If you read my blog post back on November 24th http://www.kktv.com/blogs/talkweather/73110407.html, you know that I thought December was going to be much more Wintry than November. Not that it would be hard to surpass the quiet and nice November, but several elements came together to produce a pretty active month. One of those elements that produced some pretty cold air, was a negative Arctic Oscillation, also referenced in the November 24th blog post. When the AO is negative, cold air can readily move south into the US from Canada, and boy did it ever. December 6th through the 10th were some pretty cold days, with highs in the single digits and teens for many of us. First, let's check out the December snow totals for some area cities:
Colorado Springs: 9.4"
Goodland, KS: 12.2"
Obviously, those are the official totals at the airports for those cities. Locations on the west side of Colorado Springs totaled more, as did areas just to the west of Pueblo and Denver. Bottomline, it was a pretty snowy month ( relatively speaking ).
The snowcover coupled with cold air pouring south from Canada also produced a cold month. Like I said, the AO has been strongly negative and continues to be negative:
The negative AO coupled with the snowcover produced below normal temperatures throughout the month. Check it out:
Denver: 5.6 degrees below normal
Colorado Springs: 5.7 degrees below normal
Pueblo: 6.3 degrees below normal
So, if you thought it was a cold month, you were right. Now I know we still have a few days to go, but the snowfall numbers and the temperature numbers likely won't change much. So, let's look ahead...
The AO doesn't look to change much in the near term. As you can see from the graph above, even the forecast index for the AO stays pretty negative. Thus, I wouldn't expect any long lasting warmups. That's not to say that we won't see a few days in the 40's or lower 50's, but those days will be the exception rather than the rule. What about snow? To answer that, we must look at another "oscillation". The Pacific North American Oscillation...
When the PNA is negative, we usually have an active weather pattern that involves numerous systems coming out of the Desert Southwest. As you can see, we really haven't had a long lasting negative PNA for quite some time. Some fluctuations on the negative side, but nothing to last. That's not to say that we won't have storms when the PNA is positive, but they are usually fast moving and fairly weak. Like the storm that occurred last week, lot's of folks saw snow, but nothing huge (unless you live in the Plains and Midwest). As you can see, the PNA is forecast to stay slightly positive or neutral. This should mean relatively quiet weather, with nothing huge on the immediate horizon. However, it will dip negative at some point and that may be when our next sizeable storm will occur. Rest assured, I will be watching it closely...
El Nino Update:
Here is a look at the latest sea surface temperature anomalies from the Pacific:
As you can see by the green and yellow shading in the central and eastern Pacific, El Nino is alive and well. It looks to persist and will likely be a factor in the weather we see late this Winter and Spring. If El Nino hangs around at this intensity through February, March, and early April, we may see some pretty snowy weather during that time. As most of you know, March and April are our snowiest months here in Colorado. Wouldn't be surprised to see a pretty active March and April... In fact, the Climate Prediction Center's latest three month forecast kind of goes along with what I am thinking. Here is a look:
That green shaded area means a good chance for above normal precipitation during the months of Janurary, February, and March. That would mean a pretty charged up subtropical jet stream, and potentially some pretty good storms for us. We'll see...
Chief Meteorologist Brian Bledsoe
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