First Moisture Surge Arrives This Week


7/16/23 Sunday 7:30 am

The monsoon technically started in southern Arizona over the last few days.  The traditional way of determining when the Southwest US Monsoon season kicks off is based on the dewpoint temperature. The rule was three or more consecutive days of the dewpoint reaching 55 degrees or more. For whatever reason, perhaps it was too difficult to understand, they changed it to a date range which is from June 15th to September 30th.  I prefer the old way (big shock) and according to the old way, that just happened.

Here is the regional view of the current dewpoint (as forecasted overnight). Notice the disparity between southern Arizona and basically the rest of the Southwest.

Here is the dewpoint forecast for us beginning Monday and ending late Thursday.

Another interesting thing to look at is the Precipitable Water Values (PWATs). They measure the amount of liquid available to fall in a single column of water from the sky (the higher the values are the better chance of rain). Just like during the winter, I prefer to look at the anomaly values. Here is the progression from Monday morning through late Thursday.

This shows the PWATs starting at about 30% of normal and then peaking in 160% of the normal range between Wednesday and Thursday. PWAT values in July are already typically the highest or second highest of the year, so anything at or above 100% is a very good sign.

It is too early to predict who will get what if anything. With that being said, this is very encouraging. I have been seeing this transition between July 18th-21st for a very, very long time in the long-term models. So now to see the short-term models show this moisture surge right on the 18th is exactly what I was hoping for.

I will be following this closely throughout the week, stay tuned.

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