textproduct: Columbia

WHAT HAS CHANGED

Confidence increasing that hot/humid conditions will persist into Saturday. Aviation discussion updated for 12z TAF issuance.

KEY MESSAGES

- 1. Potential for heat indices above 105F Saturday along with chance for stronger convection. Isolated to scattered storm chances persist into early next week with near normal temperatures.

- 2. Mostly dry conditions today and Friday with heat indices near 105F.

DISCUSSION

KEY MESSAGE 1. Potential for heat indices above 105F Saturday along with chance for stronger convection. Isolated to scattered storm chances persist into early next week with near normal temperatures.

The main change with this forecast package is increasing confidence in a slower moving front and thus hotter temperatures on Saturday. The upper ridge will slowly retrograde as the previously advertised trough digs into the eastern US, but 850mb temperatures are expected to remain near the NAEFS 99.5th percentile or even approach climatological max values. This is bringing lower IQR ranges in both NBM and LREF cluster guidance for maximum temperatures with increasing confidence in the persistence of max temperatures in the upper 90s. With seasonable moisture in place, heat indices between 105-108F seem reasonable and thus the need for a Heat Advisory will continue to be evaluated. Global models and LREF cluster analysis are also picking up on a shortwave moving across portions of southern VA into NC along with the surface front. This is expected to yield convection here and with the CWA in a northwest flow regime with the increasing troughing, there is the potential for this convection to move into the CWA during the late afternoon into the evening hours. With enhanced kinematics and strong instability, cannot rule out stronger convection, but as is typical with northwest flow regimes, confidence in convective evolution and longevity is a bit low at this time. Overall, heat safety precautions should be taken on Saturday with any outdoor activities and stay tuned for any changes in timing or intensity of potential convection later in the day.

The end of the weekend into next week is expected to yield near normal temperatures with continuing at least isolated chances for diurnal convection. This comes as the front slowly clears the area and troughing persists before the ridge is expected to slowly slide back in during the mid week.

KEY MESSAGE 2. Mostly dry conditions today and Friday with heat indices near 105F.

The forecast remains on track over the coming 48 hours as the robust upper ridge slides overhead today into Friday. There remains solid deterministic and ensemble agreement that as this ridge shifts in, temperatures should top out in the upper 90s each afternoon with minimal diurnal convection due to subsidence from the ridge. With PWAT's remaining near 1.90", surface dewpoints should stick toward the upper 60s to lower 70s each afternoon, bringing widespread heat indices between 100-105F each day. It is possible a few locations briefly touch or near Heat Advisory criteria today and Friday, but values are not expected to be widespread enough to warrant a Heat Advisory at this time. This will continue to be evaluated through the day today. Either way, heat safety precautions should be taken as we near the end of the week.

AVIATION /12Z THURSDAY THROUGH MONDAY/

Low impact morning fog and stratus possible in the eastern and southern Midlands, otherwise calm and VFR.

Calm weather expected through the TAF period with some sunrise MIFG and brief restrictions possible, but low confidence. OGB may briefly dip to MVFR through 13z. Otherwise, a hot typical summer day expected with cu field developing by late morning and generally southeasterly winds expected into the afternoon; sustained 5-7 knots with gusts to around 10 knots. Like Wednesday, a rogue shower- storm or two is possible, but confidence is far too low for even a prob30 mention.

EXTENDED AVIATION OUTLOOK...Chances for restrictions and thunderstorms increase this weekend as a cold front approaches.

CAE WATCHES/WARNINGS/ADVISORIES

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