Nora to bring tropical downpours to the Desert Southwest, Four Corners

Another surge of moisture is coming to the Desert Southwest and the Four Corners region as the moisture from Nora, a tropical system near Mexico, streams northward over the second half of this week.

This surge of moisture will lead to tropical downpours and the threat for flash flooding starting Tuesday night and lasting into Wednesday and Thursday.

This will not be a situation like we'll see with Ida in the eastern United States, where a large mass of rain moves from the Gulf Coast to the Northeast.

Instead, Nora will send tropical moisture northward through the Four Corners into Wednesday and Thursday. There will be an increase in thunderstorm activity, which will tap this moisture-laden air mass to produce flooding downpours in some areas. The end result will be a setup that produces localized flooding rather than widespread issues.

This tropical surge will be most noticeable in areas farther to the north. Take a look at the precipitable water (a measure of moisture content in the atmosphere) values on Wednesday.

While the large orange area in southern Arizona is very noticeable on this map, the moisture surge is just as anomolous farther north into eastern Utah and western Colorado. The record values for precipitable water in Grand Junction, Colorado in early September are generally between 1.1 and 1.3 inches, very close to what is being forecast. The average is about half of that.

The result will be the threat for flooding downpours into Utah and Colorado, especially from Wednesday afternoon into Thursday and even Friday across Colorado. The threat across Arizona and western New Mexico will be mostly from Tuesday night through Thursday.

Areas farther to the west, which were more in play when I wrote the first blog on this storm, now will likely see fairly minimal impacts. The deserts of Southern California should remain dry.

Las Vegas will be on the cusp of some of these showers and storms. While there can be a downpour or two around from Tuesday night into Wednesday, it looks like the bulk of the action will stay off to the east.

Things will largely calm down from Friday into the weekend as some drier air moves back into much of the Southwest.

It's worth noting that this is not the first time a storm named Nora has impacted the Southwest. The 1997 version of Nora brought heavy downpours to parts Southern California and Arizona. The Harquahala Mountains recorded 12.01 inches of rain, one of the highest rainfall amounts from a tropical system ever recorded in Arizona.

Meanwhile, not too far to the east, there was less of a tenth of an inch of rain in Phoenix. We will likely see drastic differences in rainfall from this iteration of Nora as well.

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