January 10th, 2010: Welcome Pattern Change ( Brian Bledsoe )

After such a cold December and a pretty cold first week of January, we are finally going to keep the Arctic Air away.  For a while...  The reason?  A big swing in the weather pattern and the various oscillations that control our weather changes.  If you read our blog regularly, you know that we've been talking about the Arctic Oscillation ( AO ), the Pacific North America Oscillation ( PNA ), and the North Atlantic Oscillation ( NAO ).  The two oscillations that are important for this blog, are the AO and the PNA.  Below is the AO index for the past several weeks and the subsequent forecast for the near future:

The AO went strongly negative early in December and has just now started to come back toward neutral territory.  Remember, when the AO goes negative, it allows bitterly cold Arctic Air to readily spill southward into the US.  Fortunately for Southern Colorado, we do not have a deep snowpack and the core of the coldest air has gone to our east.  Otherwise, this may have ended up one of the coldest Winters on record for us...  Now that the AO isn't so negative, we should have a relatively mild period of weather for the next 7 to 10 days and maybe longer...

The PNA has also started to change phase.  Check it out below:

The PNA has largely been positive for the past several months.  Thus, we haven't really had many storms come from the southwestern part of the country.  When the PNA goes negative, it allows storms to move into the southwestern part of the US, and eventually roll eastward into the Plains.  Many times, our biggest storms occur when the PNA is negative.  Also, when the PNA goes negative, it allows a milder Pacific flow to ensue.  As you can see above, the PNA is forecast to become more negative in the coming days.  This will likely mean our weather pattern will get more active, within the next couple of weeks, with storms originating farther south and potentially having more of an impact on Southern Colorado.  While January and February are typically not wet months for Southern Colorado, March and April are right around the corner and could prove to be quite active if the PNA swings toward a prolonged negative phase. 

Should be interesting to see, but for now, I'm glad the Arctic Air has retreated for a while...

Chief Meteorologist Brian Bledsoe

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  • by Jenny Location: Cragmoor on Jan 26, 2010 at 07:24 AM
    I don't know about La Nina or El Nino or whatever, but I do know that snowfall rates here are not the same as they were when I was growing up (80's/90's). Call it cycles or whatever, but I remember a LOT more snow during winters back then.
  • by Ed Location: Widefield on Jan 25, 2010 at 12:07 PM
    I might also add that the La Nina winter of 2007-2008 produced MORE than we've seen this year UP TO THIS POINT - especially in Dec. and Jan.
  • by Ed Location: Widefield on Jan 25, 2010 at 11:58 AM
    Well, I can't miss an opp to put in my 2 cents and express my opinion. We are now almost 10 full inches below the "normal" What now seems to be the normal is being below the normal. Also, we really were not THAT different last year in a la nina winter. About 3 inches difference up to this point between the two years. Not that much if you ask me. While December was cold, not a lot of snow. I long for the old days when we got snow during the winter. Not a storm here and a storm there that produce an inch or two. I guess we'll jsut have to wait till March, huh? We'll see. I wonder what the reason will be when we get to March and get little to no snow.
  • by Brian Location: Weather Center on Jan 19, 2010 at 04:11 PM
    Chris, I don't expect it to get really that active until we get into March and April. Guys, January and February on average only gives us 10" of snow. March equals that and April isn't far behind. With the El Nino likely to hang on through Spring, I still expect some decent storms. Remember, we usually see Winter in the Spring. Plus, we had a lot of Winter in December. Maybe not crazy snow, but some areas did see good snow and we were 6 degrees below normal. Julio, that is a lot different from last year... Thanks for reading our blog.
  • by Julio Location: 80907 on Jan 18, 2010 at 06:41 AM
    What is going on? I keep looking ahead at the longer forecasts and hoping to see some bigger storms headed toward us, but nothing! There is the occasional little storm, but it seems like the rest of the country is getting rocked and we've had a few cold days. We're already almost 8 inches below the norm and sinking fast. I'm so bummed! Even KRDO's 13 day forecast looks promising, but then they say the potential BIG STORM for next week will miss us. Sigh...La nina was better than this last season!
  • by Chris Location: Colorado Springs on Jan 17, 2010 at 03:24 PM
    Is there any chance that the weather pattern will change in the next week or so to a wetter pattern? It seems like last January through March was one of the driest on record and so far this year is starting out the same way. Will El Nino give us a helping hand in the near future? Thanks for your time and all that you guys do. Chris...
  • by Jay Location: 80922 on Jan 15, 2010 at 11:12 AM
    Man, what is up with this weather? I don't mind the warm spells in winter when they are offset by the occasional snow storms. But man, there's been almost nothing for quite a while now and there is nothing "serious" in regards to snow any time soon. I moved here this summer and was expecting a very snowy winter, but so far I'm not impressed. It's been cold, but certainly not as snowy as I anticipated. Judging by all the El Nino talk around here, everyone was expecting quite a bit more precipitation by now. I'm from Cali, so any snow is new to me. But it's just not as much as I thought. Is this typical? I've also read that we seem to be below the normal snowfall year after year, why do we continue to be below so constantly? I understand what makes an average an average, but if we keep getting less and less, doesn't the "normal" go down too? Has this been the case? Sorry, lot's of q's. Naive/Ignorant California boy new to Colorado here. :)
  • by Julio Location: Ed on Jan 14, 2010 at 04:18 AM
    So far this winter has been a major disappointment. Not what I expected from El Nino. I know, I know, wait till March, April or whatever. But geez, it's already mid January - no snow so far and ZERO in sight! Every long term forecast says the same thing - above average temps and a weak storm that will pass well to our south/east/north...you name it.
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