textproduct: Columbia

WHAT HAS CHANGED

Updated aviation discussion for 00z TAFs.

KEY MESSAGES

- 1. Rounds of rain through mid-week, severe thunderstorms are possible Wednesday afternoon but confidence is low.

- 2. Confidence increasing in moderate rainfall for portions of the forecast area Friday night and Saturday.

DISCUSSION

Key Message 1: Rounds of rain through mid-week, severe thunderstorms are possible Wednesday afternoon but confidence is low.

With upper ridging flattening over the Southeast we will see several rounds of shortwave troughs roll over the ridge and into the forecast area through Thursday. A cold front will also work across the Southeast Wednesday through Thursday providing some enhanced convergence for convection upstream. The timing of the convection that works into the forecast area each day should be similar to Tuesday morning with decaying thunderstorms from the previous day persisting due to the enhancement from shortwave energy.

The most active day for our area will be Wednesday when deeper moisture will be over the area. Expect widespread showers to cross through the forecast area Wednesday morning. CAMs indicate the weakening convection should limit the extent of thunder but we should see at least isolated to scattered thunderstorms in the morning with MUCAPE values below 500 J/kg. No severe weather is expected through the morning. Total rain amounts will largely depend on how much of the deeper convection can hold together but in general we should see around a quarter of an inch of rain with locally higher amounts in taller cells.

Wednesday afternoon, there is a low threat of severe weather with the main threat located in the Pee Dee and Catawba. As the cold front approaches the forecast area from the north, we may see additional convection develop ahead of the boundary. There is a question of whether we will see the air mass destabilize as models show, but if so the 35 to 45 kts of deep layer (0-6km) shear should allow for organized thunderstorms to develop. Mean sbCAPE values from the HREF and REFS are generally around 1000 J/kg in the Pee Dee and Catawba. Low level SRH (0-1km) values also approach 100 m2/s2 with STP at 0.8 to 1.0 in these areas. Ultimately the threat of severe weather will largely depend on how quickly/if we break out of the cloud cover following showers in the morning. If destabilization occurs there will be potential for organized thunderstorms with hazards of hail and damaging winds. We also cannot rule out a tornado threat.

Key Message 2: Confidence increasing in moderate rainfall for portions of the forecast area Friday night and Saturday.

Ensembles continue to favor broad troughing over the eastern half of the US from late week and into the weekend. NAEFS IVT percentiles have increased to 99.5 of climatology, with highest values in the southern portion of the forecast area. This indicates the potential for a period of moderate to heavy rainfall from late Friday through Saturday. Models are starting to come into better agreement with the timing of the rainfall and track of the low across the Southeast. That has led to a jump in probabilities for moderate rainfall. The 25th percentile from the NBM is now up to 0.25 to 0.5 inches for areas south of I-20 with means closer to 1 to 1.5 inches area wide (Friday night through Saturday totals).

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

Generally VFR conditions into tonight. Another round of restrictions possible early Wednesday as rain pushes into the area.

The forecast is pretty much on track at area sites. There remains some pesky stratus around the Augusta sites but expecting that will probably begin diminishing. High clouds will continue to push across the area as widespread convection pushes eastward out of the deep south. Winds should stay up overnight but tend to be pretty variable in terms of direction, with speed in the 4-6 knot range. The convection that is currently to our west is forecast by guidance to weaken over the next several hours as it pushes eastward. While CAMs have this area diminishing in coverage, they have been pretty bad handling the convection over the last 24 to 36 hours (see the rain holding together this morning). It is hard to trust that this convection will actually diminish so will need to keep a close eye on it over the next 2-4 hours as it pushes eastward and may adjust the rain timing up. Either way, the rain looks to approach the area after 08z with stratus developing along with it as well. HRRR and LAMP guidance suggests that IFR cigs will develop along with MVFR cigs as well, lasting through at least mid-morning and possibly after the rain exits the area. Winds should shift to westerly after the rain, with some gusty winds possible as we start mixing a bit tomorrow afternoon. Overall, an impactful period of TAFs is expected.

EXTENDED AVIATION OUTLOOK...Periods of restrictions are possible late this week into the weekend with more rain chances.

CAE WATCHES/WARNINGS/ADVISORIES

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