textproduct: Columbia

WHAT HAS CHANGED

Aviation discussion updated for 18z TAFs.

KEY MESSAGES

- 1. Dangerous heat is expected through much of the period and into next week as an upper level ridge builds south of us and then retrogrades into the OH/TN Valley. Showers and thunderstorms during the period may help but there is too much uncertainty to specify when or where that will occur.

DISCUSSION

Key Message 1: Dangerous heat is expected through much of the period and into next week as an upper level ridge builds south of us and then retrogrades into the OH/TN Valley. Showers and thunderstorms during the period may help but there is too much uncertainty to specify when or where that will occur.

The hottest portion of the summer thus far is expected to arrive beginning Friday and lasting through much of the next 7 days. Our weather today and Thursday should continue to be quite nice as upper level troughing pushes over the area and weakens by Friday. Higher heights and an increase in surface moisture is expected to begin yielding intense heat by Friday. The increase in surface moisture, in addition to the approaching & weakening upper trough, is forecast to yield scattered showers and thunderstorms on Friday afternoon. Strong storms aren't expected with this activity, just mainly garden variety thunderstorms.

From this point, the upper level ridge is forecast to begin establishing dominance across the eastern 2/3rds of the US. A strong and persistent western US trough is expected to be the impetus for the ridge building across the OH/TN valley region by early next week, with Saturday and Sunday (currently) looking like the most oppressive heat days through next Wednesday. ECE EFI values are elevated (0.7-0.8) with near 0 SOT values, indicating anomalous heat without extreme values (its tough to get high signals this time of year here so this signal is noteworthy). Low-level mixing ratios are near to slightly above normal, meaning we are unlikely to see dewpoints really mix out too much. This will help keep heat indices high and potentially near Heat Advisory criteria. This is in line with WPC Heat Risk which shows a Major Heat risk for both Saturday and Sunday. The other thing to watch for is strong storms on Sunday. The ridge is expected to build into the TN valley during this period, with a bit of a trough building on the eastern side of this. Thunderstorms are expected Sunday afternoon and evening as a result, with some strong convection possible. The best chance for this will be in the eastern/northeastern part of the forecast area where the weak shortwave is most likely to pass nearest.

As we get into early next week, the high heat is expected to continue but lower humidity is likely to push into some of the area Monday and especially Tuesday/Wednesday. Convergence aloft in the northeastern US should yield a weak surface high that will ridge down along the eastern slopes of the Appalachians through Wednesday. Lower mixing ratios in association with this surface high will likely yield lower dewpoints in the low 60s each afternoon, helping to keep heat index values more manageable. Heat Risk has actually fallen below Major risk for much of the eastern/northern FA both Monday and Tuesday in the latest run, which makes sense given the pattern showing up in model guidance. Major heat risk still remains across the western Midlands and CSRA both days, but the magnitude and intensity of the heat is somewhat uncertain given the relatively drier airmass expected to push in by Tuesday. Still, LREF ensembles show solid probabilities (>45%) of max temps >95F each day Sun- Wed, so it will still be hot. Heat Advisories may be considered given the duration of the heat, but we will likely need to evaluate that as the heat wave unfolds into next week. Wednesday through the end of next week begins to look oppressive again as the early week surface high shifts off shore and our surface flow returns to southwesterly again, bringing Gulf moisture back into the area.

AVIATION /18Z WEDNESDAY THROUGH MONDAY/

VFR conditions expected through the TAF period.

Broken to scattered clouds around 5-7kft will remain across the region through sunset this evening. Winds have mostly become variable around 5 knots across the region, and that will continue. Winds then diminish to 3 knots or less after sunset. An increase out of the south should occur by mid-morning Thursday as mixing begins. Although vfr is mainly expected through the period, there remains a possibility of brief visibility restrictions Thursday morning as low level moisture returns a bit, especially at ags/ogb. Confidence still not high enough to include in TAFs at this time.

EXTENDED AVIATION OUTLOOK...Increasing heat and humidity starting Thursday into the weekend should yield daily diurnal convection and possible associated restrictions.

CAE WATCHES/WARNINGS/ADVISORIES

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