Monday, January 9, 2012

Any Hope For Snow?

I posted last month about the possibilities of snow on Christmas. The holidays came and went, no snow. No "typical" winter weather to speak of at all. Just dull weather. A shower here and there. Fog most mornings and some decent stretches of sunshine. Will we transition into a more La Nina weather pattern which would yield a better possibility of snow? According to this morning's model run, it does not look good.

One of the four daily model runs occurs while I'm at work each morning. The 06z model runs are notorious for being "outliers" in comparison to their 00z and 12z counterparts. By the way, we use the postmark "Z" to denote "Zulu time". It is basically Greenwhich Mean Time, so 00z model run translates to 12 midnight in England. So, when this mornings 06z 850mb comparisons came out, it did not spark hope for a return to winter weather.
850mb Temperatures look boring
This is the GFS model run, just one of several separate models that Mets use to forecast. Within the GFS model, several different "perturbations" are played out. The graph above shows the 850mb temperature plotted out with each run. The 850mb temperature gives us temps at about 5,000ft elevation. We can use the 850mb temps to translate a surface temperature. Ideally, we like to see 850mb temperatures of at least -6 degrees Celsius in order to get excited about any possibility of snow in our area. The 06z run doesn't inspire hope. The green line is climatology, what we should expect. The red line is the average of all the models and the blue line represents the "operational" run, the actual model that we see each day. Just a week ago, the ensemble mean had temperatures down near -3 to -5 degrees Celsius, and I recall a few operational runs that dipped into -10 degrees Celsius last week as well. But that's life in the world of a weather forecaster. You get excited about a big arctic outbreak and 6 hours later...that model takes it away from you. I can almost guarantee that by the time I post this, the 12z model run will be drastically different!

I can tell you that this morning's 06z GFS 850mb map does not show much of anything below 0 degrees for the next 384 hours! The 7 day forecast looks nice, however. By mid-week, gusty east winds will help keep us clear of clouds and fog each morning. With the clear conditions, nights will be chilly. Lows may touch the mid 20's. Remember, peak snow season for Portland is right around the corner, so things can change in an instant!

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