Back in April, the team of university researchers creating projections for the course of the coronavirus pandemic in Colorado mapped out some scenarios.

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In the most optimistic, Coloradans would maintain 65% social distancing through the summer that is, about 65% fewer social interactions than normal. If that happened, the scientists concluded, the toughest days of the pandemic had already passed.

The team also looked at what would happen if the level of social distancing dropped further, and it wasnt good. In most scenarios, the need for critical-care hospital beds to treat people afflicted with COVID-19 would exceed the number of such beds the states health care system could provide. Thousands more people could die if the state didnt maintain enough social distancing, officials said then.

The lowest level of social distancing the research team contemplated in April? 45%.

Thats what makes the teams latest report which was released last week and apparently helped persuade Gov. Jared Polis to issue a statewide mask mandate so bracing. In that report, researchers estimate Colorados current level of social distancing is only 40%. (So thats only 40% less than we were all interacting in January.) Their projections show cases and hospitalizations increasing rapidly.

In short, even though Coloradans are moving around more than at any time since the pandemic started, the state could be as little as six weeks away from running out of critical-care hospital beds to treat COVID-19 patients and others who need them. If nothing changes, the modeling teams projections show peak hospital demand hitting in mid-October when there would be roughly 6,200 people in need of a critical-care bed about 4,400 more people than the states hospital system can handle.

The data is beginning to be alarming, Polis said last week when announcing the mask mandate.

Here are nine more charts that show just how alarming it is:

The key to predicting the spread of COVID-19 isnt really the level of social distancing taking place. Its the virus reproduction number, also known as R0 (pronounced R-naught). Thats the average number of people that each infected person passes the virus onto.

If the R0 is 1, the virus spreads linearly. One person leads to one additional case, which leads to another additional case. The virus spreads, but in a tidy, controlled, slow fashion. This is what it looks like over 10 generations of spread:

If the R0 is below 1, new cases decline over time. The virus fizzles out because not enough people are catching it to keep it alive.

During the stay-at-home period, Colorado achieved this feat, with the R0 dipping to near 0.5 and the virus in decline, according to the modeling teams estimates.

But since the stay-at-home order ended, the R0 has been on the rise. It crossed back over 1 in late June, hit around 1.2 in the first week of July and now may be as high as 1.8, according to the teams latest report.

The R0 is not as high as it was earlier in the year in Colorado, when it was perhaps as high as 5. But an R0 of 1.7 still means the state is experiencing exponential growth of the virus.

To provide a sense of what an R0 of 1.7 means, we calculated out 10 generations of case growth. Starting with just a single case in the first generation, the total number of cases rises to more than 280 by the 10th generation.

Heres what that looks like, using the same scale as the chart above:

These generations could turn over quickly, too.

The average incubation time between when someone is infected with the novel coronavirus and when they start showing symptoms is five to six days. But people can be contagious one to three days before showing symptoms.

So its entirely possible to get through 10 generations of spread within a months time. And that shows why, though everything may seem pretty mellow now, the situation can worsen rapidly with an R0 even just slightly above 1.

Heres another way of visualizing how fast that spread can occur with an R0 of 1.7. (We did some rounding to the nearest whole number to make this visualization work. Heres the chart this animation comes from.)

Until a couple weeks ago, a chart plotting COVID-19 hospitalizations over time in Colorado looked like a rather dramatic mogul rising quickly and then dropping off almost as fast. Now, though, it looks like a ski jump, with hospitalizations rising back to a level not seen since May.

Likewise, last week ended with the most new cases of COVID-19 reported to the state since late April.

So far, deaths due to COVID-19 have not shown a rebound in Colorado. But they also tend to lag behind some of these other warning signs by as much as a month. And other states where epidemics resurged sooner than in Colorado are now beginning to see rising death tolls.

This is the really alarming thing about the new modeling projections from the Colorado researchers. If social distancing levels dont change, the state will exceed its critical-care hospital bed capacity by Sept. 3 and will stay above capacity for a solid two months.

There are roughly 1,800 critical-care hospital beds in the state. But, by Oct. 16, the model predicts 6,200 people will be in need of such a bed. And that could prompt hospitals to implement their crisis standards of care, which will decide who gets a bed and who doesnt. (Its worth noting that these estimates of bed need are for the number of people who might need one for any reason heart attack, stroke, car crash and not only those who will need one due to COVID-19.)

And, as that chart also shows, even if Coloradans start staying home more, theres no guarantee that we will keep COVID-19 cases low enough to overwhelm hospitals. Instead, we need to get back to around 65% social distancing to avoid exceeding critical-care bed capacity. Thats roughly the level of social distancing we had in early June, according to the modeling team.

And theres one group that needs to hear this message more than others, frankly. The resurgence in cases has largely been driven by people under 40 years old. That group now accounts for nearly 60% of new infections and a quarter of hospitalizations.

But, whatever your age, the data in Colorado are becoming increasingly clear. The sun may be out. But, as much as you can, you need to stay in.

The good news, Polis said last week, is there is time, there is time to act. To the extent that theres been a party the last week or two, the party has to end.

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10 charts that show why the coronavirus pandemic may be about to get a lot worse in Colorado - The Colorado Sun