Saturday, March 15, 2008

Update from the Midnight Rider

This posting must be a bit loose due to upcoming graveyard shift coverage for a couple of nights. In general, there is no change in my tune from the past few postings in spite of what some models and other tools suggest. There continue to be mixed signals involving multiple time/space scales of the global weather-climate situation. In fact, this has been the case since at least February. However, from continuous monitoring of daily mean fields utilizing our GSDM framework, I have some confidence in my probabilistic feelings of what path the ocean-land-atmosphere system is taking.

We have plans of doing a detailed case study of this past winter after our GWO paper is submitted. For example, the strong MJO and other tropical convective variability that occurred is atypical for a strong El-Viejo. The latter did contribute to the observed DJF temperature and precipitation anomalies that would not be expected from La-Nina composites. Examples include the wetness across the Desert Southwest and extreme snowfall experienced for portions of the inter-mountain west as well as the Upper Mississippi Valley. It is beyond the scope of these blog discussions to properly address serious scientific matters.

Yes, I also monitor other tropical ocean basins including any possible extratropical SST feedbacks. That said, mature and strong global atmospheric La-Nina circulation characteristics remain. In fact, there is some evidence of recent strengthening (more said below). SST patterns across the Indo-Pacific Ocean sector have been undergoing a slow evolution during the past few weeks. The negative SST anomalies along the equatorial Pacific Ocean cold tongue have weakened a bit, with the coldest currently centered on the equatorial date line. The plus 1-3C SST anomaly warming along the coast of South America can be thought of as part of the ENSO cycle working with the seasonal cycle. We are at the time of year when SSTs west of South America are the warmest. The positive anomalies along the west coast of South America are very shallow while the colder anomalies farther west extend to at least 150m deep per TAO buoy array data.

The following are a few links for additional SST information: (note the initial projection) (link 18) (getting dated, but still useful).

Multiple regions of enhanced tropical convective forcing remain, including South America, Africa, the central equatorial Indian Ocean and even, at times, the very warm Southwest Pacific Ocean. Complicated Rossby wave energy dispersions (RWDs) from the extratropics have contributed to this “mess”, which involve non-linear feedback processes from (for example) the East Asian topography. In fact, I can argue that this whole confused situation started during mid/late January when intense-severe tropical convection with MJO #2 persisted in the west central-South Pacific Ocean for roughly a couple of weeks. The point is there are always these complicated forcing-response-feedbacks, etc. involving tropical and extratropical nonlinear dynamical processes. Looking for “cookbook” ideas such as circulation impacts from a SSW supposedly leading to a negative phase of the AO/NAO do not cut it with me. Life in the real atmosphere is much more complicated than that, and very important to understand if predictions of extreme weather events (for example) are to improve.

Whether or not there is a MJO is unclear. The WH (2004) 2+ standard deviation projection in phase 2 (through 14 March) is unrepresentative. This is example where careful scientific understanding of just what defines a MJO as well as the tools used to monitor it is a MUST! For instance, much of that 2 + sigma signal has been coming from anomalous upper tropospheric easterly wind flow anomalies (greater than 10m/s) across the Western Hemisphere.

I do think tropical convective forcing is slowly getting better organized across the Eastern Hemisphere centered ~0/80E. Full disk satellite imagery and other tricks I use support this notion. Animations of upper tropospheric daily mean vector wind anomalies show twin tropical anticyclones becoming established ~90E with downstream cyclones around the date line. RWDs into and out of the tropics are linked with these features, and are already impacting the USA as I type. Only monitoring will tell if this Indian Ocean forcing begins to shift east during the next few weeks. I suspect it will given increasingly warm SSTs north of Australia (totals ~29-30C).

Finally, we cannot forget about the very warm west central-South Pacific Ocean SSTs, which will shift north with the seasonal cycle. Again, only monitoring will tell if our “nemesis of the new world atmosphere” returns. In any case, international predictions of the MJO in WH (2004) phase space need to be used with extreme caution until further notice. The latter have wanted to predict “loops” in roughly phases 1-3 for the past couple of weeks, which is meteorologically unrealistic.

Global relative AAM is nearly as low as August 2007, roughly 3 AMUs (or approximately 3 standard deviations) below the R1 data climatology through 13 March. In addition to expanding zonal mean strong easterly wind flow anomalies (~10m/s at 200mb) throughout the tropical and subtropical atmospheres, a negative global frictional torque of ~10 Hadleys has been present since early February. The latter has been coming from frictional dissipation of midlatitude westerly wind flow anomalies. As I stated last week, the latter is not typical of a La-Nina. Instead, it is another feedback process that I cannot discuss here.

In any case, another monitoring issue will be if/when these upper tropospheric zonal mean easterly wind flow anomalies start propagating poleward and downward. At some point these easterlies may reach the surface and significantly ramp up (in addition to what is now occurring) the trades (leading to a positive global frictional torque), loosely similar to what happened after August 2007. Should that occur, one can then speculate that negative La-Nina SSTAs may intensify after boreal spring. The point to all this is from a relative AAM viewpoint, the global circulation has become more La-Nina like since early February, and that may feedback to the SSTs.

The GWO has a greater than 2 sigma projection in phase 3 (legacy GSDM Stage 1), and this is meteorologically realistic. Recall that the GWO takes into account non-MJO tropical convective forcing (roughly 80 percent on average, in the real world), in addition to the MJO. Zonal mean flux convergence of AAM transport (~8-12 Hadleys) has been increasing around 40N during the past week while shifting south. Regionally, this has translated to the storm track shifting southward across the lower 48 states, as was expected a week ago. I think the GWO will weakly orbit in phase 3 for at least the next few weeks, enhancing the odds of more western USA troughs in a southward shifted storm track.

Please see the following link for details about the stratosphere. As expected, anticyclonic blocking structures in the regions of Kamchatka and the North Atlantic have done their part to shift zonal mean anomalous westerlies southward. In fact, a weak zonal mean AAM sink has recently appeared ~50N. Again, these blocking patterns and their feedbacks cannot be understood from oversimplified associations.

There is no change to my USA outlooks from a week ago. Some models and even a couple of official forecasts have suggested a patter shift of sorts by week-2 meaning an eastern USA trough and western states ridge. That forecast solution is unlikely. Recent numerical ensemble predictions schemes such as the Canadian and NCEP GFS are starting to catch-up to what is proposed below.

More troughs impacting the western and central USA, probable for GWO phase 3, appear likely at least weeks 1-3. I think these storms will periodically impact the west coast. Blocking structures that are also likely to remain/occur at the higher latitudes may shift a southwest flow storm track across the Plains southward at times. This will increase the risk of high impact weather to above climatology centered on the middle of the country. Locations such as the Upper Mississippi Valley hit hard by severe winter weather may not only experience more of it, but also have “spring” delayed. Violent outbreaks of severe local storms including tornadoes may occur from the lower Mississippi Valley into Ohio Valley and portions of the Deep South. The latter is probable to shift northwest into the northern and central Plains/Upper Mississippi Valley going into May and June.

Finally, I still continue to have concerns about the dryness intensifying from far southwestern Kansas into western Texas. There are reasons tied to this base state where storm systems may remain too progressive at least for the next few weeks such that these locations get “dry intrusions”. Hence there is an increased risk of high fire dangers and dust storms for these areas. However, a southward shifted storm track and eventually the seasonal cycle may mitigate that.

Still unchanged, per WMO and other information, quite a bit of severe weather internationally continues to occur (ex., Europe early last week), tied to our on-going complicated weather-climate situation. I continue to leave it to the expertise of the appropriate weather centers internationally to alert the public of these risks.

Severe frontal rainfall across tropical South America should be waning week-1 and South Africa by the end of week-2. Much of the equatorial Indian Ocean is probable to see enhanced rainfall week-1 then extending into Indonesia as well as Northern Australia and the Philippines by weeks 2-3, latter possibly sooner. Locations east of Australia into the South Pacific islands are likely to remain at least climatologically convectively active until further notice. Finally, concerns for additional tropical cyclones remain across the South Indian Ocean, eventually shifting north of the equator (and eastward) during the next few weeks. Climatologically, the Bay of Bengal has one peak period of tropical cyclones during May.


An experimental quasi-phase space plot of the GSDM utilizing time series of normalized global relative AAM time tendency (Y-axis) and normalized global relative AAM anomaly (X-axis) can be found at

We call the behavior of this plot the Global Wind Oscillation (GWO). While the intent of the legacy GSDM is to extend current thinking beyond the MJO, the GWO quantifies variations used to derive the original GSDM in a manner that is “user friendly” analogous to the WH(2004) “convention”. In addition, the GWO plot does not have the ENSO signal removed.

Please see the revised description of the GSDM per above link. Also, I encourage the readers to study the annotated MJO and GWO phase space plots to help relate the global variations explained by those techniques to “weather”.

Links to CPC and PSD ENSO discussions: (recently updated)

These are probabilistic statements, and work is ongoing to quantify in future posts (for example, risk assessment maps, signal to noise ratio plots and shifts of probability). We hope that an opportunity will arise for us (soon) to have a dedicated web page effort to expedite more objectively, with rigor, thoroughness and verification. The WB (2007) paper on the GSDM has been published in the February issue of MWR. In addition, a paper is in preparation by WB that will formally introduce the GWO. Given shift work and upcoming travel, updates will be difficult. I will try to issue at least short posting around Friday, 21 March.

Ed Berry

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