Summary
Moisture levels have increased in southeast Arizona and New Mexico, with dewpoints rising and dust present in some areas due to outflow from yesterday’s activity. An excessive heat warning is in effect for parts of Arizona and California. The weather balloon observations indicate stable atmospheric conditions in Phoenix, limiting the chance of storms. However, some areas, especially near San Simon and Nogales, may experience gusty winds up to 45 mph and possible dust storms, should storms form, but little rain is expected due to low moisture levels.
Daily thunderstorms will continue to form in the Sierra Madre mountains, though their outflows will not be strong enough to bring much additional moisture into Arizona through midweek. Rainfall totals are expected to remain low, though some storms could bring brief rain to the Tucson area. Forecasts suggest similar patterns through Wednesday, with a chance of increased moisture later in the week, but uncertainty remains about the arrival of substantial monsoon moisture and rain.
Yesterday’s Weather
Thunderstorms developed in southern and eastern New Mexico, as shown on the satellite, radar, and lightning composite animation below. An outflow boundary from storms in southeast Arizona, Cochise County, was accompanied by dust and higher surface dew point temperatures. The dust can be seen in the Tucson mountains this morning. The large cluster of thunderstorms over northwest Texas moved south and dissipated. Dry air aloft has been pulled south behind this thunderstorm complex.
A little different view here; the satellite picture below is a low-level water vapor image. Dry air is represented by yellow and red colors. The locations of the four low-pressure systems shown yesterday are in red, and their locations this morning are in black. The dashed red line shows the motion of the lows.
We mentioned yesterday that any of the lows could contribute to deep monsoon moisture moving into the state. As of this morning, low “L1” and low “L4” are out of the monsoon picture. Low “L2” moved from northeast New Mexico into Oklahoma, pushing some of the New Mexico moisture west and dragging very dry air south. This dry air threatens to cut off any western New Mexico and eastern Arizona thunderstorms in a few days. Low “L3” has aided thunderstorm development along the Sierra Madre mountains east of Los Mochis in the Sinaloa province of Mexico. This moisture will be slowly pulled northward over the next few days by outflows from the thunderstorms. A Gulf Surge is not expected yet.
Analysis
Some 50°F dewpoints are in Cochise County this morning, along with the suspended dust. Moisture has also increased in southern New Mexico due to a combination of Gulf of Mexico moisture and thunderstorm outflow. An excessive heat warning will be in effect for parts of Arizona and California.
The observed Phoenix sounding from 5 am shows two inversions aloft. The near-surface inversion is due to overnight cooling, and the second, near 510 mb, is at the top of yesterday’s mixed layer. The inversion near 400mb is a subsidence inversion. The inversion near 200 mb marks the tropopause, where the strongest winds aloft are located. No chance of surface-based storms given this sounding. The HRRR-UA WRF 12Z initialization (below, left) matches the observations well.
The monsoon ridge is still in Mexico at 250 mb, but the ridge axis has moved northward into Colorado and Montana.
The flow around the now-established monsoon high is shown below at 500 mb. The warm air aloft is now mainly moving into California.
At 700 mb, the monsoon high is centered near El Paso, with weak easterly flow beneath the high pressure. Daily thunderstorms will form in the Sierra Madre mountains in Mexico, with outflows moving to the Gulf of California. None of the outflows appear strong enough to bring more moisture into Arizona by Wednesday, especially along the International border.
Today
The forecast sounding for San Simon below shows some Convective Available Potential Energy (CAPE), and wind gusts could reach 45 mph. Dust storms are possible along I-10 in Cochise County. The Tucson and Nogales soundings have no CAPE today.
Storms form in the mountains of western New Mexico and eastern Arizona and move southwest, associated with strong, gusty winds, but they produce little rain.
Tomorrow
Shifting to the Nogales forecast sounding for Tuesday at 12:30 pm, the thunderstorms form in the early afternoon. Like San Simon, the wind gusts will be near 45 mph, and dust storm potential is high in Pima and portions of Santa Cruz and Pinal. Precipitable water values are too low to support heavy rain at 26mm (1”).
The storms spread west into the low deserts before dissipating. Some rain may get into the Tucson metro.
The 48-hour total rainfall through to Wednesday morning at 5 am is below.
Outlook
Wednesday is almost a duplicate of Tuesday, with the storms in similar locations. Some storms move west of Tucson, but not too far. One exception is the storms southwest of Nogales, which will feed southwest towards the Gulf of California and help spread more moisture into central and western Pima County.
84-hour precipitation totals through Thursday at 5 pm.
One ensemble member from the GEFS long-range global model indicates that monsoon rain will start in Tucson on Friday. But that model run could be an out-and-out liar. More to come tomorrow on this, when forecast uncertainty drops as the event approaches.
Discussion written by Pat Holbrook and Patrick Bunn