Astronomical Fall arrives Thursday morning at 9:21AM which is the moment the sun crosses the celestial equator. If interested, you can find more information regarding the equinox and the seasons in general here. At any rate, you certainly would not know that Fall has arrived from our weather as temperatures will continue to be on the order of 10 degrees or so warmer than normal.
At least we have had a bit of a break in the oppressive heat & humidity today due to the fact that our dew points have dropped off as somewhat drier air has moved in from the east. Notice the 24 hour dew point temperature change as of mid-afternoon for example.
Temperatures today have also dropped off a few degrees from recent days as we have had a little more high level cloud cover. Here are the max/min across the state, courtesy of the OK Mesonet.
By the way the max/min for Tulsa today has been 93/72 but the relative humidity during the heat of the day was closer to 40% which produced a maximum heat index value of ‘only’ 96; certainly better than the 107 we had yesterday and the 109 on Monday. By the way, the normal max/min for this time of year is 82/60 to put things in perspective.
Those lower dew points will also allow for somewhat milder overnight conditions as we should only have some high level, cirrus type clouds for tonight. Together with a light SE breeze, temperature should then drop into the 60s area wide for tonight. Thursday will be much like today with just some of those high level clouds around and afternoon highs back into the lower 90s along with a SE breeze. Also, the somewhat drier air will keep those heat index values in check with maximum values much like today and only a few degrees above the air temperature.
Friday will see more of the same, but after that is when things finally start getting a little more interesting. Notice the upper level wind flow at the 18,000’ level from this afternoon and then compare that with the flow on Sunday. Have been using these charts for the last several days to illustrate the day to day variation in model solutions as this storm system approaches. The data runs for today are faster and have placed the main upper level low further north by Sunday which puts a very deep layer of abundant moisture over OK. That is why we have cranked up the rainfall chances on Sunday as you can see on our forecast page.
In advance of this system, could see some scattered showers/storms for the afternoon and evening hours of Saturday, but the main event still looks to be during the day Sunday. This is not a severe weather setup but certainly could produce some locally heavy rains as the 7 day QPF suggests. Keep in mind this is an areal average and does NOT mean that everyone will receive that much rainfall. As always, some locations could easily receive much more while others receive much less. Also, we have had several systems in recent weeks in which the data suggested a good soaking but which certainly underperformed. So, will take this QPF with a grain of salt, but at least the potential is there.
After Sunday, the longer range guidance diverges creating more uncertainty for early next week. At least some lingering showers/storms are expected into the day Monday and for now will go with a dry solution for Tue/Wed, but that is certainly subject to change. One thing that will occur though is a decent break in this recent heat wave with northerly winds bringing much milder conditions into the state. Actually, temperatures will just be closer to normal for a change but it will certainly feel cooler compared to recent days.
By later next week through that following weekend, the 8-14 day outlook continues to suggest above normal temperatures. Normal daytime highs are in the 70s by then so the above normal temperatures should translate into 80s for that time period which still represents some relief from recent days.
So, stay tuned and check back for updates.