OKpowdah

Moderator Meteorologist
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Everything posted by OKpowdah

  1. lol yup. My first semester I was extremely homesick for cold and snow. And then I played frisbee on a 70 degree day in the middle of January, and I was okay with it haha. And taking the Oklahoma perspective on weather everywhere -- check out the SCP from the 15z SREF. Can't upload for some reason, but just go check it out. Median > 12 in the Gulf of Maine at 15z Tuesday
  2. Still a flat ridge though, along with a very +NAO. The northern branch of the split Pacific jet is wicked strong and just spilling right into North America through week 2.
  3. You have to keep in mind that the AO is a hemispheric index. The air over the arctic will take the path of least resistance, which in this case will be over Kamchatka and across the North Pacific, not North America.
  4. Very interesting, considering this composite pattern from a 45-day lag off of the latest burst in tropical forcing. http://t.co/u4h7H4h2lX
  5. Most of the cold air shifts to the other side of the globe towards the end of the month. We do get some pretty decent shortwaves ejected at the exit of the Pacific jet, but I'd lean more away from snow threats and actually more toward thunderstorm threats.
  6. 1) Some people seemed to have based this assumption on the 1-dimensional QBO index "slowing down" last month. 1D extrapolation of the QBO index is primitive considering the data that we have at our fingertips. 2) Basing an assessment of the QBO, a 25-29 month oscillation, on weekly variations of local anomalies is extremely flawed. 3) The core of the easterlies were at 20mb this past month. There's still easterly shear at 30mb. Therefore the QBO "index" would be expected to continue to fall or at least remain nearly steady for the next few months.
  7. I disagree with the premise that the QBO easterlies will weaken substantially by December and through the winter. This seems to have become a popular idea in the last week for some reason. The MQI phase space demonstrates how the easterlies are still descending, and the core of the anomalies will reach 30mb in January and February.
  8. Hey everyone! I'm looking for daily data of max and min temps for US stations for the last 10 to 20 years. There's a page on ESRL, but it only covers 1950-1999. Obviously there's ways to get the data simply month by month, but I was wondering if anyone knows of an easily accessible long term database. Probably has been asked numerous times before, so apologies for the redundancy. Thanks!
  9. There is a connection, via the South America hadley cell. A west-based Nino yields a zonally overturning cell rising from 180 and sinking over SA, which weakens the SA HC. A weaker HC -> weaker ST warming -> weaker eddy heat flux in the mid latitudes -> reversal in the FC circulation and meridional mass field / PV gradient ~ blocking.
  10. It's all about persistence. We can discuss a few things here. Both this year's current drought situation unfolding, and also desertification of western OK and the OK/TX panhandles. Lots of positive feedback mechanisms at work, and deserts can grow gregariously unless something intervenes. Time to start thinking about major implications on crop availability for the entire U.S.
  11. Winter 2009-10 was the strongest west-based El Nino on record. Line of zonal convergence stayed right near 155w the whole winter.
  12. Here's 2n/155w and looking ahead into the summer in the other years. There's a climatological min in the spring -- a trend bucked solely by 1997 ... and 2014? (and probably several other years before 1993 ...)
  13. 0-300m heat content measured at 0N/155W over the last 90 days. Past years color coded by the following winter (DJF) ONI. http://pic.twitter.com/lgmv5oiCf1
  14. Let's organize discussion and obs for this storm in a new thread http://www.americanwx.com/bb/index.php/topic/42685-groundhog-day-winter-storm-tx-ok-ar-disco-and-obs/
  15. 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.
  16. 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.
  17. 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.
  18. Just throwing this around. Fooling around with different EOF interpretations of ENSO: Maybe some method to differentiate between east- and west-based events.
  19. 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
  20. 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
  21. Source: Pattern Change and Severe Weather Opportunities