textproduct: Columbia

WHAT HAS CHANGED

Isolated severe storm still possible this evening in the northern Midlands, but probabilities have lowered. Aviation discussion updated for 00z TAFs.

KEY MESSAGES

- 1. Isolated stronger storm possible mainly north of the I-20 corridor.

- 2. Isolated to scattered convection possible Monday and Tuesday, with greater coverage of storms expected mid to late week.

DISCUSSION

Key Message 1: Isolated stronger storm possible mainly north of the I-20 corridor.

Convective coverage has continued to struggle despite the impinging shortwave and increased surface troughing/convergence in the northern Midlands. WV imagery reveals the pocket of drier mid-level air remains in place, especially south of I-20, with a bit more moisture north of here. A recent KCHS ACARS sounding just before 22z revealed substantial dry air in the ~750-550mb layer and when looking at a 0hr BUFKIT HRRR sounding from 22z near here, it revealed dewpoints in this column a couple degrees moisture than that seen in the ACARS sounding. It appears some model guidance has underplayed the role/strength of this dry air which has likely kept meaningful vertical growth at bay this afternoon and even now. With that said, enhanced moisture convergence is seen in an area around Newberry- Fairfield-Lancaster-Chesterfield Counties with an outflow boundary approaching from the Upstate. MLCAPE values near 2500 J/kg with around 20-30 kts of cloud layer shear maintains a favorable environment if a storm/cluster can establish itself for an isolated damaging wind threat in the coming 1-3 hours. This lower end threat in the aforementioned area is also supported in the 21-23z WoFS runs. Overall, the severe threat is diminishing but cannot be ruled out with some new convection attempting to get going near this sinking outflow. After this, mostly dry conditions are expected overnight tonight.

Key Message 2: Isolated to scattered convection possible Monday and Tuesday, with greater coverage of storms expected mid to late week.

Deeper moisture from TD Two appears to remain south of the area on Monday, however weak short wave energy aloft and a surface trough positioned just north of the area could be a trigger for isolated to scattered convection in the afternoon and evening with precipitable water values still up around 2 inches. Coverage should be greatest across northern portions of the forecast area where synoptic forcing is a bit stronger. Moderate to strong instability will still be in place, with an environment not much different than today, so there will be a threat of isolated strong to severe thunderstorms.

The weak surface trough appears to retreat farther northward on Tuesday, with the bulk of any short wave energy associated with an upper level trough remaining north of the area as well. This should limit synoptic forcing across the area, with mainly isolated diurnal convection expected.

Fairly good support from the ensembles and global models in the pattern becoming more active mid to late week as an upper level trough digs across the eastern US, with a series of short waves crossing the area within the northwest flow aloft. Meanwhile at the surface, while there are some timing differences in the models, a cold front drops into the area sometime late Wednesday into Thursday, possibly lingering nearby into the weekend. Deep moisture, with precipitable water values upwards of 2.00-2.25 inches based on the blend, along with synoptic lift will support higher chances for showers and thunderstorms. There is also the potential for strong to severe thunderstorms during this time period.

AVIATION /00Z MONDAY THROUGH FRIDAY/

VFR Conditions Expected to Continue Tonight Outside of a Passing Shower....

Shower activity has been limited near the terminals today. Evening radar imagery shows one light shower passing between AGS/DNL and AIK but it appears to be dissipating. Removed any mention of restrictions with this update and will amend if anything manages to develop significantly near the terminals. Winds should continue to diminish this evening. Expect winds to ramp back up again on Monday with typical SCT cumulus development. Rain chances should be low again tomorrow afternoon and evening so did not add any chances to the TAFs with this update.

EXTENDED AVIATION OUTLOOK...Potential for restrictions from showers and thunderstorms continues with the threat increasing later in the week.

CAE WATCHES/WARNINGS/ADVISORIES

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