textproduct: Columbia

WHAT HAS CHANGED

Tweaks to Friday-Saturday forecast discussion and 18Z Aviation updates.

KEY MESSAGES

- 1. Above normal temperatures last into next week with increasing chances for showers and storms Today-Saturday.

DISCUSSION

KEY MESSAGE 1: Above normal temperatures last into next week with increasing chances for showers and storms Today-Saturday.

A slow moving trough in the central CONUS 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 the modest forcing from the approaching shortwave 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; 12z HRRR-REFS-HREF suites support more robust convection into the Midlands Friday, but likely are too slow for initiation. Much the same is expected for Saturday but the axis will shift more into the Upstate and western Midlands with better forcing and moisture convergence. 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. So this backdoor front will likely help stem the tide of the robust 500mb heights and keep temps from approaching records.

AVIATION /18Z FRIDAY THROUGH TUESDAY/

Isolated to scattered convection expected this afternoon. Brief restrictions possible again early Saturday.

VFR conditions are seen early this afternoon with light southerly to southwesterly winds. As a cumulus deck continues to grow, scattered convection is seen developing in portions of the CSRA and southeastern Midlands. This activity is expected to continue through the afternoon, possibly expanding northward. Due to this, have a mix of TEMPO or PROB30 groups for restrictions due to convection with the highest probabilities currently near OGB/AGS/DNL where storms are already developing. This activity is expected to wind down during the evening with lingering debris cloudiness likely as winds become light and variable. There is generous spread across model guidance regarding the development of fog/stratus tonight, but with plentiful low level moisture in place, and recent rainfall, current thinking is at least patchy vsby/cig restrictions could be possible early Saturday morning, with greater chances near OGB. As any stratus lifts through the morning, MVFR ceilings could be seen before giving way to VFR cumulus near the end of the TAF period. Winds should pick back up out of the south- southwest, remaining light by the late morning. Another round of convection will be possible after this TAF period.

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.