Wednesday, October 11, 2006

Weather-Climate Update

Please see past postings for web site links. I am going to discontinue inserting most of them in an effort for brevity. I also need to do the same with these postings, and this one will be short due to shift work obligations.

SSTs have changed little since my posting on October 6th. There is some evidence that the current warm phase of ENSO is peaking.

The following are links to ENSO discussions.

Please also see the following CPC link (and others therein) for further ENSO, etc., insights, and remember that official USA information on anything related to ENSO comes from CPC.

The dynamical signal with the MJO is propagating through the Western Hemisphere, with a phase speed of 10-15m/s based on Hovmollers of velocity potential and OLRA. This is an increase from about 2 weeks ago, and is typical when the MJO signal moves into the Western Hemisphere. Full disk satellite imagery suggests the dynamical signal is centered around 0/80W. Surface westerly wind anomalies of 10-20m/s have propagated northward from the equatorial date line region and have contributed to anomalous westerly flow across much of the North Pacific at ~30N during the last few days. The latter was theresult of 2 tropical convective flare-ups and westerly wind events during the last 10-14 days, and has been associated with tropical cyclone activity across the West Pacific. In fact, there is a signal in the global AAM tendency of the tropical convective flare-ups associated with the MJO.

In the upper troposphere, 200mb zonal mean zonal wind anomalies of ~5m/s are presently centered ~20N, and there is evidence of meridional symmetry. Additionally, some linkage between the anomalous zonal mean westerly flows throughout the subtropical and midlatitude atmospheres has occurred during the last few days. Loosely, GSDM Stage 2 (tilted toward Stage 3) best describes the weather-climate situation during the past week. This has impacted the USA in the form of the currently strong positive phase of the Pacific-North American teleconnection (PNA). A major cold outbreak (for this time of year) into the North Central states is occurring as a response.

Strong suppression exists across much of the Eastern Hemisphere while convection remains perhaps coupled to the warm SSTs just west of date line, oriented north-south across the equator over the 29C and greater SSTs. The latter region has been weakening after the development of Tropical Cyclone Soulik. Most of the tropical convective enhancement is along the East Pacific ITCZ (where SSTs are also warm) into the South Atlantic Convergence Zone (SACZ) and spreading into the tropical North Atlantic ITCZ. This activity is associated with "wavy" upper tropospheric westerly wind anomalies that normally develop downstream of tropical forcing over the Eastern Hemisphere.

My thoughts are for the dynamical signal to propagate into the Eastern Hemisphere by the week 2-3 time frame, and reinvigorate the tropical convection across much of the Indian Ocean (where are SSTs are also quite warm with anomalies ~plus 0.5-1C over greater than 29C water). SST boundary forced tropical convection would also be expected to continue just west of the date line. A rendition of GSDM Stage 4-1 may be probable during weeks 2-3, loosely suggesting a retrogression of existing circulation anomalies with the continuation of subtropical jets. Many numerical ensemble prediction systems are capturing this scenario for much of the northern extratropics for week 2.

Ramifications would include the possibility of an anomalously deep trough across the western USA (with a subtropical jet), along with a strong southwest flow storm track across the Plains and central portions of the country. While synoptic details are unclear (ex., the magnitude of any baroclinic cyclogenesis), there exists the possibility of an early season major winter-like storm for the Central and Northern Rockies (there will be a cold air source). Meanwhile, severe local storms and widespread rainfall (some heavy) would be possible for locations from the Plains into the Upper Mississippi/Ohio Valleys and Great Lakes states. Other weather anomalies from this type of pattern should be well known by now.

I hope to post a more complete discussion roughly a week from today.

Ed Berry


The following is a link to our recently accepted paper by MWR which discusses the GSDM (Weickmann and Berry 2006).

From taking into consideration the interactions of 4 different subseasonal time scales, a sequence of maps depicting a coherent set of repeatable events has been derived for the Northern Hemisphere cold season from November-March. This set is broken up into 4 stages, referred to as GSDM (for Global Synoptic-Dynamic Model) Stages 1-4 in the text of my Blog. Figure 13 in our paper presents a schematic of the GSDM. Ideally it would be advantageous to post our weather-climate discussions with greater frequency to provide additional detail while having a more complete weather-climate record of attribution and prediction. In these discussions I adapt the GSDM for the warm season. Our list of work includes a seasonally adjusted rendition of the GSDM and additional components.

Our latest weather-climate discussion dated August 18th, 2006 (and updated September 9th), has been posted on the ESRL/PSD MJO web site at

We hope to post another writing on the ESRL/PSD MJO web site within the next 4-6 weeks.

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