Summary

Satellite observations in southern Arizona and New Mexico show increased low-level moisture, though surface dewpoint readings do not fully capture incoming mid-level moisture from thunderstorms. The 5am sounding from Phoenix shows a significant rise in precipitable water, and model forecasts have improved in matching the observed moisture profiles. The jet stream remains steady over northern California to Nebraska, with a new trough approaching from the west, while the monsoon ridge holds its position near El Paso.

Forecasts indicate that thunderstorms are likely today mainly over mountain areas due to limited valley moisture, with potential for strong microbursts. Tomorrow’s conditions are expected to be similar, though further east with slightly less moisture, and storms will continue to favor higher terrain. By Friday, moisture shifts farther east, reducing storm chances in Arizona but leaving isolated mountain storms in New Mexico. Overall, the outlook through July 2 suggests limited rainfall potential.

Yesterday’s Weather

The two infrared satellite loops below are Monday (top) and Tuesday (bottom). The area of thunderstorms on Monday shifted northward by Tuesday and will move to Arizona today. There was also an outflow from the thunderstorm last night in Sonora as it collapsed during the evening hours spreading moisture into southern Arizona, with virga from it visible just west of Tucson this morning. Yesterday’s forecasts didn’t quite have a handle on the moisture available until last night’s model run, HRRR-UA WRF 00Z , forecasting an increase in precipitation in Arizona today. Also, outflow from the thunderstorms in western Texas moved west into central New Mexico. 

This morning, the visible satellite imagery shows lots of mid-level clouds are in western Arizona becoming more scattered eastward into eastern Arizona and New Mexico. 

Analysis

Moisture at low levels has increased in southern Arizona, but the 2m surface dewpoint temperatures below are not a reflection of the mid-level outflow moisture from thunderstorms that has made it to both Arizona and New Mexico.

The Phoenix sounding below does show an increase in low-level moisture with an increase in precipitable water (PW) from 10mm to 31mm this morning! The virga in the clouds in Arizona is falling from clouds based at 675 mb (the Lifted Condensation Level, LCL) and tops at 470mb,  the temperature inversion. The HRRR-UA WRF 12Z initialzation is much better today, and matches the PW in the observations and its ditribution across the different levels (surface, 700, 500, 200mb).

The jet stream has moved little and is in northern California to Nebraska. A new trough is approaching the west coast and will continue into the Great Basin and deepen over the weekend. The monsoon ridge is in about the same position as yesterday (marked as H in red).

At 500mb, the center of the high pressure is further north near El Paso and the circulation around it is bringing increasingly warm air into Arizona. Still within the good temperature range of –10 to –5 °C. 

At 700mb, the moisture content along either moisture axis, shown by the black arrows below, is not very high but enough to support the mid-level clouds observed on the visible satellite image this morning (shown earlier). 

Today

The 12Z HRRR-UA WRF forecast soundings at 3 pm this afternoon for Tucson (left, below) and Nogales (right, below), both indicate thunderstorms will develop, but probably over the mountains in Pima County as dry air at low-levels, in the valleys. The Downward Convective Available Potential Energy (DCAPE) values (>1400 [J/kg]) indicate a potential for microbursts around 40 to 45 knots from storms that do form. It feels a little cooler this morning due to the clouds, but the temperature at 9am was the same as yesterday, despite the overnight low temperature of 77 °F yesterday versus 81°F this morning, so the clouds are providing some surface cooling.

The simulated radar reflectivity and wind forecasts for this afternoon and evening show mountain thunderstorms in northern Arizona into western New Mexico with a few storms in eastern Pima and Santa Cruz Counties as well as Cochise County.  Note low deserts are mainly clear of storms, due to the lack of moisture in the valleys.  

Tomorrow

Forecast soundings for tomorrow have a tad less precipitable water, but are similar looking to today’s soundings.

Storms shift east and are still mainly firing on the mountain tops and propagate east.

Outlook

By Friday, moisture is shifting more to the east as the trough from the Pacific moves into the Great Basin with only isolated mountain storms in New Mexico.

Also, below is the precipitation and the precipitable water plume forecast through July 2 at 5pm. It doesn’t look too promising, but there is always hope if someone puts some laundry out on the line.  

Discussion written by Pat Holbrook and Patrick Bunn