textproduct: Columbia

WHAT HAS CHANGED

Updated aviation discussion for 12z TAFs.

KEY MESSAGES

- 1. Rounds of rain expected through mid-week. A few strong to severe thunderstorms are possible this 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 expected through mid-week. A few strong to severe thunderstorms are possible this afternoon but confidence is low.

With upper ridging flattening across the region, a series of shortwave troughs will roll over the ridge and into the forecast area through Thursday. Rain chances will ramp up quickly from west to east during the next few hours as lingering showers and thunderstorms currently in Alabama move into the FA. While convection is expected to weaken by the time it arrives, much like yesterday there could be a few leftover thunderstorms. Conditions are not favorable for strong to severe thunderstorms in our forecast area this morning but trends will be monitored. 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.

Looking ahead to this afternoon, there is a low threat of severe weather with the highest probability located in the Pee Dee and Catawba regions. As the cold front approaches the forecast area from the north, additional convection develop ahead of the boundary. The SPC Day 1 Outlook maintains a Marginal (1/5) risk for severe weather both north and south of our CWA. The severe threat in our FA will largely hinge on if we can clear out enough behind the morning activity to produce sufficient instability and PoPs may need to increase should we receive more sunshine than expected. If destabilization occurs, there will be potential for organized thunderstorms with the primary hazards of large hail and damaging wind gusts, though a tornado or two cannot be ruled out, especially near the North Carolina border.

Another round of rain is expected to move in late tonight and into Thursday morning. Much like previous nights, the evolution of this convection to our west will dictate the thunderstorm risk (which should be sub-severe), how much rain the FA receives, and which areas will get another chance for measurable precipitation. Overall, these three batches of rain will not end the ongoing drought but any rainfall will assist.

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 /10Z WEDNESDAY THROUGH SUNDAY/

Rain is beginning to enter from the west this morning with cig/vsby restrictions expected before VFR conditions return this afternoon. Another round of rain is expected early Thursday morning where more restrictions will be possible.

Radar shows a batch of rain entering near AGS/DNL this morning and is expected to continue eastward, though it may scatter out a bit more as model guidance has done poorly with handling this over the last couple hours. Southwesterly to west-southwesterly winds have picked up this morning toward 3-6 kts and will continue to increase into the afternoon, near 6-10 kts with gusts to 15-18 kts possible as a front begins to work through the region. Obs show MVFR to IFR ceilings just west of the CSRA and into the Upstate, thus as rain continues to build in, these restrictions are expected to as well, where periods of vsby restrictions will be possible in any heavier rain. Much of this rain is expected to move out between 15-18z and any stratus should mix out, giving way to SCT to BKN mid to high level clouds the remainder of the day. There is an outside chance a couple thunderstorms form early this evening, but confidence in this is low and the best chance looks to keep north of the TAF sites. Tonight, light westerly winds are expected and toward the end of the TAF period, another round of rain/storms are expected to near the TAF sites from the west, where more cig/vsby restrictions will be possible. EXTENDED AVIATION OUTLOOK...Periods of restrictions are possible late this week into the weekend with more rain chances, especially Friday night into Saturday.

CAE WATCHES/WARNINGS/ADVISORIES

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