textproduct: Columbia

WHAT HAS CHANGED

Aviation discussion updated for 18z TAFs.

KEY MESSAGES

- 1. 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.

- 2. Scattered afternoon showers and storms each day through Monday. Isolated severe storms possible Saturday and Sunday.

DISCUSSION

Key Message 1: 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.

Guidance remains impressively consistent with its signal for prolonged heat over the next 7-10 days. WV Imagery early this afternoon reveals the major players coming into place to support a long duration period of heat throughout and beyond this forecast period. A weak shortwave continues to progress towards the area, forecast to continue weakening as it does so. An upper level ridge, stretching from the central Atlantic into the Gulf is building in strength today. Further upstream, the deep and anomalous upper level trough is pushing into the western CONUS, forecast to continue digging over the coming days. This is forecast to yield a rapid amplification of the upper level ridge this weekend, with it retrograding northwest and settling in the Mid-MS and OH Valley region by early next week. Dewpoints in the upper 60s and low 70s this weekend should combine with highs in the mid to upper 90s to yield heat index values of 103F-106F across the area over the next couple of days. Afternoon showers and storms are expected to help alleviate some of the heat but it won't completely eliminate it. It is unlikely that we get to heat advisory criteria but keep heat safety tips at the front of your mind if you have outdoor activities!

As the ridge builds to the west, we will have a bit of a trough dig into the eastern CONUS briefly early next week, helping to cool temps a bit on Monday and especially Tuesday. The atmosphere will be a bit drier, with dewpoints mixing down into the mid 60s. By the middle of next week, though, intense heat continues to show up in guidance. The upper ridge is forecast to continue building by the middle of next week, with the ridge axis expected to shift more over/along the central Appalachians, with heights at the core of this ridge forecast to be in the 99th percentile from Wednesday through Friday night. Ensembles are nearly unanimous in showing high probabilities (80%+) of 850 hPa temps >20C arriving for the Fourth of July Holiday weekend. This is expected to promote highs of 100F+ each of July 2-4. The extended ECE EFI forecast for temps in this period reveals EFI values of 0.8+ and non-zero shift of tails values, indicative of intense heat in this period. We continue to stress the need to review heat safety guidance given the number of outdoor activities that are expected during the second half of next week and into the holiday weekend. Given we won't be directly underneath the ridge, there is a chance that clusters of thunderstorms could throw a wrench into this. However, that is for later forecasts. The main message remains that the synoptic scale pattern is reminiscent of intense heat waves we have had in the past, and the current forecast suggests a period of intense heat overlapping with the holiday weekend.

Key Message 2: Scattered afternoon showers and storms each day through Monday. Isolated severe storms possible Saturday and Sunday.

A plume of 2" PWs is currently passing through the area in advance of a weakening shortwave trough. SBCAPE is pretty robust given upper 80s temps and low 70s dewpoints so agitated cumulus is developing, with one specific cluster of thunderstorms currently across the eastern forecast area. Thunderstorms are likely to increase in coverage this afternoon, with a lack of shear and high 0C and -20C heights likely limiting storm intensity overall. A similar picture is expected to be painted on both Saturday and Sunday (and possibly Monday) as the combination of surface thermal troughs & decaying convection from upstream yields the potential for storms each afternoon. Strong storms are possible both days but are unlikely to be widespread. Monday's storm threat is a bit more uncertain as the trough driving Sunday's storms shifts eastward. However, guidance is a bit more aggressive with rain chances than it was 24 hours ago, so the trends will need to be watched.

AVIATION /18Z FRIDAY THROUGH TUESDAY/

Scattered showers and storms expected across the region this afternoon and evening with associated restrictions possible.

Satellite continues to show scattered to broken cumulus field across the region early this afternoon. Ceilings outside of showers should remain vfr between 3.5-4.5kft. Impacts from showers or storms will be able to bring ceilings down close to 3kft, and visibilities down to 4sm in -tsra, or even lower if stronger showers/storms can get developed. Handled convection with a tempo group at all sites through 22z, then prob30 through 01z. Once showers and storms diminish this evening, expecting mainly vfr conditions to prevail for the majority of the remainder of the taf period. Brief visibility restrictions may become possible at ags/ogb due to patchy shallow ground fog.

EXTENDED AVIATION OUTLOOK...Increasing heat and humidity Saturday afternoon and Sunday should yield diurnal convection and possible associated restrictions. Brief morning vsby/cig restrictions also possible this weekend and early next week.

CAE WATCHES/WARNINGS/ADVISORIES

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