Pacific North American Oscillation - "a climatological term for a large-scale weather pattern with two modes, denoted positive and negative, and which relates the atmospheric circulation pattern over the North Pacific Ocean.The positive phase of the PNA pattern features above-average barometric pressure heights in the vicinity of Hawaii and over the inter-mountain region of North America, and below-average heights located south of the Aleutian Islands and over the southeastern United States.The PNA pattern is associated with strong fluctuations in the strength and location of the East Asian jet stream. The positive phase is associated with an enhanced East Asian jet stream and with an eastward shift in the jet exit region toward the western United States. The negative phase is associated with a westward retraction of that jet stream toward eastern Asia, blocking activity over the high latitudes of the North Pacific, and a strong split-flow configuration over the central North Pacific."-Wikipedia
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The storm tonight, Friday, and possibly Saturday belongs to a decreasing PNA/ AO teleconnection regime, the best pattern for heavy snow in Wisconsin. Next week we head deeper into this pattern with a deeper western trough digging in the southern stream. Mid-range models are not that interesting for Wisconsin. They do show a storm system during the 2/13-2/16 timeframe crossing the country further to the south. Maybe models change to support a bigger storm in future runs? At this moment I'm betting that the peak time for this pattern is our current system as we flux into the western trough. Just not thrilled with next week yet.
Strange forecast on the AO today with many taking a nose dive by Feb 1. I don't buy it yet since I do not see it on the models, but -AO of this magitude will certainly lead to cold. Then on the PNA side you have one member totally going negative while the rest trend toward positive. 
Moisture for the Sun-Mon storm will come from eastern Mexico and western Gulf of Mexico. What I call a "moisture front" arrives just as storm #1 pulls away. The moisture will get buffeted slightly early next week but will be ready for #2 as it crosses the country. The stage is set moisture-wise for some interesting weather late January and Feb. If we can get the AO to slide back positive while holding onto a weakly negative PNA we will be in good shape. Curious to see how things come together in that 6-14 day period. It's been such a boring winter to this point. 
SUNDAY - The peak of our stormy pattern will arrive this weekend coincident with a AO/-PNA spike. If April was a seminar, the Sunday storm would be the keynote speaker. Not to understate the impact of our current system; it's certainly been interesting. It appears the week leading up to a spike are more active than the week immediately following it. Next week northwest flow interrupts our active pattern bringing seasonably cool temperatures. Wisconsin has been on the cool side of the current system and should be on the cool side this weekend. The occlusion of the Sunday storm could block us out of meaningful t-storm threat. I was wondering if this signature system would bring a severe weather event to Wisconsin but just doesn't look like conditions are in place yet though that could still change.
Taking another look at teleconnections, PNA and AO. It has been rather unsettled lately. It's been warm but not record breaking warm like it was in February. Interesting. The PNA has been gradually decreasing since late March and storminess has increased in response. Low pressure systems have been interesting and healthy. April the last few years has yielded almost nothing, nice change. Looking at the AO (see picture) it's easy to see a pattern. So I'm wondering if early May will bring a significant storm pattern?
PNA while currently positive, is trending towards neutral. AO is heading into the negative state. In February we talked about -PNA/ AO being a precursor to late Feb early Mar storminess. Boy it was wild! February and March definitely traded places this year. If the AO keeps dropping and PNA stays slightly or neutral, I'm thinking late April will be similar to early February. But I'm wondering now whether April and May will trade places; April more dry and warm with early May more stormy? This winter was just a weird enough that I'll at least entertain the thought. 

February post-> https://wisconsinwx.com/profile?i=430546&p=2
Since mid-January we've experienced consistently PNA conditions in combination with a slow and steady decline into -AO phase. This has been a relatively long and uneventful stretch of weather that will culminate with warm near-record temperatures Sunday through next week. Forecasts (at least on the teleconnection level) suggest the situation is going to flip into early March towards -PNA/ AO relationship, at least temporarily. This will more closely resemble the weather pattern we saw in December.

 Research shows this -PNA/ AO suggests a storm track through the plains and great lakes as cold air attempts to reassert itself. As we often do this time of year, I predict we will have one or two major systems will impact the great lakes by the end of February. Long range forecast models support this idea.  Learn more about PNA here ->climate.ncsu.edu/climate/patterns/PNA.html
Very warm pattern developing over the next seven days across the country and Wisconsin. At the teleconnection level the combination of PNA/-AO tends to bring boring and warm weather. 50s in February is likely to bring a few new records. Sometimes after the peak comes the valley. 
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