textproduct: Columbia

WHAT HAS CHANGED

Adjusted the key messages to highlight the higher showers and storm coverage into early next week. Aviation discussion updated for 18z TAFs.

KEY MESSAGES

- 1. Scattered storms expected Friday and Saturday afternoons with widespread showers and storms Sunday and Monday associated with a front.

- 2. Hot, humid and breezy conditions continue with cooler conditions associated with the front late weekend into next week.

DISCUSSION

Key Message 1: Scattered storms expected Friday and Saturday afternoons with widespread showers and storms Sunday and Monday associated with a front.

Today, latest RAP indicates a highly unstable environment with MLCAPE already exceeding 2000 J/kg over the entire forecast area. Convergence along a Lee side trough has already allowed storms to develop in the western portion of the forecast area with storms developing in the south as well. Coverage will continue to increase into the afternoon and while low level shear remains lacking, strengthening winds in the upper levels will likely allow for a bit stronger organization through the afternoon. SPC has continued a marginal risk for the entire area today for a damaging wind threat with very strong low level lapse rates and DCAPE nearing approaching 1000 J/kg, creating a favorable strong to potentially severe downburst environment. Freezing levels remain exceptionally high, even for this time of year limiting any hail threat. A flattening 500mb trough tonight may be able to sustain some convection into the evening and overnight but will a loss of daytime heating, coverage will continue to decrease into tonight.

Tomorrow scattered storms expected once again with coverage similar or slightly higher with a bit stronger upper level support as the weak ridging that we remained somewhat under the influence shifts to the east and weak shortwaves move through a more zonal flow. In addition, PWATs expected to increase with SPC HREF mean showing values greater than 2 inches over most of the forecast area. Environment may be slightly weaker to support severe storms based on HiRes forecast soundings with weaker cloud layer shear and not quite as unstable an environment but we remain in a marginal risk for tomorrow with the potential for a few storms to produce strong to marginally severe wind gusts.

As a front approaches the area Sunday into Monday, blended guidance supports widespread showers and storms near the front each day, favoring the afternoons where moderate instability will develop. While widespread severe weather is not expected, especially Monday where instability may struggle to develop, a few storms could approach severe limits. Storms will likely have efficient rain rates, although flow will be sufficient enough to cause major flooding concerns. It will be worth monitoring potential training with the flow generally parallel to the front. Ensemble means favor drier air pushing into the area by the middle of next week.

Key Message 2: Hot, humid and breezy conditions continue with cooler conditions associated with the front late weekend into next week.

Hot, humid and breezy conditions continue with the hottest days of the period expected to be today and tomorrow. The increased convective coverage both today and tomorrow may limit the extent of our high temperature and heat index but continue to expect triple digit heat indices for today and tomorrow with highs in the mid to upper 90s and dew points remaining in the 70s. Blended guidance IQR continues to favor lower temperatures associated with the approaching front and widespread clouds and convection each day. Given the recent hot weather, the NBM takes that into account and will likely have a warm bias. So, I would not be surprised if we end up toward the cooler end of the IQR. This air mass will be very humid, with blended dew points continuing in the low to mid 70s.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

VFR conditions expected through the TAF period except for diurnal convection which may result in temporary restrictions.

Convection has begun developing across the forecast area as temps have warmed into the low to mid 90s across the area. Scattered to broken cloud cover is noted especially at the northern sites. Showers and thunderstorms are expected to develop across the area as the afternoon progresses, first at the Columbia sites and then towards the Augusta and Orangeburg sites. Thunderstorms may be strong, leading to primarily brief visibility restrictions under them. The strongest storms may bring wind gusts of 30-40 knots as well. Thunderstorm activity is likely to persist into the evening before waning overnight tonight, with debris cloudiness hanging around through early morning. If AGS and OGB get any substantial rain today, expecting that shallow ground fog will be a problem early on tomorrow morning there. As we get into the day tomorrow, clouds should develop quickly by late morning with showers and thunderstorms redeveloping by the end of this period. Winds will likely be breezy out of the southwest while the sun is up, so expect gusts to 20 knots through 00z this evening, with 4-8 knots expected overnight, and the gustiness returning after 15z Saturday.

EXTENDED AVIATION OUTLOOK...Increasing chances for afternoon storms this weekend and into early next week.

CAE WATCHES/WARNINGS/ADVISORIES

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