Relentless! That pretty well describes our current heat wave/drought/fire danger situation. As mentioned in the morning discussion, we will be close to record level temperatures both at night as well as during the day at least through the middle of this coming week. In fact, we started the day this morning with a record morning low which also happens to be the second warmest morning low for any day and any year here in Tulsa. That is largely a function of the urban heat island in which all the concrete and asphalt in the urban environment cools off much more slowly compared to the more rural locations.
The main cause of this heat wave is a dominant, warm, dry upper level ridge that is sitting over the state. It is expected to drift a little further westward and weaken somewhat late this week and into the weekend. That is the reason for trending daytime temperatures down somewhat during that time frame, but we are still looking at triple digit heat each day. Also, there is just enough of a weakness in the eastern fringes of that upper level ridge to allow a few, very isolated showers/storms to develop during the late afternoon hours. We have seen that over the last few days and that pattern should persist through the coming week as well. That means the more E and NE counties of OK and into adjacent areas of KS/MO/AR could see a few of those late afternoon showers/storms. The chances are quite small, but at least they are non-zero. If you happen to catch one of those, there may be some strong and gusty winds associated with it as well.
Not only is it too hot and too dry, but the fire danger situation is also enhanced by these conditions. Dew point temperatures have mixed out into the 50s and in some cases even the 40s this afternoon. That has allowed relative humidity levels to drop below 20%. Notice the relative humidity map on the right, courtesy of the OK Mesonet as of late this afternoon. That places additional stress on the vegetation as well as depleting what soil moisture is left and contributes to the evaporation rates which at times are exceeding ½" per day.
Wish I could say there is a pattern change on the horizon, but as was also mentioned this morning, that does not appear very likely anytime soon. Of the longer range guidance, the ECMWF has been the more consistent and it strongly suggests triple digit heat not only through the weekend but well into that following week as well. That dominant ridge aloft is expected to flatten a bit and drift further westward over the weekend, but then should rebuild over the Plains States going into that following week. There is some disagreement in that respect with some of the other longer range guidance, but will take a wait and see approach before getting too excited about any prospects for a break in this heat wave.
So, stay cool, stay tuned, and check back for updates.