This Is All Pretty Incredible

What a deluge we are having today.  The precip totals across portions of the southwest US this August and early September are truly remarkable.  The irony is that in other parts of the so-called monsoon region, precipitation has been well below average.  

Let's have a look at some analyses and numbers. The National Weather Service produces a gridded precipitation analysis for the continental US that one can use to examine percentages relative to a long-term average.  The analysis has some serious warts in places (i.e., there are areas with poor radar coverage and no observations that cause artifacts), but for the most part, it is quite helpful in illustrating what has been going on over the past 30 days.  It shows well below average precipitation in south-central and southeast Arizona and most of New Mexico.  These are areas typically see the most monsoon precipitation.  

Then there's southern Califonia, Nevada, southern Idaho and western Utah.  Well above average including > 600% of average in some areas.  Now these are areas that see little precipitation, but still therte are widespread areas with > 2" and lots of local areas with > 5". Some of this is due to the remnants of Hurricane Hilary, but there have been other potent monsoon surges in this region. 

How about we look at some numbers from 1 August through 4 September at a few sites.  

For Salt Lake City, we've received 2.77" of rain through yesterday (3 September) and about a half an inch so far today.  That pushes us up to about 3.25" with more possible.  That will put us at least in the top 3 for the period with #2 being 1945 with 3.29" and 1968 #1 with 3.66".  Basically, this is easily one of the wettest monsoon periods on record.  

St. George has had so much rain it's ridiculous.  Not including today, they've had 5.40".  The previous record was 3.07" in 1925.  That said, there is a bit of an asterisk since the records for St. George are not complete and there are quite a few periods with a large number of missing days.  Still, that's a hell of a lot of rain.  

Las Vegas has more complete records back to 1937.  Not including today (I haven't looked to see if they have or are getting anything), they've had 2.35", good for #2 behind 1957 (2.59").  There are two other periods with more than 2", 1979 and 2012.  

Source: https://xmacis.rcc-acis.org/

What to have a laugh.  Check out these numbers for Death Valley.  The site has complete records back to 1965, but there are some gaps prior to that.  Still, they are at 2.43", compared to the prior record of 1.89" set just last year).  Most of this year's precip was from Hilary.

Source: https://xmacis.rcc-acis.org/

I could go on, but you get the point.  This is a dry region.  Portions of California really got bombarded by Hilary.  One event did the damage.  Multiple monsoon surges have affected western Utah.  Critical in nearly all of these events has been the interplay of monsoon moisture, often originating from near the Gulf of California but also potentially including moisture from the Gulf of Mexico, with troughs in the mid-latitude westerlies.  

Just as an example, below is the GFS analysis for 1800 UTC 1 September (1200 MDT Friday), which was the precursor for this current event.  At 700-mb (lower left) flow originating over the Gulf of Mexico is confluent (i.e., merges with) flow moving over Baja California and the Gulf of California over the Lower Colorado River Valley.  A corridor of strong vapor transport (lower right) extends through the Lower Colorado River Valley into Utah.  All of this ahead of a closed low over northern California and Oregon.  

The interplay between the monsoon moisture and the troughs in the midlatitude westerlies are often critical for precipitation in northern Utah as one has to get the monsoon moisture into our area.  Additionally, the flow associated with the midlatitude trough can help with thunderstorm dynamics, although for the current storm, we almost have a winterlike system with monsoon moisture.  The latest radar loop shows lots of precipitation features in northwesterly flow like we would see in the winter or spring.  Hopefully it comes out.  Blogger has been pretty cranky lately with movies.  

All of this rain makes me very happy.  I'll take wet sweater weather over 100°F nuclear summer any day.