textproduct: Columbia

WHAT HAS CHANGED

Aviation discussion updated for 18z forecast.

KEY MESSAGES

- 1. Increasing moisture this weekend leading to chances for rain through Monday when a cold front moves through.

DISCUSSION

Key Message 1: Increasing moisture this weekend leading to chances for rain through Monday night when a cold front moves through.

Broad troughing along with an active southern stream jet will bring elevated rain chances over the next few days as a series of shortwaves interact with persistent gulf moisture. The first of these will move through Saturday, with rain chances continuing mainly along and south of I-20. A decaying MCS complicates the forecast a bit and could cut off and rob some moisture as it propagates to the south of our area, like HRRR depicts. But regardless, high PWAT's and broad synoptic forcing along with weak instability should product some scattered-widespread showers, especially along and south of I-20 with relatively light QPF overall to the north, generally less than 0.5". This broad forcing will linger again on Sunday but with less instability in play, so while additional showers are likely, coverage and QPF totals will be light. More consolidated and heavier rain arrives late Sunday and Monday with stronger front and associated 500-250mb trough crossing the area. PWAT's push towards 1.75 - 2.0" across much of the ensemble guidance along with IVT above the 90th percentile. While we could have some convective MCS's that cut off some this moisture, the synoptic forcing, residual instability, and high PWAT's will allow for widespread showers-storms regardless. Instability does look lacking for any notable severe threat but skinny CAPE profiles paired with relatively high PWAT's present a heavy rain threat. Total rainfall through Tuesday morning is progged around 1-2" along and south of I-20 and 0.5-1.0" northward; 90th percentile in the LREF pushes towards 3.0" south of I-20 given the potential for efficient, convective rainfall both Saturday and Monday. Drier conditions arrive Tuesday has we eventually end up within the northwest flow regime of the persistent troughing.

AVIATION /18Z FRIDAY THROUGH WEDNESDAY/

VFR conditions will continue through early tonight, then potential for mvfr ceilings to develop towards sunrise Saturday morning.

High pressure through this afternoon will help to keep vfr conditions at all sites. All sites will see some upper level broken cirrus moving through the region through this evening ahead of an approaching shortwave late tonight. Guidance brings increase in moisture and even the potential for a few showers for Saturday after sunset. Ceilings will be deteriorating as thismoisture moves in, with mvfr conditions expected towards 11z at most sites. There remains some uncertainty as to the extent of any light rain tomorrow morning, so only included a vcsh with the 11z period for now. Winds will begin to turn more southeasterly around 5 knots as the afternoon progresses, then generally light and variable during the overnight hours. A return to more southerly is expected through the day on Saturday.

EXTENDED AVIATION OUTLOOK...Another system brings a chance for restrictions once again with showers and thunderstorms this weekend into Monday.

CAE WATCHES/WARNINGS/ADVISORIES

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