textproduct: Columbia

WHAT HAS CHANGED

Heat Advisory will be in effect from Noon to 8 PM Tuesday along/south of I-20. Conditional risk for severe weather exists Tuesday evening. Aviation discussion updated for 18z TAF.

KEY MESSAGES

- 1. Hot/humid conditions Tuesday with a Heat Advisory in effect from Noon to 8PM along and south of I-20 with heat indices up to 108F possible.

- 2. Isolated storms possible today before a cold front brings isolated to scattered chances Tuesday evening. Severe weather is possible with this activity. Drier conditions then move in for the late week.

DISCUSSION

- 1. Hot/humid conditions Tuesday with a Heat Advisory in effect from Noon to 8PM along and south of I-20 with heat indices up to 108F possible.

As southwesterly flow strengthens ahead of the incoming front Tuesday, temperatures are progged to reach the mid to upper 90s during the afternoon. A fairly moist air mass should remain in place as well with surface dewpoints sticking to the low to mid 70s. There is a bit of uncertainty in terms of how deep of mixing will occur and thus the mixing out of surface dewpoints. Model guidance indicates 925 mb dewpoints should remain near 68-72F, so I am leaning towards surface dewpoints will not mix out all too much. The aforementioned afternoon highs coupled with the moist airmass should bring heat indices between 105-108F across the FA tomorrow afternoon, highest along/south of the I-20 corridor. Due to this, a Heat Advisory will be in effect from Noon to 8 PM here. Be sure to take heat safety precautions tomorrow.

- 2. Isolated storms possible today before a cold front brings isolated to scattered chances Tuesday evening. Severe weather is possible with this activity. Drier conditions then move in for the late week.

Isolated convection is seen developing across the area this afternoon as MLCAPE values approach 2000-2500 J/kg with fairly weak deep layer shear. The slightly "drier" airmass and deeper mixing have brought DCAPE values toward 800-1000 J/kg however, so a stronger storm with strong downburst winds cannot be ruled out over the coming hours before mostly dry conditions set up overnight.

The main change in the outlook comes Tuesday with a slightly greater risk for severe weather, especially toward the Pee Dee region. Guidance is insistent that a shortwave currently moving over the apex of the large ridge centered a bit west of the Northern Plains will aid in amplifying troughing over the eastern CONUS. This should lead to a closed mid-level low developing over the Northeast during the day Tuesday with the overall troughing pattern becoming more amplified. This could bring enhanced mid-level flow and deep layer shear down toward the FA as shown in the 12z HREF and REFS. The advertised frontal boundary should begin nearing the Pee Dee toward late Tuesday evening, but ahead of this, a broken line of convection is shown developing across southern VA and north central NC during the afternoon in CAMs. This area of convection is expected to move in by the late afternoon to early evening hours from the northwest, but the potential severe risk is a bit conditional. Considerable uncertainty remains in the overall organization of convection across CAMs, with runs like the HRRR, and HRW's being a bit more isolated to scattered while the 12z NAM3km, previous RRFS runs, and the experimental RRFS-MPAS favor a quasai-linear MCS moving through the Pee Dee and possibly down into the central Midlands. With timing favoring the evening hours, waning surface based instability should limit a greater severe risk, but the potential to tap into ~1500 J/kg of MLCAPE exists as stronger kinematics move into place.

Overall, This set up brings the conditional risk for damaging cold pool driven wind gusts, and a non-zero weak tornado risk. This non- zero tornado risk mainly stems from a developing LLJ into the evening with modeled soundings indicating around 100-150 m^2/s^2 of 0-1km SRH developing, especially toward the Pee Dee where effective shear values are greatest as well (around 40-45 kts). As mentioned above, generous uncertainty remains in storm organization late Tuesday afternoon into the evening remains and any shift timing wise could bring changes to the overall thermodynamic/kinematic balance so confidence in realizing these risks is rather low, especially with southward extent. Be sure to stay tuned to future forecasts as better consensus is likely reached.

Ensemble guidance then is in good agreement that the front will push through the FA on Wednesday with much drier air moving in during the late week. This is expected to possibly drive PWATs under 1" by Thursday and into Friday as shown in deterministic global models. Moisture should gradually return during the weekend with possible rain chances.

AVIATION /18Z MONDAY THROUGH SATURDAY/

Outside of morning mvfr restrictions, mainly vfr expected to occur.

Weak trough still remains across the region again today. Isolated shower or storms will remain possible through the afternoon, but limited coverage will mean potential amendments as activity nears any taf locations. Brief mvfr restrictions could occur in any rain activity. Outside of that this afternoon and into the overnight hours, There will be some scattered to broken mid-level vfr cloudiness. Main restrictions are expected towards sunrise again Tuesday morning, with mvfr/ifr conditions possible as morning fog forms across the area. Winds generally light and variable, favoring a westerly direction on Tuesday.

EXTENDED AVIATION OUTLOOK...Rain chances increase mid-week with restrictions possible as a front pushes into the Southeast. Drier air moves in for the second half of the week.

CAE WATCHES/WARNINGS/ADVISORIES

SC...Heat Advisory from noon to 8 PM EDT Tuesday for SCZ016-022- 027>031-035-037-038-041-135>137. GA...Heat Advisory from noon to 8 PM EDT Tuesday for GAZ063>065-077.