You wouldn’t know the Fall Equinox was days away given today’s weather. Our high temperatures and heat index values were straight out of July. Even though we missed a record by a few degrees, our heat index values more than made up for that shortfall. The map below shows maximum heat index values hit 110° in a few locations in the state. That’s sweltering heat no matter what time of year. In the second half of September, that’s just ridiculous and likely record-breaking.
Moving forward, that heat is not going away. Tuesday is likely to be just as hot as Monday as an unusually strong ridge of high pressure (one we tend to only see from late June to August) has built overhead. This means, yet again, heat index values will soar to and past 100°. September? More like Sweatember.
The ridge of high pressure will slide east a bit and the heat will ease its grip just a bit. By Wednesday, stronger winds will usher in drier air. That will keep the heat index below the century mark and allow overnight lows to dip below 70°. Still, those readings will be well-above normal through the end of the week. Keep in mind Tulsa’s average high is in the lower 80s and the average low is right at 60°. Normal, at this point, is a nice taste of fall.
Summer heat can only hang on so long at this point in the year. This heat wave will give way to a stormy pattern by the weekend as a deep upper-level trough in the jet stream brings deep moisture to the region, funneled northward between the high to our east and the low to the west. The weather pattern as we start the weekend is shown above. What initially appeared to be a clean-sweeping cold front thrust southward by refreshing Canadian air is turning more into a sluggish front with that much cooler air being held in the northern tier of the states. That is because part of the upper-level energy is now likely to split off and drift westward, essentially cutting the momentum of the surface front in half. This is still several days out from being locked in, but the trend is looking wet, but not drastically cooler.
Showers and storms will start to arrive Saturday, but Sunday and Monday will be the best focus for heavier rains as the frontal boundary arrives. Since much of the upper-level energy gets held to our north and west, the higher rain totals are likely to be centered that direction in western parts of Oklahoma. As drought continues to build in eastern Oklahoma (shown below), this is somewhat unwelcome news.
If you are craving a long-overdue cool-down, next week will look nicer for you. While temperatures may only dip to near-normal on a few of those days, we will be reminded that it is in fact autumn and going to the Tulsa State Fair may seem a bit more appealing. The cool-down may be more a result of cloudier, potentially wet days, but it’s only a matter of time before that building cool air mass in the northern latitudes comes racing south our way.