Warbler Guy, how do I know if warbler migration is strong? Migrating warblers are more dense on some spring days than other ones?

Good question, Hector (in Toledo, OH)

One that I recommend: Birdcast.info

(with the following pictorial graphic a past example from its web site) 

At the above link, you'll read about the current week's presence of migrators and predictions.

It is a great resource, given the BirdCast forecast highlights migrant species that you can expect to see near where you live (and elsewhere in Ohio) — in addition to several USA regions: Upper Midwest and Northeast; Gulf Coast and Southeast; Great Plains; and West. 

Regarding your question, depending on the season (and several other factors), Birdcast can help you anticipate the density and abundance to expect on an upcoming birding outing. For example, a large arrival of transient migrant songbirds could be expected for your outing, if the red/purple colors are present just south of you in the spring while a south "Gulf Stream" wind occurs. In turn, this push may result in fine birding the following morning after you view this development (at Birdcast).

I hope this answer helps you.....Feel free to float me more questions at DanielEdelstein@att.net or visit my web page for more migration information related to "Bird Arrival Times (Via Migration) For Marin Co. (where I live in the San Francisco Bay area) at WarblerWatch.com (choose the "Birding Links" pulldown menu and click on the above category: "Bird Arrival Times".

As for my birding tours that I continue to host while employing several social-distancing methods, details are noted via the "Birding Tours" section at my web site (WarblerWatch.com).

Regards and Happy New Year to you and all my followers.....Daniel