Return of southerly flow clears smoke but re-establishes the monsoon
Thursday, August 27, 2015
The current storm is now just east of our area, and showers should linger through the rest of the day before clearing overnight.
The upper level flow weakens considerably behind this storm and stays weak through Saturday, interrupting the monsoonal moisture feed from the south that lead to the current storm. Incidentally, and not quite how I forecasted last week, the lingering smoke this past weekend was not purged from the area until the flow shifted from the northwest to the south this past Tuesday. We did get some brief clearing last Friday night, but smoke returned as the northwest flow moved smoke from the active wildfires to our northwest back over the area.
But the weak upper level flow is forecast to increase again Sunday from the southwest as a large storm currently off the West Coast moves eastward early in the weekend and is deflected by the persistent western ridge. This storm will drag a very weak cool front through the area later Sunday, and combined with the increasing moisture from southwest flow ahead of the storm, should contribute to a much greater chance of storms Sunday afternoon.
The increased chance of afternoon storms should be present on Monday as well, before the rebounding of the deflected western ridge dries the atmosphere a bit, leading to decreasing chances of afternoon storms each afternoon for most of the work week.
Another similar storm is forecast to be off the West Coast around midweek, and current model solutions again have the storm deflecting the western ridge and dragging a weak cool from across the region around the end of the next work week. As is forecast to happen this Sunday, the chance of afternoon showers should increase again sometime during Labor Day weekend.