textproduct: Columbia

WHAT HAS CHANGED

No significant changes. Aviation discussion updated for 12z TAFs.

KEY MESSAGES

- 1. Front approaching the area leading to increasing chances for rain and cooler temps this weekend and into next week. Increasing concern for localized flash flooding.

DISCUSSION

.KEY MESSAGE 1: Front approaching the area leading to increasing chances for rain and cooler temps this weekend and into next week Increasing concern for localized flash flooding.

High pressure has shifted offshore allowing a southwesterly flow return allowing Gulf moisture to surge north. Current PWATs range between 1.8 and 2.0 with dewpoints in the low 70s across the FA. Current 0Z sounding from CHS shows deep moisture from the surface to the 500 mb level with a pocket of dry air in the upper-levels. Deep tropical moisture is expected to continue moistening the atmospheric profile through the weekend.

As the upper ridge axis shifts offshore into tonight, more significant moisture increase is expected with southwesterly flow developing aloft. HREF mean indicates PWATs will rise to above 2 inches across the forecast area, closer to 2.2 inches near the Coastal Plain. This amount of moisture is unusual for October as the NAEFS is at the 99th percentile. This will lead to widespread cloud coverage and chances for scattered showers in the morning, although forcing will be generally weak so any showers will likely remain light. While instability will generally be weak with blended guidance indication probability of sbCAPE greater than 1000 J/kg around 20 percent or less. As a result, storm coverage may be somewhat isolated, with severe storms unlikely and moderate to heavy rain the main threat. Heaviest will likely be along the axis of the approaching cold front that is currently stalled over western North Carolina into Northern Georgia. Higher resolution guidance generally favors in the northern half of the area, although the exact location for heaviest rain axis remains uncertain. Trends are leaning towards along and north of I-20 with the heaviest rain setting up from east to west, however it is uncertain exactly where the heavier pockets of rain setup. Strong convergence along this boundary will likely continue into Saturday night and may lead to some general flash flooding concerns into the day on Sunday when upper level forcing strengthens as a robust shortwave likely moves through the area. Coverage looks to be more scattered Saturday and widespread Sunday evening with the bulk of the rain likely Sunday into Monday. With moisture anomalously high, the most likely scenario this weekend is widespread rainfall amounts greater than 2 inches, with blended probabilities of 60-70 percent. HREF LPMM indicates this higher axis of greater than 3 inches with localized spots of even higher amounts. Drier air will begin to move in from the north Monday with the axis of heavier rain shifting southward as an upper trough digs into the Northeast. Rain should begin to clear out by Monday afternoon. Models have generally been favoring drier air into the middle of next week with cooler air behind the front. Temperatures may drop into the low to mid 70s with overnight lows in low to mid 50s.

AVIATION /12Z SATURDAY THROUGH WEDNESDAY/

A mixture of vfr and mvfr conditions remain possible throughout the period with moisture and rainfall potential increasing.

Satellite showing plenty of cloud cover to start off the taf period overnight. Observations overnight have been a mixture of vfr and mvfr/ifr ceilings, primarily in the CSRA. However even the Midlands tafs have fluctuated briefly early this morning. Some return to vfr is expected later this morning, but will at least keep a tempo for mvfr restrictions through 15z at all locations, especially with some light rainfall developing across the area. Moisture will continue to increase through the daytime hours, and some MVFR restrictions in showers will becoming possible once again. Expecting to encounter scattered showers and isolated thunderstorms throughout the day and afternoon hours as ceilings slowly lower. However primarily vfr ceilings outside of heavier rainfall, with mvfr conditions possible in a stronger shower or storm. Rainfall will continue to be possible tonight as deeper Gulf moisture begins pushing into the region. Winds through the period should be light and variable or southerly around 7 kts or less.

EXTENDED AVIATION OUTLOOK...Scattered to widespread showers and isolated thunderstorms Sunday into Monday morning may lead to restrictions.

CAE WATCHES/WARNINGS/ADVISORIES

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