Overview

This is the first day of the Arizona monsoon season. When the monsoon season was first created for southeast Arizona, the selection of June 15 was based upon the percent chance of rain in the Chiricahua mountains being 20%.  Picking the end of monsoon season being Sep 30 was to help keep the monsoon season climatological data consistent. The old dewpoint rules did not work well because thunderstorms would develop even when the rules were not met. Creating a monsoon season allowed the forecast offices in the state to have a severe weather awareness week before the start of severe thunderstorms and flash flooding.

Analysis

250 mb flow is westerly across the state with winds of 50 knots.  A high pressure ridge remains off the west coast of the Baja Peninsula.

At 500 mb, the ridge axis is from El Paso to Guaymas with the 700 mb ridge in about the same place. No significant moisture is over Arizona and even New Mexico has dried out. Some deep tropical moisture is in Mexico near Mazatlán pushed into the region from the weakening tropical storm Dalia. This is not expected to have an impact on Arizona, although a few storms may form over the Chiricahua’s tomorrow.

Today

Some light precipitation in New Mexico.

One of the ways to determine if we have deep convection is to look for strong divergence at 250 mb. The storms will create green blobs on the map below. The 250 mb divergence map does not show any of this so no deep convection.

So far no threat of significant precipitation.

Tomorrow

Not much in the way of precipitable water although there was a slight increase in the Tucson area and southern New Mexico. This may allow for the formation of flat based clouds in southern Arizona and storms in central and southeast New Mexico as per the radar.

Outlook to late next week

The GFS and ECMWF model output of precipitable water for late next week shows the difficulty of forecasting the monsoon. Probably neither of these are correct, but there should be a ramp up in precipitation beginning next weekend and into the following week.

Discussion written by Pat Holbrook