Widespread Rain Event

View above is of Catalinas, with some stratus fractus on the east part of mountains, at 7 am MST 4 July 2012. Yesterday afternoon and evening brought rainfall to essentially 100% of the ALERT gauges (only 2 of 93 had no precipitation), although most amounts were light. Storms developed late and were strongest to the east and south. Here at the house we had a light thundershower around 10 pm and very light showers at sunrise. Total in the gauge here at the house was only 0.13". Across the ALERT network 12 stations had half an inch or more, and 3 stations had just over an inch. The heavy amounts occurred over the east and southeast portions of the network, mostly at higher elevations.

This morning it is sauna-like outside, with warm temperatures and high dewpoints. The combination of continued moisture advection from the south and substantial recycling through evaporation has raised PW content to 1.75" - 2.00" across the entire southern third of Arizona this morning. Image above is satellite water vapor image from 6 am MST - there is a broad plume of upper-level moisture from northern Mexico over most of the Southwest and on into the northern Plains. The upper-level cyclone has opened up and is located over the central GoC/central Sonora. This feature will weaken and move north to central Arizona by this evening. The associated weak shortwave at 500 mb will also move northwestward across Arizona today.

The early run of Atmo's WRF-GFS model predicts CAPE values of 1000 to 2000 J/kg by noon today (above), even though sunshine and heating will be fairly restricted by debris cloud and quick development of cumulus clouds where there is sunshine. Highest CAPE values tend to be on some of the higher peaks, although the Catalinas  and Rincons appear stable in the forecast.

The forecast skewT for TUS is shown above for noon, when CAPE maximizes in the model forecast. The sounding has almost 1600 J/kg of CAPE - this is probably too high, but nicely reflects the tropical-like atmosphere over southeast Arizona. The forecast sounding has very weak winds below 500 mb and uni-directional south-southeast winds in the upper-half of the troposphere. This is a very bad wind profile for here at the house - we will have to have storms develop nearly overhead to get rain. The sounding appears quite supportive of strong, wet microbursts though, as well as localized heavy rain.

The model forecast of accumulated precipitation through midnight is shown above. The forecast indicates two bands of heavy rainfall through eastern Pima County. The  band from the Rincons across the Catalinas is probably from early morning storms that were in the model forecast, but which did not materialize in the real world. Definitely an interesting day on tap.

The WRF-GFS forecasts substantial drying and reduced storm activity tomorrow, with very dry air moving northward from the GoC into southwestern Arizona. The moisture stays higher in the southeast part of the state, allowing increased afternoon activity on Friday.