textproduct: Columbia

WHAT HAS CHANGED

Isolated to scattered storms are developing across the area, with the potential for a few of them becoming strong. Dew points have trended a bit cooler for tomorrow afternoon.

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.

Some thunderstorms have begun to develop along a residual boundary draped across the central portions of the forecast area. A couple of these have become strong, but the severe threat continues to look low due to a lack of shear.

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 /18Z MONDAY THROUGH FRIDAY/

Temporary visibility restrictions in afternoon thunderstorms today. Highest coverage expected at AGS/DNL/AIK and OGB.

Convective coverage this afternoon has been much higher in the southern half of the forecast area than CAMs had shown. South of I-20, numerous showers and storms are expected to cause temporary VIS restrictions from periods of heavy rain from thunderstorms. Storms will diminish near sunset but we should still see a lingering shower/storm through the evening.

Convective debris clouds should hinder fog/stratus development again tonight. Model guidance already favored continued VFR conditions overnight. Since there will likely be more convective debris clouds than models had, this increases confidence in VFR TAFs. That said, we may still see brief early morning fog develop around 11Z or at sites that receive decent rainfall this afternoon. Light W or WSW winds expected each afternoon becoming light and variable around 01Z or 02Z.

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

CAE WATCHES/WARNINGS/ADVISORIES

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