textproduct: Columbia

WHAT HAS CHANGED

A bit higher confidence in heavy rainfall potential on Monday. Aviation discussion updated for 06z TAFs.

KEY MESSAGES

- 1. Scattered storms expected again this afternoon and Monday. Locally heavy rainfall and frequent lightning can be expected but damaging wind gusts will be possible in strongest storms each day, especially today.

- 2. One more hot/humid day today before cooler temperatures are expected during the first half of next week.

DISCUSSION

Key Message 1: Scattered storms expected again this afternoon and Monday. Locally heavy rainfall and frequent lightning can be expected but damaging wind gusts will be possible in strongest storms each day, especially today.

As of writing this, the slow moving frontal boundary is approaching northern NC/TN with the mid level low slowly drifting into the northern Tennessee Valley. A rather moist airmass remains in place with PWAT's above 1.70" and surface dewpoints in the low to mid 70s. Due to this, a couple showers and even a weak storm are moving into the western CSRA. This isolated activity could continue into the early morning hours, but mesoanalysis shows increased CIN over the FA, thus no strong storms are expected. If this activity persists into the early to mid morning hours, increased debris cloud cover may act to limit destabilization a bit for the main round of convection later in the day. At this time, this is not expected to be the case with little CAM support for this solution, but it is worth monitoring.

The aforementioned mid level low and surface front are expected to near the FA through the day today but ahead of these features another round of scattered convection is anticipated this afternoon into the evening. The environment is expected to be characterized by SBCAPE values between 2500-3000 J/kg, decent mixing that yields DCAPE values between 600-800 J/kg, PWAT's near 2", and TEI values between 25-28. Deep layer shear is expected to be marginal, but forecast soundings depict both this and cloud layer shear closer to 20-30 kts near the Pee Dee as the front nears. Overall, this yields a similar environment to yesterday, though with slightly more synoptic forcing and enhanced convergence along the front. Scattered strong to severe thunderstorms are expected by the early afternoon with convective temps between 90-92F and with the stronger forcing, more cell/cold pool interactions could bring a couple robust clusters across the FA as depicted in the latest HREF and HRRR runs. Overall, wet microbursts bringing a damaging wind risk will be the main hazard, but if an appreciably deep core is seen with favorable interactions, cannot rule out some sub-severe hail. Frequent lightning and heavy rainfall are also expected with this activity. It is worth noting that isolated instances of flash flooding will be possible with the increased coverage today as one location could have convection train and bringing efficient rainfall. At this time the HREF LPMM shows a couple spots of 2-4" could be possible, but confidence in the exact placement of these spots is low. Scattered showers and storms are expected to carry into the overnight with the front moving in, but the overall severe risk should diminish with instability becoming a bit more elevated. The whole CWA is outlined in SPC's Slight Risk (level 2 out of 5) for severe weather and is also outlined in WPC's Marginal Risk for excessive rainfall (level 1 out of 4), though parts of the Pee Dee and northern Midlands are in the Slight Risk (level 2 out of 4) for excessive rainfall.

On Monday, the front is expected to move through and the mid level low should drop into the region as PWAT's increase toward 2.10-2.20". 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 likely in this moist airmass. Both HREF and REFS probabilities for greater than 1" of QPF Monday approach 50-70% across the CWA and where training of convection occurs, isolated flash flooding will once again be possible, especially anywhere that sees heavy rainfall today.

Key Message 2: One more hot/humid day today before cooler temperatures are expected during the first half of next week.

There has not been a significant change in the temperature outlook for the coming days. With the expectation of little in way of morning showers/weak storms and thus debris cloudiness, robust heating is expected today with temperatures warming back into the mid 90s rather quickly. Dewpoints remaining in the low to mid 70s could bring heat indices back between 100-105F before convection cools things off a bit. Low level flow that becomes a bit more northerly to northeasterly Monday is expected to bring the first day of relief as temperatures likely stick to low to upper 80s, though things could trend a bit lower depending on how widespread showers and storms are. The north to south gradient could also end up being a bit tight depending where the frontal boundary stalls out. This cooler airmass is expected to stick around Tuesday, before warming to near normal on Wednesday as southwesterly low level flow moves back in. Heading into the second half of the week, upper height rises move back in with warming 850mb temperatures toward the NAEFS 90th percentile. This means a return to normal to above normal temperatures can be expected in this window with more diurnally driven showers/storms possible.

AVIATION /06Z SUNDAY THROUGH THURSDAY/

Monitoring Nocturnal Convection in the CSRA....

Shower and thunderstorm activity has increased across Georgia during the last hour with scattered showers and thunderstorms mostly passing north of the Augusta terminals. VCSH was added to DNL and if trends continue, it will be added to AGS and AKN. Shower activity should diminish before reaching CAE/CUB/OGB but trends will be monitored. In terms of the forecast, no significant changes were made to this update besides pushing back the PROB30 by a few hours as it appears convection will continue beyond 00z Monday. Widespread cumulus around 5kft should redevelop by 15z Sunday morning. Another round of strong thunderstorms is then expected on Sunday afternoon, so have included VCTS and a PROB30 for -TSRA at all terminals. Winds could again gust to 30-40 kts in the strongest thunderstorms. Outside of convective gusts though, surface winds should be less than 10 kts from the SW-NW.

EXTENDED AVIATION OUTLOOK...A good chance for afternoon showers and thunderstorms with associated restrictions is expected into early next week. There is potential for VSBY restrictions in fog Monday morning behind a frontal passage.

CAE WATCHES/WARNINGS/ADVISORIES

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