textproduct: Columbia

WHAT HAS CHANGED

Heat Advisory issued along and south of the I-20 corridor today. Convective coverage this afternoon has trended a bit lower. Aviation discussion updated for 06z TAFs.

KEY MESSAGES

- 1. Heat Advisory in effect from 12 PM to 8 PM along and south of the I-20 corridor as heat indices reach between 105-108F. Isolated to scattered convection expected with a couple strong to severe storms possible this afternoon/evening.

- 2. More thunderstorm chances Sunday into Monday with possible severe thunderstorms. Another chance for strong convection possible during the midweek.

DISCUSSION

Key Message 1: Heat Advisory in effect from 12 PM to 8 PM along and south of the I-20 corridor as heat indices reach between 105-108F. Isolated to scattered convection expected with a couple strong to severe storms possible this afternoon/evening.

The main change today is a Heat Advisory will be in effect along and south of the I-20 corridor from Noon to 8 PM. This comes as recent trends have been toward keeping surface dewpoints in the low to mid 70s through the day today with minimal mixing out. This is mainly due to 925mb dewpoints remaining near 70-72F today. Temperatures should once again reach the mid to upper 90s and thus heat indices are expected to reach as high as 108F in the Advisory area. The 00z suite of CAMs and the 00z HREF depict fairly similar convective coverage as today, giving increased confidence in realizing Advisory level heat indices. Be sure to take heat safety precautions today with any outdoor activity!

As mentioned above, convective coverage this afternoon/evening has trend a bit similar to that seen yesterday. This comes as BUFKIT soundings indicate lingering mid-level capping should hold on into the early afternoon before a combination of increased surface troughing and the sea breeze initiate deeper convection late in the afternoon and into the evening hours. Upper support remains very meager with effective shear values under 10 kts, but strong instability is still progged to develop (SBCAPE near 3000 J/kg) in this very moist environment. A couple strong to severe storms will be possible as robust DCAPE values between 1000-1300 J/kg, 3km CAPE near 100 J/kg, and TEI values between 25-30 bring an increased risk for strong downbursts and the associated damaging wind risk. Due to this, portions of the FA are in SPC's Marginal Risk (level 1 out of 5) for severe weather today.

Key Message 2: More thunderstorm chances Sunday into Monday with possible severe thunderstorms. Another chance for strong convection possible during the midweek.

As has been discussed, a deepening shortwave is progged to move into the Mid-Atlantic through the day Sunday, dragging a surface front that could near the Pee Dee Sunday night. Enhanced moisture advection is shown across guidance ahead of these features with PWAT's reaching above 2", partly thanks to Gulf moisture being transported northward on the eastern periphery of a developing weak tropical disturbance in the northeastern Gulf. Overall, the environment is not expected to be all that different from the last couple of days, favoring a damaging wind risk from precip-loaded downdrafts. The main difference is marginal upper support should bring increased coverage and effective shear values near 10-15 kts, especially toward the Pee Dee, which could aid in better organization of a few clusters. This has resulted in most of the FA remaining in a Marginal Risk for severe weather, but a Slight Risk (level 2 out of 5) still scrapes the Pee Dee with the greater shear here. The frontal boundary is expected to remain near the Pee Dee into Monday with weak shortwave energy passing through the region, bringing another day with increased afternoon convective coverage and the chance for a couple strong to marginally severe storms.

The EC Ensemble and Google DeepMind have trended more towards the weak tropical disturbance meandering through the northeastern Gulf early in the week before slowly drifting westward into the mid week. This should still allow deep moisture to advect into the region from the south, but both ensemble and deterministic guidance have displayed increased confidence that an even sharper shortwave should dig into the eastern CONUS during the mid-week, possibly dragging another frontal boundary near the FA. Enhanced kinematics coupled with seasonable to strong instability could bring another chance for stronger convection during the midweek as highlighted in CSU/CIPS/NCAR Machine Learning and AI guidance. Timing difference still need to be sorted out across deterministic guidance, but the pattern seems favorable for potential severe weather again.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

VFR conditions expected for much of the period with brief restrictions possible early morning and in storms.

VFR conditions are in place at all terminals as convection has diminished across the area. While VFR conditions are generally expected to continue, increased low level moisture may lead to brief restrictions, generally at OGB and AGS, although models are not overwhelmingly pointing to this solution. Any restrictions should dissipate shortly after sunrise with VFR conditions as scattered cumulus around 5kft develop. Winds increasing out of the south, generally between 5 to 10 knots. Scattered thunderstorms develop late this afternoon into evening so have included a prob30 group to account for increasing storm coverage.

EXTENDED AVIATION OUTLOOK...Potential for restrictions from showers and thunderstorms continues into next week.

CAE WATCHES/WARNINGS/ADVISORIES

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