Update Tonight On the Arctic Air Entering Our Region and Localized Areas of Snow
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The buzz is up regarding the potential for a major snow event over the lowlands of western Washington and Oregon on Friday or Saturday.
I have had nearly two dozen emails about this issue today and calls from local media….so folks know about the potential.
This is a very challenging situation with relatively low predictability and large differences in model forecasts. But slowly, the picture is getting clearer…and I will tell you about it in this blog.
Our confidence in the forecast should improve substantially tomorrow and Thursday as we get closer to the event and more powerful forecasting tools (large high-resolution ensembles of many forecasts) become available.
To show you what some of the excitement has been about, here is the forecast 48-h snowfall ending at 10 AM Sunday from the main U.S. model, the GFS (started at 4 PM yesterday).
Wow. Roughly TEN INCHES around Seattle. And this snow would have started to move in during Friday evening. Ten inches of snow is like the apocalypse in this region.
No wonder folks were getting excited.
The trouble was that other models, such as the generally more accurate European Center model, were going for very little snow over Puget Sound for the same period, but predicted snow in the Portland area (see below).
Several other major forecast models did the same (took the snow south). Another important fact was even the U.S. GFS model, run many times in an ensemble, had several forecasts with little snow in Seattle.
With all this disagreement, and thus uncertainty, I held off predicting a big snow event on Friday and early Saturday. Some folks, including a well-known local weather video purveyor, suggested I was being “conservative”, while another comment suggested I had somehow lost interest in making the hard calls. Hyping snow events may be good for getting clicks but bad science and leads to “cry wolf” reactions.
The truth is that all forecasts have uncertainty and some are more uncertain than others.
The snow forecasts varied because different forecast systems predicted different locations and intensities for a small-scale low/trough of low pressure reaching our coast.
The U.S. GFS model predicted the low to be considerably farther north than the EC model, which brought the precipitation (snow northward)in the GFS model…. see below. Both had temperatures cold enough to snow over Puget Sound.
Since the EC model is generally more skillful, the smart bet was on little snow north of Tacoma on Friday and early Saturday. And in the latest forecast (just released), the U.S. GFS has started to drift toward the European Center solution, reducing the snow over Seattle but increasing snow over the Rose City.
Assuming that the true situation will trend towards the European Center solution, here are the latest 24-h snow totals ending Saturday morning at 4 AM and Sunday morning at 4 AM from the EC model. Little snow around Seattle, but lots in Portland.
I will update more tomorrow and Thursday.
