Monday, February 18, 2013

An Encouraging but Uncertain Forecast

This is probably a poorly kept secret for those of you who are constantly on the lookout for snow in the forecast, but there is going to be a major pattern shift this week that could give us one of the more active patterns of the winter.  First lets talk about what is encouraging about the forecast.  The Climate Prediction Center 6–10 day outlook has my favorite combination of colors.  Blue for below average temperatures and green for above average precipitation.

Source: NOAA/CPC
In addition, the GFS has three major systems coming through over the next ten days.  The first is a mid week storm, the bulk of which moves through southern Utah, but the latest computer models suggest it will give some of the goods to the north too.  

This is followed by two direct hits for the weekend and early next week.  Looking at the four-panel forecasts from the GFS, you can barely tell these two storms apart.  Both feature troughs in large-scale northwesterly flow.

That's a very encouraging forecast, but I must bring up the uncertainty.  One way to evaluate uncertainty is to compare forecasts from different models and ensemble forecast systems, which produce a suite of forecasts.  For next weekend, all of the members of this morning's GFS ensemble seem quite similar to the run above and produce a direct-hit trough.  

Source: Penn State E-wall

I like that forecast, but the ECMWF (European Center for Medium-range Weather Forecasting) forecast ensemble has somewhat different solution.  It has the storm track further to the south and the trough going through the Southwest.  We'd probably get some snow, but not necessarily a lot.
Source: ECMWF
So, we can be reasonably confident that we will be seeing a pattern change and that we have a fairly cold period ahead (after tomorrow) relative to climatological averages.  For snow it appears we will see something, but how much of a pounding remains in the ether.  Keep you fingers crossed. 

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