Many interesting weather features are in play for next three days. The large MCS that moved into the southern GoC yesterday sent a strong outflow of 30 to 40 mph winds north up the Gulf. The surface time-series for Yuma this morning shows a spectacular jump in surface dewpoint as the outflow moved into southwestern Arizona. The CIRA blended PW analysis for 6 am MST this morning (below) shows that PW has increased since yesterday over south-central Arizona and the lower Colorado River Basin.
The NHC has declared that Tropical Storm Rachael has formed southwest of Cabo Corrientes (see 1330 UTC IR image above). Their current forecast for Rachael is shown below, indicating yet another storm approaching southern Baja.
The early WRF-NAM forecast for today indicates thunderstorms again hanging on the mountains of southeastern Arizona this afternoon. However, the model forecasts heavy thunderstorms for western Arizona tomorrow afternoon and across the state on Saturday. This will be a strong transition event - i.e., one in which a strong trough in the westerlies (see current NAM 500 mb forecast above valid at 5 pm on Saturday) interacts with subtropical moisture in lower levels. The early WRF-NAM forecast of PW valid at noon on Saturday is shown below. The intrusion of mT air from the GoC over Arizona will be clashing with the cold front and very dry air associated with the westerly trough. Because the wind shear profile aloft in these situations is similar to Plains settings in Spring, these transition events often produce severe thunderstorms and, at times, supercell thunderstorms - so there will be much to keep an eye on during the next three days.
Edited to ad - From David Blanchard: This is the setup for supercell thunderstorms with large hail and tornadoes for [northern] Arizona. Here's a link to a Severe Local Storms conference paper I did on synoptic patterns associated with AZ tornadoes. These events typically have low CAPE but large shear. They often have deep layers of southerly winds with nearly straight hodographs that result in splitting storms.
http://ams.confex.com/ams/pdfpapers/141836.pdf
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