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OKpowdah

Moderator Meteorologist
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Posts posted by OKpowdah


  1. That's not just an extreme cold outbreak, that has longevity followed by activity in the stratosphere that would lock that in place into February, with storm potential all the while. Probably would be talking about a very extensive snow pack east of the Rockies ...with the related positive feedback into supporting arctic surface temperatures.


  2. I agree with this concern in full. I think the issue for me moving forward is how and when does this gyre of sorts retrograde farther west than Central Canada? This is always the issue in these retrograding pattern progressions. In 2010 we saw it retrograde to a perfect spot and we had the big time blocking build into the Davis Straight at the same time. And so that progression was absolutely classic and nearly perfect -- textbook. I don't think we can compare this to that yet until we see some sustained high latitude blocking development. But what we are seeing on medium range guidance is a big first step toward it. Anyway...the other thing getting my attention is the potential split flow development once the ridge retrogrades back off the west coast. With the PV just north of us in Canada and increasing moisture available..a load of possibilities there too.

     

    Absolutely. And your emphasis of the importance of the PV enlongation is spot on. That's when we can actually get some real perturbations on the flow


  3. Great discussion!

     

    Only issue I have with getting excited for big snow storms in this pattern is the lack of true blocking over the N Atl to Greenland. Heights rise over N Greenland but we're maintaining this N Atl ridge pattern. So we drop this anomalous trough into the eastern US, up against the ridge, and upper level winds are screaming from the S/SW. Certainly a baroclinic environment, and the monster ridge in the west favors amplifying disturbances, so east coast cyclogenesis potential looks great. But without more of a block to the NE, looks like a pattern that'll have 980mb lows zipping by with 6 hours of snow. Granted that can easily be a 10" storm, but in the great quest for a MECS, I would want more blocking.


  4. Gotcha.

     

    Question, what defines the EPO loading pattern as the "proper" or "right" spot.  How do we come up with it? 

     

    The loading patterns of various teleconnections (like EPO, NAO, PNA, etc) are based on the leading modes of variability over a specific domain (could be the Northern Hemisphere, Pacific+North America domain, Atlantic domain, etc). This is done through computing the EOFs of 500mb height (or SLP) climatology.

     

    So then to calculate the daily index value, you project the daily 500mb height pattern onto the loading pattern. So basically when the current pattern matches the loading pattern, the projection will be positive, and when the current pattern is opposite the loading pattern, the projection will be negative.


  5. The wave 1 response has been a little stronger than I was seeing forecast. Hence the warming in the far upper reaches of the stratosphere right now. But it won't be enough to get things going. But we maintain this wave 2 amplitude for a while, keeping the vortex stretched across the pole, with notable mid latitude heat flux. I think better potential for a SSW in mid February. Also supported by the QBO easterly shear zone dropping to around 30mb in February. This phase in February and March is statistically most favorable for a negative AO.

    2006-7 is a really interesting analog for comparison. First, generally cold vortex sticking near the pole, with the same MQI phase. December 2006 to early January saw similar small preliminary disruption of the stratospheric polar vortex. The MAJOR difference being that the PV slid to the other side of the pole. It's actually really really cool. So the 500mb pattern is IDENTICAL over the North Atlantic and Europe (+NAO with cold vortex), and completely OPPOSITE over the Gulf of Alaska up through the Bering Strait. Well we saw what a massive difference that made in terms of sensible weather over the US!!

    Anyway, we know how the AO turned on a dime in the second half of winter in 2007. As I said, I think that flip looks good this winter too.


  6. Thanks Tip.

     

    By any chance do you have monthly values prior to 1950. Any enlargement of the sample would be helpful.

     

    Finally, I agree with you about the extremes (more frequent extremes on the negative side) not being random. I don't believe the AO is a normal distribution.

     

     

    This could be explained by the fact that a positive AO (or high index annular mode) is basically amplified climatology, whereas a negative AO can be more significantly anomalous from the background state.

     

    Can this be replicated in ENSO data? Tend to get slightly more extreme El Ninos than we do La Ninas.

     

    Of course all this is based upon the methodology of how we measure these oscillations.


  7. Pacific always, trumps the Atlantic..Always

     

    Except when it comes to highly amplified disturbances, which is really when you're concerned anyway if you want big snow.

     

    Pacific is great in dictating the arctic connection to the US, but the Atlantic dictates the evolution of s/w's across the US ... do they break into the Great Lakes, or does downstream forcing trump nonlinear growth.


  8. Tip, I don't see how you can think the Pacific doesn't influence the AO domain. In the more fundamental sense, take the distribution of tropical forcing in the equatorial Pacific, sketch a Hadley circulation accordingly, which will move the "Ferrel cell" ball bearing, thus putting some vertical torque on the polar cell.

     

    Or just take tropical forcing and the polar jet and see where the lower wavenumber Rossby rays go.

     

    All sorts of interaction. And unfortunately no matter how many three letter acronyms someone wants to come up with, it will always be a nonlinear system.


  9. That's a major pattern reversal, and as is usually the case, LR model forecasts were a little too quick with communicating it downstream (hence the chillier start to November in the east). But anyway by day 2 we have the massive Aleutian ridge, by day 4 the ridge breaks, and by day 6 huge full latitude trough in the west, and ridge in the east.

    What LR models are agreeing on now is a decent arctic intrusion into the western trough, and one heck of a temperature discontinuity in the central and southern Plains by around day 8-9. Looks like a classic Plains cold front.


  10. ECMWF and GFS currently agree on carving out a broad but positive-tilt trough over the Rockies early next week. Severe weather looks possible for the central and southern Plains, particularly Monday. As per the autumn usual, impressive kinematics but questionable thermo. Might be the last hurrah for anything worth paying attention to out here until Feb/Mar.

     

    Also potential for an E CO snowstorm, if anyone is interested (besides Howie)

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