textproduct: Columbia

WHAT HAS CHANGED

Minor tweaks to Key Message #1 to highlight increased flash flooding threat in the western CWA. Aviation updated for 12Z TAFs.

KEY MESSAGES

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

- 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 tonight.

Areas of rain and an isolated thunderstorm or two continue across the FA at daybreak. Today is expected to be the most active day 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. Modeled soundings this afternoon show an inverted-V with long, skinny CAPE profiles suggestive of both heavy rainfall and possible damaging winds, though DCAPE values are low in the modeled soundings so the severe threat will likely be a secondary concern behind the heavy rain and flood potential. Areas north and west of I-20 are most likely to see the heavy rainfall once again. Flash flooding and urban and small stream flooding are both possible with the latest LPMM showing a swath of 2 inch rain amounts from the CSRA north through the western Midlands.

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 /12Z SATURDAY THROUGH WEDNESDAY/

Lowered Ceilings Continue at some Terminals this Morning....

Areas of rain and an isolated thunderstorm or two continue across the FA at daybreak along with variable ceilings at the terminals. The lowered ceilings should improve by midday with all terminals anticipated to return to VFR by 15-16Z. Attention then turns to restrictions due to showers and thunderstorms. A PROB30 is in place from 18Z until 00Z Sunday for scattered thunderstorms. While not indicated in the TAFs a few thunderstorms could become strong to severe resulting in gusty surface winds during their passage. The rain will likely be heavy at times as well resulting in additional visibility reductions. As activity winds down this evening, low ceilings are expected to return at all terminals, though some rain may linger into the overnight period.

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.