Low-Level Moisture Increases A Bit

Sunrise this morning was a hazy yellow-orange, indicating both continued dirty air and also a bit of an increase in low-level moisture. Above is view of Catalinas from campus a bit after 6 am today (13 June 2013). The time series below of T, Td, and RH is for Yuma and shows that south winds off the Gulf of California (GoC) kicked the dewpoints up over 60 F for a brief time yesterday morning. The series indicates some gradual increase out there of dewpoint and RH yesterday and today. More moist air is also encroaching westward from New Mexico. When I walked along the Rillito this morning I actually worked up a bit of sweat for the first time this summer. There were noticeable filaments of both warm and cool air drifting about this morning - the coolest and most refreshing was sinking into the wash from a soccer field that had the sprinklers running full blast, serving as sort of a huge, outdoor swamp cooler. We have now had 6 straight days with highs of 105 to 108 F.

Satellite derived precipitable water (PW - shown above at 5 am MST) captures the northward push of higher PW up the GoC and into southwest Arizona. It appears that values have reached just over an inch over some parts of the state and are greater than 1.5 inches over the central GoC and parts of Sonora, Mexico. The early run of Leuthold's modified WRF-GFS model at Atmo forecasts some things of interest, especially tomorrow. The model forecast skew-T for Tucson valid at 3 pm MST on Friday the 14th is shown below. It forecasts the most CAPE that I've seen so far this summer, along with PW of 28 mm. The sounding is quite favorable for downbursts, with a deep boundary layer and cloud bases indicated a bit above 600 mb. I do suspect that the forecast boundary layer mixing ratio of 8 g/kg is probably too high.

Model forecast composite radar echoes valid at 5 pm MST tomorrow afternoon are shown below and indicate buildups from the Tucson area eastward into New Mexico. The model forecasts some sprinkles reaching the ground at low elevations and also indicates a threat of more dry lightning strikes. It is a rugged time of the year here, and other parts of the West.