Friday, January 31, 2014

Cold Weather is on its way

We've had a major shift in the weather pattern over the past few days.  Most of you have probably noticed this with the return of snow followed by some sunshine, and the end of the fog and stratus.  The change in the jet stream pattern was somewhat subtle, but profound.  In our last blog we talked about the end of the high pressure over our area.  Here's what the pattern looked like on January 27th:

Jet Stream (red line) on 27 Jan 2014

The red line is the jet stream.  Storms from the Pacific were diverted up into Alaska, over the top of the high pressure ridge, and then down into the central and eastern US.  Compare that with the jet stream pattern today:

Jet Stream (red line) on 31 Jan 2014

The ridge of high pressure is now over the eastern Pacific.  The jet stream is now diving from Alaska into the Pacific Northwest.  (As a side note, there is another branch of the jet stream that is directing a few storms into California, which is good news for them).

While we've seen some snow and sun as a result of our pattern change, the biggest effect will arrive next week:  cold air.  This won't be the bitter cold that the eastern US experienced recently, but we'll still be plenty cold.  Starting Tuesday, most locations will remain below 20 during the day and drop into the single digits at night.   The forecast from the GFS model for Spokane is shown below.  

Temperature forecast from the NAM (red/orange lines) and GFS (blue lines) for Spokane
Here's our current high temperature forecast for next Wednesday:

And then Wednesday night, temperatures will drop to near zero for most locations.   As we've discussed before, the ingredients for really cold nighttime temperatures are clear skies, light winds, and snow on the ground.  Take away one of the three, and the temperature can be 10 to 15 degrees warmer.  So forecasting low temperatures in these situations has a large potential to be wrong.

Before the cold arrives, there will also be a disturbance in the jet stream that will move through the area on Sunday.  It will bring more snow to the region, mainly the southern Panhandle.  Here's our current snow fall forecast:

1 comment:

  1. Winter finally got interesting! The 12z ECMWF is showing even colder temps next week (with an overunning event near the end of the run). Guess we'll see.