Train for Ultramarathon and 5K at Same Time?

Is it possible to train for an ultramarathon and 5K race at the same time? Not really. And I knew that, but...I'm not that smart. I haven't run a 5K since last fall, focusing more on ultras (Dec, Jan, and July). About a month before the July 8 ultra, I started some speed work. Figured my August 5th 5K race could use a little preparation. Unfortunately, mixing long slow trail runs with fast road sessions just doesn't work well. Too tired to push hard and the VERY slow trail runs don't contribute much to my aerobic capacity. If you want me to run a slow 50K on August 5, I can do that easily. If you want me to run a fast 5K on that date, not so much. With two days to go for the 5K race, let's look at predictions for my finish time. 

• Last year (2022) race finish time: 22:20
• Time trial 2 weeks ago: 23:14
• Coros watch prediction: 22:51
• Runalyze prediction: 24:35
• Stryd prediction: 22:45

In the past, Stryd seemed to have the most accurate prediction. Coros seems about the same as Stryd. I think Runalyze is too conservative. I ran the same course in 23:14 recently so I should beat that time. I think 22:30 is possible. Maybe I can match last year's 22:20? I was disappointed with last year's finish--thought I could break 22:00. My plan is to run by Stryd power (not pace or HR) and keep the effort steady from start to finish. The course has several hills so I need to be disciplined and keep the EFFORT steady. Stryd suggests 310W as my goal. OK, I'll set my watch for a small range around 310 watts. Won't worry about pace. Hope we have good weather (looks to be warm and humid).  

Race update: Finished in 22:28 so I beat all the predictions. It was a warm and humid day. Looking forward to cooler fall weather and faster race times!