textproduct: Columbia

WHAT HAS CHANGED

Aviation discussion updated. Rainfall forecast for late weekend remains on track, but total accumulations are trending a bit lower.

KEY MESSAGES

- 1) Beneficial rainfall on track to move into the area late tonight and continue into early Monday. Guidance remains consistent with a general 0.5"-1.0" across the area, and the potential for higher totals across the northern Midlands.

- 2) Potential for well above normal temperatures is taking shape for late next week.

DISCUSSION

KEY MESSAGE #1: Beneficial rainfall on track to move into the area late tonight and continue into early Monday. Guidance remains consistent with a general 0.5"-1.0" across the area, and the potential for higher totals across the northern Midlands.

The main forecast feature over the next seven days remains the potential for much needed rainfall over the next 24 to 48 hours. With near term and hi-res model guidance beginning to come into play, the expectation remains that a trough will move out of the Southwest and across the Deep South into the Southeast by Sunday. The surface low should consolidate and develop over the Southern Plains through the day today. Initially, isentropic ascent will drive showers developing late tonight into Sunday morning ahead of the trough as southwest flow aloft drives PWATs of 1"-1.25" over the area. As the trough and surface low near the forecast area, additional upper support will promote the potential for moderate to at times heavy rainfall, particularly along the warm front. This will make prime time for the highest accumulations Sunday afternoon through Sunday night.

LREF clusters through Monday evening depict >50% probabilities of 0.75" or higher of rainfall for locations north and west of the I-20 corridor. The highest totals are likely to be in the northern Midlands, or generally along and near wherever the warm front ends up tracking. As such, for Lancaster County there is about a 40% probability for >1" of rainfall with this system. For comparison, these values are slightly lower than 24 hours ago, so there is a trend to watch here as the event nears. A good expectation is around 0.50" of rainfall just about everywhere, with the typical localized higher and lower accumulations. There is a low but non-zero potential for some thunder as convection to our west develops and moves over the area Sunday evening. Most guidance has the rain ending from west to east, and moving out of the area sometime between 06z and 12z Monday morning.

While this system will bring beneficial rainfall to the majority of the area, we are still quite a bit behind when it comes to normal rainfall amounts to date, 2 to 3 inches below normal in some locations for both the calendar and water years. So while we may make an incremental improvement to drought conditions, we still need to see a lot more rainfall to catch up and reduce the drought category.

KEY MESSAGE #2: Potential for well above normal temperatures is taking shape for late next week.

Behind the departing upper trough, flow aloft will become northwesterly as a ridge builds over the central CONUS. Surface high pressure will take hold over the area through midweek while heights and thicknesses increase. While its too early for specifics, this pattern seems to indicate the potential for well above normal temperatures, particularly from Wednesday onward. Both the ENS mean and NAEFS mean 700 mb temps for Wednesday, Thursday and Friday next week are above the 99.5 percentile across the region, while 850 mb temps are above the 90th percentile during the same period.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

VFR conditions likely continue through the TAF period with increasing cloud cover at the end of the period.

High pressure looks to remain overhead much of the forecast period with winds remaining light and variable to calm until 15-17z, when southerly to south-southeasterly winds pick up to around 5 kts through the remainder of the day. Cirrus should continue to increase through the day, especially this evening and to the end of the period as moisture increases, but VFR conditions are expected to prevail through the end of the period before ceilings begin to lower into the morning hours on Sunday.

EXTENDED AVIATION OUTLOOK...Restrictions are expected to gradually develop in the early morning hours Sunday, continuing through the day as the next system brings widespread rain to the region. Restrictions may remain into early Monday before drier air moves in and VFR conditions return.

CAE WATCHES/WARNINGS/ADVISORIES

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