How the October 2025 Deluge Compares to the Past

More thunder and rain last night.  Observations from the Salt Lake City International Airport indicate another 0.68" in the gauge, all if it falling yesterday evening and overnight.  If my math is right, that brings the monthly total up to 4.16", topping the previous record for the month of 3.91".  Really, it wasn't even a fair fight.  It's only October 14!

With the October record easily dispatched, I thought we might aim higher.  First let's have a look at the records for each calendar month:

January 1918: 3.89" 
February 1998: 4.89" 
March 1891: 4.66" 
April 1944: 4.90"
May 1908: 5.76"
June 1998: 3.84"
July 1982: 2.57"
August 1968: 3.66"
September 1982: 7.04" (!!!)
October 2025: 4.16" and counting
November 1875: 5.81" 
December 1983 and 1889: 4.37"

And then additional months at or above 4":
March 1876: 4.00"
April 1974: 4.57"
April 1986: 4.55"
April 1984: 4.43"
April 1886: 4.43"
April 2011: 4.06"
May 2011: 5.14"
May 1977: 4.76"
May 1876: 4.30"
May 1901: 4.27"
May 2015: 4.19"
May 1898: 4.19"
September 1973: 4.07"

So, calendar months that have observed 4" of precipitation or more are February, March, April, and May in the late winter and spring and September, October, November, and December in the fall and early winter.  There have been 22 calendar months with at least 4" of precipitation, most commonly in April (6 times) and May (7 times), which aligns well with the months that on average are wettest at the airport.  The November 1875 record (5.81") is an extreme outlier for that month.  I took a quick look at the daily records though and there was nothing that was obviously bad, so I'm including it here.

Of the months with ≥ 4", 10 are before 1928 when the observing site was in downtown Salt Lake City.  Downtown is a bit wetter on average than the airport, so it's possible this contributed, but there have also been changes in observing techniques and instruments that can also affect the frequency of extreme events. 

There are also five months in the 1980s, a period that was exceptionally wet in northern Utah.  The all time monthly record of 7.04" in September 1982 is really impressive and certainly helped moistened the soils prior to the epic 1982/83 winter that ultimately led to the famous flooding during the (late) spring runoff.  

Source: Marriott Digital Library

With those numbers in mind, a reasonable target to root for this month would be the coveted 5" barrier, which has only happened four times before.  Getting to 7" seems crazy, but not impossible.  That said, I'm going to set the over/under at 6.25" based on a quick look at the extended forecasts.  There's a lot of uncertainty in those forecasts though, so place your bets and see if you can beat the house.

There are a few other ways we might look at this exceptional run, which started on October 3 and currently goes through October 13, a stretch of 11 days.  You are probably already awaer that 4 October was the 2nd wettest day in Salt Lake (2.47").  For an 11 day stretch, this Oct 3 to 13 rates as the 30th wettest, although this count includes two exceptionally wet stretches, one in Fall 1982 and the other in Spring 1901.

Like our current stretch, each of those included one exceptionally wet day, 26 Sep 1982 (2.27") and 3 May 1901 (2.64", the wettest day on record).  This illustrates that one really wet event can set the table for a record breaking run if the pattern remains favorable for precipitation.  

Given that 1982 shows up conspicuously and the 1982/83 winter was an epic, should we get excited about this winter.  Of course you should get excited about this winter!  You are going to be skiing and a bad year in Utah is better than a good year most anywhere else (Japan excluded).  

Ah, but you probably want to know if this is a harbinger of a big winter, like fall 1982 was. The two are simply not comparable.  The 1982/83 winter was an enormous El Nino year.  We're currently looking at perhaps marginal La Nina conditions.  I look at what is happening now as not an indication of what the winter will bring.  It doesn't load the dice one way or another.  Your guess is still as good as mine.