Saturday, July 16, 2016

Outflows From Mexico Bring Bit More Moisture

Thunderstorms did occur further north over Mexico yesterday evening and last night. Above is TUS radar composite at 7:17 pm MST last evening and below is IR satellite image from 7:00 pm. Second below shows detected CGs (from Atmo and Vaisala) over Mexico for the 12-hours ending at 4:30 am this morning.

Outflows from the south moved into much of southern Arizona from around 9:00 pm into the early morning hours. Values of PW are generally around 1.25 to 1.50 inches at lower elevations from Tucson to Yuma, with highest values lurking out in central Pima County.

The 12 UTC skewT plot for TWC sounding data (above from SPC) indicates a fair amount of CAPE, along with cool mid-level temperatures. However, winds below 300 mb are very light with almost no steering level flow. I suspect that the afternoon boundary layer should mix out to about 650 mb, which wold keep the CAPE about as shown above.

The WRF runs from 06 UTC were a bit too dry at morning sounding time, but both forecast strong storms, mainly to our south and southwest, this afternoon and evening. The NAM version brings a very strong outflow across TUS around 9:00 pm this evening - were that to occur it would have the potential to trigger storms in the metro area. However, the GFS version brings drier outflows in from the southwest around 7:00 pm, with less potential for local storms. Certainly a situation to keep an eye on during the day.

As for tomorrow, it will likely be a mixed bag and a difficult forecast, as both models forecast some early morning showers after the evening outflows.

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