textproduct: Columbia

WHAT HAS CHANGED

A low end severe threat is possible both today and Sunday with scattered convection. Aviation discussion updated for 12z TAFs. Minimum change to heat outlook the coming week.

KEY MESSAGES

- 1. Scattered afternoon showers and storms each day through Monday. Isolated severe storms possible today and Sunday.

- 2. Prolonged hot pattern expected with dangerous heat possible this weekend and a signal for a more impactful, intense heat event by the end of next week.

DISCUSSION

Key Message 1: Scattered afternoon showers and storms each day through Monday. Isolated severe storms possible today and Sunday.

There has not been a significant change to the outlook this weekend as surface dew points in the low to mid 70s, PWAT's near 2.0", and solid surface heating contribute to isolated to scattered convection each afternoon this weekend and possibly again Monday. Prior to the upper ridge fully building in next week, a couple weak shortwaves are progged to move near region on its eastern periphery today and again on Sunday. This subtle forcing is all that will be needed in this moisture rich environment (MLCAPE between 1500-2000 J/kg) to get scattered showers and storms going. One change today and Sunday is deeper mixing is expected during the afternoon and into the evening, aiding in creating inverted "v" profiles which contribute to DCAPE values between 700-1000 J/kg. This deeper mixing also contributes to TEI values between 20-30, indicating the increased risk for downbursts. 00z CAM's support the potential for isolated strong to severe storms/clusters late this afternoon into the evening and again Sunday afternoon as well with multiple including the HRRR, HRW-ARW, HRW-NSSL, and RRFS explicitly depicting cells with 40-55 mph wind gusts. Due to this favorable environment, and sufficient forcing, a Marginal Risk (level 1 out of 5) is seen for much of the FA north of a line from Orangeburg to Aiken to Lincolnton GA today.

The upper ridge begins to slowly build in a bit more Monday, but lingering moisture is expected to bring another afternoon/evening with scattered showers and storms. There is less confidence in potential for any isolated strong to severe storms Monday, which is also displayed in recent AI/ML guidance where a weaker signal is shown than that for this weekend.

Key Message 2: Prolonged hot pattern expected with dangerous heat possible this weekend and a signal for a more impactful, intense heat event by the end of next week.

The major message heading into this weekend and for the next 7-10 days for that matter will be the prolonged period with hot/humid temperatures. Overall, there has been little change across Cluster and other ensemble guidance. The general evolution of the synoptic pattern is as follows. Weak troughing should persist across the eastern CONUS today and Sunday, but will increasingly give way to the amplifying ridge over the central US into early next week. This pattern will aid in keeping dew points in the low to mid 70s and bringing high temperatures into the mid to upper 90s. These factors will combine to bring heat indices up to around 105F today and Sunday, though afternoon convection mentioned in Key Message #2, may aid in bringing some reprieve. Monday and Tuesday act a bit as transition days with the a deep trough across the western US amplifying the ridge toward the NAEFS 99.5th percentile as it now centers over the Ohio Valley. For the FA, this means hot temperatures in the mid to upper 90s persist, but building surface high pressure in the Northeast begins to aid in bringing slightly "drier air" that likely lingers into the mid week period. Despite this, heat indices near to just above 100F will remain likely during the early week and into the mid week.

Late this week and the holiday weekend is where the unusually consistent signal for intense heat across ensemble and cluster guidance persists. Of the four LREF clusters, nearly 70% of members fall into two clusters for the July 2nd-3rd period, which is impressive considering this is still 6-7 days out. These clusters also do not differ significantly in the strength of the robust ridge (all are near the 99th percentile), but only have slight timing differences, also showing the increased confidence. As this impressive ridge begins building into the Mid Atlantic and 850 mb temperatures likely near or exceed 20C, temperatures pushing into the upper 90s and near 100F become increasingly likely mainly Friday and Saturday. This is shown with around 70% of individual members across the LREF clusters showing max temperatures that reach 100F. With the FA not being directly under the ridge, humid conditions are likely as well, bringing heat indices that could exceed 105F. As mentioned in previous discussions, possible afternoon convection could throw a bit of a wrench in this, but confidence in this convection occurring is not too high at the moment.

Overall, prolonged heat builds into the FA starting this weekend, continuing through the week before possibly amplifying a bit more into the holiday weekend where heat products may be needed. Be sure to take heat safety precautions and monitor children, the elderly, and pets.

AVIATION /10Z SATURDAY THROUGH WEDNESDAY/

VFR conditions likely into Saturday afternoon with typical summer conditions before scattered storms develop.

The unsettled, summer pattern continues Saturday with some shallow low impact ground fog in the morning followed by cu and scattered storms in the afternoon; as of 11z, only still VFR vsby reductions from MIFG. Light southwest winds expected throughout the day outside of any storms. Convection should hold off until after 18z across the area, with the best chance for stronger storms at CAE and CUB. Regardless, confidence is only high enough for a prob30 at all sites with the expectation of a tempo likely in later TAFs.

EXTENDED AVIATION OUTLOOK...Diurnal convection and associated restrictions remain possible Sunday and into the early week before slightly drier air limits rain chances later in the week. Brief morning vsby/cig restrictions also possible into early next week.

CAE WATCHES/WARNINGS/ADVISORIES

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