Friday, September 28, 2018

Not Much Change in the Rosa Forecast

There isn't much change in the Rosa forecast from yesterday to today, other than increased confidence that the remnants will track across the southwest.  The ECMWF ensemble favors tracks across western Arizona or southern California, although there are some where it moves further west and stays over the offshore waters of the southern California bight.  The mean of this ensemble is a track that moves directly up the lower Colorado River Valley.  The GEFS ensemble is now fairly similar, with perhaps a slight tendency to bring the system a bit further to the east.

The 0600 UTC 28 Sep GFS forecast of sea-level pressure and 3-hour accumulated precipitation is below.  I am toying with some new software and have no idea how well the loop will display, but thought I would give it a shot.  Apologies for the lack of time stamps and a scale.  Note that while Rosa will get lots of attention, the surge of monsoon moisture ahead of the decaying tropical cyclone is substantial and covers a wide area.  Regardless of track details, a good portion of the southwest will see showers and thunderstorms beginning as early as late Sunday in Arizona and early next week for the four corners region and possibly southern California. 

Below is the latest Hazardous Weather Outlook issued by the National Weather Service at 0503 MDT this morning, which summarizes current understanding quite well. 

Stay tuned for more specifics the event approaches. 

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