textproduct: Columbia

WHAT HAS CHANGED

Aviation discussion updated for 12z 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.

There has been 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 isolated to scattered 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. 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 between 30- 50% on Thursday before increasing to 50-65% Friday and Saturday. This signal is also supported in the latest EC EFI where values of 0.80-0.90 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 /12Z MONDAY THROUGH FRIDAY/

VFR conditions expected through the TAF period with some spotty stratus-fog possible around sunrise this morning.

Debris clouds have generally limited fog and stratus formation this morning, but there are a few spots it has developed where more clearing is present. Lingering stratus should improve after 13z. SFC winds start the day light and increase out of the S/SW at 6-8 kts after 15z. Isolated afternoon convection possible again this afternoon, with model guidance favoring a late afternoon into the evening time frame. For now, covering this potential with VCSH which can be refined with later forecasts. Any -SHRA/-TSRA diminish this evening with mainly high and mid level clouds tonight as winds decrease to light and variable again.

EXTENDED AVIATION OUTLOOK...A seasonal pattern of early morning restrictions and diurnal thunderstorms is likely through much of the extended.

CAE WATCHES/WARNINGS/ADVISORIES

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