textproduct: Columbia

WHAT HAS CHANGED

Aviation updated for 06Z TAFs.

KEY MESSAGES

- 1. Unsettled weather into next week, with showers and thunderstorms expected each day.

- 2. Uncertainty in temperatures north of I-20 Today and Saturday.

DISCUSSION

Key Message 1: Unsettled weather into next week, with showers and thunderstorms expected each day.

An upper level ridge will remain over the western Atlantic into next week, with disturbances embedded within the southern stream lifting across the area along the western periphery of the ridge. An influx of moisture is also expected, with mean precipitable water values in the 1.5-2.0 inch range, supported by the GEFS and ECMWF ensembles and LREF, through most of next week.

At the surface, high pressure will become established over New England and build down along the lee of the Appalachians. This will result in cold air damming from the Mid-Atlantic region into the Carolinas through the weekend, with indications the wedge could erode by early next week. Locally, the best potential for wedging appears to be along and north of the I-20 corridor. The nearly stationary front associated with the southern extent of the wedge, combined with a daily sea breeze and the upper level disturbances passing through will all act as triggers for convection.

The blended guidance shows likely to categorical rain chances through the holiday weekend. While most areas will indeed see rainfall (especially northwest portions of the forecast area), this may be a bit deceiving as the convection may be more periodic as opposed to a complete washout with persistent rain. Many of the HREF members show the best potential for convection coming this evening into the early overnight hours, and again late Saturday afternoon through Saturday evening. Precipitation chances do come down a bit later in the week, but overall this is a pattern that supports greater rain chances, more diurnally driven toward the end of the forecast period.

Much needed rainfall could finally come this week. Mean QPF values through Monday from the ECMWF ensemble and the NBM support 2.0-2.5 inches along/north of I-20, with lesser amounts of 1.0-2.0 inches farther south and east. However, the GEFS and the NBM 90th percentile show as much as 3.0-3.5 inches in northwest portions of the forecast area, which would generally suggest a reasonable high-end amount, mainly due to localized heavy downpours in convection.

Although some robust convection is possible, with primarily an isolated downburst potential, the overall severe threat appears to be limited this weekend. More organized mutli-cellular clusters could occur later Saturday afternoon and evening, but widespread cloud cover and marginal lapse rates (along with a stable boundary layer north of the wedge boundary) should prevent a significant severe event from occurring.

Key Message 2: Uncertainty in temperatures north of I-20 Today and Saturday.

The aforementioned cold air damming/wedge scenario could impact temperatures this weekend, with the forecast highly dependent on the location of the wedge boundary. Convection will also influence temperatures. Overall, the NBM seems to be too warm across the Catawba region and portions of the northwestern Midlands, where the wedge is expected to be more firmly in place. Have therefore lowered temperatures in these areas today and Saturday, but they very well can still be too warm and need further adjustment.

AVIATION /12Z FRIDAY THROUGH TUESDAY/

MVFR-IFR stratus likely early this morning, with late afternoon/evening showers and thunderstorms possible later today.

Light and variable winds are expected to continue as low stratus develops and moves in early Friday morning. MVFR/IFR ceilings are fairly widespread early this morning, with the greatest potential for IFR restrictions appearing at OGB. Patchy fog may also develop, mainly across the southern and eastern portions of the area where low-level moisture remains favorable. Cold air damming conditions will persist, supporting persistent low stratus through at least mid- morning. Gradual improvement will begin after 13-15Z with southeast winds picking back up near 5-8 kts.

Another round of diurnally driven convection is expected to develop this afternoon and evening. Based on the latest HREF guidance, more widespread storms may develop near all terminals after 22-23Z, continuing to bring additional waves of showers through most of the night and into the early morning hours on Saturday. Confidence is still a bit uncertain at this time.

EXTENDED AVIATION OUTLOOK...Abundant low level moisture will bring more rounds of morning restrictions from fog/stratus into the weekend along with scattered afternoon showers and storms possible each day through the weekend.

CAE WATCHES/WARNINGS/ADVISORIES

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