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OKpowdah

Moderator Meteorologist
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Everything posted by OKpowdah

  1. A lot of uncertainty with that trough next week. (See the thread in the main forum). But GFS and Euro both have shifted to the south-southeast with the trough axis and low track, tilting the trough axis neutral over Oklahoma. I mentioned the snow possibilities for eastern Colorado, but this could get interesting for the central Plains too.
  2. Definitely has been fun to watch the influence of the Pacific on the pattern recently. All the tropical activity in the western Pacific has had really nice clear impacts downstream, translating to the very strong ridging along the west coast. The biggest change from this week to next week I think is a strong consensus for the negative NAO block to break down. The anomalously high heights over the Davis Straights is projected to erode as the trough over the Great Lakes breaks to the northeast. This is supported by the MJO moving into the E Pac and Atlantic, strengthening the South America hadley cell. The rising NAO would translate to strengthening ridging over the Southeast US. So now let's introduce the forecast problem. This comes about next week, starting around day 5-6 (Sunday 10/27). The effect of both Francisco and Lekima recurving in the next few days is the huge LHR, -PV etc. and another wave packet that reaches the west coast ridge by day 5-6, at which point it rapidly amplifies. Alright so the ridge amplifies, then quickly breaks, but then we run into this problem of the downstream pattern. This week we have a nice -2SD NAO which supports the trough in the eastern half of the CONUS. However next week, the trough that digs downstream of the latest ridge break in the west, will run into rising heights in the SE US with the developing +NAO. So by day 6-7 (Monday), the trough is digging into the four corners region, with cold high pressure behind it. The trough is forced to stay positively tilted with ridging in the west folding over, and the ridging in the SE US preventing the trough from digging toward the southeast. So here's where some model differences arise. Quick model discussion: With this trough, the GFS seems to be able to sweep eastward (then damping out as it's forced north of the SE ridge). The ECMWF however, is quick to form a cutoff over California. The cutoff positively feeds back to the SE ridge, perpetuating the cutoff. The western ridge then spills over into the Plains. A problem might be the ECMWF has a bias to overdevelop cutoff lows in the west, which then pumps up downstream ridging over S-central and southeast US. The CMC is doing the same, and it also has a bias for overamplifying these types of troughs which would result in the same cutoff development. Can also see in the GFS ensembles, there are two areas of large 500mb height spread by day 6-7: 1) Western US on the downstream side of the breaking ridge (where we have our uncertainty with the trough evolution) 2) Over southern Quebec with the increasing height gradient in the developing +NAO pattern. So rather than the nice easy forecast for the CONUS this week (+PNA, -NAO, etc.) we get this fight between the Pacific and Atlantic. Ramifications? Well one of the trickier parts of the forecast is with the arctic high that noses down the east side of the Rockies and the potential for a snow storm in E Colorado with the trough in question. But this uncertainty also builds up eastward with the strength of the SE ridge in question and the latitude of the height/temp gradient over Quebec /New England.
  3. Also potential for an E CO snowstorm, if anyone is interested (besides Howie)
  4. The Quasi-Biennial Oscillation (QBO) is a cycle of zonal wind in the equatorial stratosphere with a period that varies between 24 and 30 months. This oscillation is a product of downward propagating alternating wind regimes. The current method of monitoring this oscillation is through an index, calculated by the zonal wind anomaly at 30hPa averaged along the equator. This method excludes information on the vertical structure of winds in the stratosphere, and presents the QBO as a one-dimensional temporal oscillation. Presented here is a new framework for monitoring the QBO. This framework incorporates both the oscillation in time and in space. The two leading principle components (PCs) of equatorial stratospheric zonal winds are calculated from NCEP/NCAR reanalysis monthly mean data. These PCs are then standardized and used as X and Y coordinates in a 2-dimensional phase space. A phase angle can then be calculated from the coordinates, forming a new index that is much more representative of the state of the stratosphere. The results show a very clear pattern of zonal wind and temperature regimes in the stratosphere. Furthermore, from each of these phases, there are physical connections to characteristics in the troposphere on a monthly to seasonal basis. These include the distribution of tropical cyclone activity, the El Niño / Southern Oscillation (ENSO), and the extratropical pattern. This new framework for monitoring the QBO is shown to be much more applicable to seasonal forecasting. Compare the EOF-constructed oscillation to a 52-month reanalysis segment
  5. Moderate snow being reported in DDC
  6. OKpowdah

    Alaska/Western Canada obs and discussion

    Following the recurvature of Typhoon Francisco, we get a huge jet amplification again in the West Pacific, and it looks like both the GFS and ECMWF want to develop an intense low in the poleward exit region by day 7-10. Could get kinda windy around the Aleutians to western Alaska.
  7. A lot of bust potential with temperatures early next week in Oklahoma with the frontal passage. We'll see how far southwest that airmass can penetrate, before getting shoved eastward. NWS forecast high for Norman on Tuesday is 70. MEX guidance is 59.
  8. OKpowdah

    The early speculation on winter 2013-14

    The effect of a recurving TC can be seen in the group velocity (so basically the wave envelope that amplifies the wave pattern). So when the phase pattern change is already in motion thanks to extratropical interactions in the central and eastern Pacific, the recurving TC basically acts reinforce and to increase the amplitude of the wave pattern. At the same time producing a more stable blocking pattern than would've been. Haha thanks guys.
  9. OKpowdah

    The early speculation on winter 2013-14

    Aww thanks! This board taught me everything I know. Wait, I'm a mod. Back on topic. It's going to snow this winter.
  10. OKpowdah

    Typhoon Wipha

    We're watching another potential major Typhoon recurving in the West Pacific, passing close to Japan by day 4 (Tuesday night ET). The story begins though with just some simple extratropical cyclogenesis in the northern Sea of Japan and the amplification of downstream ridging. This ridge eventually breaks as it pinches another downstream disturbance, and then bridges with ridging over the eastern Pacific. The favored superposition of negative PV anomalies develops a very strong ridge on the west coast of North America toward Alaska. As Wipha recurves, distributing upper level latent heat and negative PV downstream, we see a huge WPac ridge form, and a rapid acceleration of the jet. On the poleward exit side of the jet, another extratropical system rapidly intensifies near the Aleutians. As the huge ridge breaks, all the cyclonic vorticity on the poleward side of the jet gets dumped into this system over the Aleutians, forming a pretty stable trough over the North Pacific. Day 5-9 (17th-21st): And so now we have the very distinct pattern of a large trough over the Aleutians and blocking ridge over western North America. As you might imagine, this could have some interesting implications over central and eastern North America, with a negative NAO in place over the north Atlantic. At the very least a period of below normal temperatures, and an opportunity for snow in the Midwest.
  11. OKpowdah

    The early speculation on winter 2013-14

    Yeah the disturbance near Hawaii plays a nice role in anchoring the anticyclonic wavebreaking along the west coast, rather than it spilling over into the CONUS
  12. OKpowdah

    The early speculation on winter 2013-14

    <3 March 2001
  13. Personally, I'm more interested in the prospects of an early season winter storm in the northern Plains. Always a challenge to get all the right factors together this early in the season though.
  14. OKpowdah

    The early speculation on winter 2013-14

    You can pull the monthly-mean data for 500mb heights from NCEP/NCAR reanalysis and calculate the leading EOFs for each month for reference.
  15. OKpowdah

    The early speculation on winter 2013-14

    Related: here's the EP/NP index, which also is referenced as a "spring-summer-fall" pattern, and you'll notice the loading pattern is not included for January either. http://www.cpc.ncep.noaa.gov/data/teledoc/ep.shtml http://www.cpc.ncep.noaa.gov/data/teledoc/ep_map.shtml
  16. OKpowdah

    The early speculation on winter 2013-14

    Right, so they calculate the EOFs of SLP/500mb height climatology for each calendar month. This is the source of the definition of most of our indices we know and love. But if in one particular month, the index does not appear as one of the leading EOFs ("leading mode of variability"), then not only is it considered "insignificant" but the index can't even be appropriately calculated without the EOF to project onto.
  17. OKpowdah

    2014 ENSO Mega Thread

    Just throwing this around. Fooling around with different EOF interpretations of ENSO: Maybe some method to differentiate between east- and west-based events.
  18. The Quasi-Biennial Oscillation (QBO) is a cycle of zonal wind in the equatorial stratosphere with a period that varies between 24 and 30 months. This oscillation is a product of downward propagating alternating wind regimes. The current method of monitoring this oscillation is through an index, calculated by the zonal wind anomaly at 30hPa averaged along the equator. This method excludes information on the vertical structure of winds in the stratosphere, and presents the QBO as a one-dimensional temporal oscillation. Presented here is a new framework for monitoring the QBO. This framework incorporates both the oscillation in time and in space. The two leading principle components (PCs) of equatorial stratospheric zonal winds are calculated from NCEP/NCAR reanalysis monthly mean data. These PCs are then standardized and used as X and Y coordinates in a 2-dimensional phase space. A phase angle can then be calculated from the coordinates, forming a new index that is much more representative of the state of the stratosphere. The results show a very clear pattern of zonal wind and temperature regimes in the stratosphere. Furthermore, from each of these phases, there are physical connections to characteristics in the troposphere on a monthly to seasonal basis. These include the distribution of tropical cyclone activity, the El Niño / Southern Oscillation (ENSO), and the extratropical pattern. This new framework for monitoring the QBO is shown to be much more applicable to seasonal forecasting. Compare the EOF-constructed oscillation to a 52-month reanalysis segment
  19. OKpowdah

    The early speculation on winter 2013-14

    I meant the general longwave pattern
  20. OKpowdah

    The early speculation on winter 2013-14

    South of the pike, definitely would do 09-10 again.
  21. OKpowdah

    The early speculation on winter 2013-14

    The relationship between the QBO and the boreal winter extratropical pattern is a little more involved than we try to make it out to be. And stats on the QBO using the 30mb index are really not all that robust. I'll try to do some sort of winter outlook with emphasis on interaction between the QBO, ENSO, and the north Pacific. Pretty interesting stuff.
  22. OKpowdah

    The early speculation on winter 2013-14

    I could go for a dominant -EPO / +NAO pattern
  23. OKpowdah

    The early speculation on winter 2013-14

    Anyone want to explain a physical connection between whether a storm dumps more than the arbitrarily decided amount of 3" of snow during the month of October at the Boston airport, and the quality of the winter that follows in southern New England?
  24. OKpowdah

    The early speculation on winter 2013-14

    2011 is the new benchmark. Anything less is weak.
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