Photo: John Moore/AP

It was 111 degrees Fahrenheit for Americans in Baghdad today (43 Celsius for the Iraqis), and it's supposed to be hotter - 117 F or 47C - for the rest of the week. That's in the shade, of course, for those who can find it. Such infernal temperatures are pretty much the same every year. Nothing is quite as predictable in Iraq as the summer heat.

But another simple fact is just as evident: the death toll among fighters tends to decline in the dog days, because nobody wants to have to do battle in that stifling air, and those who have to go into combat tend to move more slowly and cautiously.

On the other hand, to the extent public records are available on non-governmental Web sites like iraqbodycount.org and  icasualties.org (the Iraq Coalition Casualty Count, with which Newsweek did a major presentation on the Internet in December of last year), it seems that the civilian death toll, mainly from terrorist attacks, actually may remain high or rise in the heat of summer. Security forces are thinner on the ground. Roadside bombs can be put out at night and suicide drivers don't usually have to brave the hellish heat for very long before they punch their ticket to Paradise.

All of this needs to be taken into account when we look at the results of what the White House has called "The New Way Forward" in Iraq and what the rest of us call "the surge."

The last official Pentagon report on "Measuring Stability and Security in Iraq," at the beginning of June, largely ignored the impact of the weather. Its historical time lines and graphs were based on political moments that often crossed over seasons, and comparisons were made with "the previous quarter," not the same quarter the previous year. Probably the important new report due from U.S. Commanding General David H. Petraeus in September will take the same air-conditioned approach.

But a look at the Iraq Coalition Casualty Count's statistics and graphs shows that there is usually a decline in the number of Americans killed during the summer - June, July and August -- followed by big, even shocking increases as the weather gets more bearable and the fighting season resumes in October, November and December. If the rule is not infallible, the trends certainly are clear.

The carnage ebbs and flows through the rains of January and February, then, in this case without fail, declines dramatically during March, possibly because this is the annual season of blinding dust storms known as khamsins (as in the March 2003 photograph above). Sure enough, it was at the end of March this year that Sen. John McCain and others proclaimed that the surge was making great advances.

In April and May every year, however, the battle picks up again dramatically before the usual summer subsidence. This year was no exception: 81 Americans killed in March, 104 in April, 126 in May, 101 in June, 79 in July, and 48 thus far in August.

It's probably too much to say that the weather in Iraq matters more than the best-laid plans of the administrations in Baghdad and Washington, but it may be a more reliable indicator of the future.