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!

La Nina Returns?

NOAA has put out a La Nina Advisory for the 2011 winter season. That's right folks, La Nina appears to have re-developed and is here to stay a bit longer than first thought.

What exactly does La Nina mean, you may be asking? It essentially is a cooling of Sea Surface Temperatures (SST) in the central and eastern portions of the tropical Pacific Ocean. The set up has warmer than average SST's over the western Pacific and cooler than average SST's in the central and eastern Pacific. La Nina typically occurs ever 3-5 years but consecutive episodes occur nearly 50% of the time, according to the NOAA Climate Prediction Center. While La Nina stems from the anomalies of SST's, its impacts go way beyond ocean temperatures.

Sea Surface Temperatures showing a cooler eastern Pacific which signals a La Nina return. Via NOAA CPC.

Winter of 2010 in the United States was a record-setting one. High snowfall totals lead to record Spring flooding and severe weather that was off the charts! The exceptional drought that is on-going in the South...yup, put that one on La Nina. Wichita Falls, TX became the first location with 100 days at or above 100 degrees this year! So the news that La Nina has reformed does not offer much in the way of relief.

What can we expect for winter 2011? Average La Nina winters cause wetter than normal conditions here in the Pacific Northwest and can often expect cooler than average temperatures, too. La Nina doesn't offer much drought relief during the winter months either for those in the South and Southwest,

“This means drought is likely to continue in the drought-stricken states of Texas, Oklahoma and New Mexico,” said Mike Halpert, deputy director of the Climate Prediction Center.  

 

Typical La Nina setup

Beyond the upcoming winter, it is tough to tell just how long and strong La Nina will be. Should it last into next Summer, it could mean another active hurricane season. During the 2010-11 La Nina conditions, forecasters predicted a very active tropics with 14-19 named tropical storms. As of today, we are sitting at 14 named storms this season. Pretty good, huh? With those cold waters in the Pacific, oceans try to balance out by warming up the tropical Atlantic waters to above average temperatures. So, if La Nina lingers around for another Summer, things could be active again.


With La Nina's anticipated return, records could fall again this winter. That would not be welcome news to most.