textproduct: Columbia

WHAT HAS CHANGED

Evening update in Key Message #1. Aviation discussion updated for 00z TAFs.

KEY MESSAGES

- 1. Isolated diurnal storms possible each day this week, with diminishing chances midweek. A strong storm cannot be ruled out. - 2. Increasing heat and humidity is expected this week, especially by the mid to late week.

DISCUSSION

- 1. Isolated diurnal storms possible each day this week, with diminishing chances midweek. A strong storm cannot be ruled out.

After a fairly active early afternoon, conditions have quieted down this evening outside of some newly developed convection in the Upstate of SC and east-central GA. SPC mesoanalysis indicates modest recovery occurred in wake of the early afternoon convection, but lingering MLCIN remains along/south of I-20. Northern spots remain fairly untapped with MLCAPE values near 2000-2500 J/kg remaining, but increasing inhibition is expected with the loss of heating. There also appears to be an outflow from prior convection in the far northern Midlands. If convection from the Upstate can reach, a few storms could be possible (cannot rule out a stronger one), but even this activity has weakened some over the last 1-2 hours so this is not looking likely. Mostly dry conditions are then expected heading into the overnight.

There remains relatively minimal change with this forecast package in terms of rain/storm chances through the week. Maintenance of dewpoints in the low to mid 70s amidst robust heating each day is expected to yield seasonable to strong instability during the afternoon through the weekend. A weak embedded perturbation may aid in bringing additional coverage this afternoon before coverage is a bit more spotty to isolated during the mid to late week as forcing from multiple shortwaves remains just north of FA. Global models generally indicate rising mid level heights late this week into the weekend as ridging strengthens over the central CONUS with a shortwave ridge moving into the Great Lakes, but there continues to be the potential for weak troughing moving in this weekend. There is also the possibility for a diffuse frontal boundary to near FA by this weekend as well. Considerable uncertainty remains in this however, as seen in the generous spread across the LREF's four clusters. Overall, the potential for increased rain chances exists by this weekend, but confidence in realizing this is low at the moment. As is typical with our diurnal pulse convection, a strong storm or two cannot be ruled out with the risk of strong downburst winds, but widespread severe weather remains unlikely.

- 2. Increasing heat and humidity is expected this week, especially by the mid to late week.

Strengthening ridging just to our west through the week should aid in bringing a warming trend with 500mb heights peaking at the NAEFS 97.5th percentile late in the week. Temperatures likely reach the mid to upper 90s each day Tuesday through at least Friday. Persistent southwesterly flow on the periphery of a Bermuda high should also aid in keeping PWAT's near 2" and surface dewpoints in the low to mid 70s. However, dew points are have trended downward for Tuesday afternoon with the latest guidance. With the expected lower coverage of diurnal convection each day, confidence is high in heat indices above 100F during this period. The potential for heat indices above 105F and possibly nearing Advisory criteria (108F) increase during the mid to late week with LREF probabilities for indices above 105F remain between 30-50% on Thursday before increasing to 50-70% Friday and Saturday. This signal is also supported in the latest EC EFI where values of around 0.90 are seen Friday and Saturday. It is worth noting the uncertainty in the synoptic pattern and thus rain chances this weekend brings large NBM IQR spreads Saturday and Sunday (8-10 degrees). Either way, hot/humid conditions are likely most of this week with increasing confidence in heat indices exceeding 105F by the mid to late week. With the persistence of heat this week, be sure to take heat safety precautions.

AVIATION /00Z TUESDAY THROUGH SATURDAY/

Relatively high confidence in VFR conditions through the TAF forecast period.

Diurnal convection is waning with only some convective debris high clouds expected to impact the terminals this evening. While it cannot be totally ruled out that there may be some brief predawn fog in areas that received rainfall, all guidance is showing VFR conditions persisting through the forecast period. Winds should diminish to 3 knots or less overnight then pick up from the west-southwest after 15z increasing to 8 to 10 knots after 18z.

EXTENDED AVIATION OUTLOOK...A hot and drier weather pattern develops through the week. Convective coverage will be low and restrictions likely minimal as highs push into the upper 90s.

CAE WATCHES/WARNINGS/ADVISORIES

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