QBO - December '06

Nine months into its positive phase...the latest QBO comes in a solid 6.21.

Still a relatively strong value...a smidge more than +1 SD above the long-term monthly mean for December of 6.12...as well as being in the 77th percentile. December/s QBO ain/t no slacker.

When QBO is W...the PV is deeper and stronger. Considering the PV has been over the north-central PAC for weeks during a moderate +ENSO...this strongly suggests the westerly stratospheric winds along the equator played a major role in maintaining the anomalously strong PAC jet and the near continuous flux of mild PAC air masses over the CONUS.

Now that the PV is shifting quickly E to a position over north-central CN...the temperature gradient driving the jet should shift into western CN where a hi-amp...+ENSO enhanced PNA-ridge is expected to develop. The thermal contrast won/t be as strong as it was when the PV was over the PAC...but strong enough to excite the polar jet and drive arctic air masses into the lower 48.

We/re coming to the end of the QBO/s west phase...so the stratosphere/s zonally-averaged wind speed should continue its decline during the remainder of '07. As QBO decreases during the second half of winter...the PV will weaken...which would allow more opportunities for more polar cold to encroach upon lower latitudes.