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HMT Discussion for Saturday 19 January 2008

Nothing to get excited about in the short term. Bottom line: earliest date for the next IOP is next Friday, January 25. IOP seems likely between 25 January to 1 February.

GFS ensemble moves the ridge westward in earnest with a wave in the Gulf of Alaska at 00 UTC Thursday 24 January. Quite a spread as the wave approaches ARB 00 UTC Saturday 26 January. Even those that have a direct hit in which the wave lingers show little evidence of a high PW plume.

Canadian ensemble isn't completely sold on a regime shift this soon, though it is the majority opinion. The ECMWF deterministic run also has a later regime shift.

PSD retrospective ensemble also shows the regime shift well underway at 00 UTC Saturday 26 January with a large trough positioned offshore of CA in the ensemble mean, suggesting next Saturday as a potential IOP. The retrograded position of the ridge, which has an apex over the Aleutian Islands, stays in place well beyond 240 hours. This may not be the prime scenario for atmospheric rivers, as the mean position of the storm track is quite a bit north of the central Pacific.

Chris Anderson