Tuesday, October 6, 2015

Eastern Utah Is So Weird!

As noted by David, who commented on the previous post, the valleys and lowlands of eastern Utah are just plain weird climatologically.

If one classifies the precipitation climate over the southwest U.S., there are four major regimes.  The first (row a in the image below), covering most of California, northern Nevada, and the upper elevations of northern Utah and western Colorado, features a pronounced winter maximum.  The second (row b), covering much of Arizona and portions of southern Utah, New Mexico, and southwest Colorado, features a pronounced maximum during the monsoon.  The third (row c), covering the plains of eastern Colorado and New Mexico, is somewhat related and has a maximum in the summer with less precipitation in the winter.  Finally, there is a fourth regime (row d) in the lower elevations of portions of Nevada, Utah, and western Colorado where precipitation peaks in the spring.  This includes the Salt Lake Valley.

Source: Steenburgh et al. (2013)
If you look carefully at those plots, however, you can find a region that is not included and that is the valleys and lowlands of eastern Utah, including places like Vernal and Moab.  The climate there has a maximum occurring in October.

Why October?  I can speculate, but it really deserves some investigation.  As suggested by David, there could be a magic point as the monsoon tails off and we begin to see mid-latitude storm systems coming in that enables more moisture and precipitation to move into this area.  It might also be that this area got pounded by a small number of larger storms during the past few decades, skewing the stats for October (I haven't checked to evaluate the statistical significance of the October maximum).

In any event, eastern Utah has always been a little weird and even Mother Nature likes it that way.


  1. Oh No. Now all the wierdos in Sedona are going to head for Moab.

  2. Jim, this is not the first time that I've heard of a precipitation maximum in Fall in eastern Utah. As a young man trying quench my thirst for weather knowledge, I bought a copy of "Skywatch: The Western Weather Guide" by Richard Keen, Copyright 1987. (Great book, by the way, for a young meteorologist.) I pulled it off my shelf just now and found a map of the West that color-codes the season of greatest precipitation. The map is much cruder (probably hand-drawn) than the one from your paper, but indeed it shows that northeastern Utah, northwestern Colorado, and southwestern Wyoming observe the greatest precipitation in Fall. I emailed a picture of the map to you since I don't think that I can post graphics here. So yes, apparently there was a detectable signal of this phenomenon even 30+ years ago.

    --Brian Olsen

    1. Brian:

      I've seen a few plots of that type, but couldn't hunt one down quickly before I hopped on a plane this morning . I was unaware of that particular book. Thanks for sharing.


  3. Thanks for posting the plots of precipitation seasonality from the 2013 paper, I had not seen those before. Notice that the October precip max seems to show up secondarily in the areas that have an overall spring max (and vice-versa), although neither of these maxima is really apparent in the areas that are dominated by either winter or by summer monsoon precipitation. So the spring and fall maxima seem to be somewhat related at least in terms of their geographic distribution. My suspicion is that closed lows are a huge factor, with the addition (during the fall season) of monsoon moisture or tropical system remnants.

  4. Look up in the sky Utah a lot of chem trails today and yesterday . Watch the sky tomorrow this seems to happen right before a storm forcast, please research this matter for your self.