough to maintain a VCTS group with a TEMPO for moderate rain across the sites. As this occurs, the increasing low-level moisture across the area is likely to yield at least MVFR ceilings across the area. IFR cigs are possible but this isn't really a setup that yields persistent IFR cigs across a broad area. The front is likely to push through between 12z and 18z tomorrow, yielding a return to VFR by tomorrow afternoon.

EXTENDED AVIATION OUTLOOK...Aviation Conditions should improve over the weekend as dry air filters into the area.

CAE WATCHES/WARNINGS/ADVISORIES

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