This is going to be a long post since I haven't updated in a month. For those longtime readers, you know that I've discussed the difficulty in finding time to update this blog. The posts I make about the current weather trends and outlook are made on my own time and are my own thoughts and are not part of my employment at the National Weather Service. I regret that I'm not able to update more often. When I retire from the agency (not that far away) I would be able to update quite often - but of course it wouldn't be free. :-)
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So, there is a lot to discuss since I haven't updated since the post on February 5.
First, just as a refresher and perhaps the following will be new to some of you...
When fall arrives, the jet stream across the northern hemisphere starts to intensify (speeds increase) and areas of maximum and minimum speeds fluctuate as these areas move around. A pattern of where the jet stream winds intensify/amplify meridionally or latitudinally becomes established. This pattern has been known to repeat around the hemisphere on a periodicity that varies from one year to the next. I have found the repeating nature to be from 45 to 60 days, but it has been outside of that range. What causes the jetstream to behave in the way it does (differently) from one year to the next are influences from oceans and land masses - and probably the sun. Some influences are more dominant than others but those tend to change from year to year. Even on an intra-seasonal time scale the influences can change.
Some of the changes that influence the jetstream can from the tropical oceans (Atlantic, Pacific, Indian Ocean), northern latitudes of oceans, landmass/ocean interactions, Arctic oscillations of surface pressure, stratospheric warming, blocking of the jetstream across the higher latitudes, etc.
You've heard of El Nino and La Nina (warming or cooling of the equatorial Pacific oceans). Many people will give a seasonal outlook solely on these events as if THEY are the ONLY factors that influence the weather pattern. There is plenty of data available to quantify weather based on these events and that data shows a different outcome from event to event. Based on the current La Nina, here is an outlook from The Weather Channel that was valid for February:
Did they do pretty good?
What about from the Climate Prediction Center (NWS)?
Pretty good? I'd say a lot better. Now, granted, this was an updated forecast made Jan 31. Their original outlook looked similar to The Weather Channel. What I saw on Feb 5th was that the build-up of brutally cold air (causing the Arctic Oscillation to go strongly negative) was finally going to make a visit on "our" side of the hemisphere. The two other negative events (not as negative) were unleashed upon Siberia and Europe. Plus, there was strong evidence of a significant Madden Julian Oscillation (MJO) and that MJO became VERY significant and I think had the greatest impact on our February weather.
The MJO was well established and influential.
But now look what has happened to the Arctic Oscillation!
That is a major shift to the positive side! Even though we are currently seeing a dip, the AO is forecast to go strongly positive and potentially with a magnitude that I haven't witnessed. Now my question is just what influence will this have on the pattern for the next few weeks. Is the AO the main controlling factor on the jetstream? Or could be be forcing from perhaps the western Pacific (not La Nina). If the cooling on the equatorial Pacific is the main influence, then there probably wouldn't have been this storm we just had.
Now there is evidence of a resurgence of another MJO, just not as strong as the February event. Regardless, I think this developing MJO in the presence of the pattern that developed during the fall has given me confidence of several periods of active weather or changes. I actually had these dates in mind back on the 20th of February (the last time I intended to update this blog). I haven't changed my mind since then.
These following periods are not the ONLY possible weather....they just have my attention.
1) March 10-17, but especially around March 15. This should be the next active period but probably only 1 storm will impact the high plains and that would be around the 15th. Before then it could be the eastern plains. I wouldn't be surprised if there was a blizzard, especially for higher elevations of the high plains.
2) March 25-31 is a period of potentially much below normal temperatures. That could be problematic as with this recent rain and the mild temperatures coming up, there may be some early breaking of dormancy of some vegetation. Also, the b word comes to mind. The last 10 days of March are actually the most active for blizzards, based on history.
3) April 17-20 could be interesting. If the warm sector is far enough north/west then perhaps a severe weather outbreak? Hopefully no blizzard but I wouldn't be surprised for areas of the high plains.
4) April 25-May 2 could potentially see much below normal temperatures. If there is going to be a late frost or freeze, that would be the time period.
I'm not ready to venture into an outlook for the summer. For a while this winter I was seeing resemblance and similarities to 2011. Ugh. I'm not sold on that yet so don't panic.
Again, if you wouldn't mind doing the quick survey...it would help me to determine the direction I go from here.
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