textproduct: Columbia

WHAT HAS CHANGED

Updated Key Message #1 for potential fog tonight. Minimal change to the forecast for the weekend and into early next week before a bit more uncertainty is seen Wednesday and Thursday. Aviation discussion updated for 18Z TAFs.

KEY MESSAGES

- 1. Another round of fog and stratus expected tonight.

- 2. Temperatures continue to be well above normal through at least the mid week next week. - 3. Chances for diurnal showers/storms continue into the early week.

DISCUSSION

KEY MESSAGE #1: Another round of fog and stratus expected tonight.

A fairly rinse and repeat pattern is expected tonight as abundant low level moisture remains in place under mostly to partly clear skies. Humid dewpoints in the 60s are expected to remain in the region tonight, limiting lows toward the low to mid 60s and bringing potential once again for fog development. A similar situation to last night is seen where a 20-25 kt LLJ looks to set up tonight and lead to more scattered to widespread stratus across rather than widespread fog. With this said, areas of fog with spots of locally dense fog cannot be ruled out, especially toward the southeastern Midlands where periods of dense fog have been seen the last couple mornings.

KEY MESSAGE #2: Temperatures continue to be well above normal through at least the mid week next week.

The apex of the strong mid level ridge is moving near the region today with afternoon highs topping out in the upper 70s to low 80s. This ridge should remain solidly in place Saturday with 925mb temperatures reaching toward 16-19C as southerly flow continues. Continued southerly flow should lead to highs toward the lower 80s once again, and there is fairly high confidence in temperatures into the low to mid 80s continuing Sunday and into next week despite the ridge flattening out some in response to a trough moving into the Great Lakes. As a Baja low digs in and slowly starts progressing eastward early in the week, the ridge is expected to become amplified once again, leading to the continuation of well above normal temperatures into Wednesday at least. This overall pattern is highlighted well in the ECMWF EFI where values for maximum temperature are between 0.7-0.8 each day through Tuesday before reaching 0.9 on Wednesday with a SOT contour of 1 over the region, showing the potential for even warmer temperatures Wednesday. Greater IQR ranges are seen in blended guidance by Thursday however as high uncertainty remains in the progression of the Baja low. Right now, it appears troughing should replace the ridge by late Wednesday and into Thursday, possibly leading to slightly cooler temperatures on Thursday.

KEY MESSAGE #3: Chance of diurnal showers today into next week.

A couple weak showers moved through the northern Midlands this morning and as PWAT's continue to rise (currently near 1.25" from GOES-19 PW imagery) a couple more spotty showers or a weak storm could be possible this afternoon, mainly toward the western FA. Heading into Saturday, subsidence from the ridge generally hangs on and limits coverage of diurnal showers or storms until the evening hours as a weak shortwave and surface front near. CAM's show convection blossoming across the Deep South ahead of the front by the late afternoon, continuing eastward. By the evening hours instability will be waning over the FA, but a batch of showers and storms could move in as the front nears. This diffuse front fizzles out on Sunday, but may aid in bringing additional forcing for diurnal showers/storms during the afternoon hours.

Heading into the early week, more diurnal rain chances could be possible but synoptic forcing is expected to remain fairly nebulous outside of possibly a couple weak shortwaves passing as the ridge flattens further. This is represented fairly well in ensemble and global guidance before greater uncertainty enters Wednesday and Thursday. This uncertainty stems from the progression of the Baja low and how it interacts or is absorbed with the northern stream. There is nearly a even four way split between LREF clusters for this time period and deterministic guidance varies on timing and intensity of the trough/low quite a bit still. Due to this, there is lower confidence in the chance for a potential more organized system, but in general, rain and storm chances seem reasonable both Wednesday and Thursday.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

VFR expected through early Saturday before another round of IFR-LIFR conditions.

The pattern continues just like the last few days with high pressure to our east, continuing to push low level moisture with drier air aloft into the area. This led to widespread stratus that has mixed out to MVFR cigs for all sites as of 19z. Winds will remain out of the southwest throughout the afternoon and evening before going calm overnight. Another round of low cigs stratus and fog is expected Friday morning with IFR-LIFR conditions expected after 08z for all sites, lasting through roughly 15-16z. Like Friday, it will likely be a mix of fog and stratus as winds between 1-2k feet will remain elevated to prevent a pure fog event.

EXTENDED AVIATION OUTLOOK...Patchy morning fog remains possible each day. Increased shower and storm chances expected starting late Saturday into Sunday, lasting into next week.

CAE WATCHES/WARNINGS/ADVISORIES

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