textproduct: Columbia

WHAT HAS CHANGED

Added new key message to specifically address the threat of severe thunderstorms and flash flooding today. Aviation updated for 06Z TAFs.

KEY MESSAGES

- 1. Monitoring for low-end risk for strong to severe thunderstorms and localized flash flooding through Saturday night.

- 2. Showers and thunderstorms chances continue through next week.

DISCUSSION

Key Message 1: Monitoring for low-end risk for strong to severe thunderstorms and localized flash flooding through Saturday night.

Early morning radar remains active with one area of mainly stratiform rain moving from the CSRA northeast into the Midlands while a line of showers and embedded thunderstorms is moving northwest through the southeastern Midlands. PWATs remain quite high, between 1.5 and 1.9 inches, so there remains a concern for localized flooding. Having said that, the Flood Advisory that was in effect for portions of the northern Midlands was allowed to expire as gage data suggests area streams have crested and are receding courtesy of a break in the rain. While a few thunderstorms are ongoing at this hour, the severe threat is near zero through daybreak.

Saturday is expected to be the most active of the next seven with the WPC highlighting a Marginal (1/4) risk for excessive rainfall and the SPC showing a Marginal (1/5) risk for severe weather across much of the FA. Deeper moisture and better upper level support should result in scattered strong to severe thunderstorms later today which may produce locally heavy rainfall. Modeled soundings this afternoon show an inverted-V with long, skinny CAPE profiles suggestive of both heavy rainfall and possible damaging winds. Areas north and west of I-20 are most likely to see the heavy rainfall once again but most locations should see measurable rainfall today.

Key Message 2: Showers and thunderstorms chances continue through next week.

The synoptic pattern is persistent through next week with upper level ridging over the western Atlantic and upper disturbances lifting to the north and west. Global ensemble mean precipitable water values are in the 1.5-2.0 inch range through most of next week. This pattern supports at least scattered showers and thunderstorms enhanced by the shortwave activity throughout the period. The blended guidance shows likely to categorical rain chances throughout the holiday weekend. While most areas will likely see measurable rainfall, this may be a bit deceiving as the convection may be more periodic as opposed to a complete washout with persistent rain. Showers and thunderstorms will likely lead to heavy rainfall each day, particularly if training cells develop. This raises concern for the localized flash flooding threat to continue, mainly in urban and flood prone areas.

The large scale pattern remains active in the extended with a persistent ridge to our east and troughing to the west. PWAT values remain above 1.5 inches through the period with southwesterly flow over the Southeastern US. This pattern will support daily shower and thunderstorm chances through next week. In general, the convective activity should follow a diurnal trend but passing shortwave troughs may sustain convection after sunset.

AVIATION /06Z SATURDAY THROUGH WEDNESDAY/

Mix of restrictions likely throughout the TAF period with scattered showers and storms.

A fairly moisture rich summer pattern continues across the region with scattered showers and isolated thunderstorms. Most of the activity so far has remained south towards AGS/DNL as well as north and west of I-20. Another line of storms is beginning to push through the CWA which could bring light showers and thunderstorms to all terminals between 06-10Z. Coverage of showers will begin to diminish as we head into the early morning hours as winds subside to light and variable. Similar to previous nights, MVFR/IFR ceilings become fairly widespread early this morning as low-level moisture remains favorable.

Additional rounds of showers and storms are likely to pick up Saturday afternoon and evening. Based on the latest HREF guidance, more widespread storms may develop near all terminals after 19-21Z, continuing to bring additional waves of showers and thunderstorms into the overnight period. Confidence is still a bit uncertain at this time. Therefore, PROB30s for light showers have been added to all sites for this TAF issuance.

EXTENDED AVIATION OUTLOOK...Abundant low level moisture will bring more rounds of morning restrictions from fog/stratus through the weekend along with scattered afternoon showers and storms possible each day into the middle of next week.

CAE WATCHES/WARNINGS/ADVISORIES

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