Summary
The polar and subtropical jet streams are positioned such that a southward-shifted monsoon ridge in Mexico extends into Texas. At 500 mb, the polar jet dips into northern Arizona, with a split trough creating two low-pressure centers near Montana and San Francisco. This pattern of successive low-pressure systems is expected to persist through the July 4th weekend, with additional troughs and increasing moisture for eastern Arizona afterward.
Currently, the atmosphere across Arizona is dry, with southwest winds aloft and low potential for convective storms, though some storm activity is forecast east of El Paso and in parts of New Mexico. By tomorrow, moisture and storms may shift slightly westward, potentially bringing isolated storms to the Chiricahua Mountains, though not currently in model forecasts. We expect monsoon moisture to fluctuate, moving east by Wednesday and then eventually returning west, with long-range forecasts indicating monsoon-like moisture levels somewhere between July 3rd and 7th.
Yesterday’s Weather
Smoke plumes from wildfires are easy to spot from visible satellite imagery across the region, namely the Pocket Fire in Sedona, AZ. Most of the wildfires were started by lightning strikes, though some are prescribed burns (InciWeb has specific information on all of the fires in the region). Sadly, three firefighters have died fighting fires in southwest Colorado.
The monsoon moisture flow (green) has shifted into southwest New Mexico as the polar jet (black) has moved southward into the Great Basin.
Very little moisture is present in the region, except in southeast New Mexico. Red flag watches are in the areas highlighted in magenta below, and a fire weather watch is in light brown.
The Phoenix sounding below is so “not the monsoon” as the precipitable water value has dropped to .61 inches (15mm). The surface dew point temperature below the morning inversion shows a slight increase, usually due to sprinkler/irrigation systems near the sounding location. Note that the winds aloft are west to southwest. The polar jet is still north of the area, while the subtropical jet is still south. Once the monsoon flow begins, the subtropical jet will disappear, and the monsoon ridge will move farther north with mainly easterly winds aloft. The HRRR-UA WRF 12Z initialization has the winds correct, and the surface inversion, though precipitable water is 2mm too much.
Analysis
At 250mb, the location of the polar (black) and subtropical (red) jets is as shown. The monsoon ridge has shifted south, with a ridge axis extending northeast into Texas
The polar jet has dipped into northern Arizona at 500 mb, and the trough has split into two low centers: one near southwest Montana moving northeast, and one farther west near San Francisco moving southeast. This weather pattern will continue into the July 4th weekend as additional troughs move through in a similar manner. After next weekend, some moisture will start moving into eastern Arizona.
At 700 mb, the monsoon moisture axis is in southeast New Mexico. This will slowly shift back to Arizona next week.
Today
The Tucson sounding below for this afternoon shows a dry atmosphere. Winds aloft are from the southwest throughout the troposphere, with maximum speeds near the tropopause. A similar story for the rest of Arizona: low precipitable water and warm temperatures at 500 mb, so no Convective Available Potential Energy.
Some storms are forecast along the monsoon moisture axis east of El Paso and in Chihuahua. The winds have weakened in the region, though the strongest winds remain in the red flag and fire weather watch areas, shown earlier, in Apache and Navajo counties and into western New Mexico.
Tomorrow
Moisture and storms have shifted a little farther west. Some storms will form where outflow boundaries from other storms occur, so it’s possible that the Chiricahua Mountains will see a storm tomorrow, despite not being forecast by UA WRF.
Outlook
The monsoon moisture shifts east on Wednesday, and dry air at the low levels moves into Arizona. The intermittency of monsoon moisture is evident here, as we’re in the ebb part of the ebb-and-flow.
The long-range global model ensemble forecast (GEFS) below indicates temperatures will slowly increase by next week. The precipitation forecast does show storms around July 7th.
Dewpoint temperatures and precipitable water increase starting on July 3rd and approach monsoon values at the end of the forecast period.
Discussion written by Pat Holbrook and Patrick Bunn