Usual suggested dates are Aug 15 through Sept 15. Depending upon the weather, sometimes that can be stretched to Oct 15. The longer one delays, the more likely germination will suffer.

Download this
http://ir.library.oregonstate.edu/xmlui/bitstream/handle/1957/19232/ec1521.pdf

Here is a link that might be useful: maintaining a healthy lawn in western oregon

this year, fall top seeding is basically not going to work too well. unless you water the crap out of your lawn, its typical to wait till the rains start.

rainy 70 degree days are good for lawn germination. rainy 60 degree days not so much.

seed is decently cheap so i would top seed anyway. tomorrow.

I've been for waiting for rain to resume in order to overseed my lawn (Tacoma WA area), just did so the past couple of days knowing rain is supposed to start tomorrow. It's disappointing the temps dropped like a rocket but who is to say they'll stay that low? I'm hoping to get it to germinate to keep weeds/moss from invading the areas. I've tried seed when it's dry and it's a very tough thing to keep grass seed wet enough to properly germinate and not overwater to where it's TOO wet, mother nature seems to do it best...

If you're near Tacoma you're likely to be in Zone 8. The problem here is that it doesn't get consistently wet most of the time until November, at which time it also turns cold and stormy. So if you want to plant while it is still warm you have to water. However, we are supposed to now have at least a week of rain and it is not cold yet.

Since full greening of existing lawns and fresh germination of weedy grasses may not be seen until November I wonder how important it is that it be so warm during the sowing of turf grasses. In the past I believe I've seen it stated that you wanted it to at least be in the 50s for germination of grass seed, if this is true 60s should not be such a problem. 70s I have to wonder about, grasses like those used in lawns are oriented to a dry summer, during which their seed stalks dry out - why would such plants be inclined to germinate during warm weather, when it is likely to be dry?

You have to water lawns like mad to keep them green in summer here because it is against the natural annual cycle of turf grasses to be green and growing at that time.

Usually that Aug 15-Sept 15 timeframe for seeding or over seeding is associated with east of the Cascades - west of the Cascades, that is moved out 30 days (mid Sept-mid Oct). This year it is probably not out of line to extend that another couple of weeks :-)

Air temps do play a role but it is more important to maintain adequate soil temps to ensure good seed germination and those are much slower to drop. And it doesn't hurt that a later seeding date in this area tends to coincide better with our natural source of irrigation :-)

FWIW, sodding can be done any time you can comfortably work in the garden. If it's too cold or too wet for you, chances are the sod will have difficulty establishing as well. Too warm simply means you have to water more often.

Lots of differing opinions here too :-) but it all goes into the decision maling process. I think I will overseed the old lawn and sod the new part.

Many thanks.

I think that is a good decision kaybradj.
Seeding a new lawn now risks being washed out, or at the very least, the seeds being washed away.
Sod can be done anytime. I've put it down on prepared frozen ground, and came back a few days later to roll it in when it thawed.
Mike..retired landscaper.

Recent Portland rain has been of the seed-washing-away type.

Partly sunny in Portland today. You just never know at this time of year, I guess.

It's not November yet. November is when the hammer falls.