textproduct: Columbia

WHAT HAS CHANGED

Fog development is expected tonight, with spots of dense fog possible mainly south of I-20. Aviation discussion updated for 18z TAFs.

KEY MESSAGES

- 1. Another round of fog and stratus is expected tonight and into Thursday morning where spots of dense fog will be possible.

- 2. High confidence in well above normal temperatures the remainder of the week and into early next week with increasing diurnal rain chances starting this weekend.

DISCUSSION

KEY MESSAGE #1: Another round of fog and stratus is expected tonight and into Thursday morning where spots of dense fog will be possible.

Another round of fog and/or stratus is expected tonight as modest low level moisture remains in place across the region. The latest round of guidance indicates fairly high probabilities for visibilities less than 1/2 mile tonight with both the HREF and REFS between 50-70% for much of the FA, especially south of I-20. The SREF shows similar probabilities as well. The deterministic HRRR remains fairly aggressive, though the deterministic NBM has backed off some and favors a bit more stratus. The complicating factor is a 20-25 kt LLJ is seen developing in BUFKIT soundings and this may keep surface winds up enough to limit the fog threat and rather lead to a bit more stratus. Either way, a mix of fog and stratus is likely tonight and with moderate to high probabilities for visibilities less than 1/2 mile across multiple short range ensembles, the need for a Dense Fog Advisory will need to be monitored this evening and tonight. Any fog should gradually dissipate through the mid- morning hours on Thursday.

KEY MESSAGE #2: High confidence in well above normal temperatures the remainder of the week and into early next week with increasing diurnal rain chances starting this weekend.

The upper ridge is beginning to slide into the region as it strengthens with flow becoming increasingly southwesterly throughout the atmosphere. This is bringing temperatures into the 70s this afternoon before continuing to warm the remainder of the week. The strong 1.5-2 std dev above normal ridge should continue to shift overhead through the start of this weekend with 850mb temperatures reaching near the NAEFS 90th percentile. This is expected to bring temperatures 15-18 degrees above normal, into the low to mid 80s much Thursday through this weekend. The ridge is expected to flatten out some Sunday and into the early week, but warm 850mb temperatures should aid in keeping temperatures above normal through at least Tuesday. Confidence in warm weather continuing into the early week continues to increase as shown in the less than 5F IQR ranges in blended guidance.

For rain chances, PWAT's are expected to begin approaching 1" by Friday, but the strong ridge should suppress most diurnal shower activity and keep any spotty showers mainly toward the western FA. PWAT's continue to raise through the weekend and into early next week where majority of LREF members show PWAT's reaching above 1.25" by Sunday. As the ridge flattens, diurnal showers/storms are expected to increase in coverage Saturday, but especially Sunday. This pattern continues into the early week where pockets of shortwave energy ejecting from a Baja Low may bring additional lift to the region with deep moisture in place.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

VFR expected into early Thursday morning before widespread fog- stratus brings IFR-LIFR restrictions.

Steady southwest winds around 6-10 knots this afternoon will steadily bring some moisture into the area as high pressure sits to out east. Winds will weaken after sunset, with a low level jet around 20 knots developing above the inversion; likely will not reach LLWS criteria though for a TAF mention. Outside of some high strato- cirrus, no other notable cloud cover, or cig- vsby restrictions expected until after 06z Thursday. For Thursday morning a hybrid fog- stratus event is expected to impact all the TAF sites with IFR or possibly LIFR shortly before and after sunrise. As is typical with these events, a mix of vsby and cig restrictions are expected. Any residual restrictions should clear out after 14z Thursday.

EXTENDED AVIATION OUTLOOK...There is potential for additional 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.