619 FXUS62 KCAE 182337 AFDCAE Area Forecast Discussion National Weather Service Columbia SC 737 PM EDT Sat Sep 18 2021 .SYNOPSIS... Surface high pressure to our north and a plume of moisture to our west will keep us in a somewhat unsettled pattern through mid-week. Expecting near average temperatures with showers becoming more widespread each day through Tuesday. A deep upper trough will swing a fairly strong cold front through the area with cooler temperatures and much drier air filling in by Thursday and Friday. && .NEAR TERM /UNTIL 7 AM SUNDAY MORNING/... Isolated showers or a thunderstorm possible early this evening, then activity expected to dissipate with loss of heating. Otherwise, fair with some increasing high level cloudiness. Low temps around 70. && .SHORT TERM /7 AM SUNDAY MORNING THROUGH TUESDAY/... The deep upper ridge axis over the central CONUS and associated surface high pressure center near the Great Lakes will steadily shift east through the short term period. The sensible weather conditions will not change much however, with consistent easterly flow continuing Sunday and remnant moisture from Nicholas still remaining to our west. With weak lapse rates aloft, comparatively dry air with PWATs less than 1.8 inches, and little synoptic forcing, shower and thunderstorm activity Sunday will again be typical summer- like diurnal and limited in coverage. Any shower activity will be favored along the strongest moisture gradient in the CSRA. Cloud cover will limit high temperatures to the mid 80s despite impressive mid-upper level heights. Low level moisture and elevated PWATs will surge north throughout the day Monday as the surface flow develops a more southerly component. Instability will slightly increase as some subtle height falls aloft begin with the approaching upper level trough. With abundant low level moisture available for the entire forecast area, widespread showers and thunderstorms are expected again with a diurnal trend as the synoptic forcing is still fairly weak despite a subtle shortwave approaching from the southeast. The primary question is whether the moisture gradient can lift into NC or if it will stall across the SC upstate. Regardless, PoPs increase to likely by Monday afternoon particularly focused in the CSRA and central Midlands with high temps in the mid 80s. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... The remnant moisture from Nicholas will quickly be advected north Tuesday as the strong upper level trough promotes deep southeasterly flow over the region. The general setup looks similar to Monday with elevated moisture, some weak instability, and enough synoptic forcing to not inhibit shower and thunderstorm development. Blend and ensemble guidance show another day of mid-low 80s temps due to persistent cloud cover. Ensemble guidance is still in good agreement through early Wednesday as the surface cold front approaches. Synoptic forcing increases in conjunction with deep moisture and widespread showers are expected. The frontal passage is expected sometime Wednesday evening into early Thursday, but there are some timing disagreements between the blend, EC, and GEFS ensemble members primarily due to how they each handle the deepening and possible occlusion of the upper level low. Regardless, the frontal passage will usher in dry and cool air by Thursday afternoon lasting into the weekend. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/... The forecast opens with vicinity showers at all terminals as the radar continues to pick up on isolated showers, especially near CUB. This activity should quickly diminish with the loss of daytime heating. The main concern during the TAF period will be the potential for widespread low clouds at all terminals in the morning. Have added a period of MVFR ceilings for now to allow new data to come in and will adjust as needed. OGB and AGS also have a TEMPO group for MVFR fog. Conditions at the terminals should improve quickly Sunday morning with VFR conditions during the daytime hours aside from any isolated showers or thunderstorms which, while possible, have been omitted from the TAFs due to lack of coverage. EXTENDED AVIATION OUTLOOK...Chances of mainly diurnal showers and thunderstorms, along with some late night/early morning fog/stratus potential, through Wednesday. A cold front will move through Wednesday night or early Thursday with drier air. && .CAE WATCHES/WARNINGS/ADVISORIES... GA...None. SC...None. && $$