textproduct: Columbia

WHAT HAS CHANGED

Aviation discussion updated for 12z TAFs.

KEY MESSAGES

- 1. Hot and humid today with isolated chance for thunderstorms this afternoon/evening.

- 2. A front nears the area late tomorrow and Thursday, bringing scattered to widespread rain/storm chances, mainly Thursday. Severe weather and heavy rainfall could be possible with this. Active weather persist into the late week.

DISCUSSION

Key Message 1: Hot and humid today with isolated chance for thunderstorms this afternoon/evening.

Slightly "drier" air is expected to advect into the area today. This area of lower PWAT's (1.60-1.80") can be seen in the Florida Peninsula and should advect into the region due to southerly/southwesterly low-level flow on the eastern periphery of what is now TS Bertha. Little in way of forcing for convection is expected today outside of potentially reaching convective temperatures between 95-97F. Due to this, any convection this afternoon is expected to be fairly isolated and our typical summertime pulse variety. As always with these pulse storms, downpours and locally strong wind gusts could be possible. Despite the slightly drier air, dewpoints should still be in the upper 60s to low 70s with afternoon highs in the mid to upper 90s. This should bring another day with heat indices below advisory criteria, but still between 100-105F.

Key Message 2: A front nears the area late tomorrow and Thursday, bringing scattered to widespread rain/storm chances, mainly Thursday. Severe weather and heavy rainfall could be possible with this. Active weather persist into the late week.

The overall synoptic pattern and outlook has not changed significantly but as high-res ensembles reach toward Wednesday, a few more details are starting to get sorted out. The main change seen in the 00z HREF and REFS is slightly later timing of when the front nears the FA along with upper support from the trough shifting into the eastern US. This has led to Wednesday trending slightly warmer with isolated to widely scattered convection possible by the late afternoon before more scattered to widespread chances move in overnight through Thursday. AI/ML guidance continues to hint at the potential for stronger convection in this window, which is reasonable considering deep layer shear will be increasing to near 30 kts with a 30-35 kt LLJ developing late Wednesday. The main caveat here is the later timing allows less overlap of forcing with waning instability, so if this later trend continues, the severe risk could continue to decrease. As the front stalls out in the CWA during the day Thursday, another chance for stronger convection could materialize. Outside of this, the main hazard seems to be the heavy rainfall potential starting late Wednesday, continuing through the day Thursday. Skinny CAPE profiles overlapping with the aforementioned LLJ and PWAT's over 2" should aid in creating efficient rain rates and possible training of convection along the frontal boundary. NBM probabilities for greater than 1" of QPF through Thursday night have risen to 50-70% along/east of the I-26 corridor. These probabilities are likely a bit skewed a bit due to the more aggressive ECMWF solution, but the environment supports this heavy rain setup and the EC EFI shows values of 0.7-0.8 with a Shift- of-Tails of 1-2 over the area, further supporting the potential for anomalous rainfall.

The frontal boundary is shown in global models residing in the FA most of Friday as another shortwave pushes in, likely bringing another day with scattered to widespread rain chances. Heading into the weekend, there is a bit more uncertainty in the exact progression of the front, but a troughing pattern is expected to continue with a series of shortwaves training into the FA from the northwest. Due to this, an active/wet pattern should persist at least into the start of the weekend.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

Brief MVFR ceilings possible this morning but otherwise VFR Conditions Expected to Continue.

Satellite observations early this morning show patchy low clouds, generally between 1500 and 2500 feet. These may cause brief MVFR ceiling restrictions this morning with VFR conditions expected to persist by mid to late morning. Winds remain out of the south with gusts increasing between 15 to 20 knots late morning into the afternoon with cumulus developing around 6kft. Once again, convection is expected to be limited today with highest potential near 00z. With uncertainty in impacts to terminals, have left out the mention of tsra with this issuance. Gusts subside with cumulus dissipating tonight.

EXTENDED AVIATION OUTLOOK...Potential for restrictions from showers and thunderstorms continues with the threat increasing for the mid to late week period.

CAE WATCHES/WARNINGS/ADVISORIES

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