textproduct: Columbia

WHAT HAS CHANGED

Minimal change to Key Messages. Aviation discussion updated for 18z TAF.

KEY MESSAGES

- 1. A more typical summer pattern is expected through Wednesday before drier conditions move in for the late week.

DISCUSSION

- 1. A more typical summer pattern is expected through Wednesday before drier conditions move in for the late week.

The now diffuse frontal boundary remains draped across the FA along the I-26 corridor as the next shortwave is moving into the region, increasing effective shear values toward 20-30 kts. Instability is rather marginal (MLCAPE values up to ~1800 J/kg), but deep moisture remains with PWAT's pushing 2.20-2.30". Isolated convection has developed toward the southeastern Midlands and should continue this afternoon. With the increased shear, cannot rule out a stronger cell, but the main risk with this activity will be locally heavy rainfall.

Drier air is expected to work in Monday with PWATs falling toward 1.60-1.80" as low level flow becomes a bit more northerly, especially early in the day. Overall, this should bring a mostly dry day across the CWA outside of possibly an isolated shower or two. The pattern becomes a bit more amplified heading into Tuesday and Wednesday as the robust upper ridge centered over the Rockies gradually retrogrades westward with a deeper trough digging into the Mid-Atlantic with 500mb heights near the LREF 2nd percentile. A shortwave pushing out of the base of this trough is expected to help drag a surface front into the region by late Tuesday into Wednesday, but ahead of this, moisture transport is expected to increase again with EC Ensemble and GEFS PWAT's reaching back near 2". Southwesterly low level flow should also aid in bringing hot/humid conditions Tuesday. The stronger kinematics with this system still appear to keep north of the FA in 12z guidance, overall limiting the severe risk. At least modest effective shear values toward the Pee Dee could bring an isolated strong to severe storm Tuesday evening, but confidence in this is low. The front then is shown working through the area on Wednesday with northwesterly flow behind it ushering in drier air. Rainfall expectations in the Tuesday- Wednesday timeframe have not changed all too much with any activity likely being fairly scattered at best and mainly in the Tuesday evening into Wednesday morning window.

Some of the driest air in at least the last 3-4 weeks is progged to move in behind the front thanks to the deep upper trough with mean LREF PWATs dropping to under 1.50" and perhaps even under 1.25" at times Thursday and Friday. This is further supported looking across members in the EC Ensemble and GEFS. Due to this, near normal temperatures with dry conditions are expected. Global models are hinting that as the upper ridge continues to retrograde toward the Four Corners region into the weekend, another shortwave could begin nearing the Southeast in this northwest flow regime. This could bring back rain chances, but it is worth noting there remains considerable spread in LREF clusters in the progression of this shortwave.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

VFR conditions expected outside of convection through 06z then restrictions in fog and stratus possible.

Drier mid level air is moving into the region in the wake of a shortwave that is driving scattered storms this afternoon. OGB likely to be most affected by storms and will include a TEMPO for storms 18z-22z while VCSH included at other terminals with lower confidence in storms impacting terminals. Generally northerly winds around 5 knots expected through sunset then diminishing to light and variable or calm overnight. Some debris clouds may linger into the overnight but should thin with only some high clouds expected. The combination of drier air aloft and low level moisture and some clearing of skies overnight with a lack of any low level jet should favor some predawn fog, especially at prone areas OGB/AGS. Hi-res guidance and NBM favor restrictions at OGB/CAE/CUB so carrying prevailing MVFR vsbys there after 08z with tempo to IFR vsbys and LIFR cig but less confidence at DNL/AIK so kept VFR prevailing there.

EXTENDED AVIATION OUTLOOK...Restrictions unlikely early this coming week. By late Tuesday and into Wednesday, rain chances begin to increase again with associated restrictions possible.

CAE WATCHES/WARNINGS/ADVISORIES

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