Yup, that time of year.  It rained on Monday but that doesn’t mean summer or fire season is over quite yet. A classic fall offshore wind event is setting up as a low pressure system will drop in to the Great Basin that will interact with building high pressure.  When this happens, you get tightening surface pressure gradients and winds that veer to the north and northeast.  This has prompted the National Weather Service to issue a red flag warning for critical fire weather.

The system will produce:

-A rapid drop in relative humidity

-increasing wind speeds, especially above 1,000 feet as winds become compressed.

-adiabatic warming and drying.  Ie., it’s going to be warm and dry as a bone.

Take a look at the graphic below generated by the Global Forecast System  (GFS)  This shows the predicted pressure gradients.  When those red lines squish together, it becomes sort of like a turbocharged wind tunnel.  Compressed lines mean strong winds.

Global Forecast map, late Thursday night, early Friday morning pressure gradient.

-Kent Porter