textproduct: Columbia

WHAT HAS CHANGED

Forecast remains on track for mid-week. Aviation discussion updated for 00Z TAFs.

KEY MESSAGES

- 1. Periods of moderate to heavy rainfall are expected mid week with potential for severe weather.

- 2. Rain chances pick back up late week and into the weekend

DISCUSSION

Key Message 1: Periods of moderate to heavy rainfall are expected mid week with potential for severe weather.

As we draw nearer to the mid-week system, the rainfall outlook remains steady. Strong moisture transport, synoptic scale lift and convergence ahead of the front will likely lead to widespread convection Thursday morning until the front moves east later in the day. PWAT values will be near or above their climatological maxima pointing to the possibility of heavy rain in deeper showers and thunderstorms. Rainfall totals for the event are most likely to fall within the one third inch to 1 inch range but we expect isolated higher amounts from pockets of deeper convection. This could lead to isolated flash flooding concerns mainly limited to urban or flood prone areas. A tightening surface gradient and some mixing down of the robust LLJ, should bring gusty conditions where a Lake Wind Advisory could be needed.

The timing of the system continues to ultimately limit certainty in the risk of severe weather. The potential for widespread rain and cloud cover during the early morning may limit destabilization as the low level jet and deepest moisture approaches from the west. Although the question of instability remains, the ECMWF EFI values for CAPE-Shear continues to rise showing that the threat of moderate instability and strong deep layer shear remains. If destabilization occurs , a couple strong to marginally severe storms could form in this high shear environment. The area of greatest concern is in the eastern Midlands and the Pee Dee at this point, but confidence is low at this time.

Key Message 2: Rain chances pick back up late week and into the weekend

Models tend to favor a progressive pattern through the remainder of the forecast period with multiple rounds of shortwave troughs swinging through the eastern CONUS. Dry air over the region for late week and early this weekend should limit PoPs for a bit before PWAT values rise back above an inch by late weekend or early next week leading to rain chances ramping back up.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

VFR conditions expected to prevail through 12Z Wednesday.

Winds strengthen out of the south by late morning to 9-13 kt, with gusts upwards of 15-20 kt possible in the afternoon due to stronger winds aloft mixing to the surface. A few mid-level clouds are possible in the afternoon, but will not pose an impact to aviation. Wind gusts will diminish this evening, but low-level jetting will maintain sustained winds of 7-10 kt through the remainder of the forecast period. Also, expect increasing high and mid level clouds ahead of an approaching system to the west.

EXTENDED AVIATION OUTLOOK...A midweek system brings a chance for restrictions once again with showers and thunderstorms starting Wednesday evening.

CAE WATCHES/WARNINGS/ADVISORIES

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