Summary
Surface moisture remains limited to eastern New Mexico, while air quality alerts and fire weather warnings are in effect for parts of the Southwest. The atmosphere over Arizona and New Mexico is still quite dry, with minimal precipitable water and westerly winds aloft. The polar jet is shifting north and weakening, while the subtropical jet has moved into southern Arizona and New Mexico, but is expected to fade as the monsoon ridge builds.
From today into tomorrow, moisture from former Tropical Storm Douglas and decaying thunderstorms over the Sierra Madre will bring some high-based clouds and light rain, though most precipitation will likely not reach the ground. In the mountains of New Mexico and eastern Arizona, thunderstorm activity is expected to increase by Sunday and Monday, with surface dewpoints rising toward monsoon levels by early next week.
Yesterday’s Weather
The two large fires shown below are the Sacaton, NM, fire (uncontained) and the Pocket fire near Sedona, AZ, (25% contained). No wetting rain is expected until the monsoon moisture moves into the region next week.
The only thunderstorms were in far southeast New Mexico earlier in the afternoon and had mostly dissipated by evening.
Both the polar (black) and subtropical (red) jets have shifted northward. The polar jet flow is more meridional (west-to-east), with short-wave troughs moving through the mean trough position. The subtropical jet is indicated by the striped high-level clouds from the former Tropical Storm Douglas (storm 4E in previous discussions).
Analysis
Surface moisture is still limited to eastern New Mexico. Air quality alerts for ozone are in (grey), and fire weather warnings are in Colorado (not shown).
The Phoenix sounding still has minimal precipitable water, just 8mm (0.3″). Westerly winds aloft still dominate the atmosphere.
At 250 mb, the polar jet (blue) has shifted northward, with short-wave troughs moving through the system (black dashed). The subtropical jet (red) has now moved into southern Arizona and New Mexico. In the week or so, the monsoon ridge will shift north into a more typical position for the monsoon season, and the subtropical jet will fade away.
The polar jet is weakening as it shifts northward at 500 mb. The temperature in Phoenix has warmed to –6°C, and in San Diego it is –4°C. This warm air aloft is moving into the state. The monsoon ridge is forming over southeast New Mexico with easterlies across central Mexico.
At 700 mb, moisture from former Tropical Storm Douglas, shown in the far southwest of the image, will be drawn into Arizona over the next few days. It will produce some light rain, but mostly from high-based clouds. The other moisture feed will be from decaying thunderstorms over the Sierra Madre mountains each afternoon. By Sunday, the moisture transport from the Sierra Madre will move westward.
Today
The HRRR-UA WRF 12Z forecast skewT for Tucson at 3 pm below shows very little moisture, just 16mm (0.6″). The good sign is the shift to southerly winds aloft as the monsoon ridge builds and eventually will bring moisture.
The HRRR-UA WRF 12Z forecast radar reflectivity shows light blue shading over southwest Arizona, indicating upper-level moisture from former Tropical Storm Douglas. Surface dew point temperatures are low, and any precipitation falling at this time will most likely be virga. We’d need reflectivity values above 35 dBZ (light green to yellow on these plots) for precipitation to reach the ground.
Tomorrow
By early morning, the light rain/virga shifts north, and a few light showers form from dying storms in Mexico are possible. It is still too dry at the surface, and these showers will mainly be virga. Through the day, these showers move west of Phoenix, then northward into the Mogollon Rim and Flagstaff area.
Some of these storms may develop into thunderstorms, but the lightning forecast does not indicate this will happen. Other, more intense, thunderstorms develop in southeast New Mexico, where the accumulated lightning strike forecast reflects that activity.
Outlook
On Sunday, moisture from the thunderstorms in New Mexico moves into far eastern Arizona, kicking off storms by 5 pm there.
Dew point temperature forecasts for Sunday at 5 pm and Monday at 5 pm are shown below.
Dewpoint temperatures are still below monsoon levels, but thunderstorms form on both days in the mountains of eastern Arizona and New Mexico. The strong outflow forecast from the White Mountains may push surface dewpoints up in Pinal, Pima, and Santa Cruz counties to near monsoon levels Tuesday.
Ensemble forecasts from GEFS are shown below. Yesterday, we saw forecasts of slowly increasing precipitable water, but that probably won’t happen. More likely is an event in which thunderstorm outflows, beginning as early as July 7th, bring precipitable water in more quickly, and we’ll finally reach monsoon moisture levels.
Phoenix will have to wait a few more days compared to Tucson.
Discussion written by Pat Holbrook and Patrick Bunn