textproduct: Columbia

WHAT HAS CHANGED

Continued high confidence in well above normal temperatures late in the week and into this weekend. Rain chances increase into the weekend. Aviation discussion updated for 18z TAFs.

KEY MESSAGES

- 1. Areas of fog expected tonight where patchy dense fog will be possible.

- 2. Well above normal temperatures the remainder of the week with rain chances possible late in the week and this weekend.

DISCUSSION

KEY MESSAGE #1: Areas of fog expected tonight where patchy dense fog will be possible.

High pressure will continue to shift away from the region through the day and tonight with skies gradually clearing, though some cirrus may linger overnight. Wind profiles tonight remain weak with near surface winds becoming nearly calm in most locations. Solid radiational cooling conditions should allow temperatures to drop into the upper 40s to lower 50s with crossover temperatures in the mid to upper 40s. This is expected to lead to areas of fog across the FA tonight and into Wednesday morning as the boundary layer likely decouples where the latest REFS probabilities for visibilities less than 1/2 mile are now between 40-60%, highest south of the I-20 corridor. The deterministic HRRR and NBM also are fairly aggressive with showing a large area with visibilities under 1/2 mile across the Midlands. There could be patchy dense fog mainly south of I-20 as well, thus the need for a Dense Fog Advisory will continue to be assessed this evening and tonight.

KEY MESSAGE #2: Well above normal temperatures the remainder of the week with rain chances possible late in the week and this weekend.

There has not been significant change across ensemble or deterministic guidance in the synoptic pattern for the remainder of the week and into this weekend. There is solid agreement that strong upper ridging will begin to build into the region with 500mb heights reaching around 1-1.5 std dev above normal before nearing 2 std dev above normal Thursday and Friday. This, along with warming 850mb temperatures and persistent southerly to southwesterly flow should bring temperatures well above normal, especially from Thursday into this weekend. Temperatures could reach up to 15-18 degrees above normal through this period before the ridge slowly flattens out over the weekend and into the early week as a couple weak shortwaves enter the prevailing flow. There is a bit more uncertainty in temperatures early in the week, but IQR ranges show they likely will remain above normal.

The upper ridge should aid in suppressing any diurnal convection chances through at least Friday despite increasing moisture. By Friday the ridge may weaken enough for isolated showers or storms to form as PWAT's reach above 1". This trend may continue into the weekend as the ridge flattens, bringing increasing PoP's during the afternoon and evening hours. By the early week, a series of weak shortwaves may provided additional forcing for increased shower/storm chances as deep moisture likely remains in place.

AVIATION /18Z TUESDAY THROUGH SUNDAY/

MVFR ceilings give way to VFR ceilings this afternoon. Visibility restrictions expected late tonight/early Wednesday.

Satellite imagery and observations continue to show widespread MVFR ceilings across the forecast area. However, clearing is being noted in the northeastern portion of South Carolina. Expect this clearing to expand westward through the afternoon, allowing ceilings to improve over the next few hours. There is some uncertainty in when the terminals will see the improvement, though. All 5 TAF sites should be VFR by about 21z, potentially sooner. Northeast winds shift more easterly this afternoon before becoming mostly calm overnight. The calm winds combined with mainly clear skies and residual low-level moisture tonight brings increased confidence in fog development at the terminals, with potential for visibilities of 1/2 SM or less at times around daybreak.

EXTENDED AVIATION OUTLOOK...There is potential for morning stratus or fog into the latter half of the week along with increased shower chances for the weekend.

CAE WATCHES/WARNINGS/ADVISORIES

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