Lead Forecaster Daniel Crawley
Good Monday afternoon, we have a nice start to the workweek across the Western Carolinas but things will change in a big way tomorrow as the next have takes shape.
We are going to have another sprawling 500mb ridge across the Southeast US moving in Tuesday and holding firm through Thursday. While the ridge itself will not center over the Southern Appalachians, the 594dm line will be close enough to influence the pattern.
One of the differences with this heat wave compared to last week’s is that we have a much less humid airmass already in place and it will be overhead the region on Wednesday. At the 500 mb level, you can see where the ridge and the Northwest Atlantic trough works in tandem to keep a dry flow across the region. Precipitable Water values are going to be nearly bone dry compared to that of a week ago.
So, dry air at the surface will do a few things. First it will limit clouds from overspread and eventually blossoming into thunderstorms. Second it allows the actual temperature to rise a bit more compared to the dewpoints of last week.
Surface winds on Wednesday is highly suggestive of compressional heating as they will be coming out of the northwest (downslope) between 5-10 mph. That’s another factor going into the high heat potential.
The last thing working in favor of high heat is the placement of 850mb temperatures on Wednesday, reaching or exceeding 26 degrees Celsius across the region. That will be a few degrees higher than last week. Wednesday could actually turn to be the kind of day where a temp inversion sets up early in the morning, the temperatures starting the day in the mountains and high peaks could be similar if not a tad warmer to temps in the foothills.
Summary: Checklist for High Heat Potential
- Heights directly overhead the region: No
- 850 temps in excess of 24 degrees Celsius: Yes
- Low relative humidity: Yes
- Downslope Component at the surface: Yes
We have 3 out of the 4 important components in place for high heat. On Wednesday we are officially forecasting 96-98 in the foothills and 97-100 in the Western Piedmont. We are going as aggressive as the European model specificly indicates for Wednesday (101-104) but instead closer to the GFS (96-99).