I don't think I would put down a pre m, if you want to do some over seeding on thinner areas your going to stop that new seed from germinating unless your putting it down in a compost mix and top dressing. I would worry more about fertilizing at the highest rate every 4 weeks and keep good water on it and you will really see that grass go bonkers.
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Theres good even growth overall, but there are small bare patches aplenty if you look straight down at your feet... lots of dirt for weeds to get a grip, I'm particularly concerned with clover.

Will fertilizer and new grass naturally crow out weeds? Or will it give the weeds a real boost too?

Any specific fertilizer brand or percentages recommended for new grass in red rocky clay?

 

Dashunde,
I think you need the pre emergent. And there is time enough to apply it. Try to apply around the date of the first mowing. Looking at the weather data for St Louis--it looks like anytime in April would work. Try to get it down before the first 70 degree day.
http://www.climate-zone.com/climate/united-states/missouri/st-louis/

Without pre-emergent you will probably have a major crabgrass problem by the Fourth of July. It is not likely that the new grass will crowd out weeds. Fescue does not spread aggressively. If it was hydroseeded there is a good chance that a high percentage was perennial ryegrass (which comes up quick). Perennial rye may fade out; it is not at home anywhere temps get over 95 degrees. Plan to apply a top brand name fertilizer(Scotts or Greenview) with pre-emergent crabgrass control. Follow up with more fertilizer every 5 weeks. See the weather link. Spray the weeds about May and August. Overseed with new additional high-quality, disease resistant tall fescue when temperatures fall below 80 ( about September first)--try to get your grass thicker. The goal is no soil visible. Irrigation is big help.

Clover is not too hard to kill--anything with triclopyr usually is very effective. Crabgrass and spurge will be your main problems.

 

Dashunde,
I think you need the pre emergent. And there is time enough to apply it. Try to apply around the date of the first mowing. Looking at the weather data for St Louis--it looks like anytime in April would work. Try to get it down before the first 70 degree day.
http://www.climate-zone.com/climate/united-states/missouri/st-louis/

Without pre-emergent you will probably have a major crabgrass problem by the Fourth of July. It is not likely that the new grass will crowd out weeds. Fescue does not spread aggressively. If it was hydroseeded there is a good chance that a high percentage was perennial ryegrass (which comes up quick). Perennial rye may fade out; it is not at home anywhere temps get over 95 degrees. Plan to apply a top brand name fertilizer(Scotts or Greenview) with pre-emergent crabgrass control. Follow up with more fertilizer every 5 weeks. See the weather link. Spray the weeds about May and August. Overseed with new additional high-quality, disease resistant tall fescue when temperatures fall below 80 ( about September first)--try to get your grass thicker. The goal is no soil visible. Irrigation is big help.

Clover is not too hard to kill--anything with triclopyr usually is very effective. Crabgrass and spurge will be your main problems.

I say he little late for the first 70 degree day I say they had that most of the week I'm 3hrs north of him and had 4 days that hit 70 Tomorrow will be closer to 80

If Fescue was applied at heavy rate it will crowed out a lot weeds even crabgrass. But most people doesn't apply fescue at a high rate. They like to blend it with BG or rye to get that fast growth.

To OP since its Missouri clay you will need apply about 200 lbs of granular lime to keep that clay from sealing up.

You can apply crabgrass control. But if its thin I wouldn't do it. I would slit seed more fescue in it this is good time. Not sure what type fescue was used but k31 is real hardy on clay soil.
If crabgrass does come up in July hire someone to spray it .
Then come fall you can repeat the over seeding again if it needs it. Then come the next March you can apply crabgrass control.

 

Dashunde

You should put down a granular product that is high on nitrogen and includes pre emergent. This will prevent the crabgrass seeds from germinating and it will give the lawn a nice boost.

 

So far, just in the past 3 days the new growth has gone bright green and taken off again where the dog has been peeing.
From that I can only assume the whole thing needs a heavy dose of nitrogen, correct?

It looks like I should get plenty of Scotts with pre-emergent down today.

Should I over-seed today too?
I'm concerned with the slit-seeder beating the hell out of what is already there though, it will hit rocks and tear things up quite a bit.

On this is for sure... I need to get a better quality spreader.

 

So far, just in the past 3 days the new growth has gone bright green and taken off again where the dog has been peeing.
From that I can only assume the whole thing needs a heavy dose of nitrogen, correct?

It looks like I should get plenty of Scotts with pre-emergent down today.

Should I over-seed today too?
I'm concerned with the slit-seeder beating the hell out of what is already there though, it will hit rocks and tear things up quite a bit.

On this is for sure... I need to get a better quality spreader.

You do pre=emergent you cant seed now only do one or the other cant do both today

Good luck

 

Snyder is right. Pre-emergent will kill grass seed. Apply more seed in the fall.

http://www.weather.com/weather/today/l/USMO0787:1:US

Yep, its getting warm fast. Supposed to be 71 today. Hopefully the soil temperature is warming up a bit slower. Don't delay, the first crabgrass should become visible when the temperature first hits 80 degrees--its tiny--under a quarter inch--but experienced lawn professionals can spot it quickly. Once crabgrass is visible, a pre-emergent won't work.
Its difficult and expensive to have crabgrass sprayed after it appears above the soil--then you need to spray with a quinclorac product--early and often.

I would not use 13-13-13. Cheap; but no slow-release nitrogen and too much phosphorus (contaminates water and not needed). You should use a product that has about 50 percent of its nitrogen in the form of coated slow-release nitrogen, (at least 30 percent). For example Scotts 28-4-4. Slow-release is non-burning and it lasts about 6 weeks as compared to quick release which is gone after a couple heavy rains.

Get in touch with a local lawn care pro for best results. There are some good ones in your area. An owner-operated company will give you the best results. National companies will sometimes buy and use the same fertilizer analysis as in states 1000 miles from you.