textproduct: Columbia

WHAT HAS CHANGED

Updated mesoanalysis for storms expected this afternoon. Adjusted wording of key messages. Aviation discussion updated for 18z TAFs.

KEY MESSAGES

- 1. Scattered storms expected again this afternoon and evening with damaging wind gusts and heavy rain expected. Lingering moisture leading to scattered to widespread afternoon storms Monday through Wednesday.

DISCUSSION

Key Message 1: Scattered storms expected again this afternoon and evening with damaging wind gusts and heavy rain expected. Lingering moisture leading to scattered to widespread afternoon storms Monday through Wednesday.

Early this afternoon, convection has taken a bit longer to get going compared to yesterday, mainly due to the increased cloudiness and a bit longer time for us to reach convective temperatures today. As most sites are starting to rise into the low 90s by 1pm, convective temperatures are becoming reached and as a result, beginning to see some agitation to the clouds and some convection developing in the area. This activity is expected to continue to grow through the afternoon and into this evening as a robust shortwave is currently moving into the Tennessee Valley with a surface front moving into southern NC. This provide additional forcing with RAP forecast soundings indicating strong destabilization today with sbCAPE around 3000 J/kg for much of the forecast area, similar to the last couple of days. While PWATs are currently around 2 inches, especially across the northern area, a layer of mid layer dry air is visible on water vapor satellite imagery from North Georgia shifting into the area, which will likely lead to a locally enhanced area favorable for strong to severe downbursts leading to damaging wind gusts. Storms may become a bit more organized this afternoon as well with a bit stronger deep layer shear, around 20 knots, which support multicell clusters developing and maintaining through the forecast area. While storms should exhibit sufficient movement to prevent widespread flooding, will need to monitor training storms with areas generally north of I-20 (and Augusta and Columbia metros) more susceptible to flooding due both to the soil type and rainfall received the last couple days.

On Monday, the front is expected to move through and the mid level low should drop into the region as hires guidance indicates PWAT's approach 2.2 inches. Low level flow becomes increasingly northerly to northeasterly, keeping temperatures a bit cooler and increased cloud cover is expected to limit destabilization. This brings a lower risk for severe weather with more marginal thermodynamics, but a couple strong to marginally severe storms cannot be ruled out during the afternoon/evening as deep layer shear is slightly increased. The bigger risk Monday may be the heavy rainfall risk as scattered to widespread showers and storms move through the area during the day with efficient rain rates, similar to slightly higher than Sunday in this moist airmass. The highest concern will continue to be in areas highlighted today along with areas that received additional significant rainfall today.

Shower and thunderstorms will likely continue Tuesday and Wednesday and ensemble means have been slower to bring in a drier air mass with PWATs generally greater than a standard deviation above normal for at least portions of the area through Wednesday, although drier air likely starts to sneak into the northern area on Wednesday. Cooler air mass generally expected to continue early this week with a recovery expected to normal or slightly above normal temperatures for the second half of the week as the upper ridge centered over the central CONUS begins to shift eastward.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

VFR conditions expected for most of the period, with the exception of convection this afternoon and potentially ceilings later on tonight.

A more organized and robust forcing mechanism is working towards the area today. A trough will force a weak surface low on the Lee Side of the Appalachians this afternoon, helping to focus convective development across the Carolinas. The environment is favorable for numerous, strong downbursts again. Given the expected coverage of showers/storms, have kept VCTS at all sites through this evening & bumped up the wind at each site in the prob30s. Given the environment in place, it would not be surprising to see 35-45 knot gusts at the sites in stronger storms this afternoon. Expecting the convection to persist into the evening as the surface front approaches and pushes through the forecast area. Northeasterly flow behind this, combined with very rich low-level moisture, should result in MVFR ceilings developing and persisting through the end of the period. The LAMP is delaying the cigs until 11z-13z, with the NBM a bit more aggressive (~06z). Thinking that the latter is probably a bit more realistic as the convection today will likely result in the surface front sinking southward a bit quicker than models can anticipate. So bring MVFR cigs into the sites between 08z and 09z - but it could be earlier or a bit later.

EXTENDED AVIATION OUTLOOK...A good chance for afternoon showers and thunderstorms with associated restrictions is expected into early next week.

CAE WATCHES/WARNINGS/ADVISORIES

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