textproduct: Columbia

WHAT HAS CHANGED

Confidence in above normal temperatures increasing for next week. Aviation discussion updated for 18Z TAF issuance.

KEY MESSAGES

- 1. Diurnal thunderstorms expected through the weekend with the main threat of locally heavy rainfall.

- 2. Well above normal conditions expected to return by next week, with dangerous heat index values again possible.

DISCUSSION

KEY MESSAGE 1: Diurnal thunderstorms expected through the weekend with the main threat of locally heavy rainfall.

Troughing to our west remains entrenched and persistent today as shown by current WV imagery. To our southwest, a plume of robust moisture is pushing northeastward out of the Gulf of Mexico, which is currently yielding some scattered showers, storms, an mainly widespread high cloud cover across GA and SC. This surge in moisture is expected to continue pushing towards our forecast area through the day today, with at least scattered showers and storms forecast to develop as a result. The copious high cloud cover blanketing the eastern 2/3rds of the forecast area currently is adding a nice fly in the ointment to the forecast, though. Unlike the stratus we have had in recent mornings, this is less likely to thin as the day goes along and may act as an inhibitor to convective development across a lot of the area this afternoon. For instance, it is noon and we are only in the low 80s across much of the FA. Mean HREF and RRFS soundings show convective temps only ~86F-89F across the area this afternoon, so it really will not take much to get convection going. If/when it does get going, moisture-rich profiles will favor heavy, efficient rainfall. WPC has included the eastern 2/3rds of the forecast area in a Slight Risk for excessive rainfall this afternoon and evening as a result. Despite CAPE profiles >2500 j/kg, severe weather seems unlikely. DCAPE & TEI values really aren't robust enough to yield strong microbursts, so it will really take an impressive core aloft to get a severe downburst today.

More of the same is expected on Saturday and Sunday. Cloud coverage will likely hang around in the morning hours, and its extent and duration is expected to modulate storm chances & timing each afternoon. With PWs >2" both days, expect showers and storms to consistently be a threat. The better forcing does look to be in place on Saturday as the trough will still be in place to our west (despite it gradually weakening and lifting northward). Isolated instance of flash flooding will remain a threat both days, with highs in the mid to upper 80s.

KEY MESSAGE 2: Well above normal conditions expected to return by next week, with dangerous heat index values again possible.

As we get into next week (and really into the beginning of September), there remains a strong signal for above normal temperatures. An anomalous 500 hPa ridge is forecast to build across the central Plains on Sunday and begin to flex its strength eastward across the southeastern CONUS by the middle of next week. Ensembles are already painting a strong signal for an anomalous and extended heat wave. ECE EFI values for temperature of 0.7-0.8 & non-zero Shift of Tails values in the 4-8 and 5-9 day periods suggest the potential for anomalous temps across the area for an extended period from Tuesday of next week through the end of this forecast period. Some guidance disagrees on where the ridge settles by the end of next week but confidence is increasing in anomalous temps in the mid/upper 90s in the Tues- Fri period of next week. Surface dewpoints look high as well, increasing the probability that we see heat index values of at least 100F-105F multiple days in a row next week, with limited shower/storm chances to help aid in the heat.

AVIATION /18Z FRIDAY THROUGH TUESDAY/

Overcast skies have limited destabilization through early afternoon. HREF members do show convection developing in the upstate of SC along a stalled front, and along the coastal plain, then converging across the area later this afternoon and evening. Inconsistencies in coverage/timing of the various members do make for a somewhat uncertain forecast. Have included a PROB30 at each terminal, but have trended later with the timing, generally showing potential thunderstorms between 20Z-02Z at most terminals along with some flight restrictions.

Guidance is fairly consistent showing additional low stratus and fog late tonight into Saturday morning. Expect IFR or LIFR conditions at all terminals from about 09-14Z. Have also introduced showers at KOGB after 14Z as guidance is suggesting convection redeveloping along the coastal plain by Saturday morning. It's very possible that ceilings may not rise to VFR levels at most terminals until the end of the forecast period.

EXTENDED AVIATION OUTLOOK...Restrictions possible from showers and thunderstorms into this weekend. Drier conditions expected early next week.

CAE WATCHES/WARNINGS/ADVISORIES

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