FWIW - Week2 5H Z Anoms

Week2 500 mb height anomalies from the PSD, ECMEF, and NCEP (VT 2/9/06).


Good agreement wrt Ridge-W / Trof E over CONUS...but does it foreshadow any snow?

Some support for -AO tripole with above normal heights over the Pole and below normal heights INVOF Aluetians. Height anomalies in the ern ATL don't fit the pattern...so it/s two out of three.

CPC index forecast from OP GooFuS (blue bars) and the Ensembles (yellow band) suggest at AO will be least one standard deviation below the mean; however, the coefficient of determination (R²) for Op (26%) and Ensemble (21%) are meager. Less than 30% of the AO/s variability is forecast at D+14 by the model. The AO loading pattern can been seen here.



One of the
NAO/s dipoles finds above normal heights over Greenland @ D+14 ...although not a strong action center. Not much of a weakness across the ATL Ocean...either. CPC/s NAO forecast has the index near zero @ VT. The Op (Ensemble) D+14 forecast has an R² of 21% (7%). Numbers like those don/t lend themselves to awe inspiring confidence.

Note the current state of the NAO; strongly negative which goes along way in explaining why there has been so few EC snowstorms to date. The UA flow regime responsible for the intrusions of arctic air is too strong to support nearshore EC cyclogenesis. The winter storms are out there, it/s just that they/re too far out there...going through their explosive development well offshore.



The PNA dipole of above normal heights over SW CN and below normal heights INVOF the Aluetian Is. is well supported by the three models. PNA index is not particulariliy high -- less than one standard deviation above the mean -- but ridge-W is a 'typical' mid-winter feature. The D+14 forecast for slightly above normal PNA suggests a continuation of arctic airmasses invading the lower 48.



The OP GooFuS captures only 19% of the PNA/s variability; however...the Ensembles are much better (~60%) at getting the magnitude and direction correct.

The current D+14 forecasts has the AO negative to strongly negative..the NAO neutral...and the PNA weakly positive. A recent four-part study of past NEWxSFC storms suggested the best snowfalls...on average...occurred when the AO was positive or when the AO and PNA were both positive. The lowest snowfalls occurred when the AO was negative and the NAO positive.

The present forecast combination of -AO and +PNA @ D+14 has not produced the best Contest snowfalls. Instead of big snows in the E by the end of Week2...what may be more likely is a continuation of arctic cold and arctic dry.