textproduct: Columbia

WHAT HAS CHANGED

12Z Aviation Updates.

KEY MESSAGES

- 1. Above normal temperatures with increasing chances for showers and storms late week into the weekend.

DISCUSSION

KEY MESSAGE 1: Above normal temperatures with increasing chances for showers and storms late week into the weekend.

Confidence continues to be fairly high regarding the forecast through early next week. A slow moving trough is forecast to continue approaching the area from the west, with rich moisture advecting northward into the FA as a result. PWs are near 2" already, with >2" PWs expected into Saturday. With convective temps forecast in the upper 80s and lower 90s both days, along with forcing and plenty of instability, scattered to numerous showers and thunderstorms are likely both this afternoon and Saturday afternoon. The moisture rich profile should keep the severe threat relatively at bay across the area. DCAPE and TEI values are pretty low for strong downbursts both days, with precip loading the likely culprit for any stronger storms. SBCAPE values do look quite high this afternoon, so today is probably the better of the two days for any strong to severe convection. Even still, the chances for a severe storm should be relatively seasonal in nature. Highs both days are expected to be modulated by convective coverage.

Beginning Sunday, a ridge aloft is forecast to begin building eastward and shifting the trough axis to our east. Precip chances are expected to diminish as a result, with only isolated to scattered coverage expected. The ridge is then forecast to continue building into the region through much of next week, with extreme 500 hPa heights (NAEFS forecast max heights in the September 1979-2009 climatology!) set up across the region. One of the interesting things that may result from the intensity of the ridge is a series of strong troughs pushing eastward atop it into the northeastern CONUS. Typically, this wouldn't mean a ton considering the robustness of this upper ridge. However, strong convergence on the backsides of these troughs is forecast to yield an anomalous surface high settling into the Northeast and Mid-Atlantic by Tuesday, pushing a backdoor front through the area Monday night. So Monday, ahead of said front, will likely be warm as we get the combination of rising heights and compressional heating ahead of an approaching front. But behind that front, while temps don't look cool by any stretch, they likely won't be particularly hot either with respect to how strong the ridge will be. Surface dewpoints also look to drop, helping make the airmass more palatable. There is some skepticism with this forecaster that the backdoor front makes it through. However, guidance is forecasting it pretty much across the board & ensemble spread is fairly low for high temps in that period. So even though we'll have some of the highest 500 hPa heights ever for this time of year overhead, we are unlikely to face the true wrath of that setup given the backdoor front that will sweep in and save the day (hopefully).

AVIATION /12Z FRIDAY THROUGH TUESDAY/

Isolated to widely scattered convection expected this afternoon.

Some mid-level cloud cover and a 15 kt LLJ on the VAD wind profile have worked to hinder fog development this morning. As the cloud cover shifts east, allowing for some clearing, there has been patchy MVFR/IFR fog/stratus on its western edge. This may allow for some brief restrictions but the return to VFR should be quick.

Expect light winds today out of the southwest from 5 to 10 kts. Isolated to widely scattered showers and thunderstorms are expected to develop by early to mid-afternoon across the forecast area. It is unclear whether or not coverage will be high enough to make impacts likely to the terminals this afternoon. Because of this we have elected to maintain VCSH at all sites to represent the low chance of showers and thunderstorms near or at the terminals. Winds will go calm or light and variable around sunset as convection tapers off.

EXTENDED AVIATION OUTLOOK...The highest rain chances will be Saturday afternoon with widespread thunderstorms expected. The probability for early morning fog/stratus increases this weekend and early next week.

CAE WATCHES/WARNINGS/ADVISORIES

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