textproduct: Columbia

WHAT HAS CHANGED

Showers and storms continue today, however, guidance continues to trend lower with overall rainfall coverage and amounts. Aviation discussion updated for 06z TAF issuance.

KEY MESSAGES

- 1. Showers and thunderstorms are expected to continue today, bringing heavy rainfall and isolated flooding.

- 2. After a cold front on Monday, the pattern becomes more uncertain.

DISCUSSION

Key Message 1: Showers and thunderstorms are expected to continue today, bringing heavy rainfall and isolated flooding.

A shortwave trough over the lower Mississippi Valley will continue moving eastward across the Carolina's tonight. Meanwhile, a stalled boundary will shift north and advect a deep plume of moisture back into the forecast area, with PWAT values increasing to 1.7-2" early this morning. Weak wind fields have supported slow storm motions and backbuilding convection so far. Forecast soundings also indicate long, skinny CAPE profiles, which favor efficient rainfall production as multiple shortwaves interact with the stalled boundary.

Recent observations and CAM guidance showed impressive rainfall rates earlier; however, the heaviest and most persistent activity is expected to remain primarily near the CSRA (mainly south and west of the CWA as well). So far tonight, light showers are having a hard time making it up to the central Midlands. Hi-res models remain set on the activity eventually breaking through and making it further into SC around dawn, but the latest HREF guidance continues to trend lower with overall rainfall coverage and amounts.

A few breaks in the activity are possible after daybreak, however, with PWATs above the 90th percentile and stronger upper-level forcing, scattered showers and thunderstorms are expected to redevelop as the front hangs around through the day. As a result, periods of locally heavy rain will remain possible most of the day with a limited but continued threat of isolated flash flooding.

Key Message 2: After a cold front on Monday, the pattern becomes more uncertain.

An upper-level trough digging southward along the Eastern Seaboard is expected to push the stalled boundary back to our south on Sunday. Additional chances for showers are possible with cooler and direr air ushering in behind. Despite the frontal passage, poor lapse rates should limit instability and suppress most convection, with only slight Pops lingering near the CSRA, closest to the boundary.

Beyond that the forecast becomes uncertain. Most guidance indicates a brief period of drier weather Sunday followed by another round of rainfall on Monday ahead of a stronger cold front. High pressure will follow and bring in cooler and drier northerly flow to the region. Models begin to differ by midweek with some bringing in another chance for rain. However, a gradual warming trend is expected into the later part of the week, still below normal though. Moisture slowly returns as well bringing back the potential for diurnal convection potentially by Friday next week.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

Periods of showers possible, especially in the CSRA with brief restrictions possible.

While VFR conditions are mostly in place, with the exception of OGB, lingering low level moisture may lead to brief restrictions developing over the next several hours, favoring the CSRA with a stalled front just south of the forecast area. While LAMP probabilities have been decreasing somewhat for IFR ceilings for the Augusta terminals, with IFR just to the west and few clouds below 1000 feet already at AGS, think it is reasonable for temporary IFR restrictions. Higher probability of VFR conditions northeast, farther away from the front. Generally unsettled pattern today with scattered showers possible throughout much of the day. Higher resolution guidance does not favor significant destabilization today so have left out any mention of ts. Winds will generally be light and variable today.

EXTENDED AVIATION OUTLOOK...Unsettled weather should continue into early next week until drier air moves into the region mid-week.

CAE WATCHES/WARNINGS/ADVISORIES

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