At 500 mb this morning there is a cold, closed low over the Montana/Idaho border - above is NCAR RAL analysis and below is NAM analysis both at 12 UTC this morning. The low has a long, curved tail that extends west and northwest into the Gulf of Alaska. This tail will swing southward and cross the Southwest during the next several days. At issue is what its impacts will be across southern Arizona.
The early run of the WRF-NAM from midnight last night forecast minimal precipitation across southern Arizona through midnight Thursday night (above, on 5.4 km grid). The focus in this forecast was across the Great Basin from the Sierra Nevadas to the Colorado Rockies, with a second maximum along the Continental Divide in Mexico. However, the latest run of the NAM now forecasts considerably more precipitation over southeast Arizona for same period (below). So, we will watch to see how much moisture attends the trough across this region.
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